[Reassociation] Add support for reassociation with unsafe algebra.

[mcrosier]

Summary

The purpose of this patch is to add support for reassociation with unsafe algebra.

I've performed correctness testing on AArch64 with our internal test suite and saw no correctness regressions. I'm currently running correctness against ARMv7.

The performance improvements look good, but I'm unable to share the numbers at this time; I'll see what I can do(, but no promises).

Please have a look!

Chad

[chandlerc]

Is there a reason this is not CC-ed to the list?

[mcrosier]

No, this should have been sent to the list as well!

[chandlerc]

lib/Transforms/Scalar/Reassociate.cpp

362

Why a local variable above but not here? I don't care deeply about which pattern you use, but I would generally avoid the single-use variable unless things get truly terrible to read...

854

The more I see of code like this, the more I think we need a richer clone approach in instructions... but that's not for this patch...

901–902

This formatting I find hard to read... clang-format?

914

Are you actually intending to use this variable outside of the if? How (as its null)? See comment below...

963

You pass BI twice here... is that intentional? Was one of them supposed to be I?

1951–1952

Why not floating point vector instructions? That seems rather odd to group with testing for fastmath...

[mcrosier]

lib/Transforms/Scalar/Reassociate.cpp

362

I agree. I'll take care of it.

901–902

Will do.

914

No. I'll put this in the canonical form. Thanks.

if (BinaryOperator *I = isReassociableOp(V, Instruction::Add, Instruction::FAdd)) {

}

963

Unfortunately, it's intentional (for now). The 3rd argument in the insertion point and the 4th is where FastMathFlags should be copied from. For CreateMul and CreateAdd these two arguments are always the same. However, for FNeg theres one instance where these two arguments are different (i.e., Line 1129). I could pass the FPMathFlags in, but then I would be hoisting the type checking out of the static helper functions, which would defeat the purpose.

1951–1952

I've already addressed this internally, but I need to rerun correctness and performance.

[mcrosier]

lib/Transforms/Scalar/Reassociate.cpp

1951–1952

Turns out that vector instructions are not handled for either integer for floating point instructions. If you don't mind, I'd prefer to land that change as a separate patch.

[mcrosier]

Revised patch based on Chandler's comments. This adds support for scalar floating-point instructions with unsafe math only (i.e., no vector support, yet).

Please have a look!

Chad

[mcrosier]

Ping.

[mcrosier]

If someone would mind reviewing this patch, I would greatly appreciate it. It's fairly straight forward to understand.

Please! :D

Chad

p.s. Please!

[mcrosier]

How about a post-commit review, given Chandler has already given this an initial review?

*tap* *tap* *tap* ...is this thing on? :)

Help me out, please.

Chad

[grosbach]

I'm fine with that if Chandler is. It all seems reasonable to me, but I'm not a floating point expert.

[mcrosier]

Thanks, Jim. Hopefully, Chandler or someone else will chime in.

[chandlerc]

Sorry I kept failing to get back to this.

Feel free to submit whenever. See comments below for my only (minor) comments. I don't see anything needing to wait on more rounds of review though.

I look forward to seeing the next 3 things I see here:

1. Support swapping the operand order once SLP vectorizer is OK with it
2. Support for floating point vectors
3. (maybe?) Support for integer vectors?

lib/Transforms/Scalar/Reassociate.cpp

884

Why not do this before or ofter the if, but outside of the if? It's duplicated in both sides.

963

I see. This makes sense. On looking at things more carefully, I actually like the pattern you use here more than the pattern for CreateMul and CreateAdd. It seems strange to conflate "insertion point" and "fast math flags source". Is there some conceptual reason to have them be the same? If not, I'd split them in all the methods.

1965–1968

I would really, really like to know why on earth we don't reassociate integer vector operations. That seems... kind of crazy.

[mcrosier]

1. Support swapping the operand order once SLP vectorizer is OK with it I believe Erik addressed this here: http://llvm.org/viewvc/llvm-project?view=revision&revision=214485

2. Support for floating point vectors
3. (maybe?) Support for integer vectors?

I have a follow up patch that addresses both of these.

lib/Transforms/Scalar/Reassociate.cpp

884

The SubclassOptionalData contains the FastMathFlags, so we need to save and restore that state before we call clearSubclassOptionalData(). Also, the calls to getFastMathFlags() and setFastMathFlags() needs to be guarded by the isa<FPMathOperator> check. Otherwise, we hit an assert.

1968

I agree; I have a follow up patch that will take care of this..

[mcrosier]

Committed r215647.

lib/Transforms/Scalar/Reassociate.cpp

     return cast<BinaryOperator>(V);
   return nullptr;
 }
+static BinaryOperator *isReassociableOp(Value *V, unsigned Opcode1,
+                                        unsigned Opcode2) {
+  if (V->hasOneUse() && isa<Instruction>(V) &&
+      (cast<Instruction>(V)->getOpcode() == Opcode1 ||
+       cast<Instruction>(V)->getOpcode() == Opcode2))
+    return cast<BinaryOperator>(V);
+  return nullptr;
+}
 
 static bool isUnmovableInstruction(Instruction *I) {
   switch (I->getOpcode()) {

 
   // If this is a not or neg instruction, do not count it for rank.  This
   // assures us that X and ~X will have the same rank.
-  if (!I->getType()->isIntegerTy() ||
-      (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
+  Type *Ty = I->getType();
+  if ((!Ty->isIntegerTy() && !Ty->isFloatingPointTy()) ||
+      (!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I) &&
+       !BinaryOperator::isFNeg(I)))
     ++Rank;
 
   //DEBUG(dbgs() << "Calculated Rank[" << V->getName() << "] = "

