v3, 30 partsEasy to review grep & pre-PCRE changes

Makefile, configure.ac

diff --git a/Makefile b/Makefile
index e35542e631..eedadb8056 100644
--- a/Makefile
+++ b/Makefile
@@ -24,8 +24,10 @@ all::
 # Define NO_OPENSSL environment variable if you do not have OpenSSL.
 # This also implies BLK_SHA1.
 #
-# Define USE_LIBPCRE if you have and want to use libpcre. git-grep will be
-# able to use Perl-compatible regular expressions.
+# Define USE_LIBPCRE if you have and want to use libpcre. Various
+# commands such as log and grep offer runtime options to use
+# Perl-compatible regular expressions instead of standard or extended
+# POSIX regular expressions.
 #
 # Define LIBPCREDIR=/foo/bar if your libpcre header and library files are in
 # /foo/bar/include and /foo/bar/lib directories.
diff --git a/configure.ac b/configure.ac
index 128165529f..deeb968daa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -250,8 +250,10 @@ AS_HELP_STRING([--with-openssl],[use OpenSSL library (default is YES)])
 AS_HELP_STRING([],              [ARG can be prefix for openssl library and headers]),
 GIT_PARSE_WITH([openssl]))
 
-# Define USE_LIBPCRE if you have and want to use libpcre. git-grep will be
-# able to use Perl-compatible regular expressions.
+# Define USE_LIBPCRE if you have and want to use libpcre. Various
+# commands such as log and grep offer runtime options to use
+# Perl-compatible regular expressions instead of standard or extended
+# POSIX regular expressions.
 #
 # Define LIBPCREDIR=/foo/bar if your libpcre header and library files are in
 # /foo/bar/include and /foo/bar/lib directories.
@@ -499,8 +501,10 @@ GIT_CONF_SUBST([NEEDS_SSL_WITH_CRYPTO])
 GIT_CONF_SUBST([NO_OPENSSL])
 
 #
-# Define USE_LIBPCRE if you have and want to use libpcre. git-grep will be
-# able to use Perl-compatible regular expressions.
+# Define USE_LIBPCRE if you have and want to use libpcre. Various
+# commands such as log and grep offer runtime options to use
+# Perl-compatible regular expressions instead of standard or extended
+# POSIX regular expressions.
 #
 
 if test -n "$USE_LIBPCRE"; then

Documentation/git-grep.txt, Documentation/rev-list-options.txt

diff --git a/Documentation/git-grep.txt b/Documentation/git-grep.txt
index 71f32f3508..5033483db4 100644
--- a/Documentation/git-grep.txt
+++ b/Documentation/git-grep.txt
@@ -161,8 +161,11 @@ OPTIONS
 
 -P::
 --perl-regexp::
-	Use Perl-compatible regexp for patterns. Requires libpcre to be
-	compiled in.
+	Use Perl-compatible regular expressions for patterns.
++
+Support for these types of regular expressions is an optional
+compile-time dependency. If Git wasn't compiled with support for them
+providing this option will cause it to die.
 
 -F::
 --fixed-strings::
diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt
index a02f7324c0..a46f70c2b1 100644
--- a/Documentation/rev-list-options.txt
+++ b/Documentation/rev-list-options.txt
@@ -92,8 +92,12 @@ endif::git-rev-list[]
 	pattern as a regular expression).
 
 --perl-regexp::
-	Consider the limiting patterns to be Perl-compatible regular expressions.
-	Requires libpcre to be compiled in.
+	Consider the limiting patterns to be Perl-compatible regular
+	expressions.
++
+Support for these types of regular expressions is an optional
+compile-time dependency. If Git wasn't compiled with support for them
+providing this option will cause it to die.
 
 --remove-empty::
 	Stop when a given path disappears from the tree.

t/README, t/t7810-grep.sh, t/t7812-grep-icase-non-ascii.sh, t/t7813-grep-icase-iso.sh, t/test-lib.sh

diff --git a/t/README b/t/README
index ab386c3681..a90cb62583 100644
--- a/t/README
+++ b/t/README
@@ -803,9 +803,9 @@ use these, and "test_set_prereq" for how to define your own.
    Test is not run by root user, and an attempt to write to an
    unwritable file is expected to fail correctly.
 
- - LIBPCRE
+ - PCRE
 
-   Git was compiled with USE_LIBPCRE=YesPlease. Wrap any tests
+   Git was compiled with support for PCRE. Wrap any tests
    that use git-grep --perl-regexp or git-grep -P in these.
 
  - CASE_INSENSITIVE_FS
diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index cee42097b0..c84c4d99f9 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -275,7 +275,7 @@ do
 		test_cmp expected actual
 	'
 
-	test_expect_success LIBPCRE "grep $L with grep.patterntype=perl" '
+	test_expect_success PCRE "grep $L with grep.patterntype=perl" '
 		echo "${HC}ab:a+b*c" >expected &&
 		git -c grep.patterntype=perl grep "a\x{2b}b\x{2a}c" $H ab >actual &&
 		test_cmp expected actual
@@ -1053,12 +1053,12 @@ hello.c:int main(int argc, const char **argv)
 hello.c:	printf("Hello world.\n");
 EOF
 
-test_expect_success LIBPCRE 'grep --perl-regexp pattern' '
+test_expect_success PCRE 'grep --perl-regexp pattern' '
 	git grep --perl-regexp "\p{Ps}.*?\p{Pe}" hello.c >actual &&
 	test_cmp expected actual
 '
 
-test_expect_success LIBPCRE 'grep -P pattern' '
+test_expect_success PCRE 'grep -P pattern' '
 	git grep -P "\p{Ps}.*?\p{Pe}" hello.c >actual &&
 	test_cmp expected actual
 '
@@ -1070,13 +1070,13 @@ test_expect_success 'grep pattern with grep.extendedRegexp=true' '
 	test_cmp empty actual
 '
 
-test_expect_success LIBPCRE 'grep -P pattern with grep.extendedRegexp=true' '
+test_expect_success PCRE 'grep -P pattern with grep.extendedRegexp=true' '
 	git -c grep.extendedregexp=true \
 		grep -P "\p{Ps}.*?\p{Pe}" hello.c >actual &&
 	test_cmp expected actual
 '
 
-test_expect_success LIBPCRE 'grep -P -v pattern' '
+test_expect_success PCRE 'grep -P -v pattern' '
 	{
 		echo "ab:a+b*c"
 		echo "ab:a+bc"
@@ -1085,7 +1085,7 @@ test_expect_success LIBPCRE 'grep -P -v pattern' '
 	test_cmp expected actual
 '
 
-test_expect_success LIBPCRE 'grep -P -i pattern' '
+test_expect_success PCRE 'grep -P -i pattern' '
 	cat >expected <<-EOF &&
 	hello.c:	printf("Hello world.\n");
 	EOF
@@ -1093,7 +1093,7 @@ test_expect_success LIBPCRE 'grep -P -i pattern' '
 	test_cmp expected actual
 '
 
-test_expect_success LIBPCRE 'grep -P -w pattern' '
+test_expect_success PCRE 'grep -P -w pattern' '
 	{
 		echo "hello_world:Hello world"
 		echo "hello_world:HeLLo world"
@@ -1118,11 +1118,11 @@ test_expect_success 'grep invalidpattern properly dies with grep.patternType=ext
 	test_must_fail git -c grep.patterntype=extended grep "a["
 '
 
-test_expect_success LIBPCRE 'grep -P invalidpattern properly dies ' '
+test_expect_success PCRE 'grep -P invalidpattern properly dies ' '
 	test_must_fail git grep -P "a["
 '
 
-test_expect_success LIBPCRE 'grep invalidpattern properly dies with grep.patternType=perl' '
+test_expect_success PCRE 'grep invalidpattern properly dies with grep.patternType=perl' '
 	test_must_fail git -c grep.patterntype=perl grep "a["
 '
 
@@ -1191,13 +1191,13 @@ test_expect_success 'grep pattern with grep.patternType=fixed, =basic, =perl, =e
 	test_cmp expected actual
 '
 
-test_expect_success LIBPCRE 'grep -G -F -E -P pattern' '
+test_expect_success PCRE 'grep -G -F -E -P pattern' '
 	echo "d0:0" >expected &&
 	git grep -G -F -E -P "[\d]" d0 >actual &&
 	test_cmp expected actual
 '
 
-test_expect_success LIBPCRE 'grep pattern with grep.patternType=fixed, =basic, =extended, =perl' '
+test_expect_success PCRE 'grep pattern with grep.patternType=fixed, =basic, =extended, =perl' '
 	echo "d0:0" >expected &&
 	git \
 		-c grep.patterntype=fixed \
@@ -1208,7 +1208,7 @@ test_expect_success LIBPCRE 'grep pattern with grep.patternType=fixed, =basic, =
 	test_cmp expected actual
 '
 
-test_expect_success LIBPCRE 'grep -P pattern with grep.patternType=fixed' '
+test_expect_success PCRE 'grep -P pattern with grep.patternType=fixed' '
 	echo "ab:a+b*c" >expected &&
 	git \
 		-c grep.patterntype=fixed \
@@ -1343,12 +1343,12 @@ space: line with leading space2
 space: line with leading space3
 EOF
 
-test_expect_success LIBPCRE 'grep -E "^ "' '
+test_expect_success PCRE 'grep -E "^ "' '
 	git grep -E "^ " space >actual &&
 	test_cmp expected actual
 '
 
-test_expect_success LIBPCRE 'grep -P "^ "' '
+test_expect_success PCRE 'grep -P "^ "' '
 	git grep -P "^ " space >actual &&
 	test_cmp expected actual
 '
diff --git a/t/t7812-grep-icase-non-ascii.sh b/t/t7812-grep-icase-non-ascii.sh
index 169fd8d706..04a61cb8e0 100755
--- a/t/t7812-grep-icase-non-ascii.sh
+++ b/t/t7812-grep-icase-non-ascii.sh
@@ -20,13 +20,13 @@ test_expect_success REGEX_LOCALE 'grep literal string, no -F' '
 	git grep -i "TILRAUN: HALLÓ HEIMUR!"
 '
 
-test_expect_success GETTEXT_LOCALE,LIBPCRE 'grep pcre utf-8 icase' '
+test_expect_success GETTEXT_LOCALE,PCRE 'grep pcre utf-8 icase' '
 	git grep --perl-regexp    "TILRAUN: H.lló Heimur!" &&
 	git grep --perl-regexp -i "TILRAUN: H.lló Heimur!" &&
 	git grep --perl-regexp -i "TILRAUN: H.LLÓ HEIMUR!"
 '
 
-test_expect_success GETTEXT_LOCALE,LIBPCRE 'grep pcre utf-8 string with "+"' '
+test_expect_success GETTEXT_LOCALE,PCRE 'grep pcre utf-8 string with "+"' '
 	test_write_lines "TILRAUN: Hallóó Heimur!" >file2 &&
 	git add file2 &&
 	git grep -l --perl-regexp "TILRAUN: H.lló+ Heimur!" >actual &&
diff --git a/t/t7813-grep-icase-iso.sh b/t/t7813-grep-icase-iso.sh
index efef7fb81f..701e08a8e5 100755
--- a/t/t7813-grep-icase-iso.sh
+++ b/t/t7813-grep-icase-iso.sh
@@ -11,7 +11,7 @@ test_expect_success GETTEXT_ISO_LOCALE 'setup' '
 	export LC_ALL
 '
 
-test_expect_success GETTEXT_ISO_LOCALE,LIBPCRE 'grep pcre string' '
+test_expect_success GETTEXT_ISO_LOCALE,PCRE 'grep pcre string' '
 	git grep --perl-regexp -i "TILRAUN: H.ll� Heimur!" &&
 	git grep --perl-regexp -i "TILRAUN: H.LL� HEIMUR!"
 '
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 26b3edfb2e..04d857a42b 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1014,7 +1014,7 @@ esac
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_PERL" && test_set_prereq PERL
 test -z "$NO_PYTHON" && test_set_prereq PYTHON
-test -n "$USE_LIBPCRE" && test_set_prereq LIBPCRE
+test -n "$USE_LIBPCRE" && test_set_prereq PCRE
 test -z "$NO_GETTEXT" && test_set_prereq GETTEXT
 
 # Can we rely on git's output in the C locale?

diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index f577990716..a8dce0ca2d 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -262,7 +262,30 @@ test_expect_success 'log --grep -i' '
 
 test_expect_success 'log -F -E --grep=<ere> uses ere' '
 	echo second >expect &&
-	git log -1 --pretty="tformat:%s" -F -E --grep=s.c.nd >actual &&
+	# basic would need \(s\) to do the same
+	git log -1 --pretty="tformat:%s" -F -E --grep="(s).c.nd" >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success PCRE 'log -F -E --perl-regexp --grep=<pcre> uses PCRE' '
+	test_when_finished "rm -rf num_commits" &&
+	git init num_commits &&
+	(
+		cd num_commits &&
+		test_commit 1d &&
+		test_commit 2e
+	) &&
+
+	# In PCRE \d in [\d] is like saying "0-9", and matches the 2
+	# in 2e...
+	echo 2e >expect &&
+	git -C num_commits log -1 --pretty="tformat:%s" -F -E --perl-regexp --grep="[\d]" >actual &&
+	test_cmp expect actual &&
+
+	# ...in POSIX basic and extended it is the same as [d],
+	# i.e. "d", which matches 1d, but does not match 2e.
+	echo 1d >expect &&
+	git -C num_commits log -1 --pretty="tformat:%s" -F -E --grep="[\d]" >actual &&
 	test_cmp expect actual
 '
 
@@ -280,6 +303,79 @@ test_expect_success 'log with grep.patternType configuration and command line' '
 	test_cmp expect actual
 '
 
