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llvm-mirror/lib/Transforms/InstCombine/InstCombineSelect.cpp

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//===- InstCombineSelect.cpp ----------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the visitSelect function.
//
//===----------------------------------------------------------------------===//
#include "InstCombine.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/Analysis/InstructionSimplify.h"
using namespace llvm;
using namespace PatternMatch;
/// MatchSelectPattern - Pattern match integer [SU]MIN, [SU]MAX, and ABS idioms,
/// returning the kind and providing the out parameter results if we
/// successfully match.
static SelectPatternFlavor
MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
SelectInst *SI = dyn_cast<SelectInst>(V);
if (SI == 0) return SPF_UNKNOWN;
ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
if (ICI == 0) return SPF_UNKNOWN;
LHS = ICI->getOperand(0);
RHS = ICI->getOperand(1);
// (icmp X, Y) ? X : Y
if (SI->getTrueValue() == ICI->getOperand(0) &&
SI->getFalseValue() == ICI->getOperand(1)) {
switch (ICI->getPredicate()) {
default: return SPF_UNKNOWN; // Equality.
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE: return SPF_UMAX;
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_SGE: return SPF_SMAX;
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_ULE: return SPF_UMIN;
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_SLE: return SPF_SMIN;
}
}
// (icmp X, Y) ? Y : X
if (SI->getTrueValue() == ICI->getOperand(1) &&
SI->getFalseValue() == ICI->getOperand(0)) {
switch (ICI->getPredicate()) {
default: return SPF_UNKNOWN; // Equality.
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE: return SPF_UMIN;
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_SGE: return SPF_SMIN;
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_ULE: return SPF_UMAX;
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_SLE: return SPF_SMAX;
}
}
// TODO: (X > 4) ? X : 5 --> (X >= 5) ? X : 5 --> MAX(X, 5)
return SPF_UNKNOWN;
}
/// GetSelectFoldableOperands - We want to turn code that looks like this:
/// %C = or %A, %B
/// %D = select %cond, %C, %A
/// into:
/// %C = select %cond, %B, 0
/// %D = or %A, %C
///
/// Assuming that the specified instruction is an operand to the select, return
/// a bitmask indicating which operands of this instruction are foldable if they
/// equal the other incoming value of the select.
///
static unsigned GetSelectFoldableOperands(Instruction *I) {
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::Mul:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
return 3; // Can fold through either operand.
case Instruction::Sub: // Can only fold on the amount subtracted.
case Instruction::Shl: // Can only fold on the shift amount.
case Instruction::LShr:
case Instruction::AShr:
return 1;
default:
return 0; // Cannot fold
}
}
/// GetSelectFoldableConstant - For the same transformation as the previous
/// function, return the identity constant that goes into the select.
static Constant *GetSelectFoldableConstant(Instruction *I) {
switch (I->getOpcode()) {
default: llvm_unreachable("This cannot happen!");
case Instruction::Add:
case Instruction::Sub:
case Instruction::Or:
case Instruction::Xor:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
return Constant::getNullValue(I->getType());
case Instruction::And:
return Constant::getAllOnesValue(I->getType());
case Instruction::Mul:
return ConstantInt::get(I->getType(), 1);
}
}
/// FoldSelectOpOp - Here we have (select c, TI, FI), and we know that TI and FI
/// have the same opcode and only one use each. Try to simplify this.
Instruction *InstCombiner::FoldSelectOpOp(SelectInst &SI, Instruction *TI,
Instruction *FI) {
if (TI->getNumOperands() == 1) {
// If this is a non-volatile load or a cast from the same type,
// merge.
if (TI->isCast()) {
if (TI->getOperand(0)->getType() != FI->getOperand(0)->getType())
return 0;
} else {
return 0; // unknown unary op.
}
// Fold this by inserting a select from the input values.
SelectInst *NewSI = SelectInst::Create(SI.getCondition(), TI->getOperand(0),
FI->getOperand(0), SI.getName()+".v");
InsertNewInstBefore(NewSI, SI);
return CastInst::Create(Instruction::CastOps(TI->getOpcode()), NewSI,
TI->getType());
}
// Only handle binary operators here.
if (!isa<BinaryOperator>(TI))
return 0;
// Figure out if the operations have any operands in common.