   return ValueRankMap[I] = Rank;
 }
 
+static BinaryOperator *CreateAdd(Value *S1, Value *S2, const Twine &Name,
+                                 Instruction *InsertBefore) {
+  BinaryOperator *Res;
+  if (S1->getType()->isIntOrIntVectorTy())
+    Res = BinaryOperator::CreateAdd(S1, S2, Name, InsertBefore);
+  else {
+    Res = BinaryOperator::CreateFAdd(S1, S2, Name, InsertBefore);
+    FastMathFlags Flags =
+      cast<FPMathOperator>(InsertBefore)->getFastMathFlags();
+    Res->setFastMathFlags(Flags);
+  }
+  return Res;
+}
+
+static BinaryOperator *CreateMul(Value *S1, Value *S2, const Twine &Name,
+                                 Instruction *InsertBefore) {
+  BinaryOperator *Res;
+  if (S1->getType()->isIntOrIntVectorTy())
+    Res = BinaryOperator::CreateMul(S1, S2, Name, InsertBefore);
+  else {
+    Res = BinaryOperator::CreateFMul(S1, S2, Name, InsertBefore);
+    FastMathFlags Flags =
+      cast<FPMathOperator>(InsertBefore)->getFastMathFlags();
+    Res->setFastMathFlags(Flags);
+  }
+  return Res;
+}
+
+static BinaryOperator *CreateNeg(Value *S1, const Twine &Name,
+                                 Instruction *InsertBefore, Value *FlagsOp) {
+  BinaryOperator *Res;
+  if (S1->getType()->isIntOrIntVectorTy())
+    Res = BinaryOperator::CreateNeg(S1, Name, InsertBefore);
+  else {
+    Res = BinaryOperator::CreateFNeg(S1, Name, InsertBefore);
+    Res->setFastMathFlags(cast<FPMathOperator>(FlagsOp)->getFastMathFlags());
+  }
+  return Res;
+}
+
 /// LowerNegateToMultiply - Replace 0-X with X*-1.
 ///
 static BinaryOperator *LowerNegateToMultiply(Instruction *Neg) {
-  Constant *Cst = Constant::getAllOnesValue(Neg->getType());
+  Type *Ty = Neg->getType();
+  Constant *NegOne = Ty->isIntOrIntVectorTy() ?
+    ConstantInt::getAllOnesValue(Ty) : ConstantFP::get(Ty, -1.0);
 
-  BinaryOperator *Res =
-    BinaryOperator::CreateMul(Neg->getOperand(1), Cst, "",Neg);
-  Neg->setOperand(1, Constant::getNullValue(Neg->getType())); // Drop use of op.
+  BinaryOperator *Res = CreateMul(Neg->getOperand(1), NegOne, "", Neg);
+  Neg->setOperand(1, Constant::getNullValue(Ty)); // Drop use of op.
   Res->takeName(Neg);
   Neg->replaceAllUsesWith(Res);
   Res->setDebugLoc(Neg->getDebugLoc());

     LHS = 0; // 1 + 1 === 0 modulo 2.
     return;
   }
-  if (Opcode == Instruction::Add) {
+  if (Opcode == Instruction::Add || Opcode == Instruction::FAdd) {
     // TODO: Reduce the weight by exploiting nsw/nuw?
     LHS += RHS;
     return;
   }
 
-  assert(Opcode == Instruction::Mul && "Unknown associative operation!");
+  assert((Opcode == Instruction::Mul || Opcode == Instruction::FMul) &&
+         "Unknown associative operation!");
   unsigned Bitwidth = LHS.getBitWidth();
   // If CM is the Carmichael number then a weight W satisfying W >= CM+Bitwidth
   // can be replaced with W-CM.  That's because x^W=x^(W-CM) for every Bitwidth

   DEBUG(dbgs() << "LINEARIZE: " << *I << '\n');
   unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits();
   unsigned Opcode = I->getOpcode();
-  assert(Instruction::isAssociative(Opcode) &&
-         Instruction::isCommutative(Opcode) &&
+  assert(I->isAssociative() && I->isCommutative() &&
          "Expected an associative and commutative operation!");
 
   // Visit all operands of the expression, keeping track of their weight (the

 
       // If this is a multiply expression, turn any internal negations into
       // multiplies by -1 so they can be reassociated.
-      BinaryOperator *BO = dyn_cast<BinaryOperator>(Op);
-      if (Opcode == Instruction::Mul && BO && BinaryOperator::isNeg(BO)) {
-        DEBUG(dbgs() << "MORPH LEAF: " << *Op << " (" << Weight << ") TO ");
-        BO = LowerNegateToMultiply(BO);
-        DEBUG(dbgs() << *BO << 'n');
-        Worklist.push_back(std::make_pair(BO, Weight));
-        MadeChange = true;
-        continue;
-      }
+      if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op))
+        if ((Opcode == Instruction::Mul && BinaryOperator::isNeg(BO)) ||
+            (Opcode == Instruction::FMul && BinaryOperator::isFNeg(BO))) {
+          DEBUG(dbgs() << "MORPH LEAF: " << *Op << " (" << Weight << ") TO ");
+          BO = LowerNegateToMultiply(BO);
+          DEBUG(dbgs() << *BO << '\n');
+          Worklist.push_back(std::make_pair(BO, Weight));
+          MadeChange = true;
+          continue;
+        }
 
       // Failed to morph into an expression of the right type.  This really is
       // a leaf.

       Constant *Undef = UndefValue::get(I->getType());
       NewOp = BinaryOperator::Create(Instruction::BinaryOps(Opcode),
                                      Undef, Undef, "", I);
+      if (NewOp->getType()->isFPOrFPVectorTy())
+        NewOp->setFastMathFlags(I->getFastMathFlags());
     } else {
       NewOp = NodesToRewrite.pop_back_val();
     }

   // expression tree is dominated by all of Ops.
   if (ExpressionChanged)
     do {
-      ExpressionChanged->clearSubclassOptionalData();
+      // Preserve FastMathFlags.
+      if (isa<FPMathOperator>(I)) {
+        FastMathFlags Flags = I->getFastMathFlags();
+        ExpressionChanged->clearSubclassOptionalData();
+        ExpressionChanged->setFastMathFlags(Flags);
+      } else
+        ExpressionChanged->clearSubclassOptionalData();
+
       if (ExpressionChanged == I)
         break;
       ExpressionChanged->moveBefore(I);

 /// version of the value is returned, and BI is left pointing at the instruction
 /// that should be processed next by the reassociation pass.
 static Value *NegateValue(Value *V, Instruction *BI) {
-  if (Constant *C = dyn_cast<Constant>(V))
-    return ConstantExpr::getNeg(C);
+  if (Constant *C = dyn_cast<Constant>(V)) {
+    assert ((isa<ConstantInt>(V) || isa<ConstantFP>(V)) &&
+            "Unexpected constant.");
+    return isa<ConstantInt>(V) ? ConstantExpr::getNeg(C) :
+      ConstantExpr::getFNeg(C);
+  }
 
   // We are trying to expose opportunity for reassociation.  One of the things
   // that we want to do to achieve this is to push a negation as deep into an

   // the constants.  We assume that instcombine will clean up the mess later if
   // we introduce tons of unnecessary negation instructions.
   //
-  if (BinaryOperator *I = isReassociableOp(V, Instruction::Add)) {
+  BinaryOperator *I = isReassociableOp(V, Instruction::Add, Instruction::FAdd);
+  if (I) {
     // Push the negates through the add.
     I->setOperand(0, NegateValue(I->getOperand(0), BI));
     I->setOperand(1, NegateValue(I->getOperand(1), BI));

