[all-commits] [llvm/llvm-project] 8acba7: [PHIElimination] Account for PHI operands that app...

[Guy David via All-commits]

  Branch: refs/heads/users/guy-david/phi-elimination-operand-multi-use
  Home:   https://github.com/llvm/llvm-project
  Commit: 8acba7dbfa3ee142b59da56c5f8c7ee0c673d8a6
      https://github.com/llvm/llvm-project/commit/8acba7dbfa3ee142b59da56c5f8c7ee0c673d8a6
  Author: Guy David <guyda96 at gmail.com>
  Date:   2025-07-03 (Thu, 03 Jul 2025)

  Changed paths:
    M llvm/lib/CodeGen/PHIElimination.cpp
    M llvm/test/CodeGen/AArch64/PHIElimination-reuse-copy.mir
    M llvm/test/CodeGen/PowerPC/vsx.ll

  Log Message:
  -----------
  [PHIElimination] Account for PHI operands that appear more than once

During lowering, the PHI instruction is detached from the function and
thus it is not considered a user of its operands.
The previous implementation, which removed redundant COPY of COPY
instructions, skipped values which had any uses, because otherwise it
can break the function. However, it had a hidden assumption that there's
a single use for that operand in the detached PHI instruction.
By not taking into account that an operand can be referenced more than
once, it interfered with itself and created IMPLICIT_DEF's for some
incoming values instead of copying the correct ones.



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