[MachineCSE] Use isAsCheapAsAMove in TargetInstrInfo

[• pcwang-thead]

Summary

Use target dependent isAsCheapAsAMove in TargetInstrInfo
instead of the default implementation in MachineInstr.

[lkail]

IIUC, this shouldn't be an NFC change, please provide test cases.

[• pcwang-thead]

In D113885#3131136, @lkail wrote:

IIUC, this shouldn't be an NFC change, please provide test cases.

I haven't found any cases, but I think it's obvious we should use the target dependent one.

The default implementation of TargetInstrInfo.isAsCheapAsAMove is just a call to MachineInstr.isAsCheapAsAMove, but targets for different archs may override it.

[• pcwang-thead]

Format code.

[• pcwang-thead]

Done in D132981.

llvm/lib/CodeGen/MachineCSE.cpp

bool MachineCSE::PerformCSE(MachineDomTreeNode *Node) {
 
   return Changed;
 }
 
 // We use stronger checks for PRE candidate rather than for CSE ones to embrace
 // checks inside ProcessBlockCSE(), not only inside isCSECandidate(). This helps
 // to exclude instrs created by PRE that won't be CSEed later.
 bool MachineCSE::isPRECandidate(MachineInstr *MI) {
-  if (!isCSECandidate(MI) ||
-      MI->isNotDuplicable() ||
-      MI->mayLoad() ||
-      MI->isAsCheapAsAMove() ||
-      MI->getNumDefs() != 1 ||
+  if (!isCSECandidate(MI) || MI->isNotDuplicable() || MI->mayLoad() ||
+      TII->isAsCheapAsAMove(*MI) || MI->getNumDefs() != 1 ||
       MI->getNumExplicitDefs() != 1)
     return false;
 
   for (const auto &def : MI->defs())
     if (!Register::isVirtualRegister(def.getReg()))
       return false;
 
   for (const auto &use : MI->uses())