Value *MatchOp, *OtherOpT, *OtherOpF;
bool MatchIsOpZero;
if (TI->getOperand(0) == FI->getOperand(0)) {
MatchOp = TI->getOperand(0);
OtherOpT = TI->getOperand(1);
OtherOpF = FI->getOperand(1);
MatchIsOpZero = true;
} else if (TI->getOperand(1) == FI->getOperand(1)) {
MatchOp = TI->getOperand(1);
OtherOpT = TI->getOperand(0);
OtherOpF = FI->getOperand(0);
MatchIsOpZero = false;
} else if (!TI->isCommutative()) {
return 0;
} else if (TI->getOperand(0) == FI->getOperand(1)) {
MatchOp = TI->getOperand(0);
OtherOpT = TI->getOperand(1);
OtherOpF = FI->getOperand(0);
MatchIsOpZero = true;
} else if (TI->getOperand(1) == FI->getOperand(0)) {
MatchOp = TI->getOperand(1);
OtherOpT = TI->getOperand(0);
OtherOpF = FI->getOperand(1);
MatchIsOpZero = true;
} else {
return 0;
}
// If we reach here, they do have operations in common.
SelectInst *NewSI = SelectInst::Create(SI.getCondition(), OtherOpT,
OtherOpF, SI.getName()+".v");
InsertNewInstBefore(NewSI, SI);
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TI)) {
if (MatchIsOpZero)
return BinaryOperator::Create(BO->getOpcode(), MatchOp, NewSI);
else
return BinaryOperator::Create(BO->getOpcode(), NewSI, MatchOp);
}
llvm_unreachable("Shouldn't get here");
return 0;
}
static bool isSelect01(Constant *C1, Constant *C2) {
ConstantInt *C1I = dyn_cast<ConstantInt>(C1);
if (!C1I)
return false;
ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
if (!C2I)
return false;
if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
return false;
return C1I->isOne() || C1I->isAllOnesValue() ||
C2I->isOne() || C2I->isAllOnesValue();
}
/// FoldSelectIntoOp - Try fold the select into one of the operands to
/// facilitate further optimization.
Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
Value *FalseVal) {
// See the comment above GetSelectFoldableOperands for a description of the
// transformation we are doing here.
if (Instruction *TVI = dyn_cast<Instruction>(TrueVal)) {
if (TVI->hasOneUse() && TVI->getNumOperands() == 2 &&
!isa<Constant>(FalseVal)) {
if (unsigned SFO = GetSelectFoldableOperands(TVI)) {
unsigned OpToFold = 0;
if ((SFO & 1) && FalseVal == TVI->getOperand(0)) {
OpToFold = 1;
} else if ((SFO & 2) && FalseVal == TVI->getOperand(1)) {
OpToFold = 2;
}
if (OpToFold) {
Constant *C = GetSelectFoldableConstant(TVI);
Value *OOp = TVI->getOperand(2-OpToFold);
// Avoid creating select between 2 constants unless it's selecting
// between 0, 1 and -1.
if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
Instruction *NewSel = SelectInst::Create(SI.getCondition(), OOp, C);
InsertNewInstBefore(NewSel, SI);
NewSel->takeName(TVI);
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(TVI))
return BinaryOperator::Create(BO->getOpcode(), FalseVal, NewSel);
llvm_unreachable("Unknown instruction!!");
}
}
}
}
}
if (Instruction *FVI = dyn_cast<Instruction>(FalseVal)) {
if (FVI->hasOneUse() && FVI->getNumOperands() == 2 &&
!isa<Constant>(TrueVal)) {
if (unsigned SFO = GetSelectFoldableOperands(FVI)) {
unsigned OpToFold = 0;
if ((SFO & 1) && TrueVal == FVI->getOperand(0)) {
OpToFold = 1;
} else if ((SFO & 2) && TrueVal == FVI->getOperand(1)) {
OpToFold = 2;
}
if (OpToFold) {
Constant *C = GetSelectFoldableConstant(FVI);
Value *OOp = FVI->getOperand(2-OpToFold);
// Avoid creating select between 2 constants unless it's selecting
// between 0, 1 and -1.
