Update configure probes for CFLAGS needed for ARM CRC instructions.

tglsfdc · tglsfdc · commit 2fc0199a5015 · 2024-11-25T12:50:17.000-05:00
On ARM platforms where the baseline CPU target lacks CRC instructions, we need to supply a -march flag to persuade the compiler to compile such instructions. It turns out that our existing choice of "-march=armv8-a+crc" has not worked for some time, because recent gcc will interpret that as selecting software floating point, and then will spit up if the platform requires hard-float ABI, as most do nowadays. The end result was to silently fall back to software CRC, which isn't very desirable since in practice almost all currently produced ARM chips do have hardware CRC. We can fix this by using "-march=armv8-a+crc+simd" to enable the correct ABI choice. (This has no impact on the code actually generated, since neither of the files we compile with this flag does any floating-point stuff, let alone SIMD.) Keep the test for "-march=armv8-a+crc" since that's required for soft-float ABI, but try that second since most platforms we're likely to build on use hard-float. Since this isn't working as-intended on the last several years' worth of gcc releases, back-patch to all supported branches. Discussion: https://postgr.es/m/4496616.iHFcN1HehY@portable-bastien
diff --git a/configure b/configure
@@ -18651,7 +18651,8 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 # Check for ARMv8 CRC Extension intrinsics to do CRC calculations.
 #
 # First check if __crc32c* intrinsics can be used with the default compiler
-# flags. If not, check if adding -march=armv8-a+crc flag helps.
+# flags. If not, check if adding "-march=armv8-a+crc+simd" flag helps.
+# On systems using soft-float ABI, "-march=armv8-a+crc" is required instead.
 # CFLAGS_ARMV8_CRC32C is set if the extra flag is required.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __crc32cb, __crc32ch, __crc32cw, and __crc32cd with CFLAGS=" >&5
 $as_echo_n "checking for __crc32cb, __crc32ch, __crc32cw, and __crc32cd with CFLAGS=... " >&6; }
@@ -18694,7 +18695,48 @@ if test x"$pgac_cv_armv8_crc32c_intrinsics_" = x"yes"; then
 fi
 
 if test x"$pgac_armv8_crc32c_intrinsics" != x"yes"; then
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __crc32cb, __crc32ch, __crc32cw, and __crc32cd with CFLAGS=-march=armv8-a+crc" >&5
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __crc32cb, __crc32ch, __crc32cw, and __crc32cd with CFLAGS=-march=armv8-a+crc+simd" >&5
+$as_echo_n "checking for __crc32cb, __crc32ch, __crc32cw, and __crc32cd with CFLAGS=-march=armv8-a+crc+simd... " >&6; }
+if ${pgac_cv_armv8_crc32c_intrinsics__march_armv8_apcrcpsimd+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  pgac_save_CFLAGS=$CFLAGS
+CFLAGS="$pgac_save_CFLAGS -march=armv8-a+crc+simd"
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <arm_acle.h>
+int
+main ()
+{
+unsigned int crc = 0;
+   crc = __crc32cb(crc, 0);
+   crc = __crc32ch(crc, 0);
+   crc = __crc32cw(crc, 0);
+   crc = __crc32cd(crc, 0);
+   /* return computed value, to prevent the above being optimized away */
+   return crc == 0;
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  pgac_cv_armv8_crc32c_intrinsics__march_armv8_apcrcpsimd=yes
+else
+  pgac_cv_armv8_crc32c_intrinsics__march_armv8_apcrcpsimd=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+CFLAGS="$pgac_save_CFLAGS"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_armv8_crc32c_intrinsics__march_armv8_apcrcpsimd" >&5
+$as_echo "$pgac_cv_armv8_crc32c_intrinsics__march_armv8_apcrcpsimd" >&6; }
+if test x"$pgac_cv_armv8_crc32c_intrinsics__march_armv8_apcrcpsimd" = x"yes"; then
+  CFLAGS_ARMV8_CRC32C="-march=armv8-a+crc+simd"
+  pgac_armv8_crc32c_intrinsics=yes
+fi
+
+  if test x"$pgac_armv8_crc32c_intrinsics" != x"yes"; then
+    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __crc32cb, __crc32ch, __crc32cw, and __crc32cd with CFLAGS=-march=armv8-a+crc" >&5
 $as_echo_n "checking for __crc32cb, __crc32ch, __crc32cw, and __crc32cd with CFLAGS=-march=armv8-a+crc... " >&6; }
 if ${pgac_cv_armv8_crc32c_intrinsics__march_armv8_apcrc+:} false; then :
   $as_echo_n "(cached) " >&6
@@ -18734,6 +18776,7 @@ if test x"$pgac_cv_armv8_crc32c_intrinsics__march_armv8_apcrc" = x"yes"; then
   pgac_armv8_crc32c_intrinsics=yes
 fi
 
+  fi
 fi
 
 
diff --git a/configure.ac b/configure.ac
@@ -2166,11 +2166,15 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [
 # Check for ARMv8 CRC Extension intrinsics to do CRC calculations.
 #
 # First check if __crc32c* intrinsics can be used with the default compiler
-# flags. If not, check if adding -march=armv8-a+crc flag helps.
+# flags. If not, check if adding "-march=armv8-a+crc+simd" flag helps.
+# On systems using soft-float ABI, "-march=armv8-a+crc" is required instead.
 # CFLAGS_ARMV8_CRC32C is set if the extra flag is required.
 PGAC_ARMV8_CRC32C_INTRINSICS([])
 if test x"$pgac_armv8_crc32c_intrinsics" != x"yes"; then
-  PGAC_ARMV8_CRC32C_INTRINSICS([-march=armv8-a+crc])
+  PGAC_ARMV8_CRC32C_INTRINSICS([-march=armv8-a+crc+simd])
+  if test x"$pgac_armv8_crc32c_intrinsics" != x"yes"; then
+    PGAC_ARMV8_CRC32C_INTRINSICS([-march=armv8-a+crc])
+  fi
 fi
 AC_SUBST(CFLAGS_ARMV8_CRC32C)
 