+test_expect_success 'log with various grep.patternType configurations & command-lines' '
+	git init pattern-type &&
+	(
+		cd pattern-type &&
+		test_commit 1 file A &&
+
+		# The tagname is overridden here because creating a
+		# tag called "(1|2)" as test_commit would otherwise
+		# implicitly do would fail on e.g. MINGW.
+		test_commit "(1|2)" file B 2 &&
+
+		echo "(1|2)" >expect.fixed &&
+		cp expect.fixed expect.basic &&
+		cp expect.fixed expect.extended &&
+		cp expect.fixed expect.perl &&
+
+		# A strcmp-like match with fixed.
+		git -c grep.patternType=fixed log --pretty=tformat:%s \
+			--grep="(1|2)" >actual.fixed &&
+
+		# POSIX basic matches (, | and ) literally.
+		git -c grep.patternType=basic log --pretty=tformat:%s \
+			--grep="(.|.)" >actual.basic &&
+
+		# POSIX extended needs to have | escaped to match it
+		# literally, whereas under basic this is the same as
+		# (|2), i.e. it would also match "1". This test checks
+		# for extended by asserting that it is not matching
+		# what basic would match.
+		git -c grep.patternType=extended log --pretty=tformat:%s \
+			--grep="\|2" >actual.extended &&
+		if test_have_prereq PCRE
+		then
+			# Only PCRE would match [\d]\| with only
+			# "(1|2)" due to [\d]. POSIX basic would match
+			# both it and "1" since similarly to the
+			# extended match above it is the same as
+			# \([\d]\|\). POSIX extended would
+			# match neither.
+			git -c grep.patternType=perl log --pretty=tformat:%s \
+				--grep="[\d]\|" >actual.perl &&
+			test_cmp expect.perl actual.perl
+		fi &&
+		test_cmp expect.fixed actual.fixed &&
+		test_cmp expect.basic actual.basic &&
+		test_cmp expect.extended actual.extended &&
+
+		git log --pretty=tformat:%s -F \
+			--grep="(1|2)" >actual.fixed.short-arg &&
+		git log --pretty=tformat:%s -E \
+			--grep="\|2" >actual.extended.short-arg &&
+		test_cmp expect.fixed actual.fixed.short-arg &&
+		test_cmp expect.extended actual.extended.short-arg &&
+
+		git log --pretty=tformat:%s --fixed-strings \
+			--grep="(1|2)" >actual.fixed.long-arg &&
+		git log --pretty=tformat:%s --basic-regexp \
+			--grep="(.|.)" >actual.basic.long-arg &&
+		git log --pretty=tformat:%s --extended-regexp \
+			--grep="\|2" >actual.extended.long-arg &&
+		if test_have_prereq PCRE
+		then
+			git log --pretty=tformat:%s --perl-regexp \
+				--grep="[\d]\|" >actual.perl.long-arg &&
+			test_cmp expect.perl actual.perl.long-arg
+
+		fi &&
+		test_cmp expect.fixed actual.fixed.long-arg &&
+		test_cmp expect.basic actual.basic.long-arg &&
+		test_cmp expect.extended actual.extended.long-arg
+	)
+'
+
 cat > expect <<EOF
 * Second
 * sixth

diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index 8d69113695..daa906b9b0 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -1114,6 +1114,13 @@ test_expect_success PCRE 'grep -P -w pattern' '
 	test_cmp expected actual
 '
 
+test_expect_success PCRE 'grep -P backreferences work (the PCRE NO_AUTO_CAPTURE flag is not set)' '
+	git grep -P -h "(?P<one>.)(?P=one)" hello_world >actual &&
+	test_cmp hello_world actual &&
+	git grep -P -h "(.)\1" hello_world >actual &&
+	test_cmp hello_world actual
+'
+
 test_expect_success 'grep -G invalidpattern properly dies ' '
 	test_must_fail git grep -G "a["
 '

revision.c, t/t4202-log.sh

diff --git a/revision.c b/revision.c
index 8a8c1789c7..4883cdd2d0 100644
--- a/revision.c
+++ b/revision.c
@@ -1991,6 +1991,7 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 	} else if (!strcmp(arg, "--extended-regexp") || !strcmp(arg, "-E")) {
 		revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_ERE;
 	} else if (!strcmp(arg, "--regexp-ignore-case") || !strcmp(arg, "-i")) {
+		revs->grep_filter.ignore_case = 1;
 		revs->grep_filter.regflags |= REG_ICASE;
 		DIFF_OPT_SET(&revs->diffopt, PICKAXE_IGNORE_CASE);
 	} else if (!strcmp(arg, "--fixed-strings") || !strcmp(arg, "-F")) {
diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index a8dce0ca2d..547f4c19a7 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -231,14 +231,47 @@ second
 initial
 EOF
 test_expect_success 'log --invert-grep --grep' '
-	git log --pretty="tformat:%s" --invert-grep --grep=th --grep=Sec >actual &&
-	test_cmp expect actual
+	# Fixed
+	git -c grep.patternType=fixed log --pretty="tformat:%s" --invert-grep --grep=th --grep=Sec >actual &&
+	test_cmp expect actual &&
+
+	# POSIX basic
+	git -c grep.patternType=basic log --pretty="tformat:%s" --invert-grep --grep=t[h] --grep=S[e]c >actual &&
+	test_cmp expect actual &&
+
+	# POSIX extended
+	git -c grep.patternType=basic log --pretty="tformat:%s" --invert-grep --grep=t[h] --grep=S[e]c >actual &&
+	test_cmp expect actual &&
+
+	# PCRE
+	if test_have_prereq PCRE
+	then
+		git -c grep.patternType=perl log --pretty="tformat:%s" --invert-grep --grep=t[h] --grep=S[e]c >actual &&
+		test_cmp expect actual
+	fi
 '
 
 test_expect_success 'log --invert-grep --grep -i' '
 	echo initial >expect &&
-	git log --pretty="tformat:%s" --invert-grep -i --grep=th --grep=Sec >actual &&
-	test_cmp expect actual
+
+	# Fixed
+	git -c grep.patternType=fixed log --pretty="tformat:%s" --invert-grep -i --grep=th --grep=Sec >actual &&
+	test_cmp expect actual &&
+
+	# POSIX basic
+	git -c grep.patternType=basic log --pretty="tformat:%s" --invert-grep -i --grep=t[h] --grep=S[e]c >actual &&
+	test_cmp expect actual &&
+
+	# POSIX extended
+	git -c grep.patternType=extended log --pretty="tformat:%s" --invert-grep -i --grep=t[h] --grep=S[e]c >actual &&
+	test_cmp expect actual &&
+
+	# PCRE
+	if test_have_prereq PCRE
+	then
+		git -c grep.patternType=perl log --pretty="tformat:%s" --invert-grep -i --grep=t[h] --grep=S[e]c >actual &&
+		test_cmp expect actual
+	fi
 '
 
 test_expect_success 'log --grep option parsing' '
@@ -256,8 +289,25 @@ test_expect_success 'log -i --grep' '
 
 test_expect_success 'log --grep -i' '
 	echo Second >expect &&
+
+	# Fixed
 	git log -1 --pretty="tformat:%s" --grep=sec -i >actual &&
-	test_cmp expect actual
+	test_cmp expect actual &&
+
+	# POSIX basic
+	git -c grep.patternType=basic log -1 --pretty="tformat:%s" --grep=s[e]c -i >actual &&
+	test_cmp expect actual &&
+
+	# POSIX extended
+	git -c grep.patternType=extended log -1 --pretty="tformat:%s" --grep=s[e]c -i >actual &&
+	test_cmp expect actual &&
+
+	# PCRE
+	if test_have_prereq PCRE
+	then
+		git -c grep.patternType=perl log -1 --pretty="tformat:%s" --grep=s[e]c -i >actual &&
+		test_cmp expect actual
+	fi
 '
 
 test_expect_success 'log -F -E --grep=<ere> uses ere' '

builtin/grep.c, grep.c, revision.c, grep.h

diff --git a/builtin/grep.c b/builtin/grep.c
index 3ffb5b4e81..be28c37265 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -1151,8 +1151,6 @@ int cmd_grep(int argc, const char **argv, const
char *prefix)

        if (!opt.pattern_list)
                die(_("no pattern given."));
-       if (!opt.fixed && opt.ignore_case)
-               opt.regflags |= REG_ICASE;

        compile_grep_patterns(&opt);

diff --git a/grep.c b/grep.c
index 47cee45067..7b13ee1043 100644
--- a/grep.c
+++ b/grep.c
@@ -435,12 +435,11 @@ static void compile_fixed_regexp(struct grep_pat
*p, struct grep_opt *opt)

 static void compile_regexp(struct grep_pat *p, struct grep_opt *opt)
 {
-       int icase, ascii_only;
+       int ascii_only;
        int err;

        p->word_regexp = opt->word_regexp;
        p->ignore_case = opt->ignore_case;
-       icase          = opt->regflags & REG_ICASE || p->ignore_case;
        ascii_only     = !has_non_ascii(p->pattern);

        /*
@@ -456,12 +455,12 @@ static void compile_regexp(struct grep_pat *p,
struct grep_opt *opt)
         * want to use kws.
         */
        if (opt->fixed || is_fixed(p->pattern, p->patternlen))
-               p->fixed = !icase || ascii_only;
+               p->fixed = !p->ignore_case || ascii_only;
        else
                p->fixed = 0;

        if (p->fixed) {
-               p->kws = kwsalloc(icase ? tolower_trans_tbl : NULL);
+               p->kws = kwsalloc(p->ignore_case ? tolower_trans_tbl : NULL);
                kwsincr(p->kws, p->pattern, p->patternlen);
                kwsprep(p->kws);
                return;
@@ -480,6 +479,8 @@ static void compile_regexp(struct grep_pat *p,
struct grep_opt *opt)
                return;
        }

+       if (p->ignore_case)
+               opt->regflags |= REG_ICASE;
        err = regcomp(&p->regexp, p->pattern, opt->regflags);
        if (err) {
                char errbuf[1024];
diff --git a/revision.c b/revision.c
index 4883cdd2d0..30c23a1098 100644
--- a/revision.c
+++ b/revision.c
@@ -1992,7 +1992,6 @@ static int handle_revision_opt(struct rev_info
*revs, int argc, const char **arg
                revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_ERE;
        } else if (!strcmp(arg, "--regexp-ignore-case") || !strcmp(arg, "-i")) {
                revs->grep_filter.ignore_case = 1;
-               revs->grep_filter.regflags |= REG_ICASE;
                DIFF_OPT_SET(&revs->diffopt, PICKAXE_IGNORE_CASE);
        } else if (!strcmp(arg, "--fixed-strings") || !strcmp(arg, "-F")) {
                revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_FIXED;

But an even better solution is to get rid of passing the regflags
field in grep_opt entirely, this conflicts with some of my later
patches:

diff --git a/builtin/grep.c b/builtin/grep.c
index 3ffb5b4e81..be28c37265 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -1151,8 +1151,6 @@ int cmd_grep(int argc, const char **argv, const
char *prefix)

        if (!opt.pattern_list)
                die(_("no pattern given."));
-       if (!opt.fixed && opt.ignore_case)
-               opt.regflags |= REG_ICASE;

        compile_grep_patterns(&opt);
diff --git a/grep.c b/grep.c
index 47cee45067..1bde7037ba 100644
--- a/grep.c
+++ b/grep.c
@@ -34,7 +34,6 @@ void init_grep_defaults(void)
        memset(opt, 0, sizeof(*opt));
        opt->relative = 1;
        opt->pathname = 1;
-       opt->regflags = REG_NEWLINE;
        opt->max_depth = -1;
        opt->pattern_type_option = GREP_PATTERN_TYPE_UNSPECIFIED;
        opt->extended_regexp_option = 0;
@@ -156,7 +155,6 @@ void grep_init(struct grep_opt *opt, const char *prefix)
        opt->linenum = def->linenum;
        opt->max_depth = def->max_depth;
        opt->pathname = def->pathname;
-       opt->regflags = def->regflags;
        opt->relative = def->relative;
        opt->output = def->output;

@@ -179,25 +177,25 @@ static void grep_set_pattern_type_option(enum
grep_pattern_type pattern_type, st
        case GREP_PATTERN_TYPE_BRE:
                opt->fixed = 0;
                opt->pcre = 0;
-               opt->regflags &= ~REG_EXTENDED;
+               opt->extended = 0;
                break;
         case GREP_PATTERN_TYPE_ERE:
                opt->fixed = 0;
                opt->pcre = 0;
-               opt->regflags |= REG_EXTENDED;
+               opt->extended = 1;
                break;

        case GREP_PATTERN_TYPE_FIXED:
                opt->fixed = 1;
                opt->pcre = 0;
-               opt->regflags &= ~REG_EXTENDED;
+               opt->extended = 0;
                break;

        case GREP_PATTERN_TYPE_PCRE:
                opt->fixed = 0;
                opt->pcre = 1;
-               opt->regflags &= ~REG_EXTENDED;
+               opt->extended = 0;
                break;
        }
 }
@@ -415,10 +413,9 @@ static void compile_fixed_regexp(struct grep_pat
*p, struct grep_opt *opt)
 {
        struct strbuf sb = STRBUF_INIT;
        int err;
-       int regflags;
+       int regflags = REG_NEWLINE;

        basic_regex_quote_buf(&sb, p->pattern);
-       regflags = opt->regflags & ~REG_EXTENDED;
        if (opt->ignore_case)
                regflags |= REG_ICASE;
        err = regcomp(&p->regexp, sb.buf, regflags);
@@ -435,12 +432,12 @@ static void compile_fixed_regexp(struct grep_pat
*p, struct grep_opt *opt)

 static void compile_regexp(struct grep_pat *p, struct grep_opt *opt)
 {
-       int icase, ascii_only;
+       int ascii_only;
        int err;
+       int regflags = REG_NEWLINE;

        p->word_regexp = opt->word_regexp;
        p->ignore_case = opt->ignore_case;
-       icase          = opt->regflags & REG_ICASE || p->ignore_case;
        ascii_only     = !has_non_ascii(p->pattern);

        /*
@@ -456,12 +453,12 @@ static void compile_regexp(struct grep_pat *p,
struct grep_opt *opt)
         * want to use kws.
         */
        if (opt->fixed || is_fixed(p->pattern, p->patternlen))
-               p->fixed = !icase || ascii_only;
+               p->fixed = !p->ignore_case || ascii_only;
        else
                p->fixed = 0;

        if (p->fixed) {
-               p->kws = kwsalloc(icase ? tolower_trans_tbl : NULL);
+               p->kws = kwsalloc(p->ignore_case ? tolower_trans_tbl : NULL);
                kwsincr(p->kws, p->pattern, p->patternlen);
                kwsprep(p->kws);
                return;
@@ -480,7 +477,11 @@ static void compile_regexp(struct grep_pat *p,
struct grep_opt *opt)
                return;
        }

-       err = regcomp(&p->regexp, p->pattern, opt->regflags);
+       if (p->ignore_case)
+               regflags |= REG_ICASE;
+       if (opt->extended)
+               regflags |= REG_EXTENDED;
+       err = regcomp(&p->regexp, p->pattern, regflags);
        if (err) {
                char errbuf[1024];
                regerror(err, &p->regexp, errbuf, 1024);
diff --git a/grep.h b/grep.h
index 267534ca24..d9d603deb1 100644
--- a/grep.h
+++ b/grep.h
@@ -129,7 +129,6 @@ struct grep_opt {
        char color_match_selected[COLOR_MAXLEN];
        char color_selected[COLOR_MAXLEN];
        char color_sep[COLOR_MAXLEN];
-       int regflags;
        unsigned pre_context;
        unsigned post_context;
        unsigned last_shown;
diff --git a/revision.c b/revision.c
index 4883cdd2d0..67240d38af 100644
--- a/revision.c
+++ b/revision.c
@@ -1362,7 +1362,6 @@ void init_revisions(struct rev_info *revs, const
char *prefix)
        init_grep_defaults();
        grep_init(&revs->grep_filter, prefix);
        revs->grep_filter.status_only = 1;
-       revs->grep_filter.regflags = REG_NEWLINE;

        diff_setup(&revs->diffopt);
        if (prefix && !revs->diffopt.prefix) {
@@ -1992,7 +1991,6 @@ static int handle_revision_opt(struct rev_info
*revs, int argc, const char **arg
                revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_ERE;
        } else if (!strcmp(arg, "--regexp-ignore-case") || !strcmp(arg, "-i")) {
                revs->grep_filter.ignore_case = 1;
-               revs->grep_filter.regflags |= REG_ICASE;
                DIFF_OPT_SET(&revs->diffopt, PICKAXE_IGNORE_CASE);
        } else if (!strcmp(arg, "--fixed-strings") || !strcmp(arg, "-F")) {
                revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_FIXED;

