[PATCH] D103009: [DSE] Transform memset + malloc --> calloc (PR25892)

[Evgenii Stepanov via Phabricator via llvm-commits]

eugenis added a comment.

In D103009#2879416 <https://reviews.llvm.org/D103009#2879416>, @yurai007 wrote:

> Hello @kcc @eugenis @pgousseau, sorry for bothering you. I added you to this review because transformation introduced in this change breaks msan_test (memcpy_unaligned/TestUnalignedMemcpy unit test).
> I'm quite convinced that after my change Clang does what GCC would do if compliled msan_test.cpp file with -Ofast: https://godbolt.org/z/f7s81hjaM
> Therefore I'm pretty sure that transformation works correctly (as on GCC) but it simply doesn't play well with MSan.
> Since I'm not MSan expert it would be great if you could take a look on this and confirm whether or not my understanding of issue is correct.

Right, so this change replaces malloc with calloc in

  if (src_is_poisoned)
    src_origin = __msan_get_origin(src);
  else
    memset(src, 0, sz);

because the other branch contains UB.
The test can be fixed by adding `__msan_allocated_memory(ptr, size)` before the call to `__msan_get_origin`, but I'd rather disable this optimization in functions with `sanitize_memory` attribute because it could make us miss bugs.

If possible, it's OK to disable only the CFG-aware part of the opt. I.e. malloc + memset in linear code (or even same BB) is fair game.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D103009/new/

https://reviews.llvm.org/D103009