[llvm] [PowerPC]optimize the epilogue for restore non volatile cr fields (PR #202339)

[via llvm-commits]

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@@ -1768,6 +1769,22 @@ void PPCFrameLowering::emitEpilogue(MachineFunction &MF,
     }
   }
   assert(RBReg != ScratchReg && "Should have avoided ScratchReg");
+
+  auto BuildMoveToCR = [&]() {
+    assert(!Subtarget.is32BitELFABI() && "Non 32 Bit ELF ABI only.");
+    if (MustSaveCRs.size() == 1) {
+      // In Non 32 Bit ELF ABI, we are not required to restore all CR fields.
+      // If only one CR field was clobbered, use mtocrf to selectively
+      // restore just that field.
+      BuildMI(MBB, MBBI, dl, MoveToSingleCRInst, MustSaveCRs[0])
+          .addReg(TempReg, getKillRegState(true));
+    } else {
+      BuildMI(MBB, MBBI, dl, MoveToCRInst)
+          .addImm(255)
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RolandF77 wrote:

^^ Un-addressed comment.

https://github.com/llvm/llvm-project/pull/202339