But as all this code cleanup isn't needed for fixing this bug, and I'd
really like to get this series merged into next/master ASAP so I can
start submitting the grep/pcre patches that are actually interesting,
let's leave this orthogonal code cleanup for now.

t/t4202-log.sh, t/t7810-grep.sh

diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index 547f4c19a7..dbed3efeee 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -418,7 +418,9 @@ test_expect_success 'log with various grep.patternType configurations & command-
 			git log --pretty=tformat:%s --perl-regexp \
 				--grep="[\d]\|" >actual.perl.long-arg &&
 			test_cmp expect.perl actual.perl.long-arg
-
+		else
+			test_must_fail git log --perl-regexp \
+				--grep="[\d]\|"
 		fi &&
 		test_cmp expect.fixed actual.fixed.long-arg &&
 		test_cmp expect.basic actual.basic.long-arg &&
diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index c84c4d99f9..8d69113695 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -281,6 +281,10 @@ do
 		test_cmp expected actual
 	'
 
+	test_expect_success !PCRE "grep $L with grep.patterntype=perl errors without PCRE" '
+		test_must_fail git -c grep.patterntype=perl grep "foo.*bar"
+	'
+
 	test_expect_success "grep $L with grep.patternType=default and grep.extendedRegexp=true" '
 		echo "${HC}ab:abc" >expected &&
 		git \
@@ -1058,11 +1062,19 @@ test_expect_success PCRE 'grep --perl-regexp pattern' '
 	test_cmp expected actual
 '
 
+test_expect_success !PCRE 'grep --perl-regexp pattern errors without PCRE' '
+	test_must_fail git grep --perl-regexp "foo.*bar"
+'
+
 test_expect_success PCRE 'grep -P pattern' '
 	git grep -P "\p{Ps}.*?\p{Pe}" hello.c >actual &&
 	test_cmp expected actual
 '
 
+test_expect_success !PCRE 'grep -P pattern errors without PCRE' '
+	test_must_fail git grep -P "foo.*bar"
+'
+
 test_expect_success 'grep pattern with grep.extendedRegexp=true' '
 	>empty &&
 	test_must_fail git -c grep.extendedregexp=true \

diff --git a/t/t7812-grep-icase-non-ascii.sh b/t/t7812-grep-icase-non-ascii.sh
index 04a61cb8e0..0059a1f837 100755
--- a/t/t7812-grep-icase-non-ascii.sh
+++ b/t/t7812-grep-icase-non-ascii.sh
@@ -36,29 +36,14 @@ test_expect_success GETTEXT_LOCALE,PCRE 'grep pcre utf-8 string with "+"' '
 '
 
 test_expect_success REGEX_LOCALE 'grep literal string, with -F' '
-	git grep --debug -i -F "TILRAUN: Halló Heimur!"  2>&1 >/dev/null |
-		 grep fixed >debug1 &&
-	test_write_lines "fixed TILRAUN: Halló Heimur!" >expect1 &&
-	test_cmp expect1 debug1 &&
-
-	git grep --debug -i -F "TILRAUN: HALLÓ HEIMUR!"  2>&1 >/dev/null |
-		 grep fixed >debug2 &&
-	test_write_lines "fixed TILRAUN: HALLÓ HEIMUR!" >expect2 &&
-	test_cmp expect2 debug2
+	git grep -i -F "TILRAUN: Halló Heimur!" &&
+	git grep -i -F "TILRAUN: HALLÓ HEIMUR!"
 '
 
 test_expect_success REGEX_LOCALE 'grep string with regex, with -F' '
-	test_write_lines "^*TILR^AUN:.* \\Halló \$He[]imur!\$" >file &&
-
-	git grep --debug -i -F "^*TILR^AUN:.* \\Halló \$He[]imur!\$" 2>&1 >/dev/null |
-		 grep fixed >debug1 &&
-	test_write_lines "fixed \\^*TILR^AUN:\\.\\* \\\\Halló \$He\\[]imur!\\\$" >expect1 &&
-	test_cmp expect1 debug1 &&
-
-	git grep --debug -i -F "^*TILR^AUN:.* \\HALLÓ \$HE[]IMUR!\$"  2>&1 >/dev/null |
-		 grep fixed >debug2 &&
-	test_write_lines "fixed \\^*TILR^AUN:\\.\\* \\\\HALLÓ \$HE\\[]IMUR!\\\$" >expect2 &&
-	test_cmp expect2 debug2
+	test_write_lines "TILRAUN: Halló Heimur [abc]!" >file3 &&
+	git add file3 &&
+	git grep -i -F "TILRAUN: Halló Heimur [abc]!" file3
 '
 
 test_expect_success REGEX_LOCALE 'pickaxe -i on non-ascii' '

diff --git a/t/t7008-grep-binary.sh b/t/t7008-grep-binary.sh
index 9c9c378119..df93d8e44c 100755
--- a/t/t7008-grep-binary.sh
+++ b/t/t7008-grep-binary.sh
@@ -4,6 +4,29 @@ test_description='git grep in binary files'
 
 . ./test-lib.sh
 
+nul_match () {
+	matches=$1
+	flags=$2
+	pattern=$3
+	pattern_human=$(echo "$pattern" | sed 's/Q/<NUL>/g')
+
+	if test "$matches" = 1
+	then
+		test_expect_success "git grep -f f $flags '$pattern_human' a" "
+			printf '$pattern' | q_to_nul >f &&
+			git grep -f f $flags a
+		"
+	elif test "$matches" = 0
+	then
+		test_expect_success "git grep -f f $flags '$pattern_human' a" "
+			printf '$pattern' | q_to_nul >f &&
+			test_must_fail git grep -f f $flags a
+		"
+	else
+		test_expect_success "PANIC: Test framework error. Unknown matches value $matches" 'false'
+	fi
+}
+
 test_expect_success 'setup' "
 	echo 'binaryQfile' | q_to_nul >a &&
 	git add a &&
@@ -69,35 +92,12 @@ test_expect_failure 'git grep .fi a' '
 	git grep .fi a
 '
 
-test_expect_success 'git grep -F y<NUL>f a' "
-	printf 'yQf' | q_to_nul >f &&
-	git grep -f f -F a
-"
-
-test_expect_success 'git grep -F y<NUL>x a' "
-	printf 'yQx' | q_to_nul >f &&
-	test_must_fail git grep -f f -F a
-"
-
-test_expect_success 'git grep -Fi Y<NUL>f a' "
-	printf 'YQf' | q_to_nul >f &&
-	git grep -f f -Fi a
-"
-
-test_expect_success 'git grep -Fi Y<NUL>x a' "
-	printf 'YQx' | q_to_nul >f &&
-	test_must_fail git grep -f f -Fi a
-"
-
-test_expect_success 'git grep y<NUL>f a' "
-	printf 'yQf' | q_to_nul >f &&
-	git grep -f f a
-"
-
-test_expect_success 'git grep y<NUL>x a' "
-	printf 'yQx' | q_to_nul >f &&
-	test_must_fail git grep -f f a
-"
+nul_match 1 '-F' 'yQf'
+nul_match 0 '-F' 'yQx'
+nul_match 1 '-Fi' 'YQf'
+nul_match 0 '-Fi' 'YQx'
+nul_match 1 '' 'yQf'
+nul_match 0 '' 'yQx'
 
 test_expect_success 'grep respects binary diff attribute' '
 	echo text >t &&

diff --git a/t/t7814-grep-recurse-submodules.sh b/t/t7814-grep-recurse-submodules.sh
index 5b6eb3a65e..1472855e1d 100755
--- a/t/t7814-grep-recurse-submodules.sh
+++ b/t/t7814-grep-recurse-submodules.sh
@@ -9,13 +9,13 @@ submodules.
 . ./test-lib.sh
 
 test_expect_success 'setup directory structure and submodule' '
-	echo "foobar" >a &&
+	echo "(1|2)d(3|4)" >a &&
 	mkdir b &&
-	echo "bar" >b/b &&
+	echo "(3|4)" >b/b &&
 	git add a b &&
 	git commit -m "add a and b" &&
 	git init submodule &&
-	echo "foobar" >submodule/a &&
+	echo "(1|2)d(3|4)" >submodule/a &&
 	git -C submodule add a &&
 	git -C submodule commit -m "add a" &&
 	git submodule add ./submodule &&
@@ -24,18 +24,18 @@ test_expect_success 'setup directory structure and submodule' '
 
 test_expect_success 'grep correctly finds patterns in a submodule' '
 	cat >expect <<-\EOF &&
-	a:foobar
-	b/b:bar
-	submodule/a:foobar
+	a:(1|2)d(3|4)
+	b/b:(3|4)
+	submodule/a:(1|2)d(3|4)
 	EOF
 
-	git grep -e "bar" --recurse-submodules >actual &&
+	git grep -e "(3|4)" --recurse-submodules >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep and basic pathspecs' '
 	cat >expect <<-\EOF &&
-	submodule/a:foobar
+	submodule/a:(1|2)d(3|4)
 	EOF
 
 	git grep -e. --recurse-submodules -- submodule >actual &&
@@ -44,7 +44,7 @@ test_expect_success 'grep and basic pathspecs' '
 
 test_expect_success 'grep and nested submodules' '
 	git init submodule/sub &&
-	echo "foobar" >submodule/sub/a &&
+	echo "(1|2)d(3|4)" >submodule/sub/a &&
 	git -C submodule/sub add a &&
 	git -C submodule/sub commit -m "add a" &&
 	git -C submodule submodule add ./sub &&
@@ -54,117 +54,117 @@ test_expect_success 'grep and nested submodules' '
 	git commit -m "updated submodule" &&
 
 	cat >expect <<-\EOF &&
-	a:foobar
-	b/b:bar
-	submodule/a:foobar
-	submodule/sub/a:foobar
+	a:(1|2)d(3|4)
+	b/b:(3|4)
+	submodule/a:(1|2)d(3|4)
+	submodule/sub/a:(1|2)d(3|4)
 	EOF
 
-	git grep -e "bar" --recurse-submodules >actual &&
+	git grep -e "(3|4)" --recurse-submodules >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep and multiple patterns' '
 	cat >expect <<-\EOF &&
-	a:foobar
-	submodule/a:foobar
-	submodule/sub/a:foobar
+	a:(1|2)d(3|4)
+	submodule/a:(1|2)d(3|4)
+	submodule/sub/a:(1|2)d(3|4)
 	EOF
 
-	git grep -e "bar" --and -e "foo" --recurse-submodules >actual &&
+	git grep -e "(3|4)" --and -e "(1|2)" --recurse-submodules >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep and multiple patterns' '
 	cat >expect <<-\EOF &&
-	b/b:bar
+	b/b:(3|4)
 	EOF
 
-	git grep -e "bar" --and --not -e "foo" --recurse-submodules >actual &&
+	git grep -e "(3|4)" --and --not -e "(1|2)" --recurse-submodules >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'basic grep tree' '
 	cat >expect <<-\EOF &&
-	HEAD:a:foobar
-	HEAD:b/b:bar
-	HEAD:submodule/a:foobar
-	HEAD:submodule/sub/a:foobar
+	HEAD:a:(1|2)d(3|4)
+	HEAD:b/b:(3|4)
+	HEAD:submodule/a:(1|2)d(3|4)
+	HEAD:submodule/sub/a:(1|2)d(3|4)
 	EOF
 
-	git grep -e "bar" --recurse-submodules HEAD >actual &&
+	git grep -e "(3|4)" --recurse-submodules HEAD >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep tree HEAD^' '
 	cat >expect <<-\EOF &&
-	HEAD^:a:foobar
-	HEAD^:b/b:bar
-	HEAD^:submodule/a:foobar
+	HEAD^:a:(1|2)d(3|4)
+	HEAD^:b/b:(3|4)
+	HEAD^:submodule/a:(1|2)d(3|4)
 	EOF
 
-	git grep -e "bar" --recurse-submodules HEAD^ >actual &&
+	git grep -e "(3|4)" --recurse-submodules HEAD^ >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep tree HEAD^^' '
 	cat >expect <<-\EOF &&
-	HEAD^^:a:foobar
-	HEAD^^:b/b:bar
+	HEAD^^:a:(1|2)d(3|4)
+	HEAD^^:b/b:(3|4)
 	EOF
 
-	git grep -e "bar" --recurse-submodules HEAD^^ >actual &&
+	git grep -e "(3|4)" --recurse-submodules HEAD^^ >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep tree and pathspecs' '
 	cat >expect <<-\EOF &&
-	HEAD:submodule/a:foobar
-	HEAD:submodule/sub/a:foobar
+	HEAD:submodule/a:(1|2)d(3|4)
+	HEAD:submodule/sub/a:(1|2)d(3|4)
 	EOF
 
-	git grep -e "bar" --recurse-submodules HEAD -- submodule >actual &&
+	git grep -e "(3|4)" --recurse-submodules HEAD -- submodule >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep tree and pathspecs' '
 	cat >expect <<-\EOF &&
-	HEAD:submodule/a:foobar
-	HEAD:submodule/sub/a:foobar
+	HEAD:submodule/a:(1|2)d(3|4)
+	HEAD:submodule/sub/a:(1|2)d(3|4)
 	EOF
 
-	git grep -e "bar" --recurse-submodules HEAD -- "submodule*a" >actual &&
+	git grep -e "(3|4)" --recurse-submodules HEAD -- "submodule*a" >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep tree and more pathspecs' '
 	cat >expect <<-\EOF &&
-	HEAD:submodule/a:foobar
+	HEAD:submodule/a:(1|2)d(3|4)
 	EOF
 
-	git grep -e "bar" --recurse-submodules HEAD -- "submodul?/a" >actual &&
+	git grep -e "(3|4)" --recurse-submodules HEAD -- "submodul?/a" >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep tree and more pathspecs' '
 	cat >expect <<-\EOF &&
-	HEAD:submodule/sub/a:foobar
+	HEAD:submodule/sub/a:(1|2)d(3|4)
 	EOF
 
-	git grep -e "bar" --recurse-submodules HEAD -- "submodul*/sub/a" >actual &&
+	git grep -e "(3|4)" --recurse-submodules HEAD -- "submodul*/sub/a" >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success !MINGW 'grep recurse submodule colon in name' '
 	git init parent &&
 	test_when_finished "rm -rf parent" &&
-	echo "foobar" >"parent/fi:le" &&
+	echo "(1|2)d(3|4)" >"parent/fi:le" &&
 	git -C parent add "fi:le" &&
 	git -C parent commit -m "add fi:le" &&
 
 	git init "su:b" &&
 	test_when_finished "rm -rf su:b" &&
-	echo "foobar" >"su:b/fi:le" &&
+	echo "(1|2)d(3|4)" >"su:b/fi:le" &&
 	git -C "su:b" add "fi:le" &&
 	git -C "su:b" commit -m "add fi:le" &&
 
