[llvm] [CodeGen] Port DeadMachineInstructionElim to new pass manager (PR #80582)

[Arthur Eubanks via llvm-commits]

================
@@ -28,37 +29,57 @@ using namespace llvm;
 STATISTIC(NumDeletes,          "Number of dead instructions deleted");
 
 namespace {
-  class DeadMachineInstructionElim : public MachineFunctionPass {
-    bool runOnMachineFunction(MachineFunction &MF) override;
+class DeadMachineInstructionElimImpl {
+  const MachineRegisterInfo *MRI = nullptr;
+  const TargetInstrInfo *TII = nullptr;
+  LiveRegUnits LivePhysRegs;
 
-    const MachineRegisterInfo *MRI = nullptr;
-    const TargetInstrInfo *TII = nullptr;
-    LiveRegUnits LivePhysRegs;
+public:
+  bool runImpl(MachineFunction &MF);
 
-  public:
-    static char ID; // Pass identification, replacement for typeid
-    DeadMachineInstructionElim() : MachineFunctionPass(ID) {
-     initializeDeadMachineInstructionElimPass(*PassRegistry::getPassRegistry());
-    }
+private:
+  bool isDead(const MachineInstr *MI) const;
+  bool eliminateDeadMI(MachineFunction &MF);
+};
 
-    void getAnalysisUsage(AnalysisUsage &AU) const override {
-      AU.setPreservesCFG();
-      MachineFunctionPass::getAnalysisUsage(AU);
-    }
+class DeadMachineInstructionElim : public MachineFunctionPass {
+public:
+  static char ID; // Pass identification, replacement for typeid
 
-  private:
-    bool isDead(const MachineInstr *MI) const;
+  DeadMachineInstructionElim() : MachineFunctionPass(ID) {
+    initializeDeadMachineInstructionElimPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override {
+    if (skipFunction(MF.getFunction()))
+      return false;
+    return DeadMachineInstructionElimImpl().runImpl(MF);
+  }
 
-    bool eliminateDeadMI(MachineFunction &MF);
-  };
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+};
+} // namespace
+
+PreservedAnalyses
+DeadMachineInstructionElimPass::run(MachineFunction &MF,
+                                    MachineFunctionAnalysisManager &) {
+  if (!DeadMachineInstructionElimImpl().runImpl(MF))
+    return PreservedAnalyses::all();
+  PreservedAnalyses PA;
+  PA.preserveSet<CFGAnalyses>();
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aeubanks wrote:

I'm working on this sort of thing in https://github.com/aeubanks/llvm-project/commit/91e493983d7c2f135767e2a78c0247565011e864. We can port passes in the meantime though.

Question: can an MIR function pass ever modify the corresponding IR function? Module MIR passes can introduce dummy IR functions corresponding to new (e.g. outlined) MIR functions, but that's different.

https://github.com/llvm/llvm-project/pull/80582