[llvm-commits] [llvm] r136222 - /llvm/trunk/lib/Support/BlockFrequency.cpp

[Chris Lattner]

On Jul 27, 2011, at 9:00 AM, Jakub Staszak wrote:

> Author: kuba
> Date: Wed Jul 27 11:00:40 2011
> New Revision: 136222
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=136222&view=rev
> Log:
> Optimize 96-bit division a little bit.

How about:
  if (top_part1 == 0 && top_part2 == 0) 
    return low1/low2;
  .. slow path..
?

-Chris

> 
> Modified:
>    llvm/trunk/lib/Support/BlockFrequency.cpp
> 
> Modified: llvm/trunk/lib/Support/BlockFrequency.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/BlockFrequency.cpp?rev=136222&r1=136221&r2=136222&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Support/BlockFrequency.cpp (original)
> +++ llvm/trunk/lib/Support/BlockFrequency.cpp Wed Jul 27 11:00:40 2011
> @@ -46,8 +46,9 @@
> uint64_t div96bit(uint64_t W[2], uint32_t D) {
>   uint64_t y = W[0];
>   uint64_t x = W[1];
> +  int i;
> 
> -  for (int i = 1; i <= 64; ++i) {
> +  for (i = 1; i <= 64 && x; ++i) {
>     uint32_t t = (int)x >> 31;
>     x = (x << 1) | (y >> 63);
>     y = y << 1;
> @@ -57,7 +58,7 @@
>     }
>   }
> 
> -  return y;
> +  return y << (64 - i + 1);
> }
> 
> }
> 
> 
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