@@ -172,30 +172,30 @@ test_expect_success !MINGW 'grep recurse submodule colon in name' '
 	git -C parent commit -m "add submodule" &&
 
 	cat >expect <<-\EOF &&
-	fi:le:foobar
-	su:b/fi:le:foobar
+	fi:le:(1|2)d(3|4)
+	su:b/fi:le:(1|2)d(3|4)
 	EOF
-	git -C parent grep -e "foobar" --recurse-submodules >actual &&
+	git -C parent grep -e "(1|2)d(3|4)" --recurse-submodules >actual &&
 	test_cmp expect actual &&
 
 	cat >expect <<-\EOF &&
-	HEAD:fi:le:foobar
-	HEAD:su:b/fi:le:foobar
+	HEAD:fi:le:(1|2)d(3|4)
+	HEAD:su:b/fi:le:(1|2)d(3|4)
 	EOF
-	git -C parent grep -e "foobar" --recurse-submodules HEAD >actual &&
+	git -C parent grep -e "(1|2)d(3|4)" --recurse-submodules HEAD >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep history with moved submoules' '
 	git init parent &&
 	test_when_finished "rm -rf parent" &&
-	echo "foobar" >parent/file &&
+	echo "(1|2)d(3|4)" >parent/file &&
 	git -C parent add file &&
 	git -C parent commit -m "add file" &&
 
 	git init sub &&
 	test_when_finished "rm -rf sub" &&
-	echo "foobar" >sub/file &&
+	echo "(1|2)d(3|4)" >sub/file &&
 	git -C sub add file &&
 	git -C sub commit -m "add file" &&
 
@@ -203,82 +203,82 @@ test_expect_success 'grep history with moved submoules' '
 	git -C parent commit -m "add submodule" &&
 
 	cat >expect <<-\EOF &&
-	dir/sub/file:foobar
-	file:foobar
+	dir/sub/file:(1|2)d(3|4)
+	file:(1|2)d(3|4)
 	EOF
-	git -C parent grep -e "foobar" --recurse-submodules >actual &&
+	git -C parent grep -e "(1|2)d(3|4)" --recurse-submodules >actual &&
 	test_cmp expect actual &&
 
 	git -C parent mv dir/sub sub-moved &&
 	git -C parent commit -m "moved submodule" &&
 
 	cat >expect <<-\EOF &&
-	file:foobar
-	sub-moved/file:foobar
+	file:(1|2)d(3|4)
+	sub-moved/file:(1|2)d(3|4)
 	EOF
-	git -C parent grep -e "foobar" --recurse-submodules >actual &&
+	git -C parent grep -e "(1|2)d(3|4)" --recurse-submodules >actual &&
 	test_cmp expect actual &&
 
 	cat >expect <<-\EOF &&
-	HEAD^:dir/sub/file:foobar
-	HEAD^:file:foobar
+	HEAD^:dir/sub/file:(1|2)d(3|4)
+	HEAD^:file:(1|2)d(3|4)
 	EOF
-	git -C parent grep -e "foobar" --recurse-submodules HEAD^ >actual &&
+	git -C parent grep -e "(1|2)d(3|4)" --recurse-submodules HEAD^ >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep using relative path' '
 	test_when_finished "rm -rf parent sub" &&
 	git init sub &&
-	echo "foobar" >sub/file &&
+	echo "(1|2)d(3|4)" >sub/file &&
 	git -C sub add file &&
 	git -C sub commit -m "add file" &&
 
 	git init parent &&
-	echo "foobar" >parent/file &&
+	echo "(1|2)d(3|4)" >parent/file &&
 	git -C parent add file &&
 	mkdir parent/src &&
-	echo "foobar" >parent/src/file2 &&
+	echo "(1|2)d(3|4)" >parent/src/file2 &&
 	git -C parent add src/file2 &&
 	git -C parent submodule add ../sub &&
 	git -C parent commit -m "add files and submodule" &&
 
 	# From top works
 	cat >expect <<-\EOF &&
-	file:foobar
-	src/file2:foobar
-	sub/file:foobar
+	file:(1|2)d(3|4)
+	src/file2:(1|2)d(3|4)
+	sub/file:(1|2)d(3|4)
 	EOF
-	git -C parent grep --recurse-submodules -e "foobar" >actual &&
+	git -C parent grep --recurse-submodules -e "(1|2)d(3|4)" >actual &&
 	test_cmp expect actual &&
 
 	# Relative path to top
 	cat >expect <<-\EOF &&
-	../file:foobar
-	file2:foobar
-	../sub/file:foobar
+	../file:(1|2)d(3|4)
+	file2:(1|2)d(3|4)
+	../sub/file:(1|2)d(3|4)
 	EOF
-	git -C parent/src grep --recurse-submodules -e "foobar" -- .. >actual &&
+	git -C parent/src grep --recurse-submodules -e "(1|2)d(3|4)" -- .. >actual &&
 	test_cmp expect actual &&
 
 	# Relative path to submodule
 	cat >expect <<-\EOF &&
-	../sub/file:foobar
+	../sub/file:(1|2)d(3|4)
 	EOF
-	git -C parent/src grep --recurse-submodules -e "foobar" -- ../sub >actual &&
+	git -C parent/src grep --recurse-submodules -e "(1|2)d(3|4)" -- ../sub >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'grep from a subdir' '
 	test_when_finished "rm -rf parent sub" &&
 	git init sub &&
-	echo "foobar" >sub/file &&
+	echo "(1|2)d(3|4)" >sub/file &&
 	git -C sub add file &&
 	git -C sub commit -m "add file" &&
 
 	git init parent &&
 	mkdir parent/src &&
-	echo "foobar" >parent/src/file &&
+	echo "(1|2)d(3|4)" >parent/src/file &&
 	git -C parent add src/file &&
 	git -C parent submodule add ../sub src/sub &&
 	git -C parent submodule add ../sub sub &&
@@ -286,19 +286,19 @@ test_expect_success 'grep from a subdir' '
 
 	# Verify grep from root works
 	cat >expect <<-\EOF &&
-	src/file:foobar
-	src/sub/file:foobar
-	sub/file:foobar
+	src/file:(1|2)d(3|4)
+	src/sub/file:(1|2)d(3|4)
+	sub/file:(1|2)d(3|4)
 	EOF
-	git -C parent grep --recurse-submodules -e "foobar" >actual &&
+	git -C parent grep --recurse-submodules -e "(1|2)d(3|4)" >actual &&
 	test_cmp expect actual &&
 
 	# Verify grep from a subdir works
 	cat >expect <<-\EOF &&
-	file:foobar
-	sub/file:foobar
+	file:(1|2)d(3|4)
+	sub/file:(1|2)d(3|4)
 	EOF
-	git -C parent/src grep --recurse-submodules -e "foobar" >actual &&
+	git -C parent/src grep --recurse-submodules -e "(1|2)d(3|4)" >actual &&
 	test_cmp expect actual
 '
 

diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index daa906b9b0..561709ef6a 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -775,6 +775,22 @@ test_expect_success 'grep -W with userdiff' '
 	test_cmp expected actual
 '
 
+for threads in $(test_seq 0 10)
+do
+	test_expect_success "grep --threads=$threads & -c grep.threads=$threads" "
+		git grep --threads=$threads . >actual.$threads &&
+		if test $threads -ge 1
+		then
+			test_cmp actual.\$(($threads - 1)) actual.$threads
+		fi &&
+		git -c grep.threads=$threads grep . >actual.$threads &&
+		if test $threads -ge 1
+		then
+			test_cmp actual.\$(($threads - 1)) actual.$threads
+		fi
+	"
+done
+
 test_expect_success 'grep from a subdirectory to search wider area (1)' '
 	mkdir -p s &&
 	(

diff --git a/t/t7008-grep-binary.sh b/t/t7008-grep-binary.sh
index df93d8e44c..20370d6e0c 100755
--- a/t/t7008-grep-binary.sh
+++ b/t/t7008-grep-binary.sh
@@ -28,7 +28,7 @@ nul_match () {
 }
 
 test_expect_success 'setup' "
-	echo 'binaryQfile' | q_to_nul >a &&
+	echo 'binaryQfileQm[*]cQ*æQð' | q_to_nul >a &&
 	git add a &&
 	git commit -m.
 "
@@ -162,7 +162,7 @@ test_expect_success 'grep does not honor textconv' '
 '
 
 test_expect_success 'grep --textconv honors textconv' '
-	echo "a:binaryQfile" >expect &&
+	echo "a:binaryQfileQm[*]cQ*æQð" >expect &&
 	git grep --textconv Qfile >actual &&
 	test_cmp expect actual
 '
@@ -172,7 +172,7 @@ test_expect_success 'grep --no-textconv does not honor textconv' '
 '
 
 test_expect_success 'grep --textconv blob honors textconv' '
-	echo "HEAD:a:binaryQfile" >expect &&
+	echo "HEAD:a:binaryQfileQm[*]cQ*æQð" >expect &&
 	git grep --textconv Qfile HEAD:a >actual &&
 	test_cmp expect actual
 '

diff --git a/t/t7814-grep-recurse-submodules.sh b/t/t7814-grep-recurse-submodules.sh
index 1472855e1d..3a58197f47 100755
--- a/t/t7814-grep-recurse-submodules.sh
+++ b/t/t7814-grep-recurse-submodules.sh
@@ -313,4 +313,53 @@ test_incompatible_with_recurse_submodules ()
 test_incompatible_with_recurse_submodules --untracked
 test_incompatible_with_recurse_submodules --no-index
 
+test_expect_success 'grep --recurse-submodules should pass the pattern type along' '
+	# Fixed
+	test_must_fail git grep -F --recurse-submodules -e "(.|.)[\d]" &&
+	test_must_fail git -c grep.patternType=fixed grep --recurse-submodules -e "(.|.)[\d]" &&
+
+	# Basic
+	git grep -G --recurse-submodules -e "(.|.)[\d]" >actual &&
+	cat >expect <<-\EOF &&
+	a:(1|2)d(3|4)
+	submodule/a:(1|2)d(3|4)
+	submodule/sub/a:(1|2)d(3|4)
+	EOF
+	test_cmp expect actual &&
+	git -c grep.patternType=basic grep --recurse-submodules -e "(.|.)[\d]" >actual &&
+	test_cmp expect actual &&
+
+	# Extended
+	git grep -E --recurse-submodules -e "(.|.)[\d]" >actual &&
+	cat >expect <<-\EOF &&
+	.gitmodules:[submodule "submodule"]
+	.gitmodules:	path = submodule
+	.gitmodules:	url = ./submodule
+	a:(1|2)d(3|4)
+	submodule/.gitmodules:[submodule "sub"]
+	submodule/a:(1|2)d(3|4)
+	submodule/sub/a:(1|2)d(3|4)
+	EOF
+	test_cmp expect actual &&
+	git -c grep.patternType=extended grep --recurse-submodules -e "(.|.)[\d]" >actual &&
+	test_cmp expect actual &&
+	git -c grep.extendedRegexp=true grep --recurse-submodules -e "(.|.)[\d]" >actual &&
+	test_cmp expect actual &&
+
+	# Perl
+	if test_have_prereq PCRE
+	then
+		git grep -P --recurse-submodules -e "(.|.)[\d]" >actual &&
+		cat >expect <<-\EOF &&
+		a:(1|2)d(3|4)
+		b/b:(3|4)
+		submodule/a:(1|2)d(3|4)
+		submodule/sub/a:(1|2)d(3|4)
+		EOF
+		test_cmp expect actual &&
+		git -c grep.patternType=perl grep --recurse-submodules -e "(.|.)[\d]" >actual &&
+		test_cmp expect actual
+	fi
+'
+
 test_done

diff --git a/t/t7008-grep-binary.sh b/t/t7008-grep-binary.sh
index 20370d6e0c..615e7e0162 100755
--- a/t/t7008-grep-binary.sh
+++ b/t/t7008-grep-binary.sh
@@ -22,6 +22,18 @@ nul_match () {
 			printf '$pattern' | q_to_nul >f &&
 			test_must_fail git grep -f f $flags a
 		"
+	elif test "$matches" = T1
+	then
+		test_expect_failure "git grep -f f $flags '$pattern_human' a" "
+			printf '$pattern' | q_to_nul >f &&
+			git grep -f f $flags a
+		"
+	elif test "$matches" = T0
+	then
+		test_expect_failure "git grep -f f $flags '$pattern_human' a" "
+			printf '$pattern' | q_to_nul >f &&
+			test_must_fail git grep -f f $flags a
+		"
 	else
 		test_expect_success "PANIC: Test framework error. Unknown matches value $matches" 'false'
 	fi
@@ -98,6 +110,65 @@ nul_match 1 '-Fi' 'YQf'
 nul_match 0 '-Fi' 'YQx'
 nul_match 1 '' 'yQf'
 nul_match 0 '' 'yQx'
+nul_match 1 '' 'æQð'
+nul_match 1 '-F' 'eQm[*]c'
+nul_match 1 '-Fi' 'EQM[*]C'
+
+# Regex patterns that would match but shouldn't with -F
+nul_match 0 '-F' 'yQ[f]'
+nul_match 0 '-F' '[y]Qf'
+nul_match 0 '-Fi' 'YQ[F]'
+nul_match 0 '-Fi' '[Y]QF'
+nul_match 0 '-F' 'æQ[ð]'
+nul_match 0 '-F' '[æ]Qð'
+nul_match 0 '-Fi' 'ÆQ[Ð]'
+nul_match 0 '-Fi' '[Æ]QÐ'
+
+# kwset is disabled on -i & non-ASCII. No way to match non-ASCII \0
+# patterns case-insensitively.
+nul_match T1 '-i' 'ÆQÐ'
+
+# \0 implicitly disables regexes. This is an undocumented internal
+# limitation.
+nul_match T1 '' 'yQ[f]'
+nul_match T1 '' '[y]Qf'
+nul_match T1 '-i' 'YQ[F]'
+nul_match T1 '-i' '[Y]Qf'
+nul_match T1 '' 'æQ[ð]'
+nul_match T1 '' '[æ]Qð'
+nul_match T1 '-i' 'ÆQ[Ð]'
+
+# ... because of \0 implicitly disabling regexes regexes that
+# should/shouldn't match don't do the right thing.
+nul_match T1 '' 'eQm.*cQ'
+nul_match T1 '-i' 'EQM.*cQ'
+nul_match T0 '' 'eQm[*]c'
+nul_match T0 '-i' 'EQM[*]C'
+
+# Due to the REG_STARTEND extension when kwset() is disabled on -i &
+# non-ASCII the string will be matched in its entirety, but the
+# pattern will be cut off at the first \0.
+nul_match 0 '-i' 'NOMATCHQð'
+nul_match T0 '-i' '[Æ]QNOMATCH'
+nul_match T0 '-i' '[æ]QNOMATCH'
+# Matches, but for the wrong reasons, just stops at [æ]
+nul_match 1 '-i' '[Æ]Qð'
+nul_match 1 '-i' '[æ]Qð'
+
+# Ensure that the matcher doesn't regress to something that stops at
+# \0
+nul_match 0 '-F' 'yQ[f]'
+nul_match 0 '-Fi' 'YQ[F]'
+nul_match 0 '' 'yQNOMATCH'
+nul_match 0 '' 'QNOMATCH'
+nul_match 0 '-i' 'YQNOMATCH'
+nul_match 0 '-i' 'QNOMATCH'
+nul_match 0 '-F' 'æQ[ð]'
+nul_match 0 '-Fi' 'ÆQ[Ð]'
+nul_match 0 '' 'yQNÓMATCH'
+nul_match 0 '' 'QNÓMATCH'
+nul_match 0 '-i' 'YQNÓMATCH'
+nul_match 0 '-i' 'QNÓMATCH'
 
 test_expect_success 'grep respects binary diff attribute' '
 	echo text >t &&

Makefile, t/perf/README, t/perf/run

diff --git a/Makefile b/Makefile
index eedadb8056..d1587452f1 100644
--- a/Makefile
+++ b/Makefile
@@ -2272,6 +2272,9 @@ endif
 ifdef GIT_PERF_MAKE_OPTS
 	@echo GIT_PERF_MAKE_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_MAKE_OPTS)))'\' >>$@+
 endif
+ifdef GIT_PERF_MAKE_COMMAND
+	@echo GIT_PERF_MAKE_COMMAND=\''$(subst ','\'',$(subst ','\'',$(GIT_PERF_MAKE_COMMAND)))'\' >>$@+
+endif
 ifdef GIT_INTEROP_MAKE_OPTS
 	@echo GIT_INTEROP_MAKE_OPTS=\''$(subst ','\'',$(subst ','\'',$(GIT_INTEROP_MAKE_OPTS)))'\' >>$@+
 endif
diff --git a/t/perf/README b/t/perf/README
index 49ea4349be..b3d95042a8 100644
--- a/t/perf/README
+++ b/t/perf/README
@@ -60,8 +60,23 @@ You can set the following variables (also in your config.mak):
 
