[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:

The reason of needing user scan is that after clone first mi to CMBB the cloned inst'def reg doesn't have users untill processCSE. So for the second inst of subexpression, the ThenBB and the ElseBB is not same key in PREMap (operand are different), So when visit ElseBB it would not find second inst in PREMap.

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