[NFC][RemoveDIs] Prefer iterator-insertion over instructions

Continuing the patch series to get rid of debug intrinsics [0], instruction
insertion needs to be done with iterators rather than instruction pointers,
so that we can communicate information in the iterator class. This patch
adds an iterator-taking insertBefore method and converts various call sites
to take iterators. These are all sites where such debug-info needs to be
preserved so that a stage2 clang can be built identically; it's likely that
many more will need to be changed in the future.

At this stage, this is just changing the spelling of a few operations,
which will eventually become signifiant once the debug-info bearing
iterator is used.

[0] https://discourse.llvm.org/t/rfc-instruction-api-changes-needed-to-eliminate-debug-intrinsics-from-ir/68939

Differential Revision: https://reviews.llvm.org/D152537

Author: jmorse

llvm/include/llvm/IR/BasicBlock.h

@@ -173,6 +173,15 @@ class BasicBlock final : public Value, // Basic blocks are data objects also
                        static_cast<const BasicBlock *>(this)->getFirstNonPHI());
   }
 
+  /// Iterator returning form of getFirstNonPHI. Installed as a placeholder for
+  /// the RemoveDIs project that will eventually remove debug intrinsics.
+  InstListType::const_iterator getFirstNonPHIIt() const;
+  InstListType::iterator getFirstNonPHIIt() {
+    BasicBlock::iterator It =
+      static_cast<const BasicBlock *>(this)->getFirstNonPHIIt().getNonConst();
+    return It;
+  }
+
   /// Returns a pointer to the first instruction in this block that is not a
   /// PHINode or a debug intrinsic, or any pseudo operation if \c SkipPseudoOp
   /// is true.

llvm/include/llvm/IR/Instruction.h

@@ -123,6 +123,9 @@ class Instruction : public User,
   /// Insert an unlinked instruction into a basic block immediately before
   /// the specified instruction.
   void insertBefore(Instruction *InsertPos);
+  void insertBefore(SymbolTableList<Instruction>::iterator InsertPos) {
+    insertBefore(&*InsertPos);
+  }
 
   /// Insert an unlinked instruction into a basic block immediately after the
   /// specified instruction.
@@ -133,6 +136,11 @@ class Instruction : public User,
   SymbolTableList<Instruction>::iterator
   insertInto(BasicBlock *ParentBB, SymbolTableList<Instruction>::iterator It);
 
+  void insertBefore(BasicBlock &BB,
+                    SymbolTableList<Instruction>::iterator InsertPos) {
+    insertInto(&BB, InsertPos);
+  }
+
   /// Unlink this instruction from its current basic block and insert it into
   /// the basic block that MovePos lives in, right before MovePos.
   void moveBefore(Instruction *MovePos);

llvm/lib/CodeGen/CodeGenPrepare.cpp

@@ -7097,7 +7097,8 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) {
   // to get the PHI operand.
   for (SelectInst *SI : llvm::reverse(ASI)) {
     // The select itself is replaced with a PHI Node.
-    PHINode *PN = PHINode::Create(SI->getType(), 2, "", &EndBlock->front());
+    PHINode *PN = PHINode::Create(SI->getType(), 2, "");
+    PN->insertBefore(EndBlock->begin());
     PN->takeName(SI);
     PN->addIncoming(getTrueOrFalseValue(SI, true, INS), TrueBlock);
     PN->addIncoming(getTrueOrFalseValue(SI, false, INS), FalseBlock);

llvm/lib/CodeGen/SelectOptimize.cpp

@@ -505,7 +505,8 @@ void SelectOptimize::convertProfitableSIGroups(SelectGroups &ProfSIGroups) {
     for (auto It = ASI.rbegin(); It != ASI.rend(); ++It) {
       SelectInst *SI = *It;
       // The select itself is replaced with a PHI Node.
-      PHINode *PN = PHINode::Create(SI->getType(), 2, "", &EndBlock->front());
+      PHINode *PN = PHINode::Create(SI->getType(), 2, "");
+      PN->insertBefore(EndBlock->begin());
       PN->takeName(SI);
       PN->addIncoming(getTrueOrFalseValue(SI, true, INS), TrueBlock);
       PN->addIncoming(getTrueOrFalseValue(SI, false, INS), FalseBlock);

llvm/lib/IR/BasicBlock.cpp

@@ -220,6 +220,10 @@ const Instruction* BasicBlock::getFirstNonPHI() const {
   return nullptr;
 }
 
+BasicBlock::const_iterator BasicBlock::getFirstNonPHIIt() const {
+  return getFirstNonPHI()->getIterator();
+}
+
 const Instruction *BasicBlock::getFirstNonPHIOrDbg(bool SkipPseudoOp) const {
   for (const Instruction &I : *this) {
     if (isa<PHINode>(I) || isa<DbgInfoIntrinsic>(I))

llvm/lib/Target/AMDGPU/SIAnnotateControlFlow.cpp

@@ -268,7 +268,8 @@ bool SIAnnotateControlFlow::handleLoop(BranchInst *Term) {
     return false;
 
