Re: [PATCH v5 2/2] refs.c: SSE4.2 optimizations for check_refname_component

> diff --git a/git-compat-util.h b/git-compat-util.h
> index f6d3a46..254487a 100644
> --- a/git-compat-util.h
> +++ b/git-compat-util.h
> @@ -668,6 +668,26 @@ 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. It is
> + * assumed to be a power of 2. */
> +#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 dd28f2a..22a2dae 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 +80,86 @@ 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 '.'. */
> -		/*
> -		 * 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 ".". */
> +}
> +
> +#ifdef NO_SSE42
> +#define check_refname_component check_refname_component_1
> +#else
> +#define BLOCK_SIZE 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 = BLOCK_SIZE, atcurlypos = BLOCK_SIZE;
> +	for (vp = refname_vec; ; vp++) {
> +		__m128i tmp;
> +		int endpos;
> +
> +		/* Handle case of forbidden substrings .. and @{ crossing
> +		 * sixteen-byte boundaries */
> +		if (dotdotpos == 15 && *cp == '.')
> +			return -1;
> +
> +		if (atcurlypos == 15 && *cp == '{')
> +			return -1;
> +
> +		if (((uintptr_t) vp & (PAGE_SIZE - 1)) > PAGE_SIZE - BLOCK_SIZE)
> +			/* End-of-page; fall back to slow method for
> +			 * this entire component. */
> +			return check_refname_component_1(refname, flags);