[llvm-commits] [llvm] r107904 - in /llvm/trunk: lib/Target/ARM/ARMISelLowering.cpp test/CodeGen/ARM/fpcmp-opt.ll

[Dale Johannesen]

On Jul 8, 2010, at 11:30 PMPDT, Chris Lattner wrote:

> On Jul 8, 2010, at 10:27 PM, Evan Cheng wrote:
> On Jul 8, 2010, at 1:15 PM, Chris Lattner wrote:
>>>
>>> On Jul 8, 2010, at 1:12 PM, Evan Cheng wrote:
>>>
>>>> Author: evancheng
>>>> Date: Thu Jul  8 15:12:24 2010
>>>> New Revision: 107904
>>>>
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=107904&view=rev
>>>> Log:
>>>> Check for FiniteOnlyFPMath as well.
>>>
>>> Evan, this xform is not target specific.  Is there any reason not  
>>> to implement it in dag combine?
>>
>> It's profitable on ARM because it requires a vmrs which is  
>> expensive. I am not sure if other targets can benefit from it. I am  
>> also extending it to support f64 case which may have huge benefit  
>> for certain flavors of ARM.
>
> I don't know of any target where an fp compare is cheaper than an  
> int compare.  (compare (load), (load)) is similar to the "store of  
> fp immediate" which we transform into an integer immediate in target  
> independent code.


This transform also transfers register pressure from FP registers to  
int registers.  On x86-32, and perhaps elsewhere, that is probably a  
bad idea.