if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
Instruction *NewSel = SelectInst::Create(SI.getCondition(), C, OOp);
InsertNewInstBefore(NewSel, SI);
NewSel->takeName(FVI);
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(FVI))
return BinaryOperator::Create(BO->getOpcode(), TrueVal, NewSel);
llvm_unreachable("Unknown instruction!!");
}
}
}
}
}
return 0;
}
/// visitSelectInstWithICmp - Visit a SelectInst that has an
/// ICmpInst as its first operand.
///
Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
ICmpInst *ICI) {
bool Changed = false;
ICmpInst::Predicate Pred = ICI->getPredicate();
Value *CmpLHS = ICI->getOperand(0);
Value *CmpRHS = ICI->getOperand(1);
Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();
// Check cases where the comparison is with a constant that
// can be adjusted to fit the min/max idiom. We may edit ICI in
// place here, so make sure the select is the only user.
if (ICI->hasOneUse())
if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
switch (Pred) {
default: break;
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_SLT: {
// X < MIN ? T : F --> F
if (CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
return ReplaceInstUsesWith(SI, FalseVal);
// X < C ? X : C-1 --> X > C-1 ? C-1 : X
Constant *AdjustedRHS =
ConstantInt::get(CI->getContext(), CI->getValue()-1);
if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
(CmpLHS == FalseVal && AdjustedRHS == TrueVal)) {
Pred = ICmpInst::getSwappedPredicate(Pred);
CmpRHS = AdjustedRHS;
std::swap(FalseVal, TrueVal);
ICI->setPredicate(Pred);
ICI->setOperand(1, CmpRHS);
SI.setOperand(1, TrueVal);
SI.setOperand(2, FalseVal);
Changed = true;
}
break;
}
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_SGT: {
// X > MAX ? T : F --> F
if (CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
return ReplaceInstUsesWith(SI, FalseVal);
// X > C ? X : C+1 --> X < C+1 ? C+1 : X
Constant *AdjustedRHS =
ConstantInt::get(CI->getContext(), CI->getValue()+1);
if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
(CmpLHS == FalseVal && AdjustedRHS == TrueVal)) {
Pred = ICmpInst::getSwappedPredicate(Pred);
CmpRHS = AdjustedRHS;
std::swap(FalseVal, TrueVal);
ICI->setPredicate(Pred);
ICI->setOperand(1, CmpRHS);
SI.setOperand(1, TrueVal);
SI.setOperand(2, FalseVal);
Changed = true;
}
break;
}
}
}
// Transform (X >s -1) ? C1 : C2 --> ((X >>s 31) & (C2 - C1)) + C1
// and (X <s 0) ? C2 : C1 --> ((X >>s 31) & (C2 - C1)) + C1
// FIXME: Type and constness constraints could be lifted, but we have to
// watch code size carefully. We should consider xor instead of
// sub/add when we decide to do that.
if (const IntegerType *Ty = dyn_cast<IntegerType>(CmpLHS->getType())) {
if (TrueVal->getType() == Ty) {
if (ConstantInt *Cmp = dyn_cast<ConstantInt>(CmpRHS)) {
ConstantInt *C1 = NULL, *C2 = NULL;
if (Pred == ICmpInst::ICMP_SGT && Cmp->isAllOnesValue()) {
C1 = dyn_cast<ConstantInt>(TrueVal);
C2 = dyn_cast<ConstantInt>(FalseVal);
} else if (Pred == ICmpInst::ICMP_SLT && Cmp->isNullValue()) {
C1 = dyn_cast<ConstantInt>(FalseVal);
C2 = dyn_cast<ConstantInt>(TrueVal);
}
if (C1 && C2) {
// This shift results in either -1 or 0.
