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

[Tobias Stadler 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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tobias-stadler wrote:

What about the DebugLoc? It has a TrackingMDRef, which does seem to benefit from moving, because it can call MetadataTracking::retrack(). I don't understand the details of MetadataTracking though.

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