[PATCH] D48354: [LoopIdiomRecognize] Support for loops that use LSHR instruction added.

[Olga Moldovanova via Phabricator via cfe-commits]

ovmold created this revision.
ovmold added a reviewer: craig.topper.
ovmold added a project: clang.
Herald added a subscriber: cfe-commits.

In the 'detectCTLZIdiom' function support for loops that use LSHR instruction instead of ASHR has been added.

The problem is that for the following piece of code no '@llvm.ctlz' instruction has been generated in the resulting test.ll file when compiling as "clang -S -O3 -march=core-avx2 -emit-llvm test.c". The reason for this is that the LSHR instruction is used instead of ASHR in the LLVM IR when we get into the 'detectCTLZIdiom' function.




int lzcnt(int x) {

   int count = 0;
   while (x > 0)  {
        count++;
        x = x >> 1;
   }
  return count;

}

int main() {

  int x;
  scanf("%d", &x);
  int y = lzcnt(x);
  printf("count  = %d\n", y);
  return 0;

}
=


Repository:
  rC Clang

https://reviews.llvm.org/D48354

Files:
  lib/Transforms/Scalar/LoopIdiomRecognize.cpp
  test/Transforms/LoopIdiom/X86/ctlz.ll

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