[all-commits] [llvm/llvm-project] c37942: [DAG] visitFREEZE - limit freezing of multiple ope...

[Simon Pilgrim via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c37942df00e0065c432099e041a04c4d4d148c3d
      https://github.com/llvm/llvm-project/commit/c37942df00e0065c432099e041a04c4d4d148c3d
  Author: Simon Pilgrim <llvm-dev at redking.me.uk>
  Date:   2025-07-22 (Tue, 22 Jul 2025)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    M llvm/test/CodeGen/AMDGPU/div_i128.ll
    M llvm/test/CodeGen/AMDGPU/llvm.round.f64.ll
    M llvm/test/CodeGen/AMDGPU/rem_i128.ll
    M llvm/test/CodeGen/AMDGPU/srem.ll
    M llvm/test/CodeGen/NVPTX/i1-select.ll
    M llvm/test/CodeGen/NVPTX/i128.ll
    M llvm/test/CodeGen/PowerPC/ppc64-P9-vabsd.ll
    M llvm/test/CodeGen/RISCV/fpclamptosat.ll
    M llvm/test/CodeGen/RISCV/intrinsic-cttz-elts-vscale.ll
    M llvm/test/CodeGen/RISCV/wide-scalar-shift-legalization.ll
    M llvm/test/CodeGen/SystemZ/pr60413.ll
    M llvm/test/CodeGen/X86/abds-neg.ll
    M llvm/test/CodeGen/X86/avg.ll
    M llvm/test/CodeGen/X86/div-rem-pair-recomposition-signed.ll
    M llvm/test/CodeGen/X86/div-rem-pair-recomposition-unsigned.ll
    M llvm/test/CodeGen/X86/freeze-vector.ll
    M llvm/test/CodeGen/X86/setcc-non-simple-type.ll

  Log Message:
  -----------
  [DAG] visitFREEZE - limit freezing of multiple operands (#149797)

This is a partial revert of #145939 (I've kept the BUILD_VECTOR(FREEZE(UNDEF), FREEZE(UNDEF), elt2, ...) canonicalization) as we're getting reports of infinite loops (#148084).

The issue appears to be due to deep chains of nodes and how visitFREEZE replaces all instances of an operand with a common frozen version - other users of the original frozen node then get added back to the worklist but might no longer be able to confirm a node isn't poison due to recursion depth limits on isGuaranteedNotToBeUndefOrPoison.

The issue still exists with the old implementation but by only allowing a single frozen operand it helps prevent cases of interdependent frozen nodes.

I'm still working on supporting multiple operands as its critical for topological DAG handling but need to get a fix in for trunk and 21.x.

Fixes #148084



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