Value *AShr = Builder->CreateAShr(CmpLHS, Ty->getBitWidth()-1);
// Check if we can express the operation with a single or.
if (C2->isAllOnesValue())
return ReplaceInstUsesWith(SI, Builder->CreateOr(AShr, C1));
Value *And = Builder->CreateAnd(AShr, C2->getValue()-C1->getValue());
return ReplaceInstUsesWith(SI, Builder->CreateAdd(And, C1));
}
}
}
}
if (CmpLHS == TrueVal && CmpRHS == FalseVal) {
// Transform (X == Y) ? X : Y -> Y
if (Pred == ICmpInst::ICMP_EQ)
return ReplaceInstUsesWith(SI, FalseVal);
// Transform (X != Y) ? X : Y -> X
if (Pred == ICmpInst::ICMP_NE)
return ReplaceInstUsesWith(SI, TrueVal);
/// NOTE: if we wanted to, this is where to detect integer MIN/MAX
} else if (CmpLHS == FalseVal && CmpRHS == TrueVal) {
// Transform (X == Y) ? Y : X -> X
if (Pred == ICmpInst::ICMP_EQ)
return ReplaceInstUsesWith(SI, FalseVal);
// Transform (X != Y) ? Y : X -> Y
if (Pred == ICmpInst::ICMP_NE)
return ReplaceInstUsesWith(SI, TrueVal);
/// NOTE: if we wanted to, this is where to detect integer MIN/MAX
}
return Changed ? &SI : 0;
}
/// CanSelectOperandBeMappingIntoPredBlock - SI is a select whose condition is a
/// PHI node (but the two may be in different blocks). See if the true/false
/// values (V) are live in all of the predecessor blocks of the PHI. For
/// example, cases like this cannot be mapped:
///
/// X = phi [ C1, BB1], [C2, BB2]
/// Y = add
/// Z = select X, Y, 0
///
/// because Y is not live in BB1/BB2.
///
static bool CanSelectOperandBeMappingIntoPredBlock(const Value *V,
const SelectInst &SI) {
// If the value is a non-instruction value like a constant or argument, it
// can always be mapped.
const Instruction *I = dyn_cast<Instruction>(V);
if (I == 0) return true;
// If V is a PHI node defined in the same block as the condition PHI, we can
// map the arguments.
const PHINode *CondPHI = cast<PHINode>(SI.getCondition());
if (const PHINode *VP = dyn_cast<PHINode>(I))
if (VP->getParent() == CondPHI->getParent())
return true;
// Otherwise, if the PHI and select are defined in the same block and if V is
// defined in a different block, then we can transform it.
if (SI.getParent() == CondPHI->getParent() &&
I->getParent() != CondPHI->getParent())
return true;
// Otherwise we have a 'hard' case and we can't tell without doing more
// detailed dominator based analysis, punt.
return false;
}
/// FoldSPFofSPF - We have an SPF (e.g. a min or max) of an SPF of the form:
/// SPF2(SPF1(A, B), C)
Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
SelectPatternFlavor SPF1,
Value *A, Value *B,
Instruction &Outer,
SelectPatternFlavor SPF2, Value *C) {
if (C == A || C == B) {
// MAX(MAX(A, B), B) -> MAX(A, B)
// MIN(MIN(a, b), a) -> MIN(a, b)
if (SPF1 == SPF2)
return ReplaceInstUsesWith(Outer, Inner);
// MAX(MIN(a, b), a) -> a
// MIN(MAX(a, b), a) -> a
if ((SPF1 == SPF_SMIN && SPF2 == SPF_SMAX) ||
(SPF1 == SPF_SMAX && SPF2 == SPF_SMIN) ||
(SPF1 == SPF_UMIN && SPF2 == SPF_UMAX) ||
(SPF1 == SPF_UMAX && SPF2 == SPF_UMIN))
return ReplaceInstUsesWith(Outer, C);
}
// TODO: MIN(MIN(A, 23), 97)
return 0;
}
/// foldSelectICmpAnd - If one of the constants is zero (we know they can't
/// both be) and we have an icmp instruction with zero, and we have an 'and'
/// with the non-constant value and a power of two we can turn the select
/// into a shift on the result of the 'and'.
static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
ConstantInt *FalseVal,
InstCombiner::BuilderTy *Builder) {
const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
if (!IC || !IC->isEquality())
return 0;
if (ConstantInt *C = dyn_cast<ConstantInt>(IC->getOperand(1)))
if (!C->isZero())
return 0;
ConstantInt *AndRHS;
Value *LHS = IC->getOperand(0);
if (LHS->getType() != SI.getType() ||
!match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
return 0;
// If both select arms are non-zero see if we have a select of the form
// 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
// for 'x ? 2^n : 0' and fix the thing up at the end.
