[llvm-commits] [llvm] r62789 - in /llvm/trunk: lib/CodeGen/SelectionDAG/DAGCombiner.cpp lib/CodeGen/SelectionDAG/SelectionDAG.cpp test/CodeGen/X86/negate-add-zero.ll

[Dan Gohman]

On Jan 22, 2009, at 2:38 PM, Chris Lattner wrote:

>
> On Jan 22, 2009, at 1:58 PM, Dan Gohman wrote:
>
>> Author: djg
>> Date: Thu Jan 22 15:58:43 2009
>> New Revision: 62789
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=62789&view=rev
>> Log:
>> Don't create ISD::FNEG nodes after legalize if they aren't legal.
>>
>> Simplify x+0 to x in unsafe-fp-math mode. This avoids a bunch of
>> redundant work in many cases, because in unsafe-fp-math mode,
>> ISD::FADD with a constant is considered free to negate, so the
>> DAGCombiner often negates x+0 to -0-x thinking it's free, when
>> in reality the end result is -x, which is more expensive than x.
>>
>> Also, combine x*0 to 0.
>>
>> This fixes PR3374.
>
> awesome, thanks Dan!  Can you please use the 'more reduced' testcase
> in the PR, just to reduce the test size?

Hi Chris, the larger testcase actually has more interesting cases
in it than the 'more reduced' one.

Dan