     GIT_PERF_MAKE_OPTS
 	Options to use when automatically building a git tree for
-	performance testing.  E.g., -j6 would be useful.
-
+	performance testing. E.g., -j6 would be useful. Passed
+	directly to make as "make $GIT_PERF_MAKE_OPTS".
+
+    GIT_PERF_MAKE_COMMAND
+	An arbitrary command that'll be run in place of the make
+	command, if set the GIT_PERF_MAKE_OPTS variable is
+	ignored. Useful in cases where source tree changes might
+	require issuing a different make command to different
+	revisions.
+
+	This can be (ab)used to monkeypatch or otherwise change the
+	tree about to be built. Note that the build directory can be
+	re-used for subsequent runs so the make command might get
+	executed multiple times on the same tree, but don't count on
+	any of that, that's an implementation detail that might change
+	in the future.
+ 
     GIT_PERF_REPO
     GIT_PERF_LARGE_REPO
 	Repositories to copy for the performance tests.  The normal
diff --git a/t/perf/run b/t/perf/run
index c788d713ae..b61024a830 100755
--- a/t/perf/run
+++ b/t/perf/run
@@ -37,8 +37,15 @@ build_git_rev () {
 			cp "../../$config" "build/$rev/"
 		fi
 	done
-	(cd build/$rev && make $GIT_PERF_MAKE_OPTS) ||
-	die "failed to build revision '$mydir'"
+	(
+		cd build/$rev &&
+		if test -n "$GIT_PERF_MAKE_COMMAND"
+		then
+			sh -c "$GIT_PERF_MAKE_COMMAND"
+		else
+			make $GIT_PERF_MAKE_OPTS
+		fi
+	) || die "failed to build revision '$mydir'"
 }
 
 run_dirs_helper () {

diff --git a/t/perf/p7821-grep-engines-fixed.sh b/t/perf/p7821-grep-engines-fixed.sh
new file mode 100755
index 0000000000..d935194ecf
--- /dev/null
+++ b/t/perf/p7821-grep-engines-fixed.sh
@@ -0,0 +1,32 @@
+#!/bin/sh
+
+test_description="Comparison of git-grep's regex engines with -F
+
+Set GIT_PERF_7821_GREP_OPTS in the environment to pass options to
+git-grep. Make sure to include a leading space,
+e.g. GIT_PERF_7821_GREP_OPTS=' -w'. See p7820-grep-engines.sh for more
+options to try.
+"
+
+. ./perf-lib.sh
+
+test_perf_large_repo
+test_checkout_worktree
+
+for args in 'int' 'uncommon' 'æ'
+do
+	for engine in fixed basic extended perl
+	do
+		test_perf "$engine grep$GIT_PERF_7821_GREP_OPTS $args" "
+			git -c grep.patternType=$engine grep$GIT_PERF_7821_GREP_OPTS $args >'out.$engine.$args' || :
+		"
+	done
+
+	test_expect_success "assert that all engines found the same for$GIT_PERF_7821_GREP_OPTS $args" "
+		test_cmp 'out.fixed.$args' 'out.basic.$args' &&
+		test_cmp 'out.fixed.$args' 'out.extended.$args' &&
+		test_cmp 'out.fixed.$args' 'out.perl.$args'
+	"
+done
+
+test_done

diff --git a/builtin/grep.c b/builtin/grep.c
index 3ffb5b4e81..a191e2976b 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -495,6 +495,8 @@ static void compile_submodule_options(const struct grep_opt *opt,
 		break;
 	case GREP_PATTERN_TYPE_UNSPECIFIED:
 		break;
+	default:
+		die("BUG: Added a new grep pattern type without updating switch statement");
 	}
 
 	for (pattern = opt->pattern_list; pattern != NULL;

diff --git a/t/perf/p7820-grep-engines.sh b/t/perf/p7820-grep-engines.sh
new file mode 100755
index 0000000000..a3a1b9fa28
--- /dev/null
+++ b/t/perf/p7820-grep-engines.sh
@@ -0,0 +1,47 @@
+#!/bin/sh
+
+test_description="Comparison of git-grep's regex engines
+
+Set GIT_PERF_7820_GREP_OPTS in the environment to pass options to
+git-grep. Make sure to include a leading space,
+e.g. GIT_PERF_7820_GREP_OPTS=' -i'. Some options to try:
+
+	-i
+	-w
+	-v
+	-vi
+	-vw
+	-viw
+"
+
+. ./perf-lib.sh
+
+test_perf_large_repo
+test_checkout_worktree
+
+for pattern in \
+	'how.to' \
+	'^how to' \
+	'[how] to' \
+	'\(e.t[^ ]*\|v.ry\) rare' \
+	'm\(ú\|u\)lt.b\(æ\|y\)te'
+do
+	for engine in basic extended perl
+	do
+		if test $engine != "basic"
+		then
+			# Poor man's basic -> extended converter.
+			pattern=$(echo "$pattern" | sed 's/\\//g')
+		fi
+		test_perf "$engine grep$GIT_PERF_7820_GREP_OPTS '$pattern'" "
+			git -c grep.patternType=$engine grep$GIT_PERF_7820_GREP_OPTS -- '$pattern' >'out.$engine' || :
+		"
+	done
+
+	test_expect_success "assert that all engines found the same for$GIT_PERF_7820_GREP_OPTS '$pattern'" "
+		test_cmp 'out.basic' 'out.extended' &&
+		test_cmp 'out.basic' 'out.perl'
+	"
+done
+
+test_done

diff --git a/t/perf/p4220-log-grep-engines.sh b/t/perf/p4220-log-grep-engines.sh
new file mode 100755
index 0000000000..02793ac77b
--- /dev/null
+++ b/t/perf/p4220-log-grep-engines.sh
@@ -0,0 +1,44 @@
+#!/bin/sh
+
+test_description="Comparison of git-log's --grep regex engines
+
+Set GIT_PERF_4220_LOG_OPTS in the environment to pass options to
+git-grep. Make sure to include a leading space,
+e.g. GIT_PERF_4220_LOG_OPTS=' -i'. Some options to try:
+
+	-i
+	--invert-grep
+	-i --invert-grep
+"
+
+. ./perf-lib.sh
+
+test_perf_large_repo
+test_checkout_worktree
+
+for pattern in \
+	'how.to' \
+	'^how to' \
+	'[how] to' \
+	'\(e.t[^ ]*\|v.ry\) rare' \
+	'm\(ú\|u\)lt.b\(æ\|y\)te'
+do
+	for engine in basic extended perl
+	do
+		if test $engine != "basic"
+		then
+			# Poor man's basic -> extended converter.
+			pattern=$(echo $pattern | sed 's/\\//g')
+		fi
+		test_perf "$engine log$GIT_PERF_4220_LOG_OPTS --grep='$pattern'" "
+			git -c grep.patternType=$engine log --pretty=format:%h$GIT_PERF_4220_LOG_OPTS --grep='$pattern' >'out.$engine' || :
+		"
+	done
+
+	test_expect_success "assert that all engines found the same for$GIT_PERF_4220_LOG_OPTS '$pattern'" "
+		test_cmp 'out.basic' 'out.extended' &&
+		test_cmp 'out.basic' 'out.perl'
+	"
+done
+
+test_done

diff --git a/t/perf/run b/t/perf/run
index b61024a830..beb4acc0e4 100755
--- a/t/perf/run
+++ b/t/perf/run
@@ -24,6 +24,7 @@ run_one_dir () {
 
 unpack_git_rev () {
 	rev=$1
+	echo "=== Unpacking $rev in build/$rev ==="
 	mkdir -p build/$rev
 	(cd "$(git rev-parse --show-cdup)" && git archive --format=tar $rev) |
 	(cd build/$rev && tar x)
@@ -37,6 +38,7 @@ build_git_rev () {
 			cp "../../$config" "build/$rev/"
 		fi
 	done
+	echo "=== Building $rev ==="
 	(
 		cd build/$rev &&
 		if test -n "$GIT_PERF_MAKE_COMMAND"

diff --git a/grep.c b/grep.c
index 47cee45067..bf6c2494fd 100644
--- a/grep.c
+++ b/grep.c
@@ -179,7 +179,6 @@ static void grep_set_pattern_type_option(enum grep_pattern_type pattern_type, st
 	case GREP_PATTERN_TYPE_BRE:
 		opt->fixed = 0;
 		opt->pcre = 0;
-		opt->regflags &= ~REG_EXTENDED;
 		break;
 
 	case GREP_PATTERN_TYPE_ERE:
@@ -191,13 +190,11 @@ static void grep_set_pattern_type_option(enum grep_pattern_type pattern_type, st
 	case GREP_PATTERN_TYPE_FIXED:
 		opt->fixed = 1;
 		opt->pcre = 0;
-		opt->regflags &= ~REG_EXTENDED;
 		break;
 
 	case GREP_PATTERN_TYPE_PCRE:
 		opt->fixed = 0;
 		opt->pcre = 1;
-		opt->regflags &= ~REG_EXTENDED;
 		break;
 	}
 }
@@ -415,10 +412,9 @@ static void compile_fixed_regexp(struct grep_pat *p, struct grep_opt *opt)
 {
 	struct strbuf sb = STRBUF_INIT;
 	int err;
-	int regflags;
+	int regflags = opt->regflags;
 
 	basic_regex_quote_buf(&sb, p->pattern);
-	regflags = opt->regflags & ~REG_EXTENDED;
 	if (opt->ignore_case)
 		regflags |= REG_ICASE;
 	err = regcomp(&p->regexp, sb.buf, regflags);

diff --git a/grep.c b/grep.c
index bf6c2494fd..79eb681c6e 100644
--- a/grep.c
+++ b/grep.c
@@ -321,6 +321,18 @@ static NORETURN void compile_regexp_failed(const struct grep_pat *p,
 	die("%s'%s': %s", where, p->pattern, error);
 }
 
+static int has_null(const char *s, size_t len)
+{
+	/*
+	 * regcomp cannot accept patterns with NULs so when using it
+	 * we consider any pattern containing a NUL fixed.
+	 */
+	if (memchr(s, 0, len))
+		return 1;
+
+	return 0;
+}
+
 #ifdef USE_LIBPCRE
 static void compile_pcre_regexp(struct grep_pat *p, const struct grep_opt *opt)
 {
@@ -394,12 +406,6 @@ static int is_fixed(const char *s, size_t len)
 {
 	size_t i;
 
-	/* regcomp cannot accept patterns with NULs so we
-	 * consider any pattern containing a NUL fixed.
-	 */
-	if (memchr(s, 0, len))
-		return 1;
-
 	for (i = 0; i < len; i++) {
 		if (is_regex_special(s[i]))
 			return 0;
@@ -451,7 +457,7 @@ static void compile_regexp(struct grep_pat *p, struct grep_opt *opt)
 	 * simple string match using kws.  p->fixed tells us if we
 	 * want to use kws.
 	 */
-	if (opt->fixed || is_fixed(p->pattern, p->patternlen))
+	if (opt->fixed || has_null(p->pattern, p->patternlen) || is_fixed(p->pattern, p->patternlen))
 		p->fixed = !icase || ascii_only;
 	else
 		p->fixed = 0;

diff --git a/grep.c b/grep.c
index 07512346b1..1157529115 100644
--- a/grep.c
+++ b/grep.c
@@ -321,6 +321,18 @@ static NORETURN void compile_regexp_failed(const struct grep_pat *p,
 	die("%s'%s': %s", where, p->pattern, error);
 }
 
+static int is_fixed(const char *s, size_t len)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++) {
+		if (is_regex_special(s[i]))
+			return 0;
+	}
+
+	return 1;
+}
+
 static int has_null(const char *s, size_t len)
 {
 	/*
@@ -402,18 +414,6 @@ static void free_pcre1_regexp(struct grep_pat *p)
 }
 #endif /* !USE_LIBPCRE1 */
 
-static int is_fixed(const char *s, size_t len)
-{
-	size_t i;
-
-	for (i = 0; i < len; i++) {
-		if (is_regex_special(s[i]))
-			return 0;
-	}
-
-	return 1;
-}
-
 static void compile_fixed_regexp(struct grep_pat *p, struct grep_opt *opt)
 {
 	struct strbuf sb = STRBUF_INIT;

Makefile, grep.c, grep.h, t/test-lib.sh

diff --git a/Makefile b/Makefile
index d1587452f1..374fbc7e58 100644
--- a/Makefile
+++ b/Makefile
@@ -1088,7 +1088,7 @@ ifdef NO_LIBGEN_H
 endif
 
 ifdef USE_LIBPCRE
-	BASIC_CFLAGS += -DUSE_LIBPCRE
+	BASIC_CFLAGS += -DUSE_LIBPCRE1
 	ifdef LIBPCREDIR
 		BASIC_CFLAGS += -I$(LIBPCREDIR)/include
 		EXTLIBS += -L$(LIBPCREDIR)/$(lib) $(CC_LD_DYNPATH)$(LIBPCREDIR)/$(lib)
@@ -2240,7 +2240,7 @@ GIT-BUILD-OPTIONS: FORCE
 	@echo TAR=\''$(subst ','\'',$(subst ','\'',$(TAR)))'\' >>$@+
 	@echo NO_CURL=\''$(subst ','\'',$(subst ','\'',$(NO_CURL)))'\' >>$@+
 	@echo NO_EXPAT=\''$(subst ','\'',$(subst ','\'',$(NO_EXPAT)))'\' >>$@+
-	@echo USE_LIBPCRE=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE)))'\' >>$@+
+	@echo USE_LIBPCRE1=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE)))'\' >>$@+
 	@echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@+
 	@echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@+
 	@echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@+
diff --git a/grep.c b/grep.c
index 79eb681c6e..854f2404be 100644
--- a/grep.c
+++ b/grep.c
@@ -333,7 +333,7 @@ static int has_null(const char *s, size_t len)
 	return 0;
 }
 
