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Fold FP comparisons where one operand is converted from an integer

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type and the other operand is a constant into integer comparisons.
This happens surprisingly frequently (e.g. 10 times in 471.omnetpp),
which are things like this:

	%tmp8283 = sitofp i32 %tmp82 to double	
	%tmp1013 = fcmp ult double %tmp8283, 0.0

Clearly comparing tmp82 against i32 0 is cheaper here.

this also triggers 8 times in gobmk, including this one:

	%tmp375376 = sitofp i32 %tmp375 to double
	%tmp377 = fcmp ogt double %tmp375376, 8.150000e+01

which is comparing an integer against 81.5 :).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51268 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-05-19 20:18:56 +00:00
parent 13d57320bd
commit a540623ab1
2 changed files with 185 additions and 0 deletions
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160
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -185,6 +185,8 @@ namespace {
Instruction *visitAShr(BinaryOperator &I);
Instruction *visitLShr(BinaryOperator &I);
Instruction *commonShiftTransforms(BinaryOperator &I);
Instruction *FoldFCmp_IntToFP_Cst(FCmpInst &I, Instruction *LHSI,
Constant *RHSC);
Instruction *visitFCmpInst(FCmpInst &I);
Instruction *visitICmpInst(ICmpInst &I);
Instruction *visitICmpInstWithCastAndCast(ICmpInst &ICI);
@ -418,6 +420,18 @@ static const Type *getPromotedType(const Type *Ty) {
return Ty;
}
/// GetFPMantissaWidth - Return the width of the mantissa (aka significand) of
/// the specified floating point type in bits. This returns -1 if unknown.
static int GetFPMantissaWidth(const Type *FPType) {
if (FPType == Type::FloatTy)
return 24;
if (FPType == Type::DoubleTy)
return 53;
if (FPType == Type::X86_FP80Ty)
return 64;
return -1; // Unknown/crazy type.
}
/// getBitCastOperand - If the specified operand is a CastInst or a constant
/// expression bitcast, return the operand value, otherwise return null.
static Value *getBitCastOperand(Value *V) {
@ -5228,6 +5242,135 @@ Instruction *InstCombiner::FoldGEPICmp(User *GEPLHS, Value *RHS,
return 0;
}
/// FoldFCmp_IntToFP_Cst - Fold fcmp ([us]itofp x, cst) if possible.
///
Instruction *InstCombiner::FoldFCmp_IntToFP_Cst(FCmpInst &I,
Instruction *LHSI,
Constant *RHSC) {
if (!isa<ConstantFP>(RHSC)) return 0;
const APFloat &RHS = cast<ConstantFP>(RHSC)->getValueAPF();
// Get the width of the mantissa. We don't want to hack on conversions that
// might lose information from the integer, e.g. "i64 -> float"
int MantissaWidth = GetFPMantissaWidth(LHSI->getType());
if (MantissaWidth == -1) return 0; // Unknown.
// Check to see that the input is converted from an integer type that is small
// enough that preserves all bits. TODO: check here for "known" sign bits.
// This would allow us to handle (fptosi (x >>s 62) to float) if x is i64 f.e.
unsigned InputSize = LHSI->getOperand(0)->getType()->getPrimitiveSizeInBits();
// If this is a uitofp instruction, we need an extra bit to hold the sign.
if (isa<UIToFPInst>(LHSI))
++InputSize;
// If the conversion would lose info, don't hack on this.
if ((int)InputSize > MantissaWidth)
return 0;
// Otherwise, we can potentially simplify the comparison. We know that it
// will always come through as an integer value and we know the constant is
// not a NAN (it would have been previously simplified).
assert(!RHS.isNaN() && "NaN comparison not already folded!");
ICmpInst::Predicate Pred;
switch (I.getPredicate()) {
default: assert(0 && "Unexpected predicate!");
case FCmpInst::FCMP_UEQ:
case FCmpInst::FCMP_OEQ: Pred = ICmpInst::ICMP_EQ; break;
case FCmpInst::FCMP_UGT:
case FCmpInst::FCMP_OGT: Pred = ICmpInst::ICMP_SGT; break;
case FCmpInst::FCMP_UGE:
case FCmpInst::FCMP_OGE: Pred = ICmpInst::ICMP_SGE; break;
case FCmpInst::FCMP_ULT:
case FCmpInst::FCMP_OLT: Pred = ICmpInst::ICMP_SLT; break;
case FCmpInst::FCMP_ULE:
case FCmpInst::FCMP_OLE: Pred = ICmpInst::ICMP_SLE; break;
case FCmpInst::FCMP_UNE:
case FCmpInst::FCMP_ONE: Pred = ICmpInst::ICMP_NE; break;
case FCmpInst::FCMP_ORD:
return ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty, 1));
case FCmpInst::FCMP_UNO:
return ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty, 0));
}
const IntegerType *IntTy = cast<IntegerType>(LHSI->getOperand(0)->getType());
// Now we know that the APFloat is a normal number, zero or inf.
// See if the FP constant is top large for the integer. For example,
// comparing an i8 to 300.0.
unsigned IntWidth = IntTy->getPrimitiveSizeInBits();
