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

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---------------------------------------------------------------------------
 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
This commit is contained in:
Shuxin Yang 2013-01-14 22:48:41 +00:00
parent dd2e895022
commit 7d72cf892e
2 changed files with 223 additions and 8 deletions
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135
lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@ -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)) {
const APFloat &Op1F = Op1C->getValueAPF();
bool AllowReassociate = I.hasUnsafeAlgebra();
bool AllowReciprocal = I.hasAllowReciprocal();
// If the divisor has an exact multiplicative inverse we can turn the fdiv
// into a cheaper fmul.
APFloat Reciprocal(Op1F.getSemantics());
if (Op1F.getExactInverse(&Reciprocal)) {
ConstantFP *RFP = ConstantFP::get(Builder->getContext(), Reciprocal);
return BinaryOperator::CreateFMul(Op0, RFP);
if (ConstantFP *Op1C = dyn_cast<ConstantFP>(Op1)) {
if (AllowReassociate) {
ConstantFP *C1 = 0;
ConstantFP *C2 = Op1C;
Value *X;
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;
}
}

96
test/Transforms/InstCombine/fast-math.ll
View File

@ -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
}