-#ifdef USE_LIBPCRE
+#ifdef USE_LIBPCRE1
 static void compile_pcre_regexp(struct grep_pat *p, const struct grep_opt *opt)
 {
 	const char *error;
@@ -385,7 +385,7 @@ static void free_pcre_regexp(struct grep_pat *p)
 	pcre_free(p->pcre_extra_info);
 	pcre_free((void *)p->pcre_tables);
 }
-#else /* !USE_LIBPCRE */
+#else /* !USE_LIBPCRE1 */
 static void compile_pcre_regexp(struct grep_pat *p, const struct grep_opt *opt)
 {
 	die("cannot use Perl-compatible regexes when not compiled with USE_LIBPCRE");
@@ -400,7 +400,7 @@ static int pcrematch(struct grep_pat *p, const char *line, const char *eol,
 static void free_pcre_regexp(struct grep_pat *p)
 {
 }
-#endif /* !USE_LIBPCRE */
+#endif /* !USE_LIBPCRE1 */
 
 static int is_fixed(const char *s, size_t len)
 {
diff --git a/grep.h b/grep.h
index 267534ca24..073b0e4c92 100644
--- a/grep.h
+++ b/grep.h
@@ -1,7 +1,7 @@
 #ifndef GREP_H
 #define GREP_H
 #include "color.h"
-#ifdef USE_LIBPCRE
+#ifdef USE_LIBPCRE1
 #include <pcre.h>
 #else
 typedef int pcre;
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 04d857a42b..1d0f636cbd 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1014,7 +1014,7 @@ esac
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_PERL" && test_set_prereq PERL
 test -z "$NO_PYTHON" && test_set_prereq PYTHON
-test -n "$USE_LIBPCRE" && test_set_prereq PCRE
+test -n "$USE_LIBPCRE1" && test_set_prereq PCRE
 test -z "$NO_GETTEXT" && test_set_prereq GETTEXT
 
 # Can we rely on git's output in the C locale?

grep.c, grep.h

diff --git a/grep.c b/grep.c
index 854f2404be..07512346b1 100644
--- a/grep.c
+++ b/grep.c
@@ -178,23 +178,23 @@ static void grep_set_pattern_type_option(enum grep_pattern_type pattern_type, st
 
 	case GREP_PATTERN_TYPE_BRE:
 		opt->fixed = 0;
-		opt->pcre = 0;
+		opt->pcre1 = 0;
 		break;
 
 	case GREP_PATTERN_TYPE_ERE:
 		opt->fixed = 0;
-		opt->pcre = 0;
+		opt->pcre1 = 0;
 		opt->regflags |= REG_EXTENDED;
 		break;
 
 	case GREP_PATTERN_TYPE_FIXED:
 		opt->fixed = 1;
-		opt->pcre = 0;
+		opt->pcre1 = 0;
 		break;
 
 	case GREP_PATTERN_TYPE_PCRE:
 		opt->fixed = 0;
-		opt->pcre = 1;
+		opt->pcre1 = 1;
 		break;
 	}
 }
@@ -334,7 +334,7 @@ static int has_null(const char *s, size_t len)
 }
 
 #ifdef USE_LIBPCRE1
-static void compile_pcre_regexp(struct grep_pat *p, const struct grep_opt *opt)
+static void compile_pcre1_regexp(struct grep_pat *p, const struct grep_opt *opt)
 {
 	const char *error;
 	int erroffset;
@@ -342,23 +342,23 @@ static void compile_pcre_regexp(struct grep_pat *p, const struct grep_opt *opt)
 
 	if (opt->ignore_case) {
 		if (has_non_ascii(p->pattern))
-			p->pcre_tables = pcre_maketables();
+			p->pcre1_tables = pcre_maketables();
 		options |= PCRE_CASELESS;
 	}
 	if (is_utf8_locale() && has_non_ascii(p->pattern))
 		options |= PCRE_UTF8;
 
-	p->pcre_regexp = pcre_compile(p->pattern, options, &error, &erroffset,
-				      p->pcre_tables);
-	if (!p->pcre_regexp)
+	p->pcre1_regexp = pcre_compile(p->pattern, options, &error, &erroffset,
+				      p->pcre1_tables);
+	if (!p->pcre1_regexp)
 		compile_regexp_failed(p, error);
 
-	p->pcre_extra_info = pcre_study(p->pcre_regexp, 0, &error);
-	if (!p->pcre_extra_info && error)
+	p->pcre1_extra_info = pcre_study(p->pcre1_regexp, 0, &error);
+	if (!p->pcre1_extra_info && error)
 		die("%s", error);
 }
 
-static int pcrematch(struct grep_pat *p, const char *line, const char *eol,
+static int pcre1match(struct grep_pat *p, const char *line, const char *eol,
 		regmatch_t *match, int eflags)
 {
 	int ovector[30], ret, flags = 0;
@@ -366,7 +366,7 @@ static int pcrematch(struct grep_pat *p, const char *line, const char *eol,
 	if (eflags & REG_NOTBOL)
 		flags |= PCRE_NOTBOL;
 
-	ret = pcre_exec(p->pcre_regexp, p->pcre_extra_info, line, eol - line,
+	ret = pcre_exec(p->pcre1_regexp, p->pcre1_extra_info, line, eol - line,
 			0, flags, ovector, ARRAY_SIZE(ovector));
 	if (ret < 0 && ret != PCRE_ERROR_NOMATCH)
 		die("pcre_exec failed with error code %d", ret);
@@ -379,25 +379,25 @@ static int pcrematch(struct grep_pat *p, const char *line, const char *eol,
 	return ret;
 }
 
-static void free_pcre_regexp(struct grep_pat *p)
+static void free_pcre1_regexp(struct grep_pat *p)
 {
-	pcre_free(p->pcre_regexp);
-	pcre_free(p->pcre_extra_info);
-	pcre_free((void *)p->pcre_tables);
+	pcre_free(p->pcre1_regexp);
+	pcre_free(p->pcre1_extra_info);
+	pcre_free((void *)p->pcre1_tables);
 }
 #else /* !USE_LIBPCRE1 */
-static void compile_pcre_regexp(struct grep_pat *p, const struct grep_opt *opt)
+static void compile_pcre1_regexp(struct grep_pat *p, const struct grep_opt *opt)
 {
 	die("cannot use Perl-compatible regexes when not compiled with USE_LIBPCRE");
 }
 
-static int pcrematch(struct grep_pat *p, const char *line, const char *eol,
+static int pcre1match(struct grep_pat *p, const char *line, const char *eol,
 		regmatch_t *match, int eflags)
 {
 	return 1;
 }
 
-static void free_pcre_regexp(struct grep_pat *p)
+static void free_pcre1_regexp(struct grep_pat *p)
 {
 }
 #endif /* !USE_LIBPCRE1 */
@@ -477,8 +477,8 @@ static void compile_regexp(struct grep_pat *p, struct grep_opt *opt)
 		return;
 	}
 
-	if (opt->pcre) {
-		compile_pcre_regexp(p, opt);
+	if (opt->pcre1) {
+		compile_pcre1_regexp(p, opt);
 		return;
 	}
 
@@ -834,8 +834,8 @@ void free_grep_patterns(struct grep_opt *opt)
 		case GREP_PATTERN_BODY:
 			if (p->kws)
 				kwsfree(p->kws);
-			else if (p->pcre_regexp)
-				free_pcre_regexp(p);
+			else if (p->pcre1_regexp)
+				free_pcre1_regexp(p);
 			else
 				regfree(&p->regexp);
 			free(p->pattern);
@@ -914,8 +914,8 @@ static int patmatch(struct grep_pat *p, char *line, char *eol,
 
 	if (p->fixed)
 		hit = !fixmatch(p, line, eol, match);
-	else if (p->pcre_regexp)
-		hit = !pcrematch(p, line, eol, match, eflags);
+	else if (p->pcre1_regexp)
+		hit = !pcre1match(p, line, eol, match, eflags);
 	else
 		hit = !regexec_buf(&p->regexp, line, eol - line, 1, match,
 				   eflags);
diff --git a/grep.h b/grep.h
index 073b0e4c92..38ac82b638 100644
--- a/grep.h
+++ b/grep.h
@@ -46,9 +46,9 @@ struct grep_pat {
 	size_t patternlen;
 	enum grep_header_field field;
 	regex_t regexp;
-	pcre *pcre_regexp;
-	pcre_extra *pcre_extra_info;
-	const unsigned char *pcre_tables;
+	pcre *pcre1_regexp;
+	pcre_extra *pcre1_extra_info;
+	const unsigned char *pcre1_tables;
 	kwset_t kws;
 	unsigned fixed:1;
 	unsigned ignore_case:1;
@@ -111,7 +111,7 @@ struct grep_opt {
 	int allow_textconv;
 	int extended;
 	int use_reflog_filter;
-	int pcre;
+	int pcre1;
 	int relative;
 	int pathname;
 	int null_following_name;

Makefile, t/README, t/test-lib.sh

diff --git a/Makefile b/Makefile
index 374fbc7e58..a79274e5e6 100644
--- a/Makefile
+++ b/Makefile
@@ -2242,6 +2242,7 @@ GIT-BUILD-OPTIONS: FORCE
 	@echo NO_EXPAT=\''$(subst ','\'',$(subst ','\'',$(NO_EXPAT)))'\' >>$@+
 	@echo USE_LIBPCRE1=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE)))'\' >>$@+
 	@echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@+
+	@echo NO_PTHREADS=\''$(subst ','\'',$(subst ','\'',$(NO_PTHREADS)))'\' >>$@+
 	@echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@+
 	@echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@+
 	@echo PAGER_ENV=\''$(subst ','\'',$(subst ','\'',$(PAGER_ENV)))'\' >>$@+
diff --git a/t/README b/t/README
index a90cb62583..2f95860369 100644
--- a/t/README
+++ b/t/README
@@ -817,6 +817,10 @@ use these, and "test_set_prereq" for how to define your own.
    Test is run on a filesystem which converts decomposed utf-8 (nfd)
    to precomposed utf-8 (nfc).
 
+ - PTHREADS
+
+   Git wasn't compiled with NO_PTHREADS=YesPlease.
+
 Tips for Writing Tests
 ----------------------
 
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 1d0f636cbd..43529451f9 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1013,6 +1013,7 @@ esac
 
 ( COLUMNS=1 && test $COLUMNS = 1 ) && test_set_prereq COLUMNS_CAN_BE_1
 test -z "$NO_PERL" && test_set_prereq PERL
+test -z "$NO_PTHREADS" && test_set_prereq PTHREADS
 test -z "$NO_PYTHON" && test_set_prereq PYTHON
 test -n "$USE_LIBPCRE1" && test_set_prereq PCRE
 test -z "$NO_GETTEXT" && test_set_prereq GETTEXT

builtin/pack-objects.c, t/t5300-pack-object.sh

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 9b4ba8a80d..efa21a15dd 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2472,8 +2472,10 @@ static int git_pack_config(const char *k, const char *v, void *cb)
 			die("invalid number of threads specified (%d)",
 			    delta_search_threads);
 #ifdef NO_PTHREADS
-		if (delta_search_threads != 1)
+		if (delta_search_threads != 1) {
 			warning("no threads support, ignoring %s", k);
+			delta_search_threads = 0;
+		}
 #endif
 		return 0;
 	}
diff --git a/t/t5300-pack-object.sh b/t/t5300-pack-object.sh
index 6ed23ee1d2..9c68b99251 100755
--- a/t/t5300-pack-object.sh
+++ b/t/t5300-pack-object.sh
@@ -447,7 +447,7 @@ test_expect_success !PTHREADS,C_LOCALE_OUTPUT 'pack-objects --threads=N or pack.
 
 	git -c pack.threads=2 pack-objects --stdout --all </dev/null >/dev/null 2>err &&
 	grep ^warning: err >warnings &&
-	test_must_fail test_line_count = 1 warnings &&
+	test_line_count = 1 warnings &&
 	grep -F "no threads support, ignoring pack.threads" err &&
 
 	git -c pack.threads=2 pack-objects --threads=4 --stdout --all </dev/null >/dev/null 2>err &&

diff --git a/builtin/grep.c b/builtin/grep.c
index 3c721b75a5..b1095362fb 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -73,14 +73,14 @@ static pthread_mutex_t grep_mutex;
 
 static inline void grep_lock(void)
 {
-	if (num_threads)
-		pthread_mutex_lock(&grep_mutex);
+	assert(num_threads);
+	pthread_mutex_lock(&grep_mutex);
 }
 
 static inline void grep_unlock(void)
 {
-	if (num_threads)
-		pthread_mutex_unlock(&grep_mutex);
+	assert(num_threads);
+	pthread_mutex_unlock(&grep_mutex);
 }
 
 /* Signalled when a new work_item is added to todo. */

builtin/grep.c, t/t7810-grep.sh

diff --git a/builtin/grep.c b/builtin/grep.c
index a191e2976b..3c721b75a5 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -289,6 +289,17 @@ static int grep_cmd_config(const char *var, const char *value, void *cb)
 		if (num_threads < 0)
 			die(_("invalid number of threads specified (%d) for %s"),
 			    num_threads, var);
+#ifdef NO_PTHREADS
+		else if (num_threads && num_threads != 1) {
+			/*
+			 * TRANSLATORS: %s is the configuration
+			 * variable for tweaking threads, currently
+			 * grep.threads
+			 */
+			warning(_("no threads support, ignoring %s"), var);
+			num_threads = 0;
+		}
+#endif
 	}
 
 	return st;
@@ -1229,6 +1240,8 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	else if (num_threads < 0)
 		die(_("invalid number of threads specified (%d)"), num_threads);
 #else
+	if (num_threads)
+		warning(_("no threads support, ignoring --threads"));
 	num_threads = 0;
 #endif
 
diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index 561709ef6a..f106387820 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -791,6 +791,24 @@ do
 	"
 done
 
+test_expect_success !PTHREADS,C_LOCALE_OUTPUT 'grep --threads=N or pack.threads=N warns when no pthreads' '
+	git grep --threads=2 Hello hello_world 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 1 warnings &&
+	grep -F "no threads support, ignoring --threads" err &&
+	git -c grep.threads=2 grep Hello hello_world 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 1 warnings &&
+	grep -F "no threads support, ignoring grep.threads" err &&
+	git -c grep.threads=2 grep --threads=4 Hello hello_world 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 2 warnings &&
+	grep -F "no threads support, ignoring --threads" err &&
+	grep -F "no threads support, ignoring grep.threads" err &&
+	git -c grep.threads=0 grep --threads=0 Hello hello_world 2>err &&
+	test_line_count = 0 err
+'
+
 test_expect_success 'grep from a subdirectory to search wider area (1)' '
 	mkdir -p s &&
 	(

diff --git a/t/t5300-pack-object.sh b/t/t5300-pack-object.sh
index 43a672c345..6ed23ee1d2 100755
--- a/t/t5300-pack-object.sh
+++ b/t/t5300-pack-object.sh
@@ -421,6 +421,42 @@ test_expect_success 'index-pack <pack> works in non-repo' '
 	test_path_is_file foo.idx
 '
 
+test_expect_success !PTHREADS,C_LOCALE_OUTPUT 'index-pack --threads=N or pack.threads=N warns when no pthreads' '
+	test_must_fail git index-pack --threads=2 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 1 warnings &&
+	grep -F "no threads support, ignoring --threads=2" err &&
+
+	test_must_fail git -c pack.threads=2 index-pack 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 1 warnings &&
+	grep -F "no threads support, ignoring pack.threads" err &&
+
+	test_must_fail git -c pack.threads=2 index-pack --threads=4 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 2 warnings &&
+	grep -F "no threads support, ignoring --threads=4" err &&
+	grep -F "no threads support, ignoring pack.threads" err
+'
+
+test_expect_success !PTHREADS,C_LOCALE_OUTPUT 'pack-objects --threads=N or pack.threads=N warns when no pthreads' '
+	git pack-objects --threads=2 --stdout --all </dev/null >/dev/null 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 1 warnings &&
+	grep -F "no threads support, ignoring --threads" err &&
+
+	git -c pack.threads=2 pack-objects --stdout --all </dev/null >/dev/null 2>err &&
+	grep ^warning: err >warnings &&
+	test_must_fail test_line_count = 1 warnings &&
+	grep -F "no threads support, ignoring pack.threads" err &&
+
+	git -c pack.threads=2 pack-objects --threads=4 --stdout --all </dev/null >/dev/null 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 2 warnings &&
+	grep -F "no threads support, ignoring --threads" err &&
+	grep -F "no threads support, ignoring pack.threads" err
+'
+
 #
 # WARNING!
 #

Documentation/rev-list-options.txt, revision.c, t/t4202-log.sh

diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt
index a46f70c2b1..9c44eae55d 100644
--- a/Documentation/rev-list-options.txt
+++ b/Documentation/rev-list-options.txt
@@ -91,6 +91,7 @@ endif::git-rev-list[]
 	Consider the limiting patterns to be fixed strings (don't interpret
 	pattern as a regular expression).
 