   BasicBlock *Target = Term->getSuccessor(1);
-  PHINode *Broken = PHINode::Create(IntMask, 0, "phi.broken", &Target->front());
+  PHINode *Broken = PHINode::Create(IntMask, 0, "phi.broken");
+  Broken->insertBefore(Target->begin());
 
   Value *Cond = Term->getCondition();
   Term->setCondition(BoolTrue);

llvm/lib/Target/PowerPC/PPCLoopInstrFormPrep.cpp

@@ -707,8 +707,8 @@ PPCLoopInstrFormPrep::rewriteForBase(Loop *L, const SCEVAddRecExpr *BasePtrSCEV,
   BasicBlock *LoopPredecessor = L->getLoopPredecessor();
 
   PHINode *NewPHI = PHINode::Create(I8PtrTy, HeaderLoopPredCount,
-                                    getInstrName(BaseMemI, PHINodeNameSuffix),
-                                    Header->getFirstNonPHI());
+                                    getInstrName(BaseMemI, PHINodeNameSuffix));
+  NewPHI->insertBefore(Header->getFirstNonPHIIt());
 
   Value *BasePtrStart = SCEVE.expandCodeFor(BasePtrStartSCEV, I8PtrTy,
                                             LoopPredecessor->getTerminator());

llvm/lib/Transforms/Coroutines/CoroFrame.cpp

@@ -2051,8 +2051,8 @@ static void movePHIValuesToInsertedBlock(BasicBlock *SuccBB,
     int Index = PN->getBasicBlockIndex(InsertedBB);
     Value *V = PN->getIncomingValue(Index);
     PHINode *InputV = PHINode::Create(
-        V->getType(), 1, V->getName() + Twine(".") + SuccBB->getName(),
-        &InsertedBB->front());
+        V->getType(), 1, V->getName() + Twine(".") + SuccBB->getName());
+    InputV->insertBefore(InsertedBB->begin());
     InputV->addIncoming(V, PredBB);
     PN->setIncomingValue(Index, InputV);
     PN = dyn_cast<PHINode>(PN->getNextNode());
@@ -2198,7 +2198,8 @@ static void rewritePHIs(BasicBlock &BB) {
     // ehAwareSplitEdge will clone the LandingPad in all the edge blocks.
     // We replace the original landing pad with a PHINode that will collect the
     // results from all of them.
-    ReplPHI = PHINode::Create(LandingPad->getType(), 1, "", LandingPad);
+    ReplPHI = PHINode::Create(LandingPad->getType(), 1, "");
+    ReplPHI->insertBefore(LandingPad->getIterator());
     ReplPHI->takeName(LandingPad);
     LandingPad->replaceAllUsesWith(ReplPHI);
     // We will erase the original landing pad at the end of this function after

llvm/lib/Transforms/Coroutines/CoroSplit.cpp

@@ -457,7 +457,8 @@ static void createResumeEntryBlock(Function &F, coro::Shape &Shape) {
     Switch->addCase(IndexVal, ResumeBB);
 
     cast<BranchInst>(SuspendBB->getTerminator())->setSuccessor(0, LandingBB);
-    auto *PN = PHINode::Create(Builder.getInt8Ty(), 2, "", &LandingBB->front());
+    auto *PN = PHINode::Create(Builder.getInt8Ty(), 2, "");
+    PN->insertBefore(LandingBB->begin());
     S->replaceAllUsesWith(PN);
     PN->addIncoming(Builder.getInt8(-1), SuspendBB);
     PN->addIncoming(S, ResumeBB);

llvm/lib/Transforms/IPO/PartialInlining.cpp

@@ -1042,17 +1042,18 @@ void PartialInlinerImpl::FunctionCloner::normalizeReturnBlock() const {
   ClonedOI->ReturnBlock = ClonedOI->ReturnBlock->splitBasicBlock(
       ClonedOI->ReturnBlock->getFirstNonPHI()->getIterator());
   BasicBlock::iterator I = PreReturn->begin();
-  Instruction *Ins = &ClonedOI->ReturnBlock->front();
+  BasicBlock::iterator Ins = ClonedOI->ReturnBlock->begin();
   SmallVector<Instruction *, 4> DeadPhis;
   while (I != PreReturn->end()) {
     PHINode *OldPhi = dyn_cast<PHINode>(I);
     if (!OldPhi)
       break;
 
     PHINode *RetPhi =
-        PHINode::Create(OldPhi->getType(), NumPredsFromEntries + 1, "", Ins);
+        PHINode::Create(OldPhi->getType(), NumPredsFromEntries + 1, "");
+    RetPhi->insertBefore(Ins);
     OldPhi->replaceAllUsesWith(RetPhi);
-    Ins = ClonedOI->ReturnBlock->getFirstNonPHI();
+    Ins = ClonedOI->ReturnBlock->getFirstNonPHIIt();
 
     RetPhi->addIncoming(&*I, PreReturn);
     for (BasicBlock *E : ClonedOI->ReturnBlockPreds) {