[llvm-commits] patch: x86 vector udiv

[Duncan Sands]

Hi Peter,

> I've written a version in InstCombine which is now working.

I think it would be better if the same code worked for the scalar and
vector cases.  This means writing a bunch of utility functions but once
that's done hopefully it becomes trivial to convert all kinds of scalar
transforms to work also on vectors.  Maybe a good first step is to introduce
a helper class for representing either a ConstantInt or a vector of
ConstantInt, analogous to the helper classes in Operator.h (eg:
OverflowingBinaryOperator) or IntrinsicInst.h.

Ciao, Duncan.

>
> Please have a look and see if its at the right stage of compilation.
>
> Cheers,
> Pete
>
>
>
>
> On Nov 2, 2011, at 5:23 PM, Chris Lattner wrote:
>
>>
>> On Nov 1, 2011, at 6:04 PM, Eli Friedman wrote:
>>
>>> On Tue, Nov 1, 2011 at 5:40 PM, Peter Cooper<peter_cooper at apple.com>  wrote:
>>>> Hi
>>>>
>>>> Please review this patch for pr8429 to turn vector udiv into vector shrl instructions when dividing by powers of 2.  This was already done on scalars but not on vectors.
>>>>
>>>> I also found that vector shifts were always scalarised on x86 even with SSE on so i turned these into the equivalent intrinsics.
>>>
>>> The change to X86ISelLowering.cpp is wrong; the psrld instruction is
>>> not equivalent to ISD::SRL in the general case.
>>>
>>> For the rest of the changes, it would be better to handle this
>>> transformation in instcombine.
>>
>> I agree - this is a generally useful canonicalization that should be done early.
>>
>> -Chris
>
>
>
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