ConstantInt *Offset = 0;
if (!TrueVal->isZero() && !FalseVal->isZero()) {
if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
Offset = FalseVal;
else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
Offset = TrueVal;
else
return 0;
// Adjust TrueVal and FalseVal to the offset.
TrueVal = ConstantInt::get(Builder->getContext(),
TrueVal->getValue() - Offset->getValue());
FalseVal = ConstantInt::get(Builder->getContext(),
FalseVal->getValue() - Offset->getValue());
}
// Make sure the mask in the 'and' and one of the select arms is a power of 2.
if (!AndRHS->getValue().isPowerOf2() ||
(!TrueVal->getValue().isPowerOf2() &&
!FalseVal->getValue().isPowerOf2()))
return 0;
// Determine which shift is needed to transform result of the 'and' into the
// desired result.
ConstantInt *ValC = !TrueVal->isZero() ? TrueVal : FalseVal;
unsigned ValZeros = ValC->getValue().logBase2();
unsigned AndZeros = AndRHS->getValue().logBase2();
Value *V = LHS;
if (ValZeros > AndZeros)
V = Builder->CreateShl(V, ValZeros - AndZeros);
else if (ValZeros < AndZeros)
V = Builder->CreateLShr(V, AndZeros - ValZeros);
// Okay, now we know that everything is set up, we just don't know whether we
// have a icmp_ne or icmp_eq and whether the true or false val is the zero.
bool ShouldNotVal = !TrueVal->isZero();
ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
if (ShouldNotVal)
V = Builder->CreateXor(V, ValC);
// Apply an offset if needed.
if (Offset)
V = Builder->CreateAdd(V, Offset);
return V;
}
Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
Value *CondVal = SI.getCondition();
Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();
if (Value *V = SimplifySelectInst(CondVal, TrueVal, FalseVal, TD))
return ReplaceInstUsesWith(SI, V);
if (SI.getType()->isIntegerTy(1)) {
if (ConstantInt *C = dyn_cast<ConstantInt>(TrueVal)) {
if (C->getZExtValue()) {
// Change: A = select B, true, C --> A = or B, C
return BinaryOperator::CreateOr(CondVal, FalseVal);
}
// Change: A = select B, false, C --> A = and !B, C
Value *NotCond =
InsertNewInstBefore(BinaryOperator::CreateNot(CondVal,
"not."+CondVal->getName()), SI);
return BinaryOperator::CreateAnd(NotCond, FalseVal);
} else if (ConstantInt *C = dyn_cast<ConstantInt>(FalseVal)) {
if (C->getZExtValue() == false) {
// Change: A = select B, C, false --> A = and B, C
return BinaryOperator::CreateAnd(CondVal, TrueVal);
}
// Change: A = select B, C, true --> A = or !B, C
Value *NotCond =
InsertNewInstBefore(BinaryOperator::CreateNot(CondVal,
"not."+CondVal->getName()), SI);
return BinaryOperator::CreateOr(NotCond, TrueVal);
}
// select a, b, a -> a&b
// select a, a, b -> a|b
if (CondVal == TrueVal)
return BinaryOperator::CreateOr(CondVal, FalseVal);
else if (CondVal == FalseVal)
return BinaryOperator::CreateAnd(CondVal, TrueVal);
}
// Selecting between two integer constants?
