[llvm] [AArch64][GlobalISel] Fix miscompile on carry-in selection (PR #68840)

[Amara Emerson via llvm-commits]

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@@ -3552,6 +3557,13 @@ bool AArch64InstructionSelector::select(MachineInstr &I) {
   return false;
 }
 
+bool AArch64InstructionSelector::selectAndRestoreState(MachineInstr &I) {
+  MachineIRBuilderState OldMIBState = MIB.getState();
+  bool Success = select(I);
+  MIB.getState() = std::move(OldMIBState);
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aemerson wrote:

Just add a `setState()` instead? The state can be copied by value, it's just some pointers and an iterator.

https://github.com/llvm/llvm-project/pull/68840