[llvm] TwoAddressInstructions: Move the rescheduled copy chain back to front (PR #227289)

[Christudasan Devadasan via llvm-commits]

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@@ -1065,8 +1065,9 @@ bool TwoAddressInstructionImpl::rescheduleMIBelowKill(
   if (LIS) {
     // We have to move the copies (and any interleaved debug instructions)
     // first so that the MBB is still well-formed when calling handleMove().
-    for (MachineBasicBlock::iterator MBBI = AfterMI; MBBI != End;) {
-      auto CopyMI = MBBI++;
+    // Move them back to front, so a copy never ends up above its source def.
+    for (MachineBasicBlock::iterator MIIt(MI); std::next(MIIt) != End;) {
+      MachineBasicBlock::iterator CopyMI = std::prev(End);
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cdevadas wrote:

Can't we hoist it somehow outside of the loop?

https://github.com/llvm/llvm-project/pull/227289