[all-commits] [llvm/llvm-project] 9a5b0f: Reapply "[InstCombine] Match scalable splats in m_...

[Luke Lau via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 9a5b0f302be2ce155d5a4a0f0ca998ecb9bca497
      https://github.com/llvm/llvm-project/commit/9a5b0f302be2ce155d5a4a0f0ca998ecb9bca497
  Author: Luke Lau <luke at igalia.com>
  Date:   2025-04-03 (Thu, 03 Apr 2025)

  Changed paths:
    M llvm/include/llvm/IR/PatternMatch.h
    M llvm/test/Transforms/InstCombine/select.ll
    M llvm/test/Transforms/InstCombine/shl-bo.ll
    M llvm/test/Transforms/InstCombine/shl-twice-constant.ll
    M llvm/test/Transforms/InstCombine/sub.ll
    M llvm/test/Transforms/InstSimplify/vec-icmp-of-cast.ll

  Log Message:
  -----------
  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.



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