+-P::
 --perl-regexp::
 	Consider the limiting patterns to be Perl-compatible regular
 	expressions.
diff --git a/revision.c b/revision.c
index 4883cdd2d0..60329da1bd 100644
--- a/revision.c
+++ b/revision.c
@@ -1996,7 +1996,7 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		DIFF_OPT_SET(&revs->diffopt, PICKAXE_IGNORE_CASE);
 	} else if (!strcmp(arg, "--fixed-strings") || !strcmp(arg, "-F")) {
 		revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_FIXED;
-	} else if (!strcmp(arg, "--perl-regexp")) {
+	} else if (!strcmp(arg, "--perl-regexp") || !strcmp(arg, "-P")) {
 		revs->grep_filter.pattern_type_option = GREP_PATTERN_TYPE_PCRE;
 	} else if (!strcmp(arg, "--all-match")) {
 		revs->grep_filter.all_match = 1;
diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index dbed3efeee..2b07d1c0c2 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -404,8 +404,20 @@ test_expect_success 'log with various grep.patternType configurations & command-
 			--grep="(1|2)" >actual.fixed.short-arg &&
 		git log --pretty=tformat:%s -E \
 			--grep="\|2" >actual.extended.short-arg &&
+		if test_have_prereq PCRE
+		then
+			git log --pretty=tformat:%s -P \
+				--grep="[\d]\|" >actual.perl.short-arg
+		else
+			test_must_fail git log -P \
+				--grep="[\d]\|"
+		fi &&
 		test_cmp expect.fixed actual.fixed.short-arg &&
 		test_cmp expect.extended actual.extended.short-arg &&
+		if test_have_prereq PCRE
+		then
+			test_cmp expect.perl actual.perl.short-arg
+		fi &&
 
 		git log --pretty=tformat:%s --fixed-strings \
 			--grep="(1|2)" >actual.fixed.long-arg &&

grep.c, grep.h

diff --git a/grep.c b/grep.c
index 49e9aed457..3c0c30f033 100644
--- a/grep.c
+++ b/grep.c
@@ -351,7 +351,7 @@ static void compile_pcre1_regexp(struct grep_pat *p, const struct grep_opt *opt)
 	const char *error;
 	int erroffset;
 	int options = PCRE_MULTILINE;
-#ifdef PCRE_CONFIG_JIT
+#ifdef GIT_PCRE1_CAN_DO_MODERN_JIT
 	int canjit;
 #endif
 
@@ -372,7 +372,7 @@ static void compile_pcre1_regexp(struct grep_pat *p, const struct grep_opt *opt)
 	if (!p->pcre1_extra_info && error)
 		die("%s", error);
 
-#ifdef PCRE_CONFIG_JIT
+#ifdef GIT_PCRE1_CAN_DO_MODERN_JIT
 	pcre_config(PCRE_CONFIG_JIT, &canjit);
 	if (canjit == 1) {
 		p->pcre1_jit_stack = pcre_jit_stack_alloc(1, 1024 * 1024);
@@ -392,7 +392,7 @@ static int pcre1match(struct grep_pat *p, const char *line, const char *eol,
 	if (eflags & REG_NOTBOL)
 		flags |= PCRE_NOTBOL;
 
-#ifdef PCRE_CONFIG_JIT
+#ifdef GIT_PCRE1_CAN_DO_MODERN_JIT
 	if (p->pcre1_jit_on)
 		ret = pcre_jit_exec(p->pcre1_regexp, p->pcre1_extra_info, line,
 				    eol - line, 0, flags, ovector,
@@ -418,7 +418,7 @@ static void free_pcre1_regexp(struct grep_pat *p)
 {
 	pcre_free(p->pcre1_regexp);
 
-#ifdef PCRE_CONFIG_JIT
+#ifdef GIT_PCRE1_CAN_DO_MODERN_JIT
 	if (p->pcre1_jit_on) {
 		pcre_free_study(p->pcre1_extra_info);
 		pcre_jit_stack_free(p->pcre1_jit_stack);
diff --git a/grep.h b/grep.h
index 14f47189f9..73ef0ef8ec 100644
--- a/grep.h
+++ b/grep.h
@@ -3,6 +3,11 @@
 #include "color.h"
 #ifdef USE_LIBPCRE1
 #include <pcre.h>
+#ifdef PCRE_CONFIG_JIT
+#if PCRE_MAJOR >= 8 && PCRE_MINOR >= 32
+#define GIT_PCRE1_CAN_DO_MODERN_JIT
+#endif
+#endif
 #ifndef PCRE_STUDY_JIT_COMPILE
 #define PCRE_STUDY_JIT_COMPILE 0
 #endif

diff --git a/grep.h b/grep.h
index 73ef0ef8ec..b7b9d487b0 100644
--- a/grep.h
+++ b/grep.h
@@ -11,6 +11,9 @@
 #ifndef PCRE_STUDY_JIT_COMPILE
 #define PCRE_STUDY_JIT_COMPILE 0
 #endif
+#if PCRE_MAJOR <= 8 && PCRE_MINOR < 20
+typedef int pcre_jit_stack;
+#endif
 #else
 typedef int pcre;
 typedef int pcre_extra;

diff --git a/builtin/grep.c b/builtin/grep.c
index 12e62fcbf3..bd008cb100 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -1238,6 +1238,8 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 		num_threads = GREP_NUM_THREADS_DEFAULT;
 	else if (num_threads < 0)
 		die(_("invalid number of threads specified (%d)"), num_threads);
+	if (num_threads == 1)
+		num_threads = 0;
 #else
 	if (num_threads)
 		warning(_("no threads support, ignoring --threads"));

grep.c, grep.h

diff --git a/grep.c b/grep.c
index 1157529115..49e9aed457 100644
--- a/grep.c
+++ b/grep.c
@@ -351,6 +351,9 @@ static void compile_pcre1_regexp(struct grep_pat *p, const struct grep_opt *opt)
 	const char *error;
 	int erroffset;
 	int options = PCRE_MULTILINE;
+#ifdef PCRE_CONFIG_JIT
+	int canjit;
+#endif
 
 	if (opt->ignore_case) {
 		if (has_non_ascii(p->pattern))
@@ -365,9 +368,20 @@ static void compile_pcre1_regexp(struct grep_pat *p, const struct grep_opt *opt)
 	if (!p->pcre1_regexp)
 		compile_regexp_failed(p, error);
 
-	p->pcre1_extra_info = pcre_study(p->pcre1_regexp, 0, &error);
+	p->pcre1_extra_info = pcre_study(p->pcre1_regexp, PCRE_STUDY_JIT_COMPILE, &error);
 	if (!p->pcre1_extra_info && error)
 		die("%s", error);
+
+#ifdef PCRE_CONFIG_JIT
+	pcre_config(PCRE_CONFIG_JIT, &canjit);
+	if (canjit == 1) {
+		p->pcre1_jit_stack = pcre_jit_stack_alloc(1, 1024 * 1024);
+		if (!p->pcre1_jit_stack)
+			die("BUG: Couldn't allocate PCRE JIT stack");
+		pcre_assign_jit_stack(p->pcre1_extra_info, NULL, p->pcre1_jit_stack);
+		p->pcre1_jit_on = 1;
+	}
+#endif
 }
 
 static int pcre1match(struct grep_pat *p, const char *line, const char *eol,
@@ -378,8 +392,17 @@ static int pcre1match(struct grep_pat *p, const char *line, const char *eol,
 	if (eflags & REG_NOTBOL)
 		flags |= PCRE_NOTBOL;
 
+#ifdef PCRE_CONFIG_JIT
+	if (p->pcre1_jit_on)
+		ret = pcre_jit_exec(p->pcre1_regexp, p->pcre1_extra_info, line,
+				    eol - line, 0, flags, ovector,
+				    ARRAY_SIZE(ovector), p->pcre1_jit_stack);
+	else
+#endif
+	/* PCRE_CONFIG_JIT !p->pcre1_jit_on else branch */
 	ret = pcre_exec(p->pcre1_regexp, p->pcre1_extra_info, line, eol - line,
 			0, flags, ovector, ARRAY_SIZE(ovector));
+
 	if (ret < 0 && ret != PCRE_ERROR_NOMATCH)
 		die("pcre_exec failed with error code %d", ret);
 	if (ret > 0) {
@@ -394,7 +417,16 @@ static int pcre1match(struct grep_pat *p, const char *line, const char *eol,
 static void free_pcre1_regexp(struct grep_pat *p)
 {
 	pcre_free(p->pcre1_regexp);
+
+#ifdef PCRE_CONFIG_JIT
+	if (p->pcre1_jit_on) {
+		pcre_free_study(p->pcre1_extra_info);
+		pcre_jit_stack_free(p->pcre1_jit_stack);
+	} else
+#endif
+	/* PCRE_CONFIG_JIT !p->pcre1_jit_on else branch */
 	pcre_free(p->pcre1_extra_info);
+
 	pcre_free((void *)p->pcre1_tables);
 }
 #else /* !USE_LIBPCRE1 */
diff --git a/grep.h b/grep.h
index 38ac82b638..14f47189f9 100644
--- a/grep.h
+++ b/grep.h
@@ -3,9 +3,13 @@
 #include "color.h"
 #ifdef USE_LIBPCRE1
 #include <pcre.h>
+#ifndef PCRE_STUDY_JIT_COMPILE
+#define PCRE_STUDY_JIT_COMPILE 0
+#endif
 #else
 typedef int pcre;
 typedef int pcre_extra;
+typedef int pcre_jit_stack;
 #endif
 #include "kwset.h"
 #include "thread-utils.h"
@@ -48,7 +52,9 @@ struct grep_pat {
 	regex_t regexp;
 	pcre *pcre1_regexp;
 	pcre_extra *pcre1_extra_info;
+	pcre_jit_stack *pcre1_jit_stack;
 	const unsigned char *pcre1_tables;
+	int pcre1_jit_on;
 	kwset_t kws;
 	unsigned fixed:1;
 	unsigned ignore_case:1;

Makefile, configure.ac, grep.c, grep.h, t/test-lib.sh

diff --git a/Makefile b/Makefile
index a79274e5e6..d77ca4c1a5 100644
--- a/Makefile
+++ b/Makefile
@@ -29,7 +29,12 @@ all::
 # Perl-compatible regular expressions instead of standard or extended
 # POSIX regular expressions.
 #
-# Define LIBPCREDIR=/foo/bar if your libpcre header and library files are in
+# Currently USE_LIBPCRE is a synonym for USE_LIBPCRE1, define
+# USE_LIBPCRE2 instead if you'd like to use version 2 of the PCRE
+# library. The USE_LIBPCRE flag will likely be changed to mean v2 by
+# default in future releases.
+#
+# Define LIBPCREDIR=/foo/bar if your PCRE header and library files are in
 # /foo/bar/include and /foo/bar/lib directories.
 #
 # Define HAVE_ALLOCA_H if you have working alloca(3) defined in that header.
@@ -1087,15 +1092,27 @@ ifdef NO_LIBGEN_H
 	COMPAT_OBJS += compat/basename.o
 endif
 
-ifdef USE_LIBPCRE
-	BASIC_CFLAGS += -DUSE_LIBPCRE1
-	ifdef LIBPCREDIR
-		BASIC_CFLAGS += -I$(LIBPCREDIR)/include
-		EXTLIBS += -L$(LIBPCREDIR)/$(lib) $(CC_LD_DYNPATH)$(LIBPCREDIR)/$(lib)
+USE_LIBPCRE1 ?= $(USE_LIBPCRE)
+
+ifneq (,$(USE_LIBPCRE1))
+	ifdef USE_LIBPCRE2
+$(error Only set USE_LIBPCRE1 (or its alias USE_LIBPCRE) or USE_LIBPCRE2, not both!)
 	endif
+
+	BASIC_CFLAGS += -DUSE_LIBPCRE1
 	EXTLIBS += -lpcre
 endif
 
