[llvm] [MachineVerifier] Query TargetInstrInfo for PHI nodes. (PR #110507)

[Matt Arsenault via llvm-commits]

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@@ -2278,6 +2278,32 @@ class TargetInstrInfo : public MCInstrInfo {
     llvm_unreachable("unknown number of operands necessary");
   }
 
+  // This this instruction a PHI node.
+  // This function should be favored over MI.isPHI() as it allows backends to
+  // define additional PHI instructions.
+  virtual bool isPhiInstr(const MachineInstr &MI) const {
+    return MI.getOpcode() == TargetOpcode::G_PHI ||
+           MI.getOpcode() == TargetOpcode::PHI;
+  }
+
+  // Returns the number of [Value, Src] pairs this phi instruction has.
+  // Only valid to call on a phi node.
+  virtual unsigned getNumPhiIncomingPair(const MachineInstr &MI) const {
+    assert(isPhiInstr(MI));
+    // G_PHI/PHI only have a single operand before the pairs. 2 Operands per
+    // pair.
+    return (MI.getNumOperands() - 1) / 2;
+  }
+
+  // Returns the |index|'th [Value, Src] pair of this phi instruction.
+  virtual std::pair<MachineOperand, MachineBasicBlock *>
+  getPhiIncomingPair(const MachineInstr &MI, unsigned index) const {
+    // Behavior for G_PHI/PHI instructions.
+    MachineOperand Operand = MI.getOperand(index * 2 + 1);
+    MachineBasicBlock *MBB = MI.getOperand(index * 2 + 2).getMBB();
+    return {Operand, MBB};
+  }
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arsenm wrote:

I don't think the special case SPIRV operator should be treated like a generic phi like this (at least, not in any actual codegen uses). Can you attach sample failing MIR cases to the issue (or better yet, add machine verifier tests to this PR)? I think we'd be better off only touching something visible to the verifier, or otherwise avoiding clearing the NoPhis property for spirv 

https://github.com/llvm/llvm-project/pull/110507