[PATCH] D53174: X86/TargetTransformInfo: Report div/rem constant immediate costs as TCC_Free

[Matthias Braun via Phabricator via llvm-commits]

MatzeB added a comment.

This is currently not motivated by a benchmark but preparation for an upcoming commit of mine where I don't want ConstantHoisting to screw with dev/rem and mess up testcases.

However it does make sense in general and speeds up this microbenchmark by 10x on my measurements:

  #include <stdint.h>
  
  #define SIZE 100000
  
  void __attribute__((noinline)) divfoo(int64_t *signed_arr, uint64_t *unsigned_arr) {
      for (unsigned i = 0; i < SIZE; ++i) {
          signed_arr[i] /= 0xcafebabe5;
          unsigned_arr[i] /= 0xcafebabe5;
      }
  }
  
  int main(void) {
      static int64_t signed_arr[SIZE];
      static uint64_t unsigned_arr[SIZE];
      for (unsigned i = 0; i < 1000; ++i)
          divfoo(signed_arr, unsigned_arr);
  }


Repository:
  rL LLVM

https://reviews.llvm.org/D53174