[all-commits] [llvm/llvm-project] 05c3da: [MachineLICM] Do not rely on hasSideEffect when ha...

[Anatoly Trosinenko via All-commits]

  Branch: refs/heads/users/atrosinenko/machine-licm-implicit-defs
  Home:   https://github.com/llvm/llvm-project
  Commit: 05c3da95de35527ae56f187165de4828007876a8
      https://github.com/llvm/llvm-project/commit/05c3da95de35527ae56f187165de4828007876a8
  Author: Anatoly Trosinenko <atrosinenko at accesssoftek.com>
  Date:   2025-06-23 (Mon, 23 Jun 2025)

  Changed paths:
    M llvm/lib/CodeGen/MachineLICM.cpp
    M llvm/test/CodeGen/AArch64/mlicm-implicit-defs.mir

  Log Message:
  -----------
  [MachineLICM] Do not rely on hasSideEffect when handling impdefs

Take clobbered registers described as implicit-def operands into
account when deciding if an instruction can be moved.

When hasSideEffect was set to 0 in the definition of LOADgotAUTH,
MultiSource/Benchmarks/Ptrdist/ks/ks test from llvm-test-suite started
to crash. The issue was traced down to MachineLICM pass placing
LOADgotAUTH right after an unrelated copy to x16 like rewriting this
code:

    bb.0:
      renamable $x16 = COPY renamable $x12
      B %bb.1

    bb.1:
      ...
      /* use $x16 */
      ...
      renamable $x20 = LOADgotAUTH target-flags(aarch64-got) @some_variable, implicit-def dead $x16, implicit-def dead $x17, implicit-def dead $nzcv
      /* use $x20 */
      ...

like the following:

    bb.0:
      renamable $x16 = COPY renamable $x12
      renamable $x20 = LOADgotAUTH target-flags(aarch64-got) @some_variable, implicit-def dead $x16, implicit-def dead $x17, implicit-def dead $nzcv
      B %bb.1

    bb.1:
      ...
      /* use $x16 */
      ...
      /* use $x20 */
      ...



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