[PATCH] D128954: [InstCombine] Transform strrchr to memrchr for constant strings

[Martin Sebor via Phabricator via llvm-commits]

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This change adds a `memrchr` library function call emitter and simplifies the `strrchr` call handler to use it instead of duplicating a subset of the former function's transformations in the handler.  This in turn enables transforming calls with the empty string `S` such as `strrchr(S, C)` to the test `C ? S : 0`.  A call to `memrchr` when the length of the string is known is also likely to be faster than one to `strrchr` with the corresponding arguments.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D128954

Files:
  llvm/include/llvm/Transforms/Utils/BuildLibCalls.h
  llvm/lib/Transforms/Utils/BuildLibCalls.cpp
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/strcall-no-nul.ll
  llvm/test/Transforms/InstCombine/strrchr-1.ll
  llvm/test/Transforms/InstCombine/strrchr-3.ll

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