[llvm] [GlobalISel] Introduce `G_POISON` (PR #127825)

[Matt Arsenault via llvm-commits]

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In-Reply-To: <llvm.org/llvm/llvm-project/pull/127825 at github.com>


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@@ -2736,13 +2737,26 @@ bool CombinerHelper::matchAnyExplicitUseIsUndef(MachineInstr &MI) const {
   });
 }
 
+bool CombinerHelper::matchAnyExplicitUseIsPoison(MachineInstr &MI) const {
+  return any_of(MI.explicit_uses(), [this](const MachineOperand &MO) {
+    return MO.isReg() && getOpcodeDef(TargetOpcode::G_POISON, MO.getReg(), MRI);
+  });
+}
+
 bool CombinerHelper::matchAllExplicitUsesAreUndef(MachineInstr &MI) const {
   return all_of(MI.explicit_uses(), [this](const MachineOperand &MO) {
     return !MO.isReg() ||
            getOpcodeDef(TargetOpcode::G_IMPLICIT_DEF, MO.getReg(), MRI);
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arsenm wrote:

This should also catch the poison case (separate patch though, getOpcodeDef is a bad interface) 

https://github.com/llvm/llvm-project/pull/127825