[llvm-dev] RFC: [GlobalISel] propagating int/float type information

[Amara Emerson via llvm-dev]

My thinking was no, any regbanks assigned before RBS are only hints and do not have to be preserved. But for good code it would help if the legalizer preserves them.

This issue would be there with the other approaches too. Propagating information through destructive passes like the legalizer/combined is not going to be free in any case.

Amara

> On May 4, 2020, at 2:53 PM, Quentin Colombet <qcolombet at apple.com> wrote:
> 
> 
> 
>>> On May 4, 2020, at 2:01 PM, Matt Arsenault via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>> 
>>> 
>>> 
>>> On May 1, 2020, at 14:00, Amara Emerson <aemerson at apple.com> wrote:
>>> 
>>> The other thing we could do is to assign speculative regbanks to vregs during translation (if the target wants to opt-in), and then RBS can finalize the regbanks, changing some if it deems it necessary/optimal.
>> 
>> This seems reasonable to me. It wouldn’t require any new infrastructure
> 
> How would that work with illegal operations?
> 
> Would the legalizer have to preserve them?
> 
> Ditto with combines.
> 
> What I am saying is although this does not require any new infrastructure, this is not free adopt.
> 
> Cheers,
> -Quentin
> 
>> 
>> -Matt
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