[NFC][DebugInfo] Use iterator-flavour getFirstNonPHI at many call-sites (#123737)

As part of the "RemoveDIs" project, BasicBlock::iterator now carries a
debug-info bit that's needed when getFirstNonPHI and similar feed into
instruction insertion positions. Call-sites where that's necessary were
updated a year ago; but to ensure some type safety however, we'd like to
have all calls to getFirstNonPHI use the iterator-returning version.

This patch changes a bunch of call-sites calling getFirstNonPHI to use
getFirstNonPHIIt, which returns an iterator. All these call sites are
where it's obviously safe to fetch the iterator then dereference it. A
follow-up patch will contain less-obviously-safe changes.

We'll eventually deprecate and remove the instruction-pointer
getFirstNonPHI, but not before adding concise documentation of what
considerations are needed (very few).

---------

Co-authored-by: Stephen Tozer <[email protected]>

Author: jmorse

clang/lib/CodeGen/CGException.cpp

@@ -1251,11 +1251,12 @@ void CodeGenFunction::ExitCXXTryStmt(const CXXTryStmt &S, bool IsFnTryBlock) {
   llvm::BasicBlock *WasmCatchStartBlock = nullptr;
   if (EHPersonality::get(*this).isWasmPersonality()) {
     auto *CatchSwitch =
-        cast<llvm::CatchSwitchInst>(DispatchBlock->getFirstNonPHI());
+        cast<llvm::CatchSwitchInst>(DispatchBlock->getFirstNonPHIIt());
     WasmCatchStartBlock = CatchSwitch->hasUnwindDest()
                               ? CatchSwitch->getSuccessor(1)
                               : CatchSwitch->getSuccessor(0);
-    auto *CPI = cast<llvm::CatchPadInst>(WasmCatchStartBlock->getFirstNonPHI());
+    auto *CPI =
+        cast<llvm::CatchPadInst>(WasmCatchStartBlock->getFirstNonPHIIt());
     CurrentFuncletPad = CPI;
   }
 
@@ -2252,7 +2253,7 @@ void CodeGenFunction::ExitSEHTryStmt(const SEHTryStmt &S) {
   // __except blocks don't get outlined into funclets, so immediately do a
   // catchret.
   llvm::CatchPadInst *CPI =
-      cast<llvm::CatchPadInst>(CatchPadBB->getFirstNonPHI());
+      cast<llvm::CatchPadInst>(CatchPadBB->getFirstNonPHIIt());
   llvm::BasicBlock *ExceptBB = createBasicBlock("__except");
   Builder.CreateCatchRet(CPI, ExceptBB);
   EmitBlock(ExceptBB);

clang/lib/CodeGen/MicrosoftCXXABI.cpp

@@ -918,7 +918,7 @@ void MicrosoftCXXABI::emitBeginCatch(CodeGenFunction &CGF,
   VarDecl *CatchParam = S->getExceptionDecl();
   llvm::BasicBlock *CatchPadBB = CGF.Builder.GetInsertBlock();
   llvm::CatchPadInst *CPI =
-      cast<llvm::CatchPadInst>(CatchPadBB->getFirstNonPHI());
+      cast<llvm::CatchPadInst>(CatchPadBB->getFirstNonPHIIt());
   CGF.CurrentFuncletPad = CPI;
 
   // If this is a catch-all or the catch parameter is unnamed, we don't need to

llvm/include/llvm/IR/BasicBlock.h

@@ -673,7 +673,7 @@ class BasicBlock final : public Value, // Basic blocks are data objects also
   void replaceSuccessorsPhiUsesWith(BasicBlock *New);
 
   /// Return true if this basic block is an exception handling block.
-  bool isEHPad() const { return getFirstNonPHI()->isEHPad(); }
+  bool isEHPad() const { return getFirstNonPHIIt()->isEHPad(); }
 
   /// Return true if this basic block is a landing pad.
   ///

llvm/include/llvm/Transforms/Utils/Instrumentation.h

@@ -204,6 +204,11 @@ struct InstrumentationIRBuilder : IRBuilder<> {
   explicit InstrumentationIRBuilder(Instruction *IP) : IRBuilder<>(IP) {
     ensureDebugInfo(*this, *IP->getFunction());
   }
+
+  explicit InstrumentationIRBuilder(BasicBlock *BB, BasicBlock::iterator It)
+      : IRBuilder<>(BB, It) {
+    ensureDebugInfo(*this, *BB->getParent());
+  }
 };
 } // end namespace llvm
 

llvm/lib/Analysis/Loads.cpp

@@ -284,7 +284,7 @@ bool llvm::isDereferenceableAndAlignedInLoop(
                 DL.getTypeStoreSize(LI->getType()).getFixedValue());
   const Align Alignment = LI->getAlign();
 
