[PATCH] D35267: Pass Divergence Analysis data to selection DAG to drive divergence dependent instruction selection
Alexander via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Wed Feb 14 01:00:20 PST 2018
alex-t added inline comments.
Comment at: lib/Target/AMDGPU/AMDGPUISelLowering.cpp:794
+ return true;
+ return DA->isDivergent(FLI->getValueFromVirtualReg(Reg));
> rampitec wrote:
> > alex-t wrote:
> > > rampitec wrote:
> > > > !DA || DA->isDivergent(...)
> > > >
> > > > You are using getAnalysisIfAvailable, so it can be missing.
> > > if DA == nulptr in the case above we'd return ((bool)!DA) true?
> > >
> > > maybe it's better return false for the targets that have no DA?
> > >
> > > I mean " DA && DA->isDivegent()" if we have no DA we return false. In case we have, the returned value will be defined by the isDivergent result
> > That is conservatively correct to return true. Presumably targets w/o DA will have no use of the bit anyway, but if they are it is dangerous to assume uniformness.
> > targets w/o DA will have no use of the bit anyway, but if they are it is dangerous
> Sounds a bit paranoid :) I just noted that returning "true" for the target that has no divergence at all looks misleading.
Moreover, targets that have no DA have neither overridden isSDNodeSourceOfDivergence and will never get here.
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