   // Okay, we need to materialize a negated version of V with an instruction.
   // Scan the use lists of V to see if we have one already.
   for (User *U : V->users()) {
-    if (!BinaryOperator::isNeg(U)) continue;
+    if (!BinaryOperator::isNeg(U) && !BinaryOperator::isFNeg(U)) continue;
 
     // We found one!  Now we have to make sure that the definition dominates
     // this use.  We do this by moving it to the entry block (if it is a

 
   // Insert a 'neg' instruction that subtracts the value from zero to get the
   // negation.
-  return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
+  return CreateNeg(V, V->getName() + ".neg", BI, BI);
 }
 
 /// ShouldBreakUpSubtract - Return true if we should break up this subtract of
 /// X-Y into (X + -Y).
 static bool ShouldBreakUpSubtract(Instruction *Sub) {
   // If this is a negation, we can't split it up!
-  if (BinaryOperator::isNeg(Sub))
+  if (BinaryOperator::isNeg(Sub) || BinaryOperator::isFNeg(Sub))
     return false;
 
   // Don't bother to break this up unless either the LHS is an associable add or
   // subtract or if this is only used by one.
-  if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
-      isReassociableOp(Sub->getOperand(0), Instruction::Sub))
+  Value *V0 = Sub->getOperand(0);
+  if (isReassociableOp(V0, Instruction::Add, Instruction::FAdd) ||
+      isReassociableOp(V0, Instruction::Sub, Instruction::FSub))
     return true;
-  if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
-      isReassociableOp(Sub->getOperand(1), Instruction::Sub))
+  Value *V1 = Sub->getOperand(1);
+  if (isReassociableOp(V1, Instruction::Add, Instruction::FAdd) ||
+      isReassociableOp(V1, Instruction::Sub, Instruction::FSub))
     return true;
+  Value *VB = Sub->user_back();
   if (Sub->hasOneUse() &&
-      (isReassociableOp(Sub->user_back(), Instruction::Add) ||
-       isReassociableOp(Sub->user_back(), Instruction::Sub)))
+      (isReassociableOp(VB, Instruction::Add, Instruction::FAdd) ||
+       isReassociableOp(VB, Instruction::Sub, Instruction::FSub)))
     return true;
 
   return false;

   // and set it as the RHS of the add instruction we just made.
   //
   Value *NegVal = NegateValue(Sub->getOperand(1), Sub);
-  BinaryOperator *New =
-    BinaryOperator::CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
+  BinaryOperator *New = CreateAdd(Sub->getOperand(0), NegVal, "", Sub);
   Sub->setOperand(0, Constant::getNullValue(Sub->getType())); // Drop use of op.
   Sub->setOperand(1, Constant::getNullValue(Sub->getType())); // Drop use of op.
   New->takeName(Sub);

   Value *V1 = Ops.back();
   Ops.pop_back();
   Value *V2 = EmitAddTreeOfValues(I, Ops);
-  return BinaryOperator::CreateAdd(V2, V1, "tmp", I);
+  return CreateAdd(V2, V1, "tmp", I);
 }
 
 /// RemoveFactorFromExpression - If V is an expression tree that is a
 /// multiplication sequence, and if this sequence contains a multiply by Factor,
 /// remove Factor from the tree and return the new tree.
 Value *Reassociate::RemoveFactorFromExpression(Value *V, Value *Factor) {
-  BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
-  if (!BO) return nullptr;
+  BinaryOperator *BO = isReassociableOp(V, Instruction::Mul, Instruction::FMul);
+  if (!BO)
+    return nullptr;
 
   SmallVector<RepeatedValue, 8> Tree;
   MadeChange |= LinearizeExprTree(BO, Tree);

           Factors.erase(Factors.begin()+i);
           break;
         }
+    if (ConstantFP *FC1 = dyn_cast<ConstantFP>(Factor))
+      if (ConstantFP *FC2 = dyn_cast<ConstantFP>(Factors[i].Op)) {
+        APFloat F1(FC1->getValueAPF());
+        APFloat F2(FC2->getValueAPF());
+        F2.changeSign();
+        if (F1.compare(F2) == APFloat::cmpEqual) {
+          FoundFactor = NeedsNegate = true;
+          Factors.erase(Factors.begin()+i);
+          break;
+        }
+      }
   }
 
   if (!FoundFactor) {

   }
 
   if (NeedsNegate)
-    V = BinaryOperator::CreateNeg(V, "neg", InsertPt);
+    V = CreateNeg(V, "neg", InsertPt, BO);
 
   return V;
 }

 static void FindSingleUseMultiplyFactors(Value *V,
                                          SmallVectorImpl<Value*> &Factors,
                                        const SmallVectorImpl<ValueEntry> &Ops) {
-  BinaryOperator *BO = isReassociableOp(V, Instruction::Mul);
+  BinaryOperator *BO = isReassociableOp(V, Instruction::Mul, Instruction::FMul);
   if (!BO) {
     Factors.push_back(V);
     return;

       ++NumFactor;
 
       // Insert a new multiply.
-      Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
-      Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
+      Type *Ty = TheOp->getType();
+      Constant *C = Ty->isIntOrIntVectorTy() ?
+        ConstantInt::get(Ty, NumFound) : ConstantFP::get(Ty, NumFound);
+      Instruction *Mul = CreateMul(TheOp, C, "factor", I);
 
       // Now that we have inserted a multiply, optimize it. This allows us to
       // handle cases that require multiple factoring steps, such as this:
       // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
-      RedoInsts.insert(cast<Instruction>(Mul));
+      RedoInsts.insert(Mul);
 
       // If every add operand was a duplicate, return the multiply.
       if (Ops.empty())

     }
 
     // Check for X and -X or X and ~X in the operand list.
-    if (!BinaryOperator::isNeg(TheOp) && !BinaryOperator::isNot(TheOp))
+    if (!BinaryOperator::isNeg(TheOp) && !BinaryOperator::isFNeg(TheOp) &&
+        !BinaryOperator::isNot(TheOp))
       continue;
 
     Value *X = nullptr;
-    if (BinaryOperator::isNeg(TheOp))
+    if (BinaryOperator::isNeg(TheOp) || BinaryOperator::isFNeg(TheOp))
       X = BinaryOperator::getNegArgument(TheOp);
     else if (BinaryOperator::isNot(TheOp))
       X = BinaryOperator::getNotArgument(TheOp);

       continue;
 
