This change is to implement following rules under the condition C_A and/or C_R

---------------------------------------------------------------------------
 C_A: reassociation is allowed
 C_R: reciprocal of a constant C is appropriate, which means 
    - 1/C is exact, or 
    - reciprocal is allowed and 1/C is neither a special value nor a denormal.
 -----------------------------------------------------------------------------

 rule1:  (X/C1) / C2 => X / (C2*C1)  (if C_A)
                     => X * (1/(C2*C1))  (if C_A && C_R)
 rule 2:  X*C1 / C2 => X * (C1/C2)  if C_A
 rule 3: (X/Y)/Z = > X/(Y*Z)  (if C_A && at least one of Y and Z is symbolic value)
 rule 4: Z/(X/Y) = > (Z*Y)/X  (similar to rule3)

 rule 5: C1/(X*C2) => (C1/C2) / X (if C_A)
 rule 6: C1/(X/C2) => (C1*C2) / X (if C_A)
 rule 7: C1/(C2/X) => (C1/C2) * X (if C_A)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172488 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

@@ -784,21 +784,140 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
   return 0;
 }
 
+/// CvtFDivConstToReciprocal tries to convert X/C into X*1/C if C not a special
+/// FP value and:
+///    1) 1/C is exact, or 
+///    2) reciprocal is allowed.
+/// If the convertion was successful, the simplified expression "X * 1/C" is
+/// returned; otherwise, NULL is returned.
+///
+static Instruction *CvtFDivConstToReciprocal(Value *Dividend,
+                                             ConstantFP *Divisor,
+                                             bool AllowReciprocal) {
+  const APFloat &FpVal = Divisor->getValueAPF();
+  APFloat Reciprocal(FpVal.getSemantics());
+  bool Cvt = FpVal.getExactInverse(&Reciprocal);
+    
+  if (!Cvt && AllowReciprocal && FpVal.isNormal()) {
+    Reciprocal = APFloat(FpVal.getSemantics(), 1.0f);
+    (void)Reciprocal.divide(FpVal, APFloat::rmNearestTiesToEven);
+    Cvt = !Reciprocal.isDenormal();
+  }
+
+  if (!Cvt)
+    return 0;
+
+  ConstantFP *R;
+  R = ConstantFP::get(Dividend->getType()->getContext(), Reciprocal);
+  return BinaryOperator::CreateFMul(Dividend, R);
+}
+
 Instruction *InstCombiner::visitFDiv(BinaryOperator &I) {
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 
   if (Value *V = SimplifyFDivInst(Op0, Op1, TD))
     return ReplaceInstUsesWith(I, V);
 
-  if (ConstantFP *Op1C = dyn_cast<ConstantFP>(Op1)) {
+  bool AllowReassociate = I.hasUnsafeAlgebra();
-    const APFloat &Op1F = Op1C->getValueAPF();
+  bool AllowReciprocal = I.hasAllowReciprocal();
 
