[PATCH] D130922: [InstCombine] Add support for stpncpy folding

[Martin Sebor via Phabricator via llvm-commits]

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As in the case of `stlcpy`, the middle end support for `stpncpy` also consists solely of transforming calls to `__stpncpy_chk` to the standard function if the buffer overflow checking overhead can be avoided, but nothing else.  Continuing in the same vein as D130666 <https://reviews.llvm.org/D130666>, this change extends the support for `stpncpy` to also optimize a subset of calls to it, analogously to `strncpy`.  Both functions have the same semantics and differ only in the return value, with `stpncpy` returning a pointer either to the copied nul byte or to the last non-nul byte if the copy isn't a string.  In addition, it extends the folding of calls to both functions to nonconstant bounds when the source string is empty.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D130922

Files:
  llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/simplify-libcalls.ll
  llvm/test/Transforms/InstCombine/stpncpy-1.ll
  llvm/test/Transforms/InstCombine/strcpy-nonzero-as.ll
  llvm/test/Transforms/InstCombine/strncpy-1.ll
  llvm/test/Transforms/InstCombine/strncpy-4.ll

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