[PATCH] D82395: Strlen loop idiom recognition and folding

[Muhammad Usman via Phabricator via llvm-commits]

musman created this revision.
musman added reviewers: alexr, nemanjai, sanjoy, hfinkel.
Herald added subscribers: llvm-commits, jdoerfert, hiraditya.
Herald added a project: LLVM.

This adds strlen to LoopIdiomRecognize.cpp and also recognizes strlens with 16 bit chars. For these cases, a new intrinsic (strlen16) is used. If a strlen/strlen16 function call is only used for zero equality comparison then it is replaced with a load of the first element. If a strlen16 intrinsic cannot be folded, it is expanded back out to the canonical loop form.

Examples that this recognizes:

  unsigned strlen1(char *Str) {
    char *Src = Str;
    if (!Src)
      return 0;
    for (; *Src;)
      Src++;
    return Src - Str;
  }
  
  unsigned strlen2(char *Str) {
    unsigned Len = 0;
    if (!Str)
      return 0;
    while(*Str) {
      Len++;
      Str++;
    }
    return Len;
  }


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D82395

Files:
  llvm/include/llvm/Analysis/ValueTracking.h
  llvm/include/llvm/IR/Intrinsics.td
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/lib/CodeGen/CodeGenPrepare.cpp
  llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/LoopIdiom/expand-strlen16.ll
  llvm/test/Transforms/LoopIdiom/recognize-strlen.ll
  llvm/test/Transforms/LoopIdiom/strlen-fold.ll

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