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[InstCombine] Simplify pow(2.0, itofp(y)) to ldexp(1.0, y)
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Simplify `pow(2.0, itofp(y))` to `ldexp(1.0, y)`.

Differential revision: https://reviews.llvm.org/D65979

llvm-svn: 369120
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Evandro Menezes committed Aug 16, 2019
1 parent 5f865ec commit 05e9c2a
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Showing 2 changed files with 95 additions and 22 deletions.
54 changes: 32 additions & 22 deletions llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
View file
Expand Up @@ -1284,9 +1284,25 @@ static Value *getPow(Value *InnerChain[33], unsigned Exp, IRBuilder<> &B) {
return InnerChain[Exp];
}

// Return a properly extended 32-bit integer if the operation is an itofp.
static Value *getIntToFPVal(Value *I2F, IRBuilder<> &B) {
if (isa<SIToFPInst>(I2F) || isa<UIToFPInst>(I2F)) {
Value *Op = cast<Instruction>(I2F)->getOperand(0);
// Make sure that the exponent fits inside an int32_t,
// thus avoiding any range issues that FP has not.
unsigned BitWidth = Op->getType()->getPrimitiveSizeInBits();
if (BitWidth < 32 ||
(BitWidth == 32 && isa<SIToFPInst>(I2F)))
return isa<SIToFPInst>(I2F) ? B.CreateSExt(Op, B.getInt32Ty())
: B.CreateZExt(Op, B.getInt32Ty());
}

return nullptr;
}

/// Use exp{,2}(x * y) for pow(exp{,2}(x), y);
/// exp2(n * x) for pow(2.0 ** n, x); exp10(x) for pow(10.0, x);
/// exp2(log2(n) * x) for pow(n, x).
/// ldexp(1.0, x) for pow(2.0, itofp(x)); exp2(n * x) for pow(2.0 ** n, x);
/// exp10(x) for pow(10.0, x); exp2(log2(n) * x) for pow(n, x).
Value *LibCallSimplifier::replacePowWithExp(CallInst *Pow, IRBuilder<> &B) {
Value *Base = Pow->getArgOperand(0), *Expo = Pow->getArgOperand(1);
AttributeList Attrs = Pow->getCalledFunction()->getAttributes();
Expand Down Expand Up @@ -1368,6 +1384,16 @@ Value *LibCallSimplifier::replacePowWithExp(CallInst *Pow, IRBuilder<> &B) {
if (!match(Pow->getArgOperand(0), m_APFloat(BaseF)))
return nullptr;

// pow(2.0, itofp(x)) -> ldexp(1.0, x)
if (match(Base, m_SpecificFP(2.0)) &&
(isa<SIToFPInst>(Expo) || isa<UIToFPInst>(Expo)) &&
hasFloatFn(TLI, Ty, LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl)) {
if (Value *ExpoI = getIntToFPVal(Expo, B))
return emitBinaryFloatFnCall(ConstantFP::get(Ty, 1.0), ExpoI, TLI,
LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl,
B, Attrs);
}

// pow(2.0 ** n, x) -> exp2(n * x)
if (hasFloatFn(TLI, Ty, LibFunc_exp2, LibFunc_exp2f, LibFunc_exp2l)) {
APFloat BaseR = APFloat(1.0);
Expand Down Expand Up @@ -1605,16 +1631,8 @@ Value *LibCallSimplifier::optimizePow(CallInst *Pow, IRBuilder<> &B) {

// powf(x, itofp(y)) -> powi(x, y)
if (AllowApprox && (isa<SIToFPInst>(Expo) || isa<UIToFPInst>(Expo))) {
Value *IntExpo = cast<Instruction>(Expo)->getOperand(0);
Value *NewExpo = nullptr;
unsigned BitWidth = IntExpo->getType()->getPrimitiveSizeInBits();
if (isa<SIToFPInst>(Expo) && BitWidth == 32)
NewExpo = IntExpo;
else if (BitWidth < 32)
NewExpo = isa<SIToFPInst>(Expo) ? B.CreateSExt(IntExpo, B.getInt32Ty())
: B.CreateZExt(IntExpo, B.getInt32Ty());
if (NewExpo)
return createPowWithIntegerExponent(Base, NewExpo, M, B);
if (Value *ExpoI = getIntToFPVal(Expo, B))
return createPowWithIntegerExponent(Base, ExpoI, M, B);
}

return Shrunk;
Expand All @@ -1635,20 +1653,12 @@ Value *LibCallSimplifier::optimizeExp2(CallInst *CI, IRBuilder<> &B) {
// Turn exp2(uitofp(x)) -> ldexp(1.0, zext(x)) if sizeof(x) < 32
if ((isa<SIToFPInst>(Op) || isa<UIToFPInst>(Op)) &&
hasFloatFn(TLI, Ty, LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl)) {
Instruction *OpC = cast<Instruction>(Op);
Value *Exp = OpC->getOperand(0);
unsigned BitWidth = Exp->getType()->getPrimitiveSizeInBits();

if (BitWidth < 32 ||
(BitWidth == 32 && isa<SIToFPInst>(Op))) {
Exp = isa<SIToFPInst>(Op) ? B.CreateSExt(Exp, B.getInt32Ty())
: B.CreateZExt(Exp, B.getInt32Ty());

if (Value *Exp = getIntToFPVal(Op, B))
return emitBinaryFloatFnCall(ConstantFP::get(Ty, 1.0), Exp, TLI,
LibFunc_ldexp, LibFunc_ldexpf, LibFunc_ldexpl,
B, CI->getCalledFunction()->getAttributes());
}
}