     // Remove X and -X from the operand list.
-    if (Ops.size() == 2 && BinaryOperator::isNeg(TheOp))
+    if (Ops.size() == 2 && (BinaryOperator::isNeg(TheOp) ||
+                            BinaryOperator::isFNeg(TheOp)))
       return Constant::getNullValue(X->getType());
 
     // Remove X and ~X from the operand list.

   unsigned MaxOcc = 0;
   Value *MaxOccVal = nullptr;
   for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
-    BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul);
+    BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul,
+                                           Instruction::FMul);
     if (!BOp)
       continue;
 

           unsigned Occ = ++FactorOccurrences[Factor];
           if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
         }
+      if (ConstantFP *CF = dyn_cast<ConstantFP>(Factor))
+        if (CF->isNegative()) {
+          APFloat F(CF->getValueAPF());
+          F.changeSign();
+          Factor = ConstantFP::get(CF->getContext(), F);
+          assert(!Duplicates.count(Factor) &&
+                 "Shouldn't have two constant factors, missed a canonicalize");
+
+          unsigned Occ = ++FactorOccurrences[Factor];
+          if (Occ > MaxOcc) { MaxOcc = Occ; MaxOccVal = Factor; }
+        }
     }
   }
 

     // this, we could otherwise run into situations where removing a factor
     // from an expression will drop a use of maxocc, and this can cause
     // RemoveFactorFromExpression on successive values to behave differently.
-    Instruction *DummyInst = BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal);
+    Instruction *DummyInst = I->getType()->isIntOrIntVectorTy() ?
+      BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal) :
+      BinaryOperator::CreateFAdd(MaxOccVal, MaxOccVal);
+
     SmallVector<WeakVH, 4> NewMulOps;
     for (unsigned i = 0; i != Ops.size(); ++i) {
       // Only try to remove factors from expressions we're allowed to.
-      BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul);
+      BinaryOperator *BOp = isReassociableOp(Ops[i].Op, Instruction::Mul,
+                                             Instruction::FMul);
       if (!BOp)
         continue;
 

       RedoInsts.insert(VI);
 
     // Create the multiply.
-    Instruction *V2 = BinaryOperator::CreateMul(V, MaxOccVal, "tmp", I);
+    Instruction *V2 = CreateMul(V, MaxOccVal, "tmp", I);
 
     // Rerun associate on the multiply in case the inner expression turned into
     // a multiply.  We want to make sure that we keep things in canonical form.

 
   Value *LHS = Ops.pop_back_val();
   do {
-    LHS = Builder.CreateMul(LHS, Ops.pop_back_val());
+    if (LHS->getType()->isIntOrIntVectorTy())
+      LHS = Builder.CreateMul(LHS, Ops.pop_back_val());
+    else
+      LHS = Builder.CreateFMul(LHS, Ops.pop_back_val());
   } while (!Ops.empty());
 
   return LHS;

     break;
 
   case Instruction::Add:
+  case Instruction::FAdd:
     if (Value *Result = OptimizeAdd(I, Ops))
       return Result;
     break;
 
   case Instruction::Mul:
+  case Instruction::FMul:
     if (Value *Result = OptimizeMul(I, Ops))
       return Result;
     break;

       I = NI;
     }
 
-  // Floating point binary operators are not associative, but we can still
-  // commute (some) of them, to canonicalize the order of their operands.
-  // This can potentially expose more CSE opportunities, and makes writing
-  // other transformations simpler.
+  // 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.
   if ((I->getType()->isFloatingPointTy() || I->getType()->isVectorTy())) {
-    // FAdd and FMul can be commuted.
-    if (I->getOpcode() != Instruction::FMul &&
-        I->getOpcode() != Instruction::FAdd)
-      return;
-
-    Value *LHS = I->getOperand(0);
-    Value *RHS = I->getOperand(1);
-    unsigned LHSRank = getRank(LHS);
-    unsigned RHSRank = getRank(RHS);
 
-    // Sort the operands by rank.
-    if (RHSRank < LHSRank) {
-      I->setOperand(0, RHS);
-      I->setOperand(1, LHS);
+    // FAdd and FMul can be commuted.
+    if (I->isCommutative()) {
+      Value *LHS = I->getOperand(0);
+      Value *RHS = I->getOperand(1);
+      unsigned LHSRank = getRank(LHS);
+      unsigned RHSRank = getRank(RHS);
+
+      // Sort the operands by rank.
+      if (RHSRank < LHSRank) {
+        I->setOperand(0, RHS);
+        I->setOperand(1, LHS);
+      }
     }
 
-    return;
+    // Don't try to optimize floating point vector instructions or anything
+    // that doesn't have unsafe algebra.
+    if (I->getType()->isVectorTy() || !I->hasUnsafeAlgebra())
+      return;
   }
 
   // Do not reassociate boolean (i1) expressions.  We want to preserve the

         I = NI;
       }
     }
+  } else if (I->getOpcode() == Instruction::FSub) {
+    if (ShouldBreakUpSubtract(I)) {
+      Instruction *NI = BreakUpSubtract(I);
+      RedoInsts.insert(I);
+      MadeChange = true;
+      I = NI;
+    } else if (BinaryOperator::isFNeg(I)) {
+      // Otherwise, this is a negation.  See if the operand is a multiply tree
+      // and if this is not an inner node of a multiply tree.
+      if (isReassociableOp(I->getOperand(1), Instruction::FMul) &&
+          (!I->hasOneUse() ||
+           !isReassociableOp(I->user_back(), Instruction::FMul))) {
+        Instruction *NI = LowerNegateToMultiply(I);
+        RedoInsts.insert(I);
+        MadeChange = true;
+        I = NI;
+      }
+    }
   }
 
   // If this instruction is an associative binary operator, process it.

   if (BO->hasOneUse() && BO->getOpcode() == Instruction::Add &&
       cast<Instruction>(BO->user_back())->getOpcode() == Instruction::Sub)
     return;
+  if (BO->hasOneUse() && BO->getOpcode() == Instruction::FAdd &&
+      cast<Instruction>(BO->user_back())->getOpcode() == Instruction::FSub)
+    return;
 
