[llvm] [llvm][NVPTX] Fix quadratic runtime in ProxyRegErasure (PR #105730)

[Justin Fargnoli via llvm-commits]

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@@ -74,44 +72,42 @@ bool NVPTXProxyRegErasure::runOnMachineFunction(MachineFunction &MF) {
       case NVPTX::ProxyRegI32:
       case NVPTX::ProxyRegI64:
       case NVPTX::ProxyRegF32:
-      case NVPTX::ProxyRegF64:
-        replaceMachineInstructionUsage(MF, MI);
+      case NVPTX::ProxyRegF64: {
+        auto &InOp = *MI.uses().begin();
+        auto &OutOp = *MI.defs().begin();
+        assert(InOp.isReg() && "ProxyReg input should be a register.");
+        assert(OutOp.isReg() && "ProxyReg output should be a register.");
         RemoveList.push_back(&MI);
+        RAUWBatch.try_emplace(OutOp.getReg(), InOp.getReg());
         break;
       }
+      }
     }
   }
 
+  // If there were no proxy instructions, exit early.
+  if (RemoveList.empty())
+    return false;
+
+  // Erase the proxy instructions first.
   for (auto *MI : RemoveList) {
     MI->eraseFromParent();
   }
 
-  return !RemoveList.empty();
-}
-
-void NVPTXProxyRegErasure::replaceMachineInstructionUsage(MachineFunction &MF,
-                                                          MachineInstr &MI) {
-  auto &InOp = *MI.uses().begin();
-  auto &OutOp = *MI.defs().begin();
-
-  assert(InOp.isReg() && "ProxyReg input operand should be a register.");
-  assert(OutOp.isReg() && "ProxyReg output operand should be a register.");
-
+  // Now go replace the registers.
   for (auto &BB : MF) {
-    for (auto &I : BB) {
-      replaceRegisterUsage(I, OutOp, InOp);
+    for (auto &MI : BB) {
+      for (auto &Op : MI.uses()) {
+        if (Op.isReg()) {
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justinfargnoli wrote:

Ignorable nit: prefer early return. 

https://github.com/llvm/llvm-project/pull/105730