+ifdef USE_LIBPCRE2
+	BASIC_CFLAGS += -DUSE_LIBPCRE2
+	EXTLIBS += -lpcre2-8
+endif
+
+ifdef LIBPCREDIR
+	BASIC_CFLAGS += -I$(LIBPCREDIR)/include
+	EXTLIBS += -L$(LIBPCREDIR)/$(lib) $(CC_LD_DYNPATH)$(LIBPCREDIR)/$(lib)
+endif
+
 ifdef HAVE_ALLOCA_H
 	BASIC_CFLAGS += -DHAVE_ALLOCA_H
 endif
@@ -2241,6 +2258,7 @@ GIT-BUILD-OPTIONS: FORCE
 	@echo NO_CURL=\''$(subst ','\'',$(subst ','\'',$(NO_CURL)))'\' >>$@+
 	@echo NO_EXPAT=\''$(subst ','\'',$(subst ','\'',$(NO_EXPAT)))'\' >>$@+
 	@echo USE_LIBPCRE1=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE)))'\' >>$@+
+	@echo USE_LIBPCRE2=\''$(subst ','\'',$(subst ','\'',$(USE_LIBPCRE2)))'\' >>$@+
 	@echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@+
 	@echo NO_PTHREADS=\''$(subst ','\'',$(subst ','\'',$(NO_PTHREADS)))'\' >>$@+
 	@echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@+
diff --git a/configure.ac b/configure.ac
index deeb968daa..11d083fbe0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -255,21 +255,61 @@ GIT_PARSE_WITH([openssl]))
 # Perl-compatible regular expressions instead of standard or extended
 # POSIX regular expressions.
 #
-# Define LIBPCREDIR=/foo/bar if your libpcre header and library files are in
+# Currently USE_LIBPCRE is a synonym for USE_LIBPCRE1, define
+# USE_LIBPCRE2 instead if you'd like to use version 2 of the PCRE
+# library. The USE_LIBPCRE flag will likely be changed to mean v2 by
+# default in future releases.
+#
+# Define LIBPCREDIR=/foo/bar if your PCRE header and library files are in
 # /foo/bar/include and /foo/bar/lib directories.
 #
 AC_ARG_WITH(libpcre,
-AS_HELP_STRING([--with-libpcre],[support Perl-compatible regexes (default is NO)])
+AS_HELP_STRING([--with-libpcre],[synonym for --with-libpcre1]),
+    if test "$withval" = "no"; then
+	USE_LIBPCRE1=
+    elif test "$withval" = "yes"; then
+	USE_LIBPCRE1=YesPlease
+    else
+	USE_LIBPCRE1=YesPlease
+	LIBPCREDIR=$withval
+	AC_MSG_NOTICE([Setting LIBPCREDIR to $LIBPCREDIR])
+        dnl USE_LIBPCRE1 can still be modified below, so don't substitute
+        dnl it yet.
+	GIT_CONF_SUBST([LIBPCREDIR])
+    fi)
+
+AC_ARG_WITH(libpcre1,
+AS_HELP_STRING([--with-libpcre1],[support Perl-compatible regexes via libpcre1 (default is NO)])
+AS_HELP_STRING([],           [ARG can be also prefix for libpcre library and headers]),
+    if test "$withval" = "no"; then
+	USE_LIBPCRE1=
+    elif test "$withval" = "yes"; then
+	USE_LIBPCRE1=YesPlease
+    else
+	USE_LIBPCRE1=YesPlease
+	LIBPCREDIR=$withval
+	AC_MSG_NOTICE([Setting LIBPCREDIR to $LIBPCREDIR])
+        dnl USE_LIBPCRE1 can still be modified below, so don't substitute
+        dnl it yet.
+	GIT_CONF_SUBST([LIBPCREDIR])
+    fi)
+
+AC_ARG_WITH(libpcre2,
+AS_HELP_STRING([--with-libpcre2],[support Perl-compatible regexes via libpcre2 (default is NO)])
 AS_HELP_STRING([],           [ARG can be also prefix for libpcre library and headers]),
+    if test -n "$USE_LIBPCRE1"; then
+        AC_MSG_ERROR([Only supply one of --with-libpcre1 or --with-libpcre2!])
+    fi
+
     if test "$withval" = "no"; then
-	USE_LIBPCRE=
+	USE_LIBPCRE2=
     elif test "$withval" = "yes"; then
-	USE_LIBPCRE=YesPlease
+	USE_LIBPCRE2=YesPlease
     else
-	USE_LIBPCRE=YesPlease
+	USE_LIBPCRE2=YesPlease
 	LIBPCREDIR=$withval
 	AC_MSG_NOTICE([Setting LIBPCREDIR to $LIBPCREDIR])
-        dnl USE_LIBPCRE can still be modified below, so don't substitute
+        dnl USE_LIBPCRE2 can still be modified below, so don't substitute
         dnl it yet.
 	GIT_CONF_SUBST([LIBPCREDIR])
     fi)
@@ -501,13 +541,11 @@ GIT_CONF_SUBST([NEEDS_SSL_WITH_CRYPTO])
 GIT_CONF_SUBST([NO_OPENSSL])
 
 #
-# Define USE_LIBPCRE if you have and want to use libpcre. Various
-# commands such as log and grep offer runtime options to use
-# Perl-compatible regular expressions instead of standard or extended
-# POSIX regular expressions.
+# Handle the USE_LIBPCRE1 and USE_LIBPCRE2 options potentially set
+# above.
 #
 
-if test -n "$USE_LIBPCRE"; then
+if test -n "$USE_LIBPCRE1"; then
 
 GIT_STASH_FLAGS($LIBPCREDIR)
 
@@ -517,7 +555,22 @@ AC_CHECK_LIB([pcre], [pcre_version],
 
 GIT_UNSTASH_FLAGS($LIBPCREDIR)
 
-GIT_CONF_SUBST([USE_LIBPCRE])
+GIT_CONF_SUBST([USE_LIBPCRE1])
+
+fi
+
+
+if test -n "$USE_LIBPCRE2"; then
+
+GIT_STASH_FLAGS($LIBPCREDIR)
+
+AC_CHECK_LIB([pcre2-8], [pcre2_config_8],
+[USE_LIBPCRE2=YesPlease],
+[USE_LIBPCRE2=])
+
+GIT_UNSTASH_FLAGS($LIBPCREDIR)
+
+GIT_CONF_SUBST([USE_LIBPCRE2])
 
 fi
 
diff --git a/grep.c b/grep.c
index 3c0c30f033..569cf9e290 100644
--- a/grep.c
+++ b/grep.c
@@ -179,22 +179,36 @@ static void grep_set_pattern_type_option(enum grep_pattern_type pattern_type, st
 	case GREP_PATTERN_TYPE_BRE:
 		opt->fixed = 0;
 		opt->pcre1 = 0;
+		opt->pcre2 = 0;
 		break;
 
 	case GREP_PATTERN_TYPE_ERE:
 		opt->fixed = 0;
 		opt->pcre1 = 0;
+		opt->pcre2 = 0;
 		opt->regflags |= REG_EXTENDED;
 		break;
 
 	case GREP_PATTERN_TYPE_FIXED:
 		opt->fixed = 1;
 		opt->pcre1 = 0;
+		opt->pcre2 = 0;
 		break;
 
 	case GREP_PATTERN_TYPE_PCRE:
 		opt->fixed = 0;
+#ifdef USE_LIBPCRE2
+		opt->pcre1 = 0;
+		opt->pcre2 = 1;
+#else
+		/* It's important that pcre1 always be assigned to
+		 * even when there's no USE_LIBPCRE* defined. We still
+		 * call the PCRE stub function, it just dies with
+		 * "cannot use Perl-compatible regexes[...]".
+		 */
 		opt->pcre1 = 1;
+		opt->pcre2 = 0;
+#endif
 		break;
 	}
 }
@@ -446,6 +460,126 @@ static void free_pcre1_regexp(struct grep_pat *p)
 }
 #endif /* !USE_LIBPCRE1 */
 
+#ifdef USE_LIBPCRE2
+static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt)
+{
+	int error;
+	PCRE2_UCHAR errbuf[256];
+	PCRE2_SIZE erroffset;
+	int options = PCRE2_MULTILINE;
+	const uint8_t *character_tables = NULL;
+	uint32_t canjit;
+	int jitret;
+
+	assert(opt->pcre2);
+
+	p->pcre2_compile_context = NULL;
+
+	if (opt->ignore_case) {
+		if (has_non_ascii(p->pattern)) {
+			character_tables = pcre2_maketables(NULL);
+			p->pcre2_compile_context = pcre2_compile_context_create(NULL);
+			pcre2_set_character_tables(p->pcre2_compile_context, character_tables);
+		}
+		options |= PCRE2_CASELESS;
+	}
+	if (is_utf8_locale() && has_non_ascii(p->pattern))
+		options |= PCRE2_UTF;
+
+	p->pcre2_pattern = pcre2_compile((PCRE2_SPTR)p->pattern,
+					 p->patternlen, options, &error, &erroffset,
+					 p->pcre2_compile_context);
+
+	if (p->pcre2_pattern) {
+		p->pcre2_match_data = pcre2_match_data_create_from_pattern(p->pcre2_pattern, NULL);
+		if (!p->pcre2_match_data)
+			die("BUG: Couldn't allocate PCRE2 match data");
+	} else {
+		pcre2_get_error_message(error, errbuf, sizeof(errbuf));
+		compile_regexp_failed(p, (const char *)&errbuf);
+	}
+
+	pcre2_config(PCRE2_CONFIG_JIT, &canjit);
+	if (canjit == 1) {
+		jitret = pcre2_jit_compile(p->pcre2_pattern, PCRE2_JIT_COMPLETE);
+		if (!jitret)
+			p->pcre2_jit_on = 1;
+		else
+			die("BUG: Couldn't JIT the PCRE2 pattern '%s', got '%d'\n", p->pattern, jitret);
+		p->pcre2_jit_stack = pcre2_jit_stack_create(1, 1024 * 1024, NULL);
+		if (!p->pcre2_jit_stack)
+			die("BUG: Couldn't allocate PCRE2 JIT stack");
+		p->pcre2_match_context = pcre2_match_context_create(NULL);
+		if (!p->pcre2_jit_stack)
+			die("BUG: Couldn't allocate PCRE2 match context");
+		pcre2_jit_stack_assign(p->pcre2_match_context, NULL, p->pcre2_jit_stack);
+	}
+}
+
+static int pcre2match(struct grep_pat *p, const char *line, const char *eol,
+		regmatch_t *match, int eflags)
+{
+	int ret, flags = 0;
+	PCRE2_SIZE *ovector;
+	PCRE2_UCHAR errbuf[256];
+
+	if (eflags & REG_NOTBOL)
+		flags |= PCRE2_NOTBOL;
+
+	if (p->pcre2_jit_on)
+		ret = pcre2_jit_match(p->pcre2_pattern, (unsigned char *)line,
+				      eol - line, 0, flags, p->pcre2_match_data,
+				      NULL);
+	else
+		ret = pcre2_match(p->pcre2_pattern, (unsigned char *)line,
+				  eol - line, 0, flags, p->pcre2_match_data,
+				  NULL);
+
+	if (ret < 0 && ret != PCRE2_ERROR_NOMATCH) {
+		pcre2_get_error_message(ret, errbuf, sizeof(errbuf));
+		die("%s failed with error code %d: %s",
+		    (p->pcre2_jit_on ? "pcre2_jit_match" : "pcre2_match"), ret,
+		    errbuf);
+	}
+	if (ret > 0) {
+		ovector = pcre2_get_ovector_pointer(p->pcre2_match_data);
+		ret = 0;
+		match->rm_so = (int)ovector[0];
+		match->rm_eo = (int)ovector[1];
+	}
+
+	return ret;
+}
+
+static void free_pcre2_pattern(struct grep_pat *p)
+{
+	pcre2_compile_context_free(p->pcre2_compile_context);
+	pcre2_code_free(p->pcre2_pattern);
+	pcre2_match_data_free(p->pcre2_match_data);
+	pcre2_jit_stack_free(p->pcre2_jit_stack);
+	pcre2_match_context_free(p->pcre2_match_context);
+}
+#else /* !USE_LIBPCRE2 */
+static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt)
+{
+	/* Unreachable until USE_LIBPCRE2 becomes synonymous with
+	 * USE_LIBPCRE. See the sibling comment in
+	 * grep_set_pattern_type_option().
+	 */
+	die("cannot use Perl-compatible regexes when not compiled with USE_LIBPCRE");
+}
+
+static int pcre2match(struct grep_pat *p, const char *line, const char *eol,
+		regmatch_t *match, int eflags)
+{
+	return 1;
+}
+
+static void free_pcre2_pattern(struct grep_pat *p)
+{
+}
+#endif /* !USE_LIBPCRE2 */
+
 static void compile_fixed_regexp(struct grep_pat *p, struct grep_opt *opt)
 {
 	struct strbuf sb = STRBUF_INIT;
@@ -509,6 +643,11 @@ static void compile_regexp(struct grep_pat *p, struct grep_opt *opt)
 		return;
 	}
 
+	if (opt->pcre2) {
+		compile_pcre2_pattern(p, opt);
+		return;
+	}
+
 	if (opt->pcre1) {
 		compile_pcre1_regexp(p, opt);
 		return;
@@ -868,6 +1007,8 @@ void free_grep_patterns(struct grep_opt *opt)
 				kwsfree(p->kws);
 			else if (p->pcre1_regexp)
 				free_pcre1_regexp(p);
+			else if (p->pcre2_pattern)
+				free_pcre2_pattern(p);
 			else
 				regfree(&p->regexp);
 			free(p->pattern);
@@ -948,6 +1089,8 @@ static int patmatch(struct grep_pat *p, char *line, char *eol,
 		hit = !fixmatch(p, line, eol, match);
 	else if (p->pcre1_regexp)
 		hit = !pcre1match(p, line, eol, match, eflags);
+	else if (p->pcre2_pattern)
+		hit = !pcre2match(p, line, eol, match, eflags);
 	else
 		hit = !regexec_buf(&p->regexp, line, eol - line, 1, match,
 				   eflags);
diff --git a/grep.h b/grep.h
index b7b9d487b0..b40afc2e2f 100644
--- a/grep.h
+++ b/grep.h
@@ -19,6 +19,16 @@ typedef int pcre;
 typedef int pcre_extra;
 typedef int pcre_jit_stack;
 #endif
+#ifdef USE_LIBPCRE2
+#define PCRE2_CODE_UNIT_WIDTH 8
+#include <pcre2.h>
+#else
+typedef int pcre2_code;
+typedef int pcre2_match_data;
+typedef int pcre2_compile_context;
+typedef int pcre2_match_context;
+typedef int pcre2_jit_stack;
+#endif
 #include "kwset.h"
 #include "thread-utils.h"
 #include "userdiff.h"
@@ -63,6 +73,12 @@ struct grep_pat {
 	pcre_jit_stack *pcre1_jit_stack;
 	const unsigned char *pcre1_tables;
 	int pcre1_jit_on;
+	pcre2_code *pcre2_pattern;
+	pcre2_match_data *pcre2_match_data;
+	pcre2_compile_context *pcre2_compile_context;
+	pcre2_match_context *pcre2_match_context;
+	pcre2_jit_stack *pcre2_jit_stack;
+	int pcre2_jit_on;
 	kwset_t kws;
 	unsigned fixed:1;
 	unsigned ignore_case:1;
@@ -126,6 +142,7 @@ struct grep_opt {
 	int extended;
 	int use_reflog_filter;
 	int pcre1;
+	int pcre2;
 	int relative;
 	int pathname;
 	int null_following_name;
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 43529451f9..f5da636bea 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -1015,7 +1015,7 @@ esac
 test -z "$NO_PERL" && test_set_prereq PERL
 test -z "$NO_PTHREADS" && test_set_prereq PTHREADS
 test -z "$NO_PYTHON" && test_set_prereq PYTHON
-test -n "$USE_LIBPCRE1" && test_set_prereq PCRE
+test -n "$USE_LIBPCRE1$USE_LIBPCRE2" && test_set_prereq PCRE
 test -z "$NO_GETTEXT" && test_set_prereq GETTEXT
 
 # Can we rely on git's output in the C locale?

diff --git a/builtin/grep.c b/builtin/grep.c
index b1095362fb..12e62fcbf3 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -224,7 +224,8 @@ static void start_threads(struct grep_opt *opt)
 		int err;
 		struct grep_opt *o = grep_opt_dup(opt);
 		o->output = strbuf_out;
-		o->debug = 0;
+		if (i)
+			o->debug = 0;
 		compile_grep_patterns(o);
 		err = pthread_create(&threads[i], NULL, run, o);
 
@@ -1167,8 +1168,6 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	if (!opt.fixed && opt.ignore_case)
 		opt.regflags |= REG_ICASE;
 
-	compile_grep_patterns(&opt);
-
 	/*
 	 * We have to find "--" in a separate pass, because its presence
 	 * influences how we will parse arguments that come before it.
@@ -1245,6 +1244,15 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	num_threads = 0;
 #endif
 
+	if (!num_threads)
+		/*
+		 * The compiled patterns on the main path are only
+		 * used when not using threading. Otherwise
+		 * start_threads() below calls compile_grep_patterns()
+		 * for each thread.
+		 */
+		compile_grep_patterns(&opt);
+
 #ifndef NO_PTHREADS
 	if (num_threads) {
 		if (!(opt.name_only || opt.unmatch_name_only || opt.count)