-    // If the divisor has an exact multiplicative inverse we can turn the fdiv
+  if (ConstantFP *Op1C = dyn_cast<ConstantFP>(Op1)) {
-    // into a cheaper fmul.
+    if (AllowReassociate) {
-    APFloat Reciprocal(Op1F.getSemantics());
+      ConstantFP *C1 = 0;
-    if (Op1F.getExactInverse(&Reciprocal)) {
+      ConstantFP *C2 = Op1C;
-      ConstantFP *RFP = ConstantFP::get(Builder->getContext(), Reciprocal);
+      Value *X;
-      return BinaryOperator::CreateFMul(Op0, RFP);
+      Instruction *Res = 0;
+
+      if (match(Op0, m_FMul(m_Value(X), m_ConstantFP(C1)))) {
+        // (X*C1)/C2 => X * (C1/C2)
+        //
+        Constant *C = ConstantExpr::getFDiv(C1, C2);
+        const APFloat &F = cast<ConstantFP>(C)->getValueAPF();
+        if (F.isNormal() && !F.isDenormal())
+          Res = BinaryOperator::CreateFMul(X, C);
+      } else if (match(Op0, m_FDiv(m_Value(X), m_ConstantFP(C1)))) {
+        // (X/C1)/C2 => X /(C2*C1) [=> X * 1/(C2*C1) if reciprocal is allowed]
+        //
+        Constant *C = ConstantExpr::getFMul(C1, C2);
+        const APFloat &F = cast<ConstantFP>(C)->getValueAPF();
+        if (F.isNormal() && !F.isDenormal()) {
+          Res = CvtFDivConstToReciprocal(X, cast<ConstantFP>(C), 
+                                         AllowReciprocal);
+          if (!Res)
+            Res = BinaryOperator::CreateFDiv(X, C); 
+        }
+      }
+
+      if (Res) {
+        Res->setFastMathFlags(I.getFastMathFlags());
+        return Res;
+      }
+    }
+
+    // X / C => X * 1/C
+    if (Instruction *T = CvtFDivConstToReciprocal(Op0, Op1C, AllowReciprocal))
+      return T;
+
+    return 0;
+  }
+
+  if (AllowReassociate && isa<ConstantFP>(Op0)) {
+    ConstantFP *C1 = cast<ConstantFP>(Op0), *C2;
+    Constant *Fold = 0;
+    Value *X;
+    bool CreateDiv = true;
+
+    // C1 / (X*C2) => (C1/C2) / X
+    if (match(Op1, m_FMul(m_Value(X), m_ConstantFP(C2))))
+      Fold = ConstantExpr::getFDiv(C1, C2);
+    else if (match(Op1, m_FDiv(m_Value(X), m_ConstantFP(C2)))) {
+      // C1 / (X/C2) => (C1*C2) / X
+      Fold = ConstantExpr::getFMul(C1, C2);
+    } else if (match(Op1, m_FDiv(m_ConstantFP(C2), m_Value(X)))) {
+      // C1 / (C2/X) => (C1/C2) * X
+      Fold = ConstantExpr::getFDiv(C1, C2);
+      CreateDiv = false;
+    }
+
+    if (Fold) {
+      const APFloat &FoldC = cast<ConstantFP>(Fold)->getValueAPF();
+      if (FoldC.isNormal() && !FoldC.isDenormal()) {
+        Instruction *R = CreateDiv ? 
+                         BinaryOperator::CreateFDiv(Fold, X) :
+                         BinaryOperator::CreateFMul(X, Fold);
+        R->setFastMathFlags(I.getFastMathFlags());
+        return R;
+      }
+    }
+    return 0;
+  }
+
+  if (AllowReassociate) {
+    Value *X, *Y;
+    Value *NewInst = 0;
+    Instruction *SimpR = 0;
+
+    if (Op0->hasOneUse() && match(Op0, m_FDiv(m_Value(X), m_Value(Y)))) {
+      // (X/Y) / Z => X / (Y*Z)
+      //
+      if (!isa<ConstantFP>(Y) || !isa<ConstantFP>(Op1)) {
+        NewInst = Builder->CreateFMul(Y, Op1);
+        SimpR = BinaryOperator::CreateFDiv(X, NewInst);
+      }
+    } else if (Op1->hasOneUse() && match(Op1, m_FDiv(m_Value(X), m_Value(Y)))) {
+      // Z / (X/Y) => Z*Y / X
+      //
+      if (!isa<ConstantFP>(Y) || !isa<ConstantFP>(Op0)) {
+        NewInst = Builder->CreateFMul(Op0, Y);
+        SimpR = BinaryOperator::CreateFDiv(NewInst, X);
+      }
+    }
+
+    if (NewInst) {
+      if (Instruction *T = dyn_cast<Instruction>(NewInst))
+        T->setDebugLoc(I.getDebugLoc());
+      SimpR->setFastMathFlags(I.getFastMathFlags());
+      return SimpR;
     }
   }
 

