[llvm-commits] [llvm] r103881 - in /llvm/trunk: lib/Target/ARM/ARMISelLowering.cpp test/CodeGen/ARM/mul_const.ll

[Dale Johannesen]

On May 16, 2010, at 12:31 PM, Chris Lattner wrote:

> On May 16, 2010, at 10:32 AM, Jakob Stoklund Olesen wrote:
>>
>> But it is not clear that this transform would be a benefit to all  
>> targets, and the first one is better than the second for X86  
>> because it partially matches an addressing mode.
>
> The best way to handle this IMO is to have target-independent code  
> do this, and have TargetLower* expose hooks that the code can query  
> for its cost model.
>
> -Chris

I agree (and, fwiw, that's what gcc does).  You can do a reasonable  
job knowing the relative cycle counts for multiply-by-constant (which  
depends on the value of the constant in some hardware), add, sub, and  
shift.