[PATCH] D35267: Pass Divergence Analysis data to selection DAG to drive divergence dependent instruction selection

[Alexander via Phabricator via llvm-commits]

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.


https://reviews.llvm.org/D35267