[llvm] [MachineCP] Correctly handle register masks and sub-registers (PR #122734)

[Jinsong Ji via llvm-commits]

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@@ -978,9 +1012,11 @@ void MachineCopyPropagation::ForwardCopyPropagateBlock(MachineBasicBlock &MBB) {
         LLVM_DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
                    MaybeDead->dump());
 
-        // Make sure we invalidate any entries in the copy maps before erasing
-        // the instruction.
-        Tracker.clobberRegister(Reg, *TRI, *TII, UseCopyInstr);
+        // Invalidate all entries in the copy map which are not preserved by
+        // this register mask.
+        for (unsigned RegUnit : TRI->regunits(Reg))
+          if (!PreservedRegUnits.test(RegUnit))
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jsji wrote:

Looks like this might cause an invalid pointer problem. Some of the RegUnit in CopyInfo is still referencing the MaybeDead using pointer. Then after we call MaybeDead->eraseFromParent(); in following 2 lines, the MI pointer might become invalidated , we will then run into problem in next iteration

https://github.com/llvm/llvm-project/pull/122734