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[PATCH v6 2/2] refs.c: SSE4.2 optimizations for check_refname_component

From
David Turner <dturner@twopensource.com>
Date
Jun 4, 2014, 03:38 UTC
Message-ID
<1401853091-15535-2-git-send-email-dturner@twitter.com>
In-Reply-To
<1401853091-15535-1-git-send-email-dturner@twitter.com>
Optimize check_refname_component using SSE4.2, where available.

git rev-parse HEAD is a good test-case for this, since it does almost nothing except parse refs. For one particular repo with about 60k refs, almost all packed, the timings are:

Look up table: 29 ms SSE4.2: 25 ms

This is about a 15% improvement.

The configure.ac changes include code from the GNU C Library written by Joseph S. Myers <joseph at codesourcery dot com>.

Signed-off-by: David Turner <dturner@twitter.com>
---
 Makefile           |   6 +++
 aclocal.m4         |   6 +++
 configure.ac       |  17 ++++++++
 git-compat-util.h  |  22 ++++++++++
 refs.c             | 117 ++++++++++++++++++++++++++++++++++++++++++++++-------
 t/t5511-refspec.sh |  13 ++++++
 6 files changed, 166 insertions(+), 15 deletions(-)
diff --git a/Makefile b/Makefile
index a53f3a8..dd2127a 100644
--- a/Makefile
+++ b/Makefile
@@ -1326,6 +1326,11 @@ else
 		COMPAT_OBJS += compat/win32mmap.o
 	endif
 endif
+ifdef NO_SSE42
+	BASIC_CFLAGS += -DNO_SSE42
+else
+	BASIC_CFLAGS += -msse4.2
+endif
 ifdef OBJECT_CREATION_USES_RENAMES
 	COMPAT_CFLAGS += -DOBJECT_CREATION_MODE=1
 endif
@@ -2199,6 +2204,7 @@ GIT-BUILD-OPTIONS: FORCE
 	@echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@
 	@echo NO_PYTHON=\''$(subst ','\'',$(subst ','\'',$(NO_PYTHON)))'\' >>$@
 	@echo NO_UNIX_SOCKETS=\''$(subst ','\'',$(subst ','\'',$(NO_UNIX_SOCKETS)))'\' >>$@
+	@echo NO_SSE42=\''$(subst ','\'',$(subst ','\'',$(NO_SSE42)))'\' >>$@
 ifdef TEST_OUTPUT_DIRECTORY
 	@echo TEST_OUTPUT_DIRECTORY=\''$(subst ','\'',$(subst ','\'',$(TEST_OUTPUT_DIRECTORY)))'\' >>$@
 endif
diff --git a/aclocal.m4 b/aclocal.m4
index f11bc7e..d9f3f19 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -38,3 +38,9 @@ AC_DEFUN([TYPE_SOCKLEN_T],
       [#include <sys/types.h>
 #include <sys/socket.h>])
 ])
+
+dnl Test a compiler option or options with an empty input file.
+dnl LIBC_TRY_CC_OPTION([options], [action-if-true], [action-if-false])
+AC_DEFUN([LIBC_TRY_CC_OPTION],
+[AS_IF([AC_TRY_COMMAND([${CC-cc} $1 -xc /dev/null -S -o /dev/null])],
+	[$2], [$3])])
diff --git a/configure.ac b/configure.ac
index b711254..3a5bda9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -382,6 +382,23 @@ AS_HELP_STRING([],[Tcl/Tk interpreter will be found in a system.]),
 GIT_PARSE_WITH(tcltk))
 #
 
+# Declare the with-sse42/without-sse42 options.
+AC_ARG_WITH(sse42,
+AS_HELP_STRING([--with-sse42],[use SSE4.2 instructions])
+AS_HELP_STRING([],[(default is YES if your compiler supports -msse4.2)]),
+GIT_PARSE_WITH(sse42))
+
+if test "$NO_SSE42" != "YesPlease"; then
+   dnl Check if -msse4.2 works.
+   AC_CACHE_CHECK(for SSE4.2 support, cc_cv_sse42, [dnl
+   LIBC_TRY_CC_OPTION([-msse4.2], [cc_cv_sse42=yes], [cc_cv_sse42=no])
+   ])
+   if test $cc_cv_sse42 = no; then
+     NO_SSE42=1
+   fi
+fi
+
+GIT_CONF_SUBST([NO_SSE42])
 
 ## Checks for programs.
 AC_MSG_NOTICE([CHECKS for programs])
diff --git a/git-compat-util.h b/git-compat-util.h
index f6d3a46..218d510 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -668,6 +668,28 @@ void git_qsort(void *base, size_t nmemb, size_t size,
 #endif
 #endif
 
