[llvm] [MCP] Avoid Folding Spill Chains Over Across Source Clobbers (PR #207169)

[Matt Arsenault via llvm-commits]

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@@ -1337,6 +1337,9 @@ void MachineCopyPropagation::eliminateSpillageCopies(MachineBasicBlock &MBB) {
   // If a COPY's Source has use or def until next COPY defines the Source,
   // we put the COPY in this set to keep property#2.
   DenseSet<const MachineInstr *> CopySourceInvalid;
+  // Track uses of a register as a source for a previous COPY
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arsenm wrote:

This function is getting hard to follow. Every time I see a PR on this pass, a new map gets added. 

https://github.com/llvm/llvm-project/pull/207169