[llvm] [MachineCSE] Enhance MachineCSE simple PRE to find common subexpressi… (PR #129860)

[via llvm-commits]

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@@ -887,6 +887,23 @@ bool MachineCSEImpl::ProcessBlockPRE(MachineDominatorTree *DT,
         NewMI.setDebugLoc(EmptyDL);
 
         NewMI.getOperand(0).setReg(NewReg);
+        for (MachineOperand &MO :
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emelliu wrote:

Maybe another simple solution is that put 
```
  ChangedPRE = PerformSimplePRE(DT);
  ChangedCSE = PerformCSE(DT->getRootNode());
```
in a do-while loop, stop until no changed.

https://github.com/llvm/llvm-project/pull/129860