+#ifndef NO_SSE42
+#include <nmmintrin.h>
+/*
+ * Clang ships with a version of nmmintrin.h that's incomplete; if
+ * necessary, we define the constants that we're going to use.
+ */
+#ifndef _SIDD_UBYTE_OPS
+#define _SIDD_UBYTE_OPS                 0x00
+#define _SIDD_CMP_EQUAL_ANY             0x00
+#define _SIDD_CMP_RANGES                0x04
+#define _SIDD_CMP_EQUAL_ORDERED         0x0c
+#define _SIDD_NEGATIVE_POLARITY         0x10
+#endif
+
+/* This is the system memory page size; it's used so that we can read
+ * outside the bounds of an allocation without segfaulting.
+ */
+#ifndef PAGE_SIZE
+#define PAGE_SIZE 4096
+#endif
+#endif
+
 #ifdef UNRELIABLE_FSTAT
 #define fstat_is_reliable() 0
 #else
diff --git a/refs.c b/refs.c
index 46139d2..2fe0075 100644
--- a/refs.c
+++ b/refs.c
@@ -24,6 +24,25 @@ static unsigned char refname_disposition[256] = {
 	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 4, 4
 };
 
+static int check_refname_component_trailer(const char *cp, const char *refname, int flags)
+{
+	if (cp == refname)
+		return 0; /* Component has zero length. */
+	if (refname[0] == '.') {
+		if (!(flags & REFNAME_DOT_COMPONENT))
+			return -1; /* Component starts with '.'. */
+		/*
+		 * Even if leading dots are allowed, don't allow "."
+		 * as a component (".." is prevented by a rule above).
+		 */
+		if (refname[1] == '\0')
+			return -1; /* Component equals ".". */
+	}
+	if (cp - refname >= 5 && !memcmp(cp - 5, ".lock", 5))
+		return -1; /* Refname ends with ".lock". */
+	return cp - refname;
+}
+
 /*
  * Try to read one refname component from the front of refname.
  * Return the length of the component found, or -1 if the component is
@@ -37,7 +56,7 @@ static unsigned char refname_disposition[256] = {
  * - it ends with ".lock"
  * - it contains a "\" (backslash)
  */
-static int check_refname_component(const char *refname, int flags)
+static int check_refname_component_1(const char *refname, int flags)
 {
 	const char *cp;
 	char last = '\0';
@@ -47,7 +66,7 @@ static int check_refname_component(const char *refname, int flags)
 		unsigned char disp = refname_disposition[ch];
 		switch(disp) {
 		case 1:
-			goto out;
+			return check_refname_component_trailer(cp, refname, flags);
 		case 2:
 			if (last == '.')
 				return -1; /* Refname contains "..". */
@@ -61,23 +80,91 @@ static int check_refname_component(const char *refname, int flags)
 		}
 		last = ch;
 	}
-out:
-	if (cp == refname)
-		return 0; /* Component has zero length. */
-	if (refname[0] == '.') {
-		if (!(flags & REFNAME_DOT_COMPONENT))
-			return -1; /* Component starts with '.'. */
+}
+
+#ifdef NO_SSE42
+#define check_refname_component check_refname_component_1
+#else
+#define SSE_VECTOR_BYTES 16
+
+/* Vectorized version of check_refname_component */
+static int check_refname_component(const char *refname, int flags)
+{
+	const __m128i *refname_vec = (__m128i*) refname;
+
+	/* Character ranges for characters forbidden in refs; see above */
+	static const __v16qi bad = {
+		0x01, 0x20,  0x7e, 0x7f,  0x5e, 0x5e,  0x3a, 0x3a,
+		0x5b, 0x5c,  0x2a, 0x2a,  0x3f, 0x3f,  0x3f, 0x3f};
+
+	static const __v16qi nonslashes = {
+		'\001', '/' -1, '/' + 1, 0xff,
+	};
+
+	static const __v16qi dotdot = {'.', '.', 0};
+	static const __v16qi atcurly = {'@', '{', 0};
+
+	const __m128i *vp;
+	const char *cp = (const char *)refname_vec;
+
+	int dotdotpos = SSE_VECTOR_BYTES, atcurlypos = SSE_VECTOR_BYTES;
+	for (vp = refname_vec; ; vp++) {
+		__m128i tmp;
+		int endpos;
+
 		/*
-		 * Even if leading dots are allowed, don't allow "."
-		 * as a component (".." is prevented by a rule above).
+		 * Handle case of forbidden substrings .. and @{ crossing
+		 * sixteen-byte boundaries
 		 */
-		if (refname[1] == '\0')
-			return -1; /* Component equals ".". */
+		if (dotdotpos == 15 && *cp == '.')
+			return -1;
+
+		if (atcurlypos == 15 && *cp == '{')
+			return -1;
+
+		if (((uintptr_t) vp % PAGE_SIZE) > PAGE_SIZE - SSE_VECTOR_BYTES)
+			/*
+			 * End-of-page; fall back to slow method for
+			 * this entire component.
+			 */
+			return check_refname_component_1(refname, flags);
+
+		tmp = _mm_lddqu_si128(vp);
+
+		/*
+		 * Find slashes or end-of-string. The double-negative
+		 * (negative-polarity search for non-slashes) is
+		 * necessary so that \0 will also be counted.
+		 */
+		endpos = _mm_cmpistri((__m128i) nonslashes, tmp,
+				      _SIDD_UBYTE_OPS | _SIDD_CMP_RANGES |
+				      _SIDD_NEGATIVE_POLARITY);
+
+		if (_mm_cmpestrc((__m128i) bad, SSE_VECTOR_BYTES, tmp, endpos,
+				 _SIDD_UBYTE_OPS | _SIDD_CMP_RANGES))
+			return -1;
+
+		dotdotpos = _mm_cmpestri((__m128i) dotdot, 2, tmp, endpos,
+					 _SIDD_UBYTE_OPS |
+					 _SIDD_CMP_EQUAL_ORDERED);
+		if (dotdotpos < 15)
+			return -1;
+
+		atcurlypos = _mm_cmpestri((__m128i) atcurly, 2, tmp, endpos,
+					  _SIDD_UBYTE_OPS |
+					  _SIDD_CMP_EQUAL_ORDERED);
+		if (atcurlypos < 15)
+			return -1;
+
+		if (endpos < SSE_VECTOR_BYTES) {
+			cp = ((const char*) vp) + endpos;
+			break;
+		}
+		cp = (const char*) vp + SSE_VECTOR_BYTES;
 	}
-	if (cp - refname >= 5 && !memcmp(cp - 5, ".lock", 5))
-		return -1; /* Refname ends with ".lock". */
-	return cp - refname;
+	return check_refname_component_trailer(cp, refname, flags);
 }
+#endif
 
