[llvm] [RISCV] Use DenseMap to track V0 definition. NFC (PR #84465)

[Luke Lau via llvm-commits]

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@@ -198,20 +198,29 @@ bool RISCVFoldMasks::runOnMachineFunction(MachineFunction &MF) {
   // $v0:vr = COPY %mask:vr
   // %x:vr = Pseudo_MASK %a:vr, %b:br, $v0:vr
   //
-  // Because $v0 isn't in SSA, keep track of it so we can check the mask operand
-  // on each pseudo.
-  MachineInstr *CurrentV0Def;
-  for (MachineBasicBlock &MBB : MF) {
-    CurrentV0Def = nullptr;
-    for (MachineInstr &MI : MBB) {
-      Changed |= convertToUnmasked(MI, CurrentV0Def);
-      Changed |= convertVMergeToVMv(MI, CurrentV0Def);
+  // Because $v0 isn't in SSA, keep track of its definition at each use so we
+  // can check mask operands.
+  for (const MachineBasicBlock &MBB : MF) {
+    const MachineInstr *CurrentV0Def = nullptr;
+    for (const MachineInstr &MI : MBB) {
+      auto IsV0 = [](const auto &MO) {
+        return MO.isReg() && MO.getReg() == RISCV::V0;
+      };
+      if (any_of(MI.uses(), IsV0))
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lukel97 wrote:

Thanks, thats exactly what I was looking for

https://github.com/llvm/llvm-project/pull/84465