pmatos added a comment. In D150670#4368238 <https://reviews.llvm.org/D150670#4368238>, @pmatos wrote:
> In D150670#4352163 <https://reviews.llvm.org/D150670#4352163>, @nikic wrote: > >> 1. Say that we prefer preserving rotates over "simplifying" funnel shifts >> (ending up with the rot2 pattern). Basically by skipping the optimization at >> https://github.com/llvm/llvm-project/blob/7f54b38e28b3b66195de672848f2b5366d0d51e3/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp#L927-L931 >> if both fsh operands are the same. Assuming this doesn't cause test >> regressions, I think this would be acceptable to do. From a backend >> perspective, even for targets that have a native funnel shift (aarch64, >> x86), the difference between the rot1/rot2 patterns looks pretty neutral. OK, I just re-read your comment above and I am starting to assume that what you mean is skipping the optimization for all targets if the funnel shift is a rotate (i.e. same first two operands). Is this correct? > I am surprised this option is viable for example. This was my initial thought > to avoid the rotate, but I assumed adding something like : > > if (!getTarget().getTriple().isWasm()) { > APInt DemandedMaskLHS(DemandedMask.lshr(ShiftAmt)); > APInt DemandedMaskRHS(DemandedMask.shl(BitWidth - ShiftAmt)); > if (SimplifyDemandedBits(I, 0, DemandedMaskLHS, LHSKnown, Depth + 1) || > SimplifyDemandedBits(I, 1, DemandedMaskRHS, RHSKnown, Depth + 1)) > return I; > } > > would not be well received. Also, I cannot find precedent for doing this. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D150670/new/ https://reviews.llvm.org/D150670 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