   ReassociateExpression(BO);
 }

   // this is a multiply tree used only by an add, and the immediate is a -1.
   // In this case we reassociate to put the negation on the outside so that we
   // can fold the negation into the add: (-X)*Y + Z -> Z-X*Y
-  if (I->getOpcode() == Instruction::Mul && I->hasOneUse() &&
-      cast<Instruction>(I->user_back())->getOpcode() == Instruction::Add &&
-      isa<ConstantInt>(Ops.back().Op) &&
-      cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
-    ValueEntry Tmp = Ops.pop_back_val();
-    Ops.insert(Ops.begin(), Tmp);
+  if (I->hasOneUse()) {
+    if (I->getOpcode() == Instruction::Mul &&
+        cast<Instruction>(I->user_back())->getOpcode() == Instruction::Add &&
+        isa<ConstantInt>(Ops.back().Op) &&
+        cast<ConstantInt>(Ops.back().Op)->isAllOnesValue()) {
+      ValueEntry Tmp = Ops.pop_back_val();
+      Ops.insert(Ops.begin(), Tmp);
+    } else if (I->getOpcode() == Instruction::FMul &&
+          cast<Instruction>(I->user_back())->getOpcode() == Instruction::FAdd &&
+               isa<ConstantFP>(Ops.back().Op) &&
+               cast<ConstantFP>(Ops.back().Op)->isExactlyValue(-1.0)) {
+      ValueEntry Tmp = Ops.pop_back_val();
+      Ops.insert(Ops.begin(), Tmp);
+    }
   }
 
   DEBUG(dbgs() << "RAOut:\t"; PrintOps(I, Ops); dbgs() << '\n');

test/Transforms/Reassociate/fast-2002-05-15-AgressiveSubMove.ll

+; RUN: opt < %s -reassociate -S | FileCheck %s
+
+define float @test1(float %A) {
+; CHECK-LABEL: test1
+; CHECK-NEXT: %X = fadd float 1.000000e+00, %A
+; CHECK-NEXT: %Y = fadd float 1.000000e+00, %A
+; CHECK-NEXT: %r = fsub float %X, %Y
+; CHECK-NEXT: ret float %r
+
+  %X = fadd float %A, 1.000000e+00
+  %Y = fadd float %A, 1.000000e+00
+  %r = fsub float %X, %Y
+  ret float %r
+}
+
+define float @test2(float %A) {
+; CHECK-LABEL: test2
+; CHECK-NEXT: ret float 0.000000e+00
+
+  %X = fadd fast float 1.000000e+00, %A
+  %Y = fadd fast float 1.000000e+00, %A
+  %r = fsub fast float %X, %Y
+  ret float %r
+}

test/Transforms/Reassociate/fast-2002-05-15-MissedTree.ll

+; RUN: opt < %s -reassociate -instcombine -S | FileCheck %s
+
+define float @test1(float %A, float %B) {
+; CHECK-LABEL: test1
+; CHECK: %Z = fadd fast float %A, %B
+; CHECK: ret float %Z
+  %W = fadd fast float %B, -5.0
+  %Y = fadd fast float %A, 5.0
+  %Z = fadd fast float %W, %Y
+  ret float %Z
+}
+

test/Transforms/Reassociate/fast-2002-05-15-SubReassociate.ll

+; RUN: opt < %s -reassociate -constprop -instcombine -S | FileCheck %s
+
+define float @test1(float %A, float %B) {
+; CHECK-LABEL: test1
+; CHECK-NEXT: %W = fadd float %B, 5.000000e+00
+; CHECK-NEXT: %X = fadd float %A, -7.000000e+00
+; CHECK-NEXT: %Y = fsub float %X, %W
+; CHECK-NEXT: %Z = fadd float %Y, 1.200000e+01
+; CHECK-NEXT: ret float %Z
+
+  %W = fadd float 5.0, %B
+  %X = fadd float -7.0, %A
+  %Y = fsub float %X, %W
+  %Z = fadd float %Y, 12.0
+  ret float %Z
+}
+
+; With sub reassociation, constant folding can eliminate all of the constants.
+define float @test2(float %A, float %B) {
+; CHECK-LABEL: test2
+; CHECK-NEXT: %Z = fsub fast float %A, %B
+; CHECK-NEXT: ret float %Z
+
+  %W = fadd fast float %B, 5.000000e+00
+  %X = fadd fast float %A, -7.000000e+00
+  %Y = fsub fast float %X, %W
+  %Z = fadd fast float %Y, 1.200000e+01
+  ret float %Z
+
+}
+
+define float @test3(float %A, float %B, float %C, float %D) {
+; CHECK-LABEL: test3
+; CHECK-NEXT: %M = fadd float %A, 1.200000e+01
+; CHECK-NEXT: %N = fadd float %M, %B
+; CHECK-NEXT: %O = fadd float %N, %C
+; CHECK-NEXT: %P = fsub float %D, %O
+; CHECK-NEXT: %Q = fadd float %P, 1.200000e+01
+; CHECK-NEXT: ret float %Q
+
+  %M = fadd float %A, 1.200000e+01
+  %N = fadd float %M, %B
+  %O = fadd float %N, %C
+  %P = fsub float %D, %O
+  %Q = fadd float %P, 1.200000e+01
+  ret float %Q
+}
+
+; With sub reassociation, constant folding can eliminate the two 12 constants.
+define float @test4(float %A, float %B, float %C, float %D) {
+; CHECK-LABEL: test4
+; CHECK-NEXT: %B.neg = fsub fast float -0.000000e+00, %B
+; CHECK-NEXT: %O.neg = fsub fast float %B.neg, %A
+; CHECK-NEXT: %P = fsub fast float %O.neg, %C
+; CHECK-NEXT: %Q = fadd fast float %P, %D
+; CHECK-NEXT: ret float %Q
+
+; FIXME: InstCombine should be able to get us to the following:
+; %sum = fadd fast float %B, %A
+; %sum1 = fadd fast float %sum, %C
+; %Q = fsub fast float %D, %sum1
+; ret i32 %Q
+
+  %M = fadd fast float 1.200000e+01, %A
+  %N = fadd fast float %M, %B
+  %O = fadd fast float %N, %C
+  %P = fsub fast float %D, %O
+  %Q = fadd fast float 1.200000e+01, %P
+  ret float %Q
+}

