1 files changed, 42 insertions, 101 deletions

diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index a9d6c89a35c..0d5ad7311fb 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -193,8 +193,9 @@ namespace {
     Value *OptimizeMul(BinaryOperator *I, SmallVectorImpl<ValueEntry> &Ops);
     Value *RemoveFactorFromExpression(Value *V, Value *Factor);
     void EraseInst(Instruction *I);
+    void optimizeFAddNegExpr(ConstantFP *ConstOperand, Instruction *I,
+                             int OperandNr);
     void OptimizeInst(Instruction *I);
-    Instruction *canonicalizeNegConstExpr(Instruction *I);
   };
 }
 
@@ -1929,105 +1930,31 @@ void Reassociate::EraseInst(Instruction *I) {
     }
 }
 
-// Canonicalize expressions of the following form:
-//  x + (-Constant * y) -> x - (Constant * y)
-//  x - (-Constant * y) -> x + (Constant * y)
-Instruction *Reassociate::canonicalizeNegConstExpr(Instruction *I) {
-  if (!I->hasOneUse() || I->getType()->isVectorTy())
-    return nullptr;
-
-  // Must have at least one constant operand.
-  Constant *C0 = dyn_cast<Constant>(I->getOperand(0));
-  Constant *C1 = dyn_cast<Constant>(I->getOperand(1));
-  if (!C0 && !C1)
-    return nullptr;
-
-  // Must be a negative ConstantInt or ConstantFP.
-  Constant *C = C0 ? C0 : C1;
-  unsigned ConstIdx = C0 ? 0 : 1;
-  if (auto *CI = dyn_cast<ConstantInt>(C)) {
-    if (!CI->isNegative())
-      return nullptr;
-  } else if (auto *CF = dyn_cast<ConstantFP>(C)) {
-    if (!CF->isNegative())
-      return nullptr;
-  } else
-    return nullptr;
-
-  // User must be a binary operator with one or more uses.
-  Instruction *User = I->user_back();
-  if (!isa<BinaryOperator>(User) || !User->getNumUses())
-    return nullptr;
-
-  // Must be a binary operator with higher precedence that add/sub.
-  switch(I->getOpcode()) {
-  default:
-    return nullptr;
-  case Instruction::Mul:
-  case Instruction::FMul:
-  case Instruction::UDiv:
-  case Instruction::SDiv:
-  case Instruction::FDiv:
-  case Instruction::URem:
-  case Instruction::SRem:
-  case Instruction::FRem:
-   break;
-  }
-
-  unsigned UserOpcode = User->getOpcode();
-  if (UserOpcode != Instruction::Add && UserOpcode != Instruction::FAdd &&
-      UserOpcode != Instruction::Sub && UserOpcode != Instruction::FSub)
-    return nullptr;
-
-  // Subtraction is not commutative. Explicitly, the following transform is
-  // not valid: (-Constant * y) - x  -> x + (Constant * y)
-  if (!User->isCommutative() && User->getOperand(1) != I)
-    return nullptr;
-
+void Reassociate::optimizeFAddNegExpr(ConstantFP *ConstOperand, Instruction *I,
+                                      int OperandNr) {
   // Change the sign of the constant.
-  if (ConstantInt *CI = dyn_cast<ConstantInt>(C))
-    I->setOperand(ConstIdx, ConstantInt::get(CI->getContext(), -CI->getValue()));
-  else {
-    ConstantFP *CF = cast<ConstantFP>(C);
-    APFloat Val = CF->getValueAPF();
-    Val.changeSign();
-    I->setOperand(ConstIdx, ConstantFP::get(CF->getContext(), Val));
-  }
-
-  // Canonicalize I to RHS to simplify the next bit of logic. E.g.,
-  // ((-Const*y) + x) -> (x + (-Const*y)).
-  if (User->getOperand(0) == I && User->isCommutative())
-    cast<BinaryOperator>(User)->swapOperands();
-
-  Value *Op0 = User->getOperand(0);
-  Value *Op1 = User->getOperand(1);
-  BinaryOperator *NI;
-  switch(UserOpcode) {
-  default:
-    llvm_unreachable("Unexpected Opcode!");
-  case Instruction::Add:
-    NI = BinaryOperator::CreateSub(Op0, Op1);
-    break;
-  case Instruction::Sub:
-    NI = BinaryOperator::CreateAdd(Op0, Op1);
-    break;
-  case Instruction::FAdd:
-    NI = BinaryOperator::CreateFSub(Op0, Op1);
-    NI->setFastMathFlags(cast<FPMathOperator>(User)->getFastMathFlags());
-    break;
-  case Instruction::FSub:
-    NI = BinaryOperator::CreateFAdd(Op0, Op1);
-    NI->setFastMathFlags(cast<FPMathOperator>(User)->getFastMathFlags());
-    break;
-  }
-
-  NI->insertBefore(User);
-  NI->setName(User->getName());
-  User->replaceAllUsesWith(NI);
+  APFloat Val = ConstOperand->getValueAPF();
+  Val.changeSign();
+  I->setOperand(0, ConstantFP::get(ConstOperand->getContext(), Val));
+
+  assert(I->hasOneUse() && "Only a single use can be replaced.");
+  Instruction *Parent = I->user_back();
+
+  Value *OtherOperand = Parent->getOperand(1 - OperandNr);
+
+  unsigned Opcode = Parent->getOpcode();
+  assert(Opcode == Instruction::FAdd ||
+         (Opcode == Instruction::FSub && Parent->getOperand(1) == I));
+
+  BinaryOperator *NI = Opcode == Instruction::FAdd
+                           ? BinaryOperator::CreateFSub(OtherOperand, I)
+                           : BinaryOperator::CreateFAdd(OtherOperand, I);
+  NI->setFastMathFlags(cast<FPMathOperator>(Parent)->getFastMathFlags());
+  NI->insertBefore(Parent);
+  NI->setName(Parent->getName() + ".repl");
+  Parent->replaceAllUsesWith(NI);
   NI->setDebugLoc(I->getDebugLoc());
-  RedoInsts.insert(I);
   MadeChange = true;
-  return NI;
 }
 
