Fix incorrect results of AVX512 DGEMM kernel when built on pre-AVX2 machine

Origin: upstream, https://github.com/xianyi/OpenBLAS/pull/3579
Bug: https://github.com/xianyi/OpenBLAS/issues/2986
     https://github.com/xianyi/OpenBLAS/issues/3454
     https://github.com/xianyi/OpenBLAS/issues/3557
Bug-Debian: https://bugs.debian.org/1025480
Applied-Upstream: 0.3.21
Reviewed-by: Sébastien Villemot <sebastien@debian.org>
Last-Update: 2023-06-26

When building OpenBLAS with dynamic arch selection on x86-64 hardware
that does not support AVX2 (e.g. Intel Ivybridge or earlier), then
the AVX512 (SkylakeX) kernel for DGEMM would produce incorrect
results (of course when run on AVX512-capable hardware).

The problem was that the check for determining whether the compiler
is able to understand AVX512 assembly/intrinsics was doubly
incorrect: it would test the build machine capabilities (instead of
the compiler capabilities); and it would check for AVX2 instead of
AVX512. As a consequence, on pre-AVX2 hardware, the build system
would conclude that the compiler is not able to understand AVX512
primitives, and would create a broken AVX512 (SkylakeX) DGEMM kernel
(essentially a Haswell kernel, but with some wrong assumptions, hence
leading to incorrect numerical results).
Last-Update: 2023-06-26
Gbp-Pq: Name avx512-dgemm.patch

diff --git a/Makefile.prebuild b/Makefile.prebuild
index d6395da7b0b93afbb297b5254d97a8f5b82a125f..05f102d62a9b5797cfc4b1707abf4c7acd585a6a 100644 (file)
--- a/Makefile.prebuild
+++ b/Makefile.prebuild
@@ -67,7 +67,8 @@ endif
 
 
 getarch : getarch.c cpuid.S dummy $(CPUIDEMU)
-       $(HOSTCC) $(HOST_CFLAGS) $(EXFLAGS) -o $(@F) getarch.c cpuid.S $(CPUIDEMU)
+       avx512=$$(perl c_check - - gcc | grep NO_AVX512); \
+       $(HOSTCC) $(HOST_CFLAGS) $(EXFLAGS) $${avx512:+-D$${avx512}} -o $(@F) getarch.c cpuid.S $(CPUIDEMU)
 
 getarch_2nd : getarch_2nd.c config.h dummy
 ifndef TARGET_CORE

diff --git a/c_check b/c_check
index 970d475d7b8367f93141de85773612924858e457..1d2464dc5ba54bd845a362e2fd6ee9fea037610a 100644 (file)
--- a/c_check
+++ b/c_check
@@ -240,7 +240,7 @@ if (($architecture eq "x86") || ($architecture eq "x86_64")) {
 #      $tmpf = new File::Temp( UNLINK => 1 );
        ($fh,$tmpf) = tempfile( SUFFIX => '.c' , UNLINK => 1 );
        $code = '"vbroadcastss -4 * 4(%rsi), %zmm2"';
-       print $tmpf "#include <immintrin.h>\n\nint main(void){ __asm__ volatile($code); }\n";
+       print $fh "#include <immintrin.h>\n\nint main(void){ __asm__ volatile($code); }\n";
        $args = " -march=skylake-avx512 -c -o $tmpf.o $tmpf";
        if ($compiler eq "PGI") {
            $args = " -tp skylake -c -o $tmpf.o $tmpf";
@@ -264,7 +264,7 @@ if ($data =~ /HAVE_C11/) {
        $c11_atomics = 0;
     } else {
        ($fh,$tmpf) = tempfile( SUFFIX => '.c' , UNLINK => 1 );
-       print $tmpf "#include <stdatomic.h>\nint main(void){}\n";
+       print $fh "#include <stdatomic.h>\nint main(void){}\n";
        $args = " -c -o $tmpf.o $tmpf";
        my @cmd = ("$compiler_name $flags $args >/dev/null 2>/dev/null");
        system(@cmd) == 0;

diff --git a/getarch.c b/getarch.c
index f48944f36662cb43983d9d4b1f3e90fdad5c83d9..7d59d0e7092ebe410ac382d3903996b012a0bb94 100644 (file)
--- a/getarch.c
+++ b/getarch.c
@@ -94,14 +94,6 @@ USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <sys/sysinfo.h>
 #endif
 
-#if defined(__x86_64__) || defined(_M_X64)
-#if (( defined(__GNUC__)  && __GNUC__   > 6 && defined(__AVX2__)) || (defined(__clang__) && __clang_major__ >= 6))
-#else
-#ifndef NO_AVX512
-#define NO_AVX512
-#endif
-#endif
-#endif
 /* #define FORCE_P2            */
 /* #define FORCE_KATMAI                */
 /* #define FORCE_COPPERMINE    */