test/Transforms/Reassociate/fast-2005-09-01-ArrayOutOfBounds.ll

+; RUN: opt < %s -reassociate -instcombine -S | FileCheck %s
+
+; Not marked as fast, so must not change.
+define float @test1(float %a0, float %a1, float %a2, float %a3, float %a4) {
+; CHECK-LABEL: test1
+; CHECK-NEXT: %tmp.2 = fadd float %a3, %a4
+; CHECK-NEXT: %tmp.4 = fadd float %tmp.2, %a2
+; CHECK-NEXT: %tmp.6 = fadd float %tmp.4, %a1
+; CHECK-NEXT: %tmp.8 = fadd float %tmp.6, %a0
+; CHECK-NEXT: %tmp.11 = fadd float %a2, %a3
+; CHECK-NEXT: %tmp.13 = fadd float %tmp.11, %a1
+; CHECK-NEXT: %tmp.15 = fadd float %tmp.13, %a0
+; CHECK-NEXT: %tmp.18 = fadd float %a1, %a2
+; CHECK-NEXT: %tmp.20 = fadd float %tmp.18, %a0
+; CHECK-NEXT: %tmp.23 = fadd float %a0, %a1
+; CHECK-NEXT: %tmp.26 = fsub float %tmp.8, %tmp.15
+; CHECK-NEXT: %tmp.28 = fadd float %tmp.20, %tmp.26
+; CHECK-NEXT: %tmp.30 = fsub float %tmp.28, %tmp.23
+; CHECK-NEXT: %tmp.32 = fsub float %tmp.30, %a4
+; CHECK-NEXT: %tmp.34 = fsub float %tmp.32, %a2
+; CHECK-NEXT: %T = fmul float %tmp.34, %tmp.34
+; CHECK-NEXT: ret float %T
+
+  %tmp.2 = fadd float %a4, %a3
+  %tmp.4 = fadd float %tmp.2, %a2
+  %tmp.6 = fadd float %tmp.4, %a1
+  %tmp.8 = fadd float %tmp.6, %a0
+  %tmp.11 = fadd float %a3, %a2
+  %tmp.13 = fadd float %tmp.11, %a1
+  %tmp.15 = fadd float %tmp.13, %a0
+  %tmp.18 = fadd float %a2, %a1
+  %tmp.20 = fadd float %tmp.18, %a0
+  %tmp.23 = fadd float %a1, %a0
+  %tmp.26 = fsub float %tmp.8, %tmp.15
+  %tmp.28 = fadd float %tmp.26, %tmp.20
+  %tmp.30 = fsub float %tmp.28, %tmp.23
+  %tmp.32 = fsub float %tmp.30, %a4
+  %tmp.34 = fsub float %tmp.32, %a2
+  %T = fmul float %tmp.34, %tmp.34
+  ret float %T
+}
+
+; Should be able to eliminate everything.
+define float @test2(float %a0, float %a1, float %a2, float %a3, float %a4) {
+; CHECK-LABEL: test2
+; CHECK: ret float 0.000000e+00
+
+  %tmp.2 = fadd fast float %a4, %a3
+  %tmp.4 = fadd fast float %tmp.2, %a2
+  %tmp.6 = fadd fast float %tmp.4, %a1
+  %tmp.8 = fadd fast float %tmp.6, %a0
+  %tmp.11 = fadd fast float %a3, %a2
+  %tmp.13 = fadd fast float %tmp.11, %a1
+  %tmp.15 = fadd fast float %tmp.13, %a0
+  %tmp.18 = fadd fast float %a2, %a1
+  %tmp.20 = fadd fast float %tmp.18, %a0
+  %tmp.23 = fadd fast float %a1, %a0
+  %tmp.26 = fsub fast float %tmp.8, %tmp.15
+  %tmp.28 = fadd fast float %tmp.26, %tmp.20
+  %tmp.30 = fsub fast float %tmp.28, %tmp.23
+  %tmp.32 = fsub fast float %tmp.30, %a4
+  %tmp.34 = fsub fast float %tmp.32, %a2
+  %T = fmul fast float %tmp.34, %tmp.34
+  ret float %T
+}

test/Transforms/Reassociate/fast-2006-04-27-ReassociateVector.ll

+; RUN: opt < %s -reassociate -S | FileCheck %s
+
+; Don't handle floating point vector operations.
+define <4 x float> @test1() {
+; CHECK-LABEL: test1
+; CHECK-NEXT: %tmp1 = fsub fast <4 x float> zeroinitializer, zeroinitializer
+; CHECK-NEXT: %tmp2 = fmul fast <4 x float> zeroinitializer, %tmp1
+
+  %tmp1 = fsub fast <4 x float> zeroinitializer, zeroinitializer
+  %tmp2 = fmul fast <4 x float> zeroinitializer, %tmp1
+  ret <4 x float> %tmp2
+}
+