if (ConstantInt *TrueValC = dyn_cast<ConstantInt>(TrueVal))
if (ConstantInt *FalseValC = dyn_cast<ConstantInt>(FalseVal)) {
// select C, 1, 0 -> zext C to int
if (FalseValC->isZero() && TrueValC->getValue() == 1)
return new ZExtInst(CondVal, SI.getType());
// select C, -1, 0 -> sext C to int
if (FalseValC->isZero() && TrueValC->isAllOnesValue())
return new SExtInst(CondVal, SI.getType());
// select C, 0, 1 -> zext !C to int
if (TrueValC->isZero() && FalseValC->getValue() == 1) {
Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
return new ZExtInst(NotCond, SI.getType());
}
// select C, 0, -1 -> sext !C to int
if (TrueValC->isZero() && FalseValC->isAllOnesValue()) {
Value *NotCond = Builder->CreateNot(CondVal, "not."+CondVal->getName());
return new SExtInst(NotCond, SI.getType());
}
if (Value *V = foldSelectICmpAnd(SI, TrueValC, FalseValC, Builder))
return ReplaceInstUsesWith(SI, V);
}
// See if we are selecting two values based on a comparison of the two values.
if (FCmpInst *FCI = dyn_cast<FCmpInst>(CondVal)) {
if (FCI->getOperand(0) == TrueVal && FCI->getOperand(1) == FalseVal) {
// Transform (X == Y) ? X : Y -> Y
if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
// This is not safe in general for floating point:
// consider X== -0, Y== +0.
// It becomes safe if either operand is a nonzero constant.
ConstantFP *CFPt, *CFPf;
if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
!CFPt->getValueAPF().isZero()) ||
((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
!CFPf->getValueAPF().isZero()))
return ReplaceInstUsesWith(SI, FalseVal);
}
// Transform (X une Y) ? X : Y -> X
if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
// This is not safe in general for floating point:
// consider X== -0, Y== +0.
// It becomes safe if either operand is a nonzero constant.
ConstantFP *CFPt, *CFPf;
if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
!CFPt->getValueAPF().isZero()) ||
((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
!CFPf->getValueAPF().isZero()))
return ReplaceInstUsesWith(SI, TrueVal);
}
// NOTE: if we wanted to, this is where to detect MIN/MAX
} else if (FCI->getOperand(0) == FalseVal && FCI->getOperand(1) == TrueVal){
// Transform (X == Y) ? Y : X -> X
if (FCI->getPredicate() == FCmpInst::FCMP_OEQ) {
// This is not safe in general for floating point:
// consider X== -0, Y== +0.
// It becomes safe if either operand is a nonzero constant.
ConstantFP *CFPt, *CFPf;
if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
!CFPt->getValueAPF().isZero()) ||
((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
!CFPf->getValueAPF().isZero()))
return ReplaceInstUsesWith(SI, FalseVal);
}
// Transform (X une Y) ? Y : X -> Y
if (FCI->getPredicate() == FCmpInst::FCMP_UNE) {
// This is not safe in general for floating point:
// consider X== -0, Y== +0.
// It becomes safe if either operand is a nonzero constant.
ConstantFP *CFPt, *CFPf;
if (((CFPt = dyn_cast<ConstantFP>(TrueVal)) &&
!CFPt->getValueAPF().isZero()) ||
((CFPf = dyn_cast<ConstantFP>(FalseVal)) &&
!CFPf->getValueAPF().isZero()))
return ReplaceInstUsesWith(SI, TrueVal);
}
// NOTE: if we wanted to, this is where to detect MIN/MAX
}
// NOTE: if we wanted to, this is where to detect ABS
}
// See if we are selecting two values based on a comparison of the two values.
if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))
if (Instruction *Result = visitSelectInstWithICmp(SI, ICI))
return Result;
if (Instruction *TI = dyn_cast<Instruction>(TrueVal))
if (Instruction *FI = dyn_cast<Instruction>(FalseVal))
if (TI->hasOneUse() && FI->hasOneUse()) {
Instruction *AddOp = 0, *SubOp = 0;
// Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
if (TI->getOpcode() == FI->getOpcode())
if (Instruction *IV = FoldSelectOpOp(SI, TI, FI))
return IV;
// Turn select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y))). This is
// even legal for FP.
