llvm-project

9a5b0f30 - Reapply "[InstCombine] Match scalable splats in m_ImmConstant (#132522)" (#134262)

Reapply "[InstCombine] Match scalable splats in m_ImmConstant (#132522)" (#134262) This reapplies #132522. Previously casts of scalable m_ImmConstant splats weren't being folded by ConstantFoldCastOperand, triggering the "Constant-fold of ImmConstant should not fail" assertion. There are no changes to the code in this PR, instead we just needed #133207 to land first. A test has been added for the assertion in llvm/test/Transforms/InstSimplify/vec-icmp-of-cast.ll @icmp_ult_sext_scalable_splat_is_true. <hr/> #118806 fixed an infinite loop in FoldShiftByConstant that could occur when the shift amount was a ConstantExpr. However this meant that FoldShiftByConstant no longer kicked in for scalable vectors because scalable splats are represented by ConstantExprs. This fixes it by allowing scalable splats of non-ConstantExprs in m_ImmConstant, which also fixes a few other test cases where scalable splats were being missed. But I'm also hoping that UseConstantIntForScalableSplat will eventually remove the need for this. I noticed this when trying to reverse a combine on RISC-V in #132245, and saw that the resulting vector and scalar forms were different.