[WebAssembly] Simplify iterator navigations (NFC)

Summary:
- Replaces some uses of `MachineFunction::iterator(MBB)` with
  `MBB->getIterator()` and `MachineBasicBlock::iterator(MI)` with
  `MI->getIterator()`, which are simpler.
- Replaces some uses of `std::prev` of `std::next` that takes a
  MachineFunction or MachineBasicBlock iterator with `getPrevNode` and
  `getNextNode`, which are also simpler.

Reviewers: sbc100

Subscribers: dschuff, sunfish, jgravelle-google, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58913

llvm-svn: 355444

lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp

@@ -229,7 +229,7 @@ void WebAssemblyCFGStackify::placeBlockMarker(MachineBasicBlock &MBB) {
     return;
 
   assert(&MBB != &MF.front() && "Header blocks shouldn't have predecessors");
-  MachineBasicBlock *LayoutPred = &*std::prev(MachineFunction::iterator(&MBB));
+  MachineBasicBlock *LayoutPred = MBB.getPrevNode();
 
   // If the nearest common dominator is inside a more deeply nested context,
   // walk out to the nearest scope which isn't more deeply nested.
@@ -237,7 +237,7 @@ void WebAssemblyCFGStackify::placeBlockMarker(MachineBasicBlock &MBB) {
     if (MachineBasicBlock *ScopeTop = ScopeTops[I->getNumber()]) {
       if (ScopeTop->getNumber() > Header->getNumber()) {
         // Skip over an intervening scope.
-        I = std::next(MachineFunction::iterator(ScopeTop));
+        I = std::next(ScopeTop->getIterator());
       } else {
         // We found a scope level at an appropriate depth.
         Header = ScopeTop;
@@ -259,8 +259,7 @@ void WebAssemblyCFGStackify::placeBlockMarker(MachineBasicBlock &MBB) {
     // the BLOCK.
     if (MI.getOpcode() == WebAssembly::LOOP ||
         MI.getOpcode() == WebAssembly::TRY) {
-      auto *BottomBB =
-          &*std::prev(MachineFunction::iterator(BeginToEnd[&MI]->getParent()));
+      auto *BottomBB = BeginToEnd[&MI]->getParent()->getPrevNode();
       if (MBB.getNumber() > BottomBB->getNumber())
         AfterSet.insert(&MI);
 #ifndef NDEBUG
@@ -373,13 +372,13 @@ void WebAssemblyCFGStackify::placeLoopMarker(MachineBasicBlock &MBB) {
   // The operand of a LOOP is the first block after the loop. If the loop is the
   // bottom of the function, insert a dummy block at the end.
   MachineBasicBlock *Bottom = WebAssembly::getBottom(Loop);
-  auto Iter = std::next(MachineFunction::iterator(Bottom));
+  auto Iter = std::next(Bottom->getIterator());
   if (Iter == MF.end()) {
     MachineBasicBlock *Label = MF.CreateMachineBasicBlock();
     // Give it a fake predecessor so that AsmPrinter prints its label.
     Label->addSuccessor(Label);
     MF.push_back(Label);
-    Iter = std::next(MachineFunction::iterator(Bottom));
+    Iter = std::next(Bottom->getIterator());
   }
   MachineBasicBlock *AfterLoop = &*Iter;
 
@@ -457,19 +456,18 @@ void WebAssemblyCFGStackify::placeTryMarker(MachineBasicBlock &MBB) {
   assert(WE);
   MachineBasicBlock *Bottom = WebAssembly::getBottom(WE);
 
-  auto Iter = std::next(MachineFunction::iterator(Bottom));
+  auto Iter = std::next(Bottom->getIterator());
   if (Iter == MF.end()) {
     MachineBasicBlock *Label = MF.CreateMachineBasicBlock();
     // Give it a fake predecessor so that AsmPrinter prints its label.
     Label->addSuccessor(Label);
     MF.push_back(Label);
-    Iter = std::next(MachineFunction::iterator(Bottom));
+    Iter = std::next(Bottom->getIterator());
   }
   MachineBasicBlock *Cont = &*Iter;
 
   assert(Cont != &MF.front());
-  MachineBasicBlock *LayoutPred =
-      &*std::prev(MachineFunction::iterator(Cont));
+  MachineBasicBlock *LayoutPred = Cont->getPrevNode();
 
