[MachineOutliner] Refactor iterating over Candidate's instructions (#78972)

Make Candidate's front() and back() functions return references to
MachineInstr and introduce begin() and end() returning iterators, the
same way it is usually done in other container-like classes.

This makes possible to iterate over the instructions contained in
Candidate the same way one can iterate over MachineBasicBlock (note that
begin() and end() return bundled iterators, just like MachineBasicBlock
does, but no instr_begin() and instr_end() are defined yet).

1 files changed, 13 insertions, 14 deletions

diff --git a/llvm/lib/CodeGen/MachineOutliner.cpp b/llvm/lib/CodeGen/MachineOutliner.cpp
index a0769105c929..b8d3b2e30e6e 100644
--- a/llvm/lib/CodeGen/MachineOutliner.cpp
+++ b/llvm/lib/CodeGen/MachineOutliner.cpp
@@ -525,7 +525,7 @@ void MachineOutliner::emitNotOutliningCheaperRemark(
   MachineOptimizationRemarkEmitter MORE(*(C.getMF()), nullptr);
   MORE.emit([&]() {
     MachineOptimizationRemarkMissed R(DEBUG_TYPE, "NotOutliningCheaper",
-                                      C.front()->getDebugLoc(), C.getMBB());
+                                      C.front().getDebugLoc(), C.getMBB());
     R << "Did not outline " << NV("Length", StringLen) << " instructions"
       << " from " << NV("NumOccurrences", CandidatesForRepeatedSeq.size())
       << " locations."
@@ -538,7 +538,7 @@ void MachineOutliner::emitNotOutliningCheaperRemark(
     // Tell the user the other places the candidate was found.
     for (unsigned i = 1, e = CandidatesForRepeatedSeq.size(); i < e; i++) {
       R << NV((Twine("OtherStartLoc") + Twine(i)).str(),
-              CandidatesForRepeatedSeq[i].front()->getDebugLoc());
+              CandidatesForRepeatedSeq[i].front().getDebugLoc());
       if (i != e - 1)
         R << ", ";
     }
@@ -563,7 +563,7 @@ void MachineOutliner::emitOutlinedFunctionRemark(OutlinedFunction &OF) {
   for (size_t i = 0, e = OF.Candidates.size(); i < e; i++) {
 
     R << NV((Twine("StartLoc") + Twine(i)).str(),
-            OF.Candidates[i].front()->getDebugLoc());
+            OF.Candidates[i].front().getDebugLoc());
     if (i != e - 1)
       R << ", ";
   }
@@ -732,23 +732,22 @@ MachineFunction *MachineOutliner::createOutlinedFunction(
   // Insert the new function into the module.
   MF.insert(MF.begin(), &MBB);
 
-  MachineFunction *OriginalMF = FirstCand.front()->getMF();
+  MachineFunction *OriginalMF = FirstCand.front().getMF();
   const std::vector<MCCFIInstruction> &Instrs =
       OriginalMF->getFrameInstructions();
-  for (auto I = FirstCand.front(), E = std::next(FirstCand.back()); I != E;
-       ++I) {
-    if (I->isDebugInstr())
+  for (auto &MI : FirstCand) {
+    if (MI.isDebugInstr())
       continue;
 
     // Don't keep debug information for outlined instructions.
     auto DL = DebugLoc();
-    if (I->isCFIInstruction()) {
-      unsigned CFIIndex = I->getOperand(0).getCFIIndex();
+    if (MI.isCFIInstruction()) {
+      unsigned CFIIndex = MI.getOperand(0).getCFIIndex();
       MCCFIInstruction CFI = Instrs[CFIIndex];
       BuildMI(MBB, MBB.end(), DL, TII.get(TargetOpcode::CFI_INSTRUCTION))
           .addCFIIndex(MF.addFrameInst(CFI));
     } else {
-      MachineInstr *NewMI = MF.CloneMachineInstr(&*I);
+      MachineInstr *NewMI = MF.CloneMachineInstr(&MI);
       NewMI->dropMemRefs(MF);
       NewMI->setDebugLoc(DL);
       MBB.insert(MBB.end(), NewMI);
@@ -768,11 +767,11 @@ MachineFunction *MachineOutliner::createOutlinedFunction(
   LivePhysRegs LiveIns(TRI);
   for (auto &Cand : OF.Candidates) {
     // Figure out live-ins at the first instruction.
-    MachineBasicBlock &OutlineBB = *Cand.front()->getParent();
+    MachineBasicBlock &OutlineBB = *Cand.front().getParent();
     LivePhysRegs CandLiveIns(TRI);
     CandLiveIns.addLiveOuts(OutlineBB);
     for (const MachineInstr &MI :
-         reverse(make_range(Cand.front(), OutlineBB.end())))
+         reverse(make_range(Cand.begin(), OutlineBB.end())))
       CandLiveIns.stepBackward(MI);
 
     // The live-in set for the outlined function is the union of the live-ins
@@ -884,8 +883,8 @@ bool MachineOutliner::outline(Module &M,
     LLVM_DEBUG(dbgs() << "CREATE OUTLINED CALLS\n");
     for (Candidate &C : OF.Candidates) {
       MachineBasicBlock &MBB = *C.getMBB();
-      MachineBasicBlock::iterator StartIt = C.front();
-      MachineBasicBlock::iterator EndIt = C.back();
+      MachineBasicBlock::iterator StartIt = C.begin();
+      MachineBasicBlock::iterator EndIt = std::prev(C.end());
 
       // Insert the call.
       auto CallInst = TII.insertOutlinedCall(M, MBB, StartIt, *MF, C);