pmatos added a comment. 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. 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
