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llvm-project/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp

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//===- InstCombineShifts.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 visitShl, visitLShr, and visitAShr functions.
//
//===----------------------------------------------------------------------===//
#include "InstCombineInternal.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "instcombine"
Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
assert(I.getOperand(1)->getType() == I.getOperand(0)->getType());
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
// See if we can fold away this shift.
if (SimplifyDemandedInstructionBits(I))
return &I;
// Try to fold constant and into select arguments.
if (isa<Constant>(Op0))
if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
if (Instruction *R = FoldOpIntoSelect(I, SI))
return R;
if (Constant *CUI = dyn_cast<Constant>(Op1))
if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I))
return Res;
// (C1 shift (A add C2)) -> (C1 shift C2) shift A)
// iff A and C2 are both positive.
Value *A;
Constant *C;
if (match(Op0, m_Constant()) && match(Op1, m_Add(m_Value(A), m_Constant(C))))
if (isKnownNonNegative(A, DL) && isKnownNonNegative(C, DL))
return BinaryOperator::Create(
I.getOpcode(), Builder->CreateBinOp(I.getOpcode(), Op0, C), A);
// X shift (A srem B) -> X shift (A and B-1) iff B is a power of 2.
// Because shifts by negative values (which could occur if A were negative)
// are undefined.
const APInt *B;
if (Op1->hasOneUse() && match(Op1, m_SRem(m_Value(A), m_Power2(B)))) {
// FIXME: Should this get moved into SimplifyDemandedBits by saying we don't
// demand the sign bit (and many others) here??
Value *Rem = Builder->CreateAnd(A, ConstantInt::get(I.getType(), *B-1),
Op1->getName());
I.setOperand(1, Rem);
return &I;
}
return nullptr;
}
/// Return true if we can simplify two logical (either left or right) shifts
/// that have constant shift amounts.
static bool canEvaluateShiftedShift(unsigned FirstShiftAmt,
bool IsFirstShiftLeft,
Instruction *SecondShift, InstCombiner &IC,
Instruction *CxtI) {
assert(SecondShift->isLogicalShift() && "Unexpected instruction type");
// We need constant shifts.
auto *SecondShiftConst = dyn_cast<ConstantInt>(SecondShift->getOperand(1));
if (!SecondShiftConst)
return false;
unsigned SecondShiftAmt = SecondShiftConst->getZExtValue();
bool IsSecondShiftLeft = SecondShift->getOpcode() == Instruction::Shl;
// We can always fold shl(c1) + shl(c2) -> shl(c1+c2).
// We can always fold lshr(c1) + lshr(c2) -> lshr(c1+c2).
if (IsFirstShiftLeft == IsSecondShiftLeft)
return true;
// We can always fold lshr(c) + shl(c) -> and(c2).
// We can always fold shl(c) + lshr(c) -> and(c2).
if (FirstShiftAmt == SecondShiftAmt)
return true;
unsigned TypeWidth = SecondShift->getType()->getScalarSizeInBits();
// If the 2nd shift is bigger than the 1st, we can fold:
// lshr(c1) + shl(c2) -> shl(c3) + and(c4) or
// shl(c1) + lshr(c2) -> lshr(c3) + and(c4),
// but it isn't profitable unless we know the and'd out bits are already zero.
// Also check that the 2nd shift is valid (less than the type width) or we'll
// crash trying to produce the bit mask for the 'and'.
if (SecondShiftAmt > FirstShiftAmt && SecondShiftAmt < TypeWidth) {
unsigned MaskShift = IsSecondShiftLeft ? TypeWidth - SecondShiftAmt
: SecondShiftAmt - FirstShiftAmt;
APInt Mask = APInt::getLowBitsSet(TypeWidth, FirstShiftAmt) << MaskShift;
if (IC.MaskedValueIsZero(SecondShift->getOperand(0), Mask, 0