[NFC][RemoveDIs] Provide an iterator-taking split-block method

As per the stack of patches this is attached to, allow users of
BasicBlock::splitBasicBlock to provide an iterator for a position, instead
of just an instruction pointer. This is to fit with my proposal for how to
get rid of debug intrinsics [0]. There are other call-sites that would need
to change, but this is sufficient for a stage2clang self host and some
other C++ projects to build identical binaries, in the context of the whole
remove-DIs project.

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

Differential Revision: https://reviews.llvm.org/D152545

3 files changed, 18 insertions, 16 deletions

diff --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
index 475b460..769a4e9 100644
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -610,7 +610,7 @@ static bool unswitchTrivialBranch(Loop &L, BranchInst &BI, DominatorTree &DT,
     UnswitchedBB = LoopExitBB;
   } else {
     UnswitchedBB =
-        SplitBlock(LoopExitBB, &LoopExitBB->front(), &DT, &LI, MSSAU);
+        SplitBlock(LoopExitBB, LoopExitBB->begin(), &DT, &LI, MSSAU, "", false);
   }
 
   if (MSSAU && VerifyMemorySSA)
@@ -883,7 +883,7 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
       rewritePHINodesForUnswitchedExitBlock(*DefaultExitBB, *ParentBB, *OldPH);
     } else {
       auto *SplitBB =
-          SplitBlock(DefaultExitBB, &DefaultExitBB->front(), &DT, &LI, MSSAU);
+          SplitBlock(DefaultExitBB, DefaultExitBB->begin(), &DT, &LI, MSSAU);
       rewritePHINodesForExitAndUnswitchedBlocks(*DefaultExitBB, *SplitBB,
                                                 *ParentBB, *OldPH,
                                                 /*FullUnswitch*/ true);
@@ -910,7 +910,7 @@ static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
     BasicBlock *&SplitExitBB = SplitExitBBMap[ExitBB];
     if (!SplitExitBB) {
       // If this is the first time we see this, do the split and remember it.
-      SplitExitBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI, MSSAU);
+      SplitExitBB = SplitBlock(ExitBB, ExitBB->begin(), &DT, &LI, MSSAU);
       rewritePHINodesForExitAndUnswitchedBlocks(*ExitBB, *SplitExitBB,
                                                 *ParentBB, *OldPH,
                                                 /*FullUnswitch*/ true);
@@ -1211,7 +1211,7 @@ static BasicBlock *buildClonedLoopBlocks(
     // place to merge the CFG, so split the exit first. This is always safe to
     // do because there cannot be any non-loop predecessors of a loop exit in
     // loop simplified form.
-    auto *MergeBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI, MSSAU);
+    auto *MergeBB = SplitBlock(ExitBB, ExitBB->begin(), &DT, &LI, MSSAU);
 
     // Rearrange the names to make it easier to write test cases by having the
     // exit block carry the suffix rather than the merge block carrying the
diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 7c081cb..389aab3 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -879,7 +879,7 @@ llvm::SplitAllCriticalEdges(Function &F,
   return NumBroken;
 }
 
-static BasicBlock *SplitBlockImpl(BasicBlock *Old, Instruction *SplitPt,
+static BasicBlock *SplitBlockImpl(BasicBlock *Old, BasicBlock::iterator SplitPt,
                                   DomTreeUpdater *DTU, DominatorTree *DT,
                                   LoopInfo *LI, MemorySSAUpdater *MSSAU,
                                   const Twine &BBName, bool Before) {
@@ -889,7 +889,7 @@ static BasicBlock *SplitBlockImpl(BasicBlock *Old, Instruction *SplitPt,
                             DTU ? DTU : (DT ? &LocalDTU : nullptr), LI, MSSAU,
                             BBName);
   }
-  BasicBlock::iterator SplitIt = SplitPt->getIterator();
+  BasicBlock::iterator SplitIt = SplitPt;
   while (isa<PHINode>(SplitIt) || SplitIt->isEHPad()) {
     ++SplitIt;
     assert(SplitIt != SplitPt->getParent()->end());
@@ -935,14 +935,14 @@ static BasicBlock *SplitBlockImpl(BasicBlock *Old, Instruction *SplitPt,
   return New;
 }
 
-BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
+BasicBlock *llvm::SplitBlock(BasicBlock *Old, BasicBlock::iterator SplitPt,
                              DominatorTree *DT, LoopInfo *LI,
                              MemorySSAUpdater *MSSAU, const Twine &BBName,
                              bool Before) {
   return SplitBlockImpl(Old, SplitPt, /*DTU=*/nullptr, DT, LI, MSSAU, BBName,
                         Before);
 }
-BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
+BasicBlock *llvm::SplitBlock(BasicBlock *Old, BasicBlock::iterator SplitPt,
                              DomTreeUpdater *DTU, LoopInfo *LI,
                              MemorySSAUpdater *MSSAU, const Twine &BBName,
                              bool Before) {
@@ -950,12 +950,12 @@ BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
                         Before);
 }
 
-BasicBlock *llvm::splitBlockBefore(BasicBlock *Old, Instruction *SplitPt,
+BasicBlock *llvm::splitBlockBefore(BasicBlock *Old, BasicBlock::iterator SplitPt,
                                    DomTreeUpdater *DTU, LoopInfo *LI,
                                    MemorySSAUpdater *MSSAU,
                                    const Twine &BBName) {
 
-  BasicBlock::iterator SplitIt = SplitPt->getIterator();
+  BasicBlock::iterator SplitIt = SplitPt;
   while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
     ++SplitIt;
   std::string Name = BBName.str();
@@ -1471,7 +1471,7 @@ ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
 }
 
 Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
-                                             Instruction *SplitBefore,
+                                             BasicBlock::iterator SplitBefore,
                                              bool Unreachable,
                                              MDNode *BranchWeights,
                                              DomTreeUpdater *DTU, LoopInfo *LI,
@@ -1484,7 +1484,7 @@ Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
 }
 
 Instruction *llvm::SplitBlockAndInsertIfElse(Value *Cond,
-                                             Instruction *SplitBefore,
+                                             BasicBlock::iterator SplitBefore,
                                              bool Unreachable,
                                              MDNode *BranchWeights,
                                              DomTreeUpdater *DTU, LoopInfo *LI,
@@ -1496,7 +1496,7 @@ Instruction *llvm::SplitBlockAndInsertIfElse(Value *Cond,
   return ElseBlock->getTerminator();
 }
 
-void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
+void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, BasicBlock::iterator SplitBefore,
                                          Instruction **ThenTerm,
                                          Instruction **ElseTerm,
                                          MDNode *BranchWeights,
@@ -1512,7 +1512,7 @@ void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
 }
 
 void llvm::SplitBlockAndInsertIfThenElse(
-    Value *Cond, Instruction *SplitBefore, BasicBlock **ThenBlock,
+    Value *Cond, BasicBlock::iterator SplitBefore, BasicBlock **ThenBlock,
     BasicBlock **ElseBlock, bool UnreachableThen, bool UnreachableElse,
     MDNode *BranchWeights, DomTreeUpdater *DTU, LoopInfo *LI) {
   assert((ThenBlock || ElseBlock) &&
@@ -1529,7 +1529,7 @@ void llvm::SplitBlockAndInsertIfThenElse(
   }
 
   LLVMContext &C = Head->getContext();
-  BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
+  BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
   BasicBlock *TrueBlock = Tail;
   BasicBlock *FalseBlock = Tail;
   bool ThenToTailEdge = false;
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index e00e960..b99037e 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4015,9 +4015,11 @@ static bool mergeConditionalStoreToAddress(
     QPred = QB.CreateNot(QPred);
   Value *CombinedPred = QB.CreateOr(PPred, QPred);
 
-  auto *T = SplitBlockAndInsertIfThen(CombinedPred, &*QB.GetInsertPoint(),
+  BasicBlock::iterator InsertPt = QB.GetInsertPoint();
+  auto *T = SplitBlockAndInsertIfThen(CombinedPred, InsertPt,
                                       /*Unreachable=*/false,
                                       /*BranchWeights=*/nullptr, DTU);
+
   QB.SetInsertPoint(T);
   StoreInst *SI = cast<StoreInst>(QB.CreateStore(QPHI, Address));
   SI->setAAMetadata(PStore->getAAMetadata().merge(QStore->getAAMetadata()));