Use __attribute__((target(...))) for SSE4.2 CRC-32C support.

Presently, we check for compiler support for the required
intrinsics both with and without the -msse4.2 compiler flag, and
then depending on the results of those checks, we pick which files
to compile with which flags.  This is tedious and complicated, and
it results in unsustainable coding patterns such as separate files
for each portion of code that may need to be built with different
compiler flags.

This commit makes use of the newly-added support for
__attribute__((target(...))) in the SSE4.2 CRC-32C code.  This
simplifies both the configure-time checks and the build scripts,
and it allows us to place the functions that use the intrinsics in
files that we otherwise do not want to build with special CPU
instructions (although this commit refrains from doing so).  This
is also preparatory work for a proposed follow-up commit that will
further optimize the CRC-32C code with AVX-512 instructions.

While at it, this commit modifies meson's checks for SSE4.2 CRC
support to be the same as autoconf's.  meson was choosing whether
to use a runtime check based purely on whether -msse4.2 is
required, while autoconf has long checked for the __SSE4_2__
preprocessor symbol to decide.  meson's previous approach seems to
work just fine, but this change avoids needing to build multiple
test programs and to keep track of whether to actually use
pg_attribute_target().

Ideally we'd use __attribute__((target(...))) for ARMv8 CRC
support, too, but there's little point in doing so because until
clang 16, using the ARM intrinsics still requires special compiler
flags.  Perhaps we can re-evaluate this decision after some time
has passed.

Author: Raghuveer Devulapalli
Discussion: https://postgr.es/m/PH8PR11MB8286BE735A463468415D46B5FB5C2%40PH8PR11MB8286.namprd11.prod.outlook.com

1 files changed, 17 insertions, 15 deletions

diff --git a/config/c-compiler.m4 b/config/c-compiler.m4
index a129edb88e1..309d5b04b46 100644
--- a/config/c-compiler.m4
+++ b/config/c-compiler.m4
@@ -605,24 +605,26 @@ fi])# PGAC_HAVE_GCC__ATOMIC_INT64_CAS
 # test the 8-byte variant, _mm_crc32_u64, but it is assumed to be present if
 # the other ones are, on x86-64 platforms)
 #
-# An optional compiler flag can be passed as argument (e.g. -msse4.2). If the
-# intrinsics are supported, sets pgac_sse42_crc32_intrinsics, and CFLAGS_CRC.
+# If the intrinsics are supported, sets pgac_sse42_crc32_intrinsics.
 AC_DEFUN([PGAC_SSE42_CRC32_INTRINSICS],
-[define([Ac_cachevar], [AS_TR_SH([pgac_cv_sse42_crc32_intrinsics_$1])])dnl
-AC_CACHE_CHECK([for _mm_crc32_u8 and _mm_crc32_u32 with CFLAGS=$1], [Ac_cachevar],
-[pgac_save_CFLAGS=$CFLAGS
-CFLAGS="$pgac_save_CFLAGS $1"
-AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <nmmintrin.h>],
-  [unsigned int crc = 0;
-   crc = _mm_crc32_u8(crc, 0);
-   crc = _mm_crc32_u32(crc, 0);
-   /* return computed value, to prevent the above being optimized away */
-   return crc == 0;])],
+[define([Ac_cachevar], [AS_TR_SH([pgac_cv_sse42_crc32_intrinsics])])dnl
+AC_CACHE_CHECK([for _mm_crc32_u8 and _mm_crc32_u32], [Ac_cachevar],
+[AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <nmmintrin.h>
+    #if defined(__has_attribute) && __has_attribute (target)
+    __attribute__((target("sse4.2")))
+    #endif
+    static int crc32_sse42_test(void)
+    {
+      unsigned int crc = 0;
+      crc = _mm_crc32_u8(crc, 0);
+      crc = _mm_crc32_u32(crc, 0);
+      /* return computed value, to prevent the above being optimized away */
+      return crc == 0;
+    }],
+  [return crc32_sse42_test();])],
   [Ac_cachevar=yes],
-  [Ac_cachevar=no])
-CFLAGS="$pgac_save_CFLAGS"])
+  [Ac_cachevar=no])])
 if test x"$Ac_cachevar" = x"yes"; then
-  CFLAGS_CRC="$1"
   pgac_sse42_crc32_intrinsics=yes
 fi
 undefine([Ac_cachevar])dnl