[PATCH] D124633: [SimplifyLibCalls] Pointers passed to libcalls must point to valid objects

[Dávid Bolvanský via Phabricator via llvm-commits]

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> c99: 7.21.2.1 "The memcpy function copies n characters from the object pointed to by s2 into the
> object pointed to by s1. If copying takes place between objects that overlap, the behavior
> is undefined."

**null is not a pointer to an object**

So even when size is zero, pointer(s) must be valid.

If this rule is broken, UBSan catches this UB without any problems, as recently shown in: https://reviews.llvm.org/D124524 / https://godbolt.org/z/qx4sK43f6


https://reviews.llvm.org/D124633

Files:
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/bcmp-1.ll
  llvm/test/Transforms/InstCombine/bcopy.ll
  llvm/test/Transforms/InstCombine/mem-deref-bytes-addrspaces.ll
  llvm/test/Transforms/InstCombine/mem-deref-bytes.ll
  llvm/test/Transforms/InstCombine/memcmp-1.ll
  llvm/test/Transforms/InstCombine/memcpy-1.ll
  llvm/test/Transforms/InstCombine/memcpy-2.ll
  llvm/test/Transforms/InstCombine/memmove-1.ll
  llvm/test/Transforms/InstCombine/memmove.ll
  llvm/test/Transforms/InstCombine/mempcpy.ll
  llvm/test/Transforms/InstCombine/memrchr-3.ll
  llvm/test/Transforms/InstCombine/memset-1.ll
  llvm/test/Transforms/InstCombine/memset_chk-1.ll
  llvm/test/Transforms/InstCombine/sprintf-1.ll
  llvm/test/Transforms/PhaseOrdering/ARM/arm_fill_q7.ll

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