[llvm] promote Pseduo Opcode from 32bit to 64bits after eliminating the `extsw` instruction in PPCMIPeepholes optimization (PR #85451)

[Amy Kwan via llvm-commits]

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@@ -5234,6 +5234,218 @@ bool PPCInstrInfo::isTOCSaveMI(const MachineInstr &MI) const {
 // We limit the max depth to track incoming values of PHIs or binary ops
 // (e.g. AND) to avoid excessive cost.
 const unsigned MAX_BINOP_DEPTH = 1;
+
+void PPCInstrInfo::replaceInstrAfterElimExt32To64(const Register &Reg,
+                                                  MachineRegisterInfo *MRI,
+                                                  unsigned BinOpDepth,
+                                                  LiveVariables *LV) const {
+  MachineInstr *MI = MRI->getVRegDef(Reg);
+  if (!MI)
+    return;
+
+  unsigned Opcode = MI->getOpcode();
+  bool IsReplaceInstr = false;
+  int NewOpcode = -1;
+
+  auto SetNewOpcode = [&](int NewOpc) {
+    if (!IsReplaceInstr) {
+      NewOpcode = NewOpc;
+      IsReplaceInstr = true;
+    }
+  };
+
+  switch (Opcode) {
+  case PPC::OR:
+    SetNewOpcode(PPC::OR8);
+    [[fallthrough]];
+  case PPC::ISEL:
+    SetNewOpcode(PPC::ISEL8);
+    [[fallthrough]];
+  case PPC::OR8:
+  case PPC::PHI:
+    if (BinOpDepth < MAX_BINOP_DEPTH) {
+      unsigned OperandEnd = 3, OperandStride = 1;
+      if (Opcode == PPC::PHI) {
+        OperandEnd = MI->getNumOperands();
+        OperandStride = 2;
+      }
+
+      for (unsigned I = 1; I != OperandEnd; I += OperandStride) {
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amy-kwan wrote:

It would be better to use `<` instead of `!=` here.

https://github.com/llvm/llvm-project/pull/85451