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

[Matt Arsenault 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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arsenm wrote:

Is it possible to reverse the iteration order? This is doing a forward scan over the instructions. If we did this over the block backwards, the users would be processed first 

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