return Ret;
}

Expand Down
63 changes: 63 additions & 0 deletions llvm/test/Transforms/InstCombine/pow_fp_int.ll
View file
Expand Up @@ -49,6 +49,18 @@ define double @pow_uitofp_double_const_base_fast(i31 %x) {
ret double %pow
}

define double @pow_sitofp_double_const_base_2_fast(i32 %x) {
; CHECK-LABEL: @pow_sitofp_double_const_base_2_fast(
; CHECK-NEXT: [[LDEXPF:%.*]] = call afn float @ldexpf(float 1.000000e+00, i32 [[X:%.*]]) #1
; CHECK-NEXT: [[RES:%.*]] = fpext float [[LDEXPF]] to double
; CHECK-NEXT: ret double [[RES]]
;
%subfp = sitofp i32 %x to float
%pow = tail call afn float @llvm.pow.f32(float 2.000000e+00, float %subfp)
%res = fpext float %pow to double
ret double %res
}

define double @pow_sitofp_double_const_base_power_of_2_fast(i32 %x) {
; CHECK-LABEL: @pow_sitofp_double_const_base_power_of_2_fast(
; CHECK-NEXT: [[SUBFP:%.*]] = sitofp i32 [[X:%.*]] to float
Expand All @@ -63,6 +75,19 @@ define double @pow_sitofp_double_const_base_power_of_2_fast(i32 %x) {
ret double %res
}

define double @pow_uitofp_const_base_2_fast(i31 %x) {
; CHECK-LABEL: @pow_uitofp_const_base_2_fast(
; CHECK-NEXT: [[TMP1:%.*]] = zext i31 [[X:%.*]] to i32
; CHECK-NEXT: [[LDEXPF:%.*]] = call afn float @ldexpf(float 1.000000e+00, i32 [[TMP1]]) #1
; CHECK-NEXT: [[RES:%.*]] = fpext float [[LDEXPF]] to double
; CHECK-NEXT: ret double [[RES]]
;
%subfp = uitofp i31 %x to float
%pow = tail call afn float @llvm.pow.f32(float 2.000000e+00, float %subfp)
%res = fpext float %pow to double
ret double %res
}

define double @pow_uitofp_const_base_power_of_2_fast(i31 %x) {
; CHECK-LABEL: @pow_uitofp_const_base_power_of_2_fast(
; CHECK-NEXT: [[SUBFP:%.*]] = uitofp i31 [[X:%.*]] to float
Expand Down Expand Up @@ -210,6 +235,19 @@ define double @pow_uitofp_const_base_fast_i32(i32 %x) {
ret double %res
}

define double @pow_uitofp_const_base_2_fast_i32(i32 %x) {
; CHECK-LABEL: @pow_uitofp_const_base_2_fast_i32(
; CHECK-NEXT: [[SUBFP:%.*]] = uitofp i32 [[X:%.*]] to float
; CHECK-NEXT: [[EXP2:%.*]] = call fast float @llvm.exp2.f32(float [[SUBFP]])
; CHECK-NEXT: [[RES:%.*]] = fpext float [[EXP2]] to double
; CHECK-NEXT: ret double [[RES]]
;
%subfp = uitofp i32 %x to float
%pow = tail call fast float @llvm.pow.f32(float 2.000000e+00, float %subfp)
%res = fpext float %pow to double
ret double %res
}

define double @pow_uitofp_const_base_power_of_2_fast_i32(i32 %x) {
; CHECK-LABEL: @pow_uitofp_const_base_power_of_2_fast_i32(
; CHECK-NEXT: [[SUBFP:%.*]] = uitofp i32 [[X:%.*]] to float
Expand Down Expand Up @@ -303,6 +341,18 @@ define double @pow_uitofp_const_base_no_fast(i32 %x) {
ret double %res
}

define double @pow_sitofp_const_base_2_no_fast(i32 %x) {
; CHECK-LABEL: @pow_sitofp_const_base_2_no_fast(
; CHECK-NEXT: [[LDEXPF:%.*]] = call float @ldexpf(float 1.000000e+00, i32 [[X:%.*]]) #1
; CHECK-NEXT: [[RES:%.*]] = fpext float [[LDEXPF]] to double
; CHECK-NEXT: ret double [[RES]]
;
%subfp = sitofp i32 %x to float
%pow = tail call float @llvm.pow.f32(float 2.000000e+00, float %subfp)
%res = fpext float %pow to double
ret double %res
}

define double @pow_sitofp_const_base_power_of_2_no_fast(i32 %x) {
; CHECK-LABEL: @pow_sitofp_const_base_power_of_2_no_fast(
; CHECK-NEXT: [[SUBFP:%.*]] = sitofp i32 [[X:%.*]] to float
Expand All @@ -317,6 +367,19 @@ define double @pow_sitofp_const_base_power_of_2_no_fast(i32 %x) {
ret double %res
}

define double @pow_uitofp_const_base_2_no_fast(i32 %x) {
; CHECK-LABEL: @pow_uitofp_const_base_2_no_fast(
; CHECK-NEXT: [[SUBFP:%.*]] = uitofp i32 [[X:%.*]] to float
; CHECK-NEXT: [[EXP2:%.*]] = call float @llvm.exp2.f32(float [[SUBFP]])
; CHECK-NEXT: [[RES:%.*]] = fpext float [[EXP2]] to double
; CHECK-NEXT: ret double [[RES]]
;
%subfp = uitofp i32 %x to float
%pow = tail call float @llvm.pow.f32(float 2.000000e+00, float %subfp)
%res = fpext float %pow to double
ret double %res
}

define double @pow_uitofp_const_base_power_of_2_no_fast(i32 %x) {
; CHECK-LABEL: @pow_uitofp_const_base_power_of_2_no_fast(
; CHECK-NEXT: [[SUBFP:%.*]] = uitofp i32 [[X:%.*]] to float
Expand Down

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