[all-commits] [llvm/llvm-project] 2efff4: [NFCI][msan] Show that shadow for partially undefi...

[Thurston Dang via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 2efff47363f18966cd37461323b5db5418183534
      https://github.com/llvm/llvm-project/commit/2efff47363f18966cd37461323b5db5418183534
  Author: Thurston Dang <thurston at google.com>
  Date:   2025-06-11 (Wed, 11 Jun 2025)

  Changed paths:
    M llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
    A llvm/test/Instrumentation/MemorySanitizer/partial-poison.ll

  Log Message:
  -----------
  [NFCI][msan] Show that shadow for partially undefined constant vectors is computed as fully initialized (#143823)

This happens because `getShadow(Value *V)` has a special case for fully undefined/poisoned values, but partially undefined values fall-through and are given a clean shadow. This leads to false negatives (no false positives).

Note: MSan correctly handles InsertElementInst, but the shadow of the initial constant vector may still be wrong and be propagated.

Showing that the same approximation happens for other composite types is left as an exercise for the reader.



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