[llvm-commits] [PATCH] optimization of max-like struct for x86

[Manman Ren]

Hi Sean,

Thanks for providing the feedback.
This patch will generate 
xorl %ecx, %ecx
subl %edx, %eax
cmovsl %ecx, %eax
while the proposed sequence has a dependency chain from 1st instruction to 2nd then to 3rd.

-- Manman

On Apr 25, 2012, at 11:01 AM, Sean Silva <silvas at purdue.edu> wrote:

> Why not turn it into e.g.
> 
> cmp ebx, eax
> cmovg ebx, eax
> sub ebx, eax
> 
> ?
> 
> --Sean Silva
> 
> 
> 
> On Wed, Apr 25, 2012 at 12:33 PM, Manman Ren <mren at apple.com> wrote:
> 
> This patch is intended to optimize the following cases for x86:
> (b > a) ? (b-a) : 0
> (a < b) ? (b-a) : 0
> It will use cmovs in generated x86 code.
> 
> The patch modified one source file: lib/Target/X86/X86ISelLowering.cpp
> 
> Please review & provide feedback.
> Thanks,
> 
> 
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