[all-commits] [llvm/llvm-project] ca5549: Reland "[msan] Apply handleGenericVectorConvertInt...

[Thurston Dang via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: ca5549224e06c5ed57332bf1bc89c0ac06c69e60
      https://github.com/llvm/llvm-project/commit/ca5549224e06c5ed57332bf1bc89c0ac06c69e60
  Author: Thurston Dang <thurston at google.com>
  Date:   2026-07-30 (Thu, 30 Jul 2026)

  Changed paths:
    M llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
    M llvm/test/Instrumentation/MemorySanitizer/AArch64/arm64-vcvt.ll
    M llvm/test/Instrumentation/MemorySanitizer/AArch64/arm64-vcvt_f32_su32.ll
    M llvm/test/Instrumentation/MemorySanitizer/AArch64/vararg_shadow.ll
    M llvm/test/Instrumentation/MemorySanitizer/X86/f16c-intrinsics-upgrade.ll
    M llvm/test/Instrumentation/MemorySanitizer/X86/vararg_shadow.ll
    M llvm/test/Instrumentation/MemorySanitizer/i386/vararg_shadow.ll

  Log Message:
  -----------
  Reland "[msan] Apply handleGenericVectorConvertIntrinsic() to fptrunc/fpext" (#213161)

Reverts llvm/llvm-project#204221 i.e., reapplies
https://github.com/llvm/llvm-project/pull/204197. The original patch was
reverted was due to a buildbot failure in vararg_shadow.cpp that relied
on undefined behavior as well as an unwarranted assumption that the
shadow is preserved when round-tripping from float->double->float. The
UB cases have been disabled in
https://github.com/llvm/llvm-project/pull/204246.

Original commit message:

The current instrumentation uses handleShadowOr(), which effectively
truncates or zero-extends the shadows for fptrunc/fpext respectively;
this is overly lax because floating-point has both mantissa and exponent
components (e.g., if the mantissa is initialized but the exponent is
uninitialized, an fptrunc might end up with a fully initialized shadow,
which is incorrect; conversely, if a floating-point value is fully
uninitialized, we want the fpext'ed shadow to be fully uninitialized,
not zero-extended). This patch strengthens the instrumentation of
fptrunc/fpext by using handleGenericVectorConvertIntrinsic(), which
applies an "all-or-nothing" approach to uninitialized bits of each
scalar.

Note: https://github.com/llvm/llvm-project/pull/203903 auto-upgraded
aarch64_neon_vcvtfp2hf and aarch64_neon_vcvthf2fp to fptrunc and fpext,
which had the effect of weakening MSan's instrumentation for those NEON
intrinsics. This patch restores the stronger instrumentation for them
(and also generalizes it to all instances of fptrunc and fpext).



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