test/Transforms/Reassociate/fast-basictest.ll

+; RUN: opt < %s -reassociate -gvn -instcombine -S | FileCheck %s
+
+; With reassociation, constant folding can eliminate the 12 and -12 constants.
+define float @test1(float %arg) {
+; CHECK-LABEL: @test1
+; CHECK-NEXT: fsub fast float -0.000000e+00, %arg
+; CHECK-NEXT: ret float
+
+  %tmp1 = fsub fast float -1.200000e+01, %arg
+  %tmp2 = fadd fast float %tmp1, 1.200000e+01
+  ret float %tmp2
+}
+
+define float @test2(float %reg109, float %reg1111) {
+; CHECK-LABEL: @test2
+; CHECK-NEXT: fadd float %reg109, -3.000000e+01
+; CHECK-NEXT: fadd float %reg115, %reg1111
+; CHECK-NEXT: fadd float %reg116, 3.000000e+01
+; CHECK-NEXT: ret float
+
+  %reg115 = fadd float %reg109, -3.000000e+01
+  %reg116 = fadd float %reg115, %reg1111
+  %reg117 = fadd float %reg116, 3.000000e+01
+  ret float %reg117
+}
+
+define float @test3(float %reg109, float %reg1111) {
+; CHECK-LABEL: @test3
+; CHECK-NEXT: %reg117 = fadd fast float %reg109, %reg1111
+; CHECK-NEXT:  ret float %reg117
+
+  %reg115 = fadd fast float %reg109, -3.000000e+01
+  %reg116 = fadd fast float %reg115, %reg1111
+  %reg117 = fadd fast float %reg116, 3.000000e+01
+  ret float %reg117
+}
+
+@fe = external global float
+@fa = external global float
+@fb = external global float
+@fc = external global float
+@ff = external global float
+
+define void @test4() {
+; CHECK-LABEL: @test4
+; CHECK: fadd fast float
+; CHECK: fadd fast float
+; CHECK-NOT: fadd fast float
+; CHECK: ret void
+
+  %A = load float* @fa
+  %B = load float* @fb
+  %C = load float* @fc
+  %t1 = fadd fast float %A, %B
+  %t2 = fadd fast float %t1, %C
+  %t3 = fadd fast float %C, %A
+  %t4 = fadd fast float %t3, %B
+  ; e = (a+b)+c;
+  store float %t2, float* @fe
+  ; f = (a+c)+b
+  store float %t4, float* @ff
+  ret void
+}
+
+define void @test5() {
+; CHECK-LABEL: @test5
+; CHECK: fadd fast float
+; CHECK: fadd fast float
+; CHECK-NOT: fadd
+; CHECK: ret void
+
+  %A = load float* @fa
+  %B = load float* @fb
+  %C = load float* @fc
+  %t1 = fadd fast float %A, %B
+  %t2 = fadd fast float %t1, %C
+  %t3 = fadd fast float %C, %A
+  %t4 = fadd fast float %t3, %B
+  ; e = c+(a+b)
+  store float %t2, float* @fe
+  ; f = (c+a)+b
+  store float %t4, float* @ff
+  ret void
+}
+
+define void @test6() {
+; CHECK-LABEL: @test6
+; CHECK: fadd fast float
+; CHECK: fadd fast float
+; CHECK-NOT: fadd
+; CHECK: ret void
+
+  %A = load float* @fa
+  %B = load float* @fb
+  %C = load float* @fc
+  %t1 = fadd fast float %B, %A
+  %t2 = fadd fast float %t1, %C
+  %t3 = fadd fast float %C, %A
+  %t4 = fadd fast float %t3, %B
+  ; e = c+(b+a)
+  store float %t2, float* @fe
+  ; f = (c+a)+b
+  store float %t4, float* @ff
+  ret void
+}
+
+define float @test7(float %A, float %B, float %C) {
+; CHECK-LABEL: @test7
+; CHECK-NEXT: fadd fast float %C, %B
+; CHECK-NEXT: fmul fast float
+; CHECK-NEXT: fmul fast float
+; CHECK-NEXT: ret float
+
+  ; A*A*B + A*C*A
+  %aa = fmul fast float %A, %A
+  %aab = fmul fast float %aa, %B
+  %ac = fmul fast float %A, %C
+  %aac = fmul fast float %ac, %A
+  %r = fadd fast float %aab, %aac
+  ret float %r
+}
+
+define float @test8(float %X, float %Y, float %Z) {
+; CHECK-LABEL: @test8
+; CHECK-NEXT: fmul fast float %Y, %X
+; CHECK-NEXT: fsub fast float %Z, %A
+; CHECK-NEXT: ret float
+
+  %A = fsub fast float 0.0, %X
+  %B = fmul fast float %A, %Y
+  ; (-X)*Y + Z -> Z-X*Y
+  %C = fadd fast float %B, %Z
+  ret float %C
+}
+
+define float @test9(float %X) {
+; CHECK-LABEL: @test9
+; CHECK-NEXT: fmul fast float %X, 9.400000e+01
+; CHECK-NEXT: ret float
+
+  %Y = fmul fast float %X, 4.700000e+01
+  %Z = fadd fast float %Y, %Y
+  ret float %Z
+}
+
+define float @test10(float %X) {
+; CHECK-LABEL: @test10
+; CHECK-NEXT: fmul fast float %X, 3.000000e+00
+; CHECK-NEXT: ret float
+
+  %Y = fadd fast float %X ,%X
+  %Z = fadd fast float %Y, %X
+  ret float %Z
+}
+
+define float @test11(float %W) {
+; CHECK-LABEL: test11
+; CHECK-NEXT: fmul fast float %W, 3.810000e+02
+; CHECK-NEXT: ret float
+
+  %X = fmul fast float %W, 127.0
+  %Y = fadd fast float %X ,%X
+  %Z = fadd fast float %Y, %X
+  ret float %Z
+}
+
+define float @test12(float %X) {
+; CHECK-LABEL: @test12
+; CHECK-NEXT: fmul fast float %X, -3.000000e+00
+; CHECK-NEXT: fadd fast float %factor, 6.000000e+00
+; CHECK-NEXT: ret float
+
+  %A = fsub fast float 1.000000e+00, %X
+  %B = fsub fast float 2.000000e+00, %X
+  %C = fsub fast float 3.000000e+00, %X
+  %Y = fadd fast float %A ,%B
+  %Z = fadd fast float %Y, %C
+  ret float %Z
+}
+
+define float @test13(float %X1, float %X2, float %X3) {
+; CHECK-LABEL: @test13
+; CHECK-NEXT: fsub fast float %X3, %X2
+; CHECK-NEXT: fmul fast float {{.*}}, %X1
+; CHECK-NEXT: ret float
+
+  %A = fsub fast float 0.000000e+00, %X1
+  %B = fmul fast float %A, %X2   ; -X1*X2
+  %C = fmul fast float %X1, %X3  ; X1*X3
+  %D = fadd fast float %B, %C    ; -X1*X2 + X1*X3 -> X1*(X3-X2)
+  ret float %D
+}
+
+define float @test14(float %X1, float %X2) {
+; CHECK-LABEL: @test14
+; CHECK-NEXT: fsub fast float %X1, %X2
+; CHECK-NEXT: fmul fast float %tmp, 4.700000e+01
+; CHECK-NEXT: ret float
+
+  %B = fmul fast float %X1, 47.   ; X1*47
+  %C = fmul fast float %X2, -47.  ; X2*-47
+  %D = fadd fast float %B, %C    ; X1*47 + X2*-47 -> 47*(X1-X2)
+  ret float %D
+}
+
+define float @test15(float %arg) {
+; CHECK-LABEL: test15
+; CHECK-NEXT: fmul fast float %arg, 1.440000e+02
+; CHECK-NEXT: ret float %tmp2
+
+  %tmp1 = fmul fast float 1.200000e+01, %arg
+  %tmp2 = fmul fast float %tmp1, 1.200000e+01
+  ret float %tmp2
+}
+
+; (b+(a+1234))+-a -> b+1234
+define float @test16(float %b, float %a) {
+; CHECK-LABEL: @test16
+; CHECK-NEXT: fadd fast float %b, 1.234000e+03
+; CHECK-NEXT: ret float
+
+  %1 = fadd fast float %a, 1234.0
+  %2 = fadd fast float %b, %1
+  %3 = fsub fast float 0.0, %a
+  %4 = fadd fast float %2, %3
+  ret float %4
+}
+
+; Test that we can turn things like X*-(Y*Z) -> X*-1*Y*Z.
+
+define float @test17(float %a, float %b, float %z) {
+; CHECK-LABEL: test17
+; CHECK-NEXT: fmul fast float %a, 1.234500e+04
+; CHECK-NEXT: fmul fast float %e, %b
+; CHECK-NEXT: fmul fast float %f, %z
+; CHECK-NEXT: ret float
+
+  %c = fsub fast float 0.000000e+00, %z
+  %d = fmul fast float %a, %b
+  %e = fmul fast float %c, %d
+  %f = fmul fast float %e, 1.234500e+04
+  %g = fsub fast float 0.000000e+00, %f
+  ret float %g
+}
+
+define float @test18(float %a, float %b, float %z) {
+; CHECK-LABEL: test18
+; CHECK-NEXT: fmul fast float %a, 4.000000e+01
+; CHECK-NEXT: fmul fast float %e, %z
+; CHECK-NEXT: ret float
+
+  %d = fmul fast float %z, 4.000000e+01
+  %c = fsub fast float 0.000000e+00, %d
+  %e = fmul fast float %a, %c
+  %f = fsub fast float 0.000000e+00, %e
+  ret float %f
+}
+
+; With sub reassociation, constant folding can eliminate the 12 and -12 constants.
+define float @test19(float %A, float %B) {
+; CHECK-LABEL: @test19
+; CHECK-NEXT: fsub fast float %A, %B
+; CHECK-NEXT: ret float
+  %X = fadd fast float -1.200000e+01, %A
+  %Y = fsub fast float %X, %B
+  %Z = fadd fast float %Y, 1.200000e+01
+  ret float %Z
+}
+
+; With sub reassociation, constant folding can eliminate the uses of %a.
+define float @test20(float %a, float %b, float %c) nounwind  {
+; CHECK-LABEL: @test20
+; CHECK-NEXT: fsub fast float -0.000000e+00, %b
+; CHECK-NEXT: fsub fast float %b.neg, %c
+; CHECK-NEXT: ret float
+
+; FIXME: Should be able to generate the below, which may expose more
+;        opportunites for FAdd reassociation.
+; %sum = fadd fast float %c, %b
+; %tmp7 = fsub fast float 0, %sum
+
+  %tmp3 = fsub fast float %a, %b
+  %tmp5 = fsub fast float %tmp3, %c
+  %tmp7 = fsub fast float %tmp5, %a
+  ret float %tmp7
+}