// If the RHS value is > SignedMax, fold the comparison. This handles +INF
// and large values.
APFloat SMax(RHS.getSemantics(), APFloat::fcZero, false);
SMax.convertFromAPInt(APInt::getSignedMaxValue(IntWidth), true,
APFloat::rmNearestTiesToEven);
if (SMax.compare(RHS) == APFloat::cmpLessThan) { // smax < 13123.0
if (ICmpInst::ICMP_NE || ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE)
return ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty, 1));
return ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty, 0));
}
// See if the RHS value is < SignedMin.
APFloat SMin(RHS.getSemantics(), APFloat::fcZero, false);
SMin.convertFromAPInt(APInt::getSignedMinValue(IntWidth), true,
APFloat::rmNearestTiesToEven);
if (SMin.compare(RHS) == APFloat::cmpGreaterThan) { // smin > 12312.0
if (ICmpInst::ICMP_NE || ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE)
return ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty, 1));
return ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty, 0));
}
// Okay, now we know that the FP constant fits in the range [SMIN, SMAX] but
// it may still be fractional. See if it is fractional by casting the FP
// value to the integer value and back, checking for equality. Don't do this
// for zero, because -0.0 is not fractional.
Constant *RHSInt = ConstantExpr::getFPToSI(RHSC, IntTy);
if (!RHS.isZero() &&
ConstantExpr::getSIToFP(RHSInt, RHSC->getType()) != RHSC) {
// If we had a comparison against a fractional value, we have to adjust
// the compare predicate and sometimes the value. RHSC is rounded towards
// zero at this point.
switch (Pred) {
default: assert(0 && "Unexpected integer comparison!");
case ICmpInst::ICMP_NE: // (float)int != 4.4 --> true
return ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty, 1));
case ICmpInst::ICMP_EQ: // (float)int == 4.4 --> false
return ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty, 0));
case ICmpInst::ICMP_SLE:
// (float)int <= 4.4 --> int <= 4
// (float)int <= -4.4 --> int < -4
if (RHS.isNegative())
Pred = ICmpInst::ICMP_SLT;
break;
case ICmpInst::ICMP_SLT:
// (float)int < -4.4 --> int < -4
// (float)int < 4.4 --> int <= 4
if (!RHS.isNegative())
Pred = ICmpInst::ICMP_SLE;
break;
case ICmpInst::ICMP_SGT:
// (float)int > 4.4 --> int > 4
// (float)int > -4.4 --> int >= -4
if (RHS.isNegative())
Pred = ICmpInst::ICMP_SGE;
break;
case ICmpInst::ICMP_SGE:
// (float)int >= -4.4 --> int >= -4
// (float)int >= 4.4 --> int > 4
if (!RHS.isNegative())
Pred = ICmpInst::ICMP_SGT;
break;
}
}
// Lower this FP comparison into an appropriate integer version of the
// comparison.
return new ICmpInst(Pred, LHSI->getOperand(0), RHSInt);
}
Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
bool Changed = SimplifyCompare(I);
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
@ -5276,12 +5419,29 @@ Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
// Handle fcmp with constant RHS
if (Constant *RHSC = dyn_cast<Constant>(Op1)) {
// If the constant is a nan, see if we can fold the comparison based on it.
if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
if (CFP->getValueAPF().isNaN()) {
if (FCmpInst::isOrdered(I.getPredicate())) // True if ordered and...
return ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty, 0));
if (FCmpInst::isUnordered(I.getPredicate())) // True if unordered or...
return ReplaceInstUsesWith(I, ConstantInt::get(Type::Int1Ty, 1));
if (FCmpInst::isUnordered(I.getPredicate())) // Undef on unordered.
return ReplaceInstUsesWith(I, UndefValue::get(Type::Int1Ty));
}
}
if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
switch (LHSI->getOpcode()) {
case Instruction::PHI:
if (Instruction *NV = FoldOpIntoPhi(I))
return NV;
break;
case Instruction::SIToFP:
case Instruction::UIToFP:
if (Instruction *NV = FoldFCmp_IntToFP_Cst(I, LHSI, RHSC))
return NV;
break;
case Instruction::Select:
// If either operand of the select is a constant, we can fold the
// comparison into the select arms, which will cause one to be

25
test/Transforms/InstCombine/sitofp.ll Normal file
View File

@ -0,0 +1,25 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep sitofp
define i1 @test1(i8 %A) {
%B = sitofp i8 %A to double
%C = fcmp ult double %B, 128.0
ret i1 %C ; True!
}
define i1 @test2(i8 %A) {
%B = sitofp i8 %A to double
%C = fcmp ugt double %B, -128.1
ret i1 %C ; True!
}
define i1 @test3(i8 %A) {
%B = sitofp i8 %A to double
%C = fcmp ule double %B, 127.0
ret i1 %C ; true!
}
define i1 @test4(i8 %A) {
%B = sitofp i8 %A to double
%C = fcmp ult double %B, 127.0
ret i1 %C ; A != 127
}