if ((TI->getOpcode() == Instruction::Sub &&
FI->getOpcode() == Instruction::Add) ||
(TI->getOpcode() == Instruction::FSub &&
FI->getOpcode() == Instruction::FAdd)) {
AddOp = FI; SubOp = TI;
} else if ((FI->getOpcode() == Instruction::Sub &&
TI->getOpcode() == Instruction::Add) ||
(FI->getOpcode() == Instruction::FSub &&
TI->getOpcode() == Instruction::FAdd)) {
AddOp = TI; SubOp = FI;
}
if (AddOp) {
Value *OtherAddOp = 0;
if (SubOp->getOperand(0) == AddOp->getOperand(0)) {
OtherAddOp = AddOp->getOperand(1);
} else if (SubOp->getOperand(0) == AddOp->getOperand(1)) {
OtherAddOp = AddOp->getOperand(0);
}
if (OtherAddOp) {
// So at this point we know we have (Y -> OtherAddOp):
// select C, (add X, Y), (sub X, Z)
Value *NegVal; // Compute -Z
if (Constant *C = dyn_cast<Constant>(SubOp->getOperand(1))) {
NegVal = ConstantExpr::getNeg(C);
} else if (SI.getType()->isFloatingPointTy()) {
NegVal = InsertNewInstBefore(
BinaryOperator::CreateFNeg(SubOp->getOperand(1),
"tmp"), SI);
} else {
NegVal = InsertNewInstBefore(
BinaryOperator::CreateNeg(SubOp->getOperand(1),
"tmp"), SI);
}
Value *NewTrueOp = OtherAddOp;
Value *NewFalseOp = NegVal;
if (AddOp != TI)
std::swap(NewTrueOp, NewFalseOp);
Instruction *NewSel =
SelectInst::Create(CondVal, NewTrueOp,
NewFalseOp, SI.getName() + ".p");
NewSel = InsertNewInstBefore(NewSel, SI);
if (SI.getType()->isFloatingPointTy())
return BinaryOperator::CreateFAdd(SubOp->getOperand(0), NewSel);
else
return BinaryOperator::CreateAdd(SubOp->getOperand(0), NewSel);
}
}
}
// See if we can fold the select into one of our operands.
if (SI.getType()->isIntegerTy()) {
if (Instruction *FoldI = FoldSelectIntoOp(SI, TrueVal, FalseVal))
return FoldI;
// MAX(MAX(a, b), a) -> MAX(a, b)
// MIN(MIN(a, b), a) -> MIN(a, b)
// MAX(MIN(a, b), a) -> a
// MIN(MAX(a, b), a) -> a
Value *LHS, *RHS, *LHS2, *RHS2;
if (SelectPatternFlavor SPF = MatchSelectPattern(&SI, LHS, RHS)) {
if (SelectPatternFlavor SPF2 = MatchSelectPattern(LHS, LHS2, RHS2))
if (Instruction *R = FoldSPFofSPF(cast<Instruction>(LHS),SPF2,LHS2,RHS2,
SI, SPF, RHS))
return R;
if (SelectPatternFlavor SPF2 = MatchSelectPattern(RHS, LHS2, RHS2))
if (Instruction *R = FoldSPFofSPF(cast<Instruction>(RHS),SPF2,LHS2,RHS2,
SI, SPF, LHS))
return R;
}
// TODO.
// ABS(-X) -> ABS(X)
// ABS(ABS(X)) -> ABS(X)
}
// See if we can fold the select into a phi node if the condition is a select.
if (isa<PHINode>(SI.getCondition()))
// The true/false values have to be live in the PHI predecessor's blocks.
if (CanSelectOperandBeMappingIntoPredBlock(TrueVal, SI) &&
CanSelectOperandBeMappingIntoPredBlock(FalseVal, SI))
if (Instruction *NV = FoldOpIntoPhi(SI))
return NV;
if (BinaryOperator::isNot(CondVal)) {
SI.setOperand(0, BinaryOperator::getNotArgument(CondVal));
SI.setOperand(1, FalseVal);
SI.setOperand(2, TrueVal);
return &SI;
}
return 0;
}
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