[PATCH] [AArch64] Lower sdiv x, pow2 using add + select + shift.

James Molloy james.molloy at arm.com
Thu Jul 10 03:22:18 PDT 2014

Hi Chad,


I’ve taken a look at the performance of that code sequence, and can confirm that it is no worse in all situations than the current sequence. In some situations it causes a ~5% performance uplift on A53, and in some cases a ~20% performance uplift in A57 (on a microbenchmark running this sequence in a loop).


So the code sequence itself looks good to me, but I haven’t yet looked at the implementation.






From: Chad Rosier [mailto:mcrosier at codeaurora.org] 
Sent: 09 July 2014 21:22
To: 'James Molloy'; reviews+D4438+public+a452d711668fdd91 at reviews.llvm.org
Cc: 'Tim Northover'; 'Chandler Carruth'; 'Jiangning Liu'; James Molloy; 'Jim Grosbach'; 'LLVM Commits'; silviu.baranga at gmail.com
Subject: RE: [PATCH] [AArch64] Lower sdiv x, pow2 using add + select + shift.




From: mankeyrabbit at gmail.com [mailto:mankeyrabbit at gmail.com] On Behalf Of James Molloy
Sent: Wednesday, July 09, 2014 3:25 PM
To: reviews+D4438+public+a452d711668fdd91 at reviews.llvm.org
Cc: mcrosier at codeaurora.org; Tim Northover; Chandler Carruth; Jiangning Liu; James Molloy; Jim Grosbach; LLVM Commits; silviu.baranga at gmail.com
Subject: Re: [PATCH] [AArch64] Lower sdiv x, pow2 using add + select + shift.


>> I can create a synthetic benchmark, if that helps.


>That would help a lot, and would save me from doing the exact same thing to test it on C-A57 :)


Ok, I’ll try to put something together shortly.




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