 /// OptimizeInst - Inspect and optimize the given instruction. Note that erasing
@@ -2050,10 +1977,6 @@ void Reassociate::OptimizeInst(Instruction *I) {
       I = NI;
     }
 
-  // Canonicalize negative constants out of expressions.
-  if (Instruction *Res = canonicalizeNegConstExpr(I))
-    I = Res;
-
   // Commute floating point binary operators, to canonicalize the order of their
   // operands.  This can potentially expose more CSE opportunities, and makes
   // writing other transformations simpler.
@@ -2074,6 +1997,24 @@ void Reassociate::OptimizeInst(Instruction *I) {
       }
     }
 
+    // Reassociate: x + -ConstantFP * y -> x - ConstantFP * y
+    // The FMul can also be an FDiv, and FAdd can be a FSub.
+    if (Opcode == Instruction::FMul || Opcode == Instruction::FDiv) {
+      if (ConstantFP *LHSConst = dyn_cast<ConstantFP>(I->getOperand(0))) {
+        if (LHSConst->isNegative() && I->hasOneUse()) {
+          Instruction *Parent = I->user_back();
+          if (Parent->getOpcode() == Instruction::FAdd) {
+            if (Parent->getOperand(0) == I)
+              optimizeFAddNegExpr(LHSConst, I, 0);
+            else if (Parent->getOperand(1) == I)
+              optimizeFAddNegExpr(LHSConst, I, 1);
+          } else if (Parent->getOpcode() == Instruction::FSub)
+            if (Parent->getOperand(1) == I)
+              optimizeFAddNegExpr(LHSConst, I, 1);
+        }
+      }
+    }
+
     // FIXME: We should commute vector instructions as well.  However, this 
     // requires further analysis to determine the effect on later passes.