   // If the nearest common dominator is inside a more deeply nested context,
   // walk out to the nearest scope which isn't more deeply nested.
@@ -477,7 +475,7 @@ void WebAssemblyCFGStackify::placeTryMarker(MachineBasicBlock &MBB) {
     if (MachineBasicBlock *ScopeTop = ScopeTops[I->getNumber()]) {
       if (ScopeTop->getNumber() > Header->getNumber()) {
         // Skip over an intervening scope.
-        I = std::next(MachineFunction::iterator(ScopeTop));
+        I = std::next(ScopeTop->getIterator());
       } else {
         // We found a scope level at an appropriate depth.
         Header = ScopeTop;
@@ -633,8 +631,7 @@ void WebAssemblyCFGStackify::removeUnnecessaryInstrs(MachineFunction &MF) {
 
     MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
     SmallVector<MachineOperand, 4> Cond;
-    MachineBasicBlock *EHPadLayoutPred =
-        &*std::prev(MachineFunction::iterator(&MBB));
+    MachineBasicBlock *EHPadLayoutPred = MBB.getPrevNode();
     MachineBasicBlock *Cont = BeginToEnd[EHPadToTry[&MBB]]->getParent();
     bool Analyzable = !TII.analyzeBranch(*EHPadLayoutPred, TBB, FBB, Cond);
     if (Analyzable && ((Cond.empty() && TBB && TBB == Cont) ||
@@ -663,8 +660,7 @@ void WebAssemblyCFGStackify::removeUnnecessaryInstrs(MachineFunction &MF) {
       MachineBasicBlock *TryBB = Try->getParent();
       MachineBasicBlock *Cont = EndTry->getParent();
       int64_t RetType = Try->getOperand(0).getImm();
-      for (auto B = MachineBasicBlock::iterator(Try),
-                E = std::next(MachineBasicBlock::iterator(EndTry));
+      for (auto B = Try->getIterator(), E = std::next(EndTry->getIterator());
            B != TryBB->begin() && E != Cont->end() &&
            std::prev(B)->getOpcode() == WebAssembly::BLOCK &&
            E->getOpcode() == WebAssembly::END_BLOCK &&

lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp

@@ -274,7 +274,7 @@ bool WebAssemblyExplicitLocals::runOnMachineFunction(MachineFunction &MF) {
         if (!MFI.isVRegStackified(OldReg)) {
           const TargetRegisterClass *RC = MRI.getRegClass(OldReg);
           unsigned NewReg = MRI.createVirtualRegister(RC);
-          auto InsertPt = std::next(MachineBasicBlock::iterator(&MI));
+          auto InsertPt = std::next(MI.getIterator());
           if (MI.getOpcode() == WebAssembly::IMPLICIT_DEF) {
             MI.eraseFromParent();
             Changed = true;

lib/Target/WebAssembly/WebAssemblyFixIrreducibleControlFlow.cpp

@@ -319,8 +319,7 @@ bool LoopFixer::run() {
 
       // This is a successor we need to rewrite.
       MachineBasicBlock *Split = MF.CreateMachineBasicBlock();
-      MF.insert(MBB->isLayoutSuccessor(Succ) ? MachineFunction::iterator(Succ)
-                                             : MF.end(),
+      MF.insert(MBB->isLayoutSuccessor(Succ) ? Succ->getIterator() : MF.end(),
                 Split);
       MLI.changeLoopFor(Split, Loop);
 

lib/Target/WebAssembly/WebAssemblyISelLowering.cpp

@@ -358,8 +358,7 @@ static MachineBasicBlock *LowerFPToInt(MachineInstr &MI, DebugLoc DL,
   F->insert(It, DoneMBB);
 
   // Transfer the remainder of BB and its successor edges to DoneMBB.
-  DoneMBB->splice(DoneMBB->begin(), BB,
-                  std::next(MachineBasicBlock::iterator(MI)), BB->end());
+  DoneMBB->splice(DoneMBB->begin(), BB, std::next(MI.getIterator()), BB->end());
   DoneMBB->transferSuccessorsAndUpdatePHIs(BB);
 
   BB->addSuccessor(TrueMBB);

lib/Target/WebAssembly/WebAssemblyLateEHPrepare.cpp

@@ -132,7 +132,7 @@ bool WebAssemblyLateEHPrepare::removeUnnecessaryUnreachables(
       // another BB that should eventually lead to an unreachable. Delete it
       // because throw itself is a terminator, and also delete successors if
       // any.
-      MBB.erase(std::next(MachineBasicBlock::iterator(MI)), MBB.end());
+      MBB.erase(std::next(MI.getIterator()), MBB.end());
       SmallVector<MachineBasicBlock *, 8> Succs(MBB.succ_begin(),
                                                 MBB.succ_end());
       for (auto *Succ : Succs)