[PATCH 1/3] zstd: use ZSTD_cpuSupportsBmi2() in ZSTD_initStaticCCtx()

[Usama Arif]

ZSTD_initStaticCCtx() open-codes its BMI2 probe as
ZSTD_cpuid_bmi2(ZSTD_cpuid()).  Every other context setup -
ZSTD_initCCtx() and ZSTD_initDCtx_internal() - goes through
ZSTD_cpuSupportsBmi2(), which requires BMI1 as well as BMI2.

Requiring both is the correct test.  The alternate function bodies the
flag selects are tagged BMI2_TARGET_ATTRIBUTE, which is
TARGET_ATTRIBUTE("lzcnt,bmi,bmi2"), so the compiler may emit BMI1 and
LZCNT instructions in them; BMI2 alone does not make that safe.  No
shipping x86 CPU implements BMI2 without BMI1, so this is a latent
inconsistency rather than an observed failure.

Route the static path through the same helper.  That also leaves a
single place where the probe is issued, which the following patches
build on.

No functional change on any CPU in the field.

Signed-off-by: Usama Arif <usama.arif@xxxxxxxxx>
---
 lib/zstd/compress/zstd_compress.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/zstd/compress/zstd_compress.c b/lib/zstd/compress/zstd_compress.c
index c41a747413e01..4ab67d679bb63 100644
--- a/lib/zstd/compress/zstd_compress.c
+++ b/lib/zstd/compress/zstd_compress.c
@@ -142,7 +142,7 @@ ZSTD_CCtx* ZSTD_initStaticCCtx(void* workspace, size_t workspaceSize)
     cctx->blockState.nextCBlock = (ZSTD_compressedBlockState_t*)ZSTD_cwksp_reserve_object(&cctx->workspace, sizeof(ZSTD_compressedBlockState_t));
     cctx->tmpWorkspace = ZSTD_cwksp_reserve_object(&cctx->workspace, TMP_WORKSPACE_SIZE);
     cctx->tmpWkspSize = TMP_WORKSPACE_SIZE;
-    cctx->bmi2 = ZSTD_cpuid_bmi2(ZSTD_cpuid());
+    cctx->bmi2 = ZSTD_cpuSupportsBmi2();
     return cctx;
 }
 
-- 
2.53.0-Meta