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Bug 1945507 - improve asm memory barrier in AnnotateMozCrashReason r=gsvelto

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Adding explicit reference to gMozCrashReason as an input memory operand
with r/w effect seems to prevent extra optimisation. The original
snippet is inspired from google benchmark implementation of
`DoNotOptimize`.

Differential Revision: https://phabricator.services.mozilla.com/D236553
This commit is contained in:
serge-sans-paille
2025-02-20 05:08:22 +00:00
parent feb5e07602
commit 187ba0c3f7
1 changed files with 7 additions and 3 deletions
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10
mfbt/Assertions.h
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@@ -53,9 +53,13 @@ MOZ_END_EXTERN_C
#if defined(MOZ_HAS_MOZGLUE) || defined(MOZILLA_INTERNAL_API)
static inline void AnnotateMozCrashReason(const char* reason) {
gMozCrashReason = reason;
// See bug 1681846, on 32-bit Android ARM the compiler removes the store to
// gMozCrashReason if this barrier is not present.
asm volatile("" ::: "memory");
// The following assembly fakes a memory read/write to the compiler, which
// prevents the removal of gMozCrashReason store. See bug 1681846 and 1945507.
# if defined(__clang__)
asm volatile("" : "+r,m"(gMozCrashReason) : : "memory");
# else
asm volatile("" : "+m,r"(gMozCrashReason) : : "memory");
# endif
}
# define MOZ_CRASH_ANNOTATE(...) AnnotateMozCrashReason(__VA_ARGS__)
#else