-  Instruction *HeaderFirstNonPHI = L->getHeader()->getFirstNonPHI();
+  Instruction *HeaderFirstNonPHI = &*L->getHeader()->getFirstNonPHIIt();
 
   // If given a uniform (i.e. non-varying) address, see if we can prove the
   // access is safe within the loop w/o needing predication.

llvm/lib/Analysis/LoopNestAnalysis.cpp

@@ -346,7 +346,7 @@ static bool checkLoopsStructure(const Loop &OuterLoop, const Loop &InnerLoop,
   // "guarded" inner loop which contains "only" Phi nodes corresponding to the
   // LCSSA Phi nodes in the exit block.
   auto IsExtraPhiBlock = [&](const BasicBlock &BB) {
-    return BB.getFirstNonPHI() == BB.getTerminator() &&
+    return &*BB.getFirstNonPHIIt() == BB.getTerminator() &&
            all_of(BB.phis(), [&](const PHINode &PN) {
              return all_of(PN.blocks(), [&](const BasicBlock *IncomingBlock) {
                return IncomingBlock == InnerLoopExit ||

llvm/lib/Analysis/MustExecute.cpp

@@ -275,7 +275,7 @@ bool SimpleLoopSafetyInfo::isGuaranteedToExecute(const Instruction &Inst,
     // exit.  At the moment, we use a (cheap) hack for the common case where
     // the instruction of interest is the first one in the block.
     return !HeaderMayThrow ||
-           Inst.getParent()->getFirstNonPHIOrDbg() == &Inst;
+           &*Inst.getParent()->getFirstNonPHIOrDbg() == &Inst;
 
   // If there is a path from header to exit or latch that doesn't lead to our
   // instruction's block, return false.

llvm/lib/Analysis/ValueTracking.cpp

@@ -8246,7 +8246,7 @@ static bool programUndefinedIfUndefOrPoison(const Value *V,
     if (!BB || !Visited.insert(BB).second)
       break;
 
-    Begin = BB->getFirstNonPHI()->getIterator();
+    Begin = BB->getFirstNonPHIIt();
     End = BB->end();
   }
   return false;

llvm/lib/CodeGen/AsmPrinter/WinException.cpp

@@ -928,8 +928,8 @@ void WinException::computeIP2StateTable(
       BaseState = NullState;
       StartLabel = Asm->getFunctionBegin();
     } else {
-      auto *FuncletPad =
-          cast<FuncletPadInst>(FuncletStart->getBasicBlock()->getFirstNonPHI());
+      auto *FuncletPad = cast<FuncletPadInst>(
+          FuncletStart->getBasicBlock()->getFirstNonPHIIt());
       assert(FuncInfo.FuncletBaseStateMap.count(FuncletPad) != 0);
       BaseState = FuncInfo.FuncletBaseStateMap.find(FuncletPad)->second;
       StartLabel = getMCSymbolForMBB(Asm, &*FuncletStart);

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

@@ -2866,7 +2866,7 @@ bool IRTranslator::findUnwindDestinations(
   }
 
   while (EHPadBB) {
-    const Instruction *Pad = EHPadBB->getFirstNonPHI();
+    BasicBlock::const_iterator Pad = EHPadBB->getFirstNonPHIIt();
     BasicBlock *NewEHPadBB = nullptr;
     if (isa<LandingPadInst>(Pad)) {
       // Stop on landingpads. They are not funclets.
@@ -2927,7 +2927,7 @@ bool IRTranslator::translateInvoke(const User &U,
     return false;
 
   // FIXME: support Windows exception handling.
-  if (!isa<LandingPadInst>(EHPadBB->getFirstNonPHI()))
+  if (!isa<LandingPadInst>(EHPadBB->getFirstNonPHIIt()))
     return false;
 
   // FIXME: support Windows dllimport function calls and calls through
@@ -4031,7 +4031,7 @@ bool IRTranslator::runOnMachineFunction(MachineFunction &CurMF) {
   MF->push_back(EntryBB);
   EntryBuilder->setMBB(*EntryBB);
 
-  DebugLoc DbgLoc = F.getEntryBlock().getFirstNonPHI()->getDebugLoc();
+  DebugLoc DbgLoc = F.getEntryBlock().getFirstNonPHIIt()->getDebugLoc();
   SwiftError.setFunction(CurMF);
   SwiftError.createEntriesInEntryBlock(DbgLoc);