[llvm] [AArch64] Fold UBFMXri to UBFMWri when it's an LSR or LSL alias (PR #106968)

[Csanád Hajdú via llvm-commits]

================
@@ -715,6 +719,45 @@ bool AArch64MIPeepholeOpt::visitFMOVDr(MachineInstr &MI) {
   return true;
 }
 
+bool AArch64MIPeepholeOpt::visitUBFMXri(MachineInstr &MI) {
+  // Check if the instruction is equivalent to a 32 bit LSR or LSL alias of
+  // UBFM, and replace the UBFMXri instruction with its 32 bit variant, UBFMWri.
+  int64_t Immr = MI.getOperand(2).getImm();
+  int64_t Imms = MI.getOperand(3).getImm();
+
+  bool IsLSR = Imms == 31 && Immr <= Imms;
+  bool IsLSL = Immr == Imms + 33;
+  if (IsLSR || IsLSL) {
+    if (IsLSL) {
+      Immr -= 32;
+    }
+
+    const TargetRegisterClass *RegClass64 =
+        TII->getRegClass(TII->get(MI.getOpcode()), 0, TRI, *MI.getMF());
+    const TargetRegisterClass *RegClass32 =
+        TRI->getSubRegisterClass(RegClass64, AArch64::sub_32);
+
+    Register DstReg32 = MRI->createVirtualRegister(RegClass32);
+    Register DstReg64 = MI.getOperand(0).getReg();
+    Register SrcReg = MI.getOperand(1).getReg();
+
+    BuildMI(*MI.getParent(), MI, MI.getDebugLoc(), TII->get(AArch64::UBFMWri),
+            DstReg32)
+        .addReg(SrcReg, 0, AArch64::sub_32)
----------------
Il-Capitano wrote:

I added the extra COPY with the latest commit.

https://github.com/llvm/llvm-project/pull/106968