test/Transforms/InstCombine/fast-math.ll

@@ -256,3 +256,99 @@ define float @fneg1(float %f1, float %f2) {
 ; CHECK: @fneg1
 ; CHECK: fmul float %f1, %f2
 }
+
+; =========================================================================
+;
+;   Testing-cases about div
+;
+; =========================================================================
+; X/C1 / C2 => X * (1/(C2*C1))
+
+define float @fdiv1(float %x) {
+  %div = fdiv float %x, 0x3FF3333340000000
+  %div1 = fdiv fast float %div, 0x4002666660000000
+  ret float %div1
+; 0x3FF3333340000000 = 1.2f
+; 0x4002666660000000 = 2.3f
+; 0x3FD7303B60000000 = 0.36231884057971014492
+; CHECK: @fdiv1
+; CHECK: fmul fast float %x, 0x3FD7303B60000000
+}
+
+; X*C1 / C2 => X * (C1/C2)
+define float @fdiv2(float %x) {
+  %mul = fmul float %x, 0x3FF3333340000000
+  %div1 = fdiv fast float %mul, 0x4002666660000000
+  ret float %div1
+
+; 0x3FF3333340000000 = 1.2f
+; 0x4002666660000000 = 2.3f
+; 0x3FE0B21660000000 = 0.52173918485641479492
+; CHECK: @fdiv2
+; CHECK: fmul fast float %x, 0x3FE0B21660000000
+}
+
+; "X/C1 / C2 => X * (1/(C2*C1))" is disabled (for now) is C2/C1 is a denormal
+; 
+define float @fdiv3(float %x) {
+  %div = fdiv float %x, 0x47EFFFFFE0000000
+  %div1 = fdiv fast float %div, 0x4002666660000000
+  ret float %div1
+; CHECK: @fdiv3
+; CHECK: fdiv float %x, 0x47EFFFFFE0000000
+}
+
+; "X*C1 / C2 => X * (C1/C2)" is disabled if C1/C2 is a denormal
+define float @fdiv4(float %x) {
+  %mul = fmul float %x, 0x47EFFFFFE0000000
+  %div = fdiv float %mul, 0x3FC99999A0000000
+  ret float %div
+; CHECK: @fdiv4
+; CHECK: fmul float %x, 0x47EFFFFFE0000000
+}
+
+; (X/Y)/Z = > X/(Y*Z)
+define float @fdiv5(float %f1, float %f2, float %f3) {
+  %t1 = fdiv float %f1, %f2
+  %t2 = fdiv fast float %t1, %f3
+  ret float %t2
+; CHECK: @fdiv5
+; CHECK: fmul float %f2, %f3
+}
+
+; Z/(X/Y) = > (Z*Y)/X
+define float @fdiv6(float %f1, float %f2, float %f3) {
+  %t1 = fdiv float %f1, %f2
+  %t2 = fdiv fast float %f3, %t1
+  ret float %t2
+; CHECK: @fdiv6
+; CHECK: fmul float %f3, %f2
+}
+
+; C1/(X*C2) => (C1/C2) / X
+define float @fdiv7(float %x) {
+  %t1 = fmul float %x, 3.0e0
+  %t2 = fdiv fast float 15.0e0, %t1
+  ret float %t2
+; CHECK: @fdiv7
+; CHECK: fdiv fast float 5.000000e+00, %x
+}
+
+; C1/(X/C2) => (C1*C2) / X
+define float @fdiv8(float %x) {
+  %t1 = fdiv float %x, 3.0e0
+  %t2 = fdiv fast float 15.0e0, %t1
+  ret float %t2
+; CHECK: @fdiv8
+; CHECK: fdiv fast float 4.500000e+01, %x
+}
+
+; C1/(C2/X) => (C1/C2) * X
+define float @fdiv9(float %x) {
+  %t1 = fdiv float 3.0e0, %x
+  %t2 = fdiv fast float 15.0e0, %t1
+  ret float %t2
+; CHECK: @fdiv9
+; CHECK: fmul fast float %x, 5.000000e+00
+}
+