 int check_refname_format(const char *refname, int flags)
 {
diff --git a/t/t5511-refspec.sh b/t/t5511-refspec.sh
index de6db86..7f1bd74 100755
--- a/t/t5511-refspec.sh
+++ b/t/t5511-refspec.sh
@@ -88,4 +88,17 @@ test_refspec fetch "refs/heads/${good}"
 bad=$(printf '\011tab')
 test_refspec fetch "refs/heads/${bad}"				invalid
 
+test_refspec fetch 'refs/heads/a-very-long-refname'
+test_refspec fetch 'refs/heads/.a-very-long-refname'		invalid
+test_refspec fetch 'refs/heads/abcdefgh0123..'			invalid
+test_refspec fetch 'refs/heads/abcdefgh01234..'			invalid
+test_refspec fetch 'refs/heads/abcdefgh012345..'		invalid
+test_refspec fetch 'refs/heads/abcdefgh0123456..'		invalid
+test_refspec fetch 'refs/heads/abcdefgh01234567..'		invalid
+test_refspec fetch 'refs/heads/abcdefgh0123.a'
+test_refspec fetch 'refs/heads/abcdefgh01234.a'
+test_refspec fetch 'refs/heads/abcdefgh012345.a'
+test_refspec fetch 'refs/heads/abcdefgh0123456.a'
+test_refspec fetch 'refs/heads/abcdefgh01234567.a'
+
 test_done

-- 
2.0.0.rc1.18.gf763c0f
Previous: David TurnerNext: Torsten Bögershausen
Message 2 of 14 in “refs.c: optimize check_refname_component()”
  1. 1/2 refs.c: optimize check_refname_component()David Turner, Jun 4, 2014
  2. 2/2 refs.c: SSE4.2 optimizations for check_refname_componentDavid Turner, Jun 4, 2014
  3. Torsten BögershausenJun 4, 2014
  4. Duy NguyenJun 4, 2014
  5. Torsten BögershausenJun 4, 2014
  6. David TurnerJun 4, 2014
  7. Torsten BögershausenJun 5, 2014
  8. Ondřej BílkaJun 5, 2014
  9. David TurnerJun 5, 2014
  10. Torsten BögershausenJun 5, 2014
  11. David TurnerJun 5, 2014
  12. David TurnerJun 4, 2014
  13. Junio C HamanoJun 4, 2014
  14. David TurnerJun 5, 2014

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