nlopes added a comment. In D143287#4202174 <https://reviews.llvm.org/D143287#4202174>, @ManuelJBrito wrote:
> Implementing the 128 to 512 casts by filling the rest of the vector with the > same definition of a nondeterministic_value is not correct because : > > a = freeze poison > v = <a, a> > > is not the same as > > v = freeze poison > > The only solution I'm seeing ,using the shufflevector, is doing the > conversion in two steps: > > - build a 256 vector with the upper half being undefined( freeze poison) > - build a 512 vector where the lower half is the previous 256 vector and the > upper half being undefined > > I think this would require two shuffles which is unfortunate. > > This would ensure no miscompilations due to multiple uses of the same freeze > undef/poison but would probably require some backend work to ensure the > pattern is recognized to emit efficient assembly. Semantically that is correct. But the backend may require some tweaks to recognize this pattern. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D143287/new/ https://reviews.llvm.org/D143287 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
