[llvm-commits] [PATCH] Add a instcombine optimization.
Benjamin Kramer
benny.kra at googlemail.com
Thu Jul 8 04:29:03 PDT 2010
On 08.07.2010, at 09:12, Duncan Sands wrote:
> Hi Benjamin,
>
>> The attached patch adds a new transformation to instcombine:
>> (X>s -1) ? C1 : C2 --> ((X>>s 31)& (C2 - C1)) + C1
>
> how about (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 xor C1)) xor C1
> instead? It might interact better with other bit fiddling optimizations.
> Otherwise the patch looks good.
Hmm, but we wont get a lea on x86 with xor. I don't think xor is profitable
unless we extend the optimization to transform non-const C1 and C2 too.
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