[PATCH] D83595: [Draft][MSAN] Optimize away poisoning allocas that are always written before load

[Gui Andrade via Phabricator via llvm-commits]

guiand created this revision.
guiand added reviewers: eugenis, vitalybuka.
Herald added subscribers: llvm-commits, hiraditya.
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If we know that every path from an alloca leads to a store, we can optimize away poisoning its shadow (it'll be overwritten anyway).

I'm wondering if there's a better approach for finding all these def-uses. I investigated the `DominatorTree`, but I'm not sure how I would use that to check *all* the uses without blowing up the runtime for instrumenting an alloca to O(N^2) (N=# uses) or so.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D83595

Files:
  llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
  llvm/test/Instrumentation/MemorySanitizer/alloca.ll
  llvm/test/Instrumentation/MemorySanitizer/msan_x86_bts_asm.ll

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