[NFC][RemoveDIs] Have CreateNeg only accept iterators (#82999)

Removing debug-intrinsics requires that we always insert with an
iterator, not with an instruction position. To enforce that, we need to
eliminate the `Instruction *` taking functions. It's safe to leave the
insert-at-end-of-block functions as the intention is clear for debug
info purposes (i.e., insert after both instructions and debug-info at
the end of the function).

This patch demonstrates how that needs to happen. At a variety of
call-sites to the `CreateNeg` constructor we need to consider:
* Has this instruction been selected because of the operation it
performs? In that case, just call `getIterator` and pass an iterator in.
* Has this instruction been selected because of it's position? If so, we
need to keep the iterator identifying that position (see the 3rd hunk
changing Reassociate.cpp, although it's coincidentally not debug-info
significant).

This also demonstrates what we'll try and do with the constructor
methods going forwards: have one fully explicit set of parameters
including iterator, and another with default-arguments where the
block-to-insert-into argument defaults to nullptr / no-position,
creating an instruction that hasn't been inserted yet.

llvm/include/llvm/IR/InstrTypes.h

@@ -468,9 +468,7 @@ class BinaryOperator : public Instruction {
   static BinaryOperator *CreateNeg(Value *Op, const Twine &Name,
                                    BasicBlock::iterator InsertBefore);
   static BinaryOperator *CreateNeg(Value *Op, const Twine &Name = "",
-                                   Instruction *InsertBefore = nullptr);
-  static BinaryOperator *CreateNeg(Value *Op, const Twine &Name,
-                                   BasicBlock *InsertAtEnd);
+                                   BasicBlock *InsertAtEnd = nullptr);
   static BinaryOperator *CreateNSWNeg(Value *Op, const Twine &Name,
                                       BasicBlock::iterator InsertBefore);
   static BinaryOperator *CreateNSWNeg(Value *Op, const Twine &Name = "",

llvm/lib/IR/Instruction.cpp

@@ -46,11 +46,11 @@ Instruction::Instruction(Type *ty, unsigned it, Use *Ops, unsigned NumOps,
 
 Instruction::Instruction(Type *ty, unsigned it, Use *Ops, unsigned NumOps,
                          BasicBlock *InsertAtEnd)
-  : User(ty, Value::InstructionVal + it, Ops, NumOps), Parent(nullptr) {
+    : User(ty, Value::InstructionVal + it, Ops, NumOps), Parent(nullptr) {
 
-  // append this instruction into the basic block
-  assert(InsertAtEnd && "Basic block to append to may not be NULL!");
-  insertInto(InsertAtEnd, InsertAtEnd->end());
+  // If requested, append this instruction into the basic block.
+  if (InsertAtEnd)
+    insertInto(InsertAtEnd, InsertAtEnd->end());
 }
 
 Instruction::~Instruction() {
@@ -73,7 +73,6 @@ Instruction::~Instruction() {
   setMetadata(LLVMContext::MD_DIAssignID, nullptr);
 }
 
-
 void Instruction::setParent(BasicBlock *P) {
   Parent = P;
 }

llvm/lib/IR/Instructions.cpp

@@ -3245,14 +3245,6 @@ BinaryOperator *BinaryOperator::CreateNeg(Value *Op, const Twine &Name,
                             InsertBefore);
 }
 
-BinaryOperator *BinaryOperator::CreateNeg(Value *Op, const Twine &Name,
-                                          Instruction *InsertBefore) {
-  Value *Zero = ConstantInt::get(Op->getType(), 0);
-  return new BinaryOperator(Instruction::Sub,
-                            Zero, Op,
-                            Op->getType(), Name, InsertBefore);
-}
-
 BinaryOperator *BinaryOperator::CreateNeg(Value *Op, const Twine &Name,
                                           BasicBlock *InsertAtEnd) {
   Value *Zero = ConstantInt::get(Op->getType(), 0);

llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp

@@ -905,8 +905,8 @@ static bool processSRem(BinaryOperator *SDI, const ConstantRange &LCR,
   for (Operand &Op : Ops) {
     if (Op.D == Domain::NonNegative)
       continue;
-    auto *BO =
-        BinaryOperator::CreateNeg(Op.V, Op.V->getName() + ".nonneg", SDI);
+    auto *BO = BinaryOperator::CreateNeg(Op.V, Op.V->getName() + ".nonneg",
+                                         SDI->getIterator());
     BO->setDebugLoc(SDI->getDebugLoc());
     Op.V = BO;
   }
@@ -919,7 +919,8 @@ static bool processSRem(BinaryOperator *SDI, const ConstantRange &LCR,
 
   // If the divident was non-positive, we need to negate the result.
   if (Ops[0].D == Domain::NonPositive) {
-    Res = BinaryOperator::CreateNeg(Res, Res->getName() + ".neg", SDI);
+    Res = BinaryOperator::CreateNeg(Res, Res->getName() + ".neg",
+                                    SDI->getIterator());
     Res->setDebugLoc(SDI->getDebugLoc());
   }
 
@@ -966,8 +967,8 @@ static bool processSDiv(BinaryOperator *SDI, const ConstantRange &LCR,
   for (Operand &Op : Ops) {
     if (Op.D == Domain::NonNegative)
       continue;
-    auto *BO =
-        BinaryOperator::CreateNeg(Op.V, Op.V->getName() + ".nonneg", SDI);
+    auto *BO = BinaryOperator::CreateNeg(Op.V, Op.V->getName() + ".nonneg",
+                                         SDI->getIterator());
     BO->setDebugLoc(SDI->getDebugLoc());
     Op.V = BO;
   }
@@ -981,7 +982,8 @@ static bool processSDiv(BinaryOperator *SDI, const ConstantRange &LCR,
 
   // If the operands had two different domains, we need to negate the result.
   if (Ops[0].D != Ops[1].D) {
-    Res = BinaryOperator::CreateNeg(Res, Res->getName() + ".neg", SDI);
+    Res = BinaryOperator::CreateNeg(Res, Res->getName() + ".neg",
+                                    SDI->getIterator());
     Res->setDebugLoc(SDI->getDebugLoc());
   }
 

llvm/lib/Transforms/Scalar/Reassociate.cpp

@@ -270,7 +270,8 @@ static BinaryOperator *CreateMul(Value *S1, Value *S2, const Twine &Name,
 }
 
 static Instruction *CreateNeg(Value *S1, const Twine &Name,
-                              Instruction *InsertBefore, Value *FlagsOp) {
+                              BasicBlock::iterator InsertBefore,
+                              Value *FlagsOp) {
   if (S1->getType()->isIntOrIntVectorTy())
     return BinaryOperator::CreateNeg(S1, Name, InsertBefore);
 
@@ -958,7 +959,8 @@ static Value *NegateValue(Value *V, Instruction *BI,
 
   // Insert a 'neg' instruction that subtracts the value from zero to get the
   // negation.
-  Instruction *NewNeg = CreateNeg(V, V->getName() + ".neg", BI, BI);
+  Instruction *NewNeg =
+      CreateNeg(V, V->getName() + ".neg", BI->getIterator(), BI);
   ToRedo.insert(NewNeg);
   return NewNeg;
 }
@@ -1246,7 +1248,7 @@ Value *ReassociatePass::RemoveFactorFromExpression(Value *V, Value *Factor) {
   }
 
   if (NeedsNegate)
-    V = CreateNeg(V, "neg", &*InsertPt, BO);
+    V = CreateNeg(V, "neg", InsertPt, BO);
 
   return V;
 }