test/Transforms/Reassociate/fast-fp-commute.ll

+; RUN: opt -reassociate -S < %s | FileCheck %s
+
+declare void @use(float)
+
+define void @test1(float %x, float %y) {
+; CHECK-LABEL: test1
+; CHECK: fmul fast float %y, %x
+; CHECK: fmul fast float %y, %x
+; CHECK: fsub fast float %1, %2
+; CHECK: call void @use(float %{{.*}})
+; CHECK: call void @use(float %{{.*}})
+
+  %1 = fmul fast float %x, %y
+  %2 = fmul fast float %y, %x
+  %3 = fsub fast float %1, %2
+  call void @use(float %1)
+  call void @use(float %3)
+  ret void
+}
+
+define float @test2(float %x, float %y) {
+; CHECK-LABEL: test2
+; CHECK-NEXT: fmul fast float %y, %x
+; CHECK-NEXT: fmul fast float %y, %x
+; CHECK-NEXT: fsub fast float %1, %2
+; CHECK-NEXT: ret float %3
+
+  %1 = fmul fast float %x, %y
+  %2 = fmul fast float %y, %x
+  %3 = fsub fast float %1, %2
+  ret float %3
+}
+
+define float @test3(float %x, float %y) {
+; CHECK-LABEL: test3
+; CHECK-NEXT: %factor = fmul fast float 2.000000e+00, %y
+; CHECK-NEXT: %tmp1 = fmul fast float %factor, %x
+; CHECK-NEXT: ret float %tmp1
+
+  %1 = fmul fast float %x, %y
+  %2 = fmul fast float %y, %x
+  %3 = fadd fast float %1, %2
+  ret float %3
+}

test/Transforms/Reassociate/fast-mightymul.ll

+; RUN: opt < %s -reassociate -disable-output
+; PR13021
+
+define float @test2(float %x) {
+  %t0 = fmul fast float %x, %x
+  %t1 = fmul fast float %t0, %t0
+  %t2 = fmul fast float %t1, %t1
+  %t3 = fmul fast float %t2, %t2
+  %t4 = fmul fast float %t3, %t3
+  %t5 = fmul fast float %t4, %t4
+  %t6 = fmul fast float %t5, %t5
+  %t7 = fmul fast float %t6, %t6
+  %t8 = fmul fast float %t7, %t7
+  %t9 = fmul fast float %t8, %t8
+  %t10 = fmul fast float %t9, %t9
+  %t11 = fmul fast float %t10, %t10
+  %t12 = fmul fast float %t11, %t11
+  %t13 = fmul fast float %t12, %t12
+  %t14 = fmul fast float %t13, %t13
+  %t15 = fmul fast float %t14, %t14
+  %t16 = fmul fast float %t15, %t15
+  %t17 = fmul fast float %t16, %t16
+  %t18 = fmul fast float %t17, %t17
+  %t19 = fmul fast float %t18, %t18
+  %t20 = fmul fast float %t19, %t19
+  %t21 = fmul fast float %t20, %t20
+  %t22 = fmul fast float %t21, %t21
+  %t23 = fmul fast float %t22, %t22
+  %t24 = fmul fast float %t23, %t23
+  %t25 = fmul fast float %t24, %t24
+  %t26 = fmul fast float %t25, %t25
+  %t27 = fmul fast float %t26, %t26
+  %t28 = fmul fast float %t27, %t27
+  ret float %t28
+}

test/Transforms/Reassociate/fast-multistep.ll

+; RUN: opt < %s -reassociate -S | FileCheck %s
+
+define float @fmultistep1(float %a, float %b, float %c) {
+; Check that a*a*b+a*a*c is turned into a*(a*(b+c)).
+; CHECK-LABEL: @fmultistep1
+; CHECK-NEXT: fadd fast float %c, %b
+; CHECK-NEXT: fmul fast float %a, %tmp2
+; CHECK-NEXT: fmul fast float %tmp3, %a
+; CHECK-NEXT: ret float
+
+  %t0 = fmul fast float %a, %b
+  %t1 = fmul fast float %a, %t0 ; a*(a*b)
+  %t2 = fmul fast float %a, %c
+  %t3 = fmul fast float %a, %t2 ; a*(a*c)
+  %t4 = fadd fast float %t1, %t3
+  ret float %t4
+}
+
+define float @fmultistep2(float %a, float %b, float %c, float %d) {
+; Check that a*b+a*c+d is turned into a*(b+c)+d.
+; CHECK-LABEL: @fmultistep2
+; CHECK-NEXT: fadd fast float %c, %b
+; CHECK-NEXT: fmul fast float %tmp, %a
+; CHECK-NEXT: fadd fast float %tmp1, %d
+; CHECK-NEXT: ret float
+
+  %t0 = fmul fast float %a, %b
+  %t1 = fmul fast float %a, %c
+  %t2 = fadd fast float %t1, %d ; a*c+d
+  %t3 = fadd fast float %t0, %t2 ; a*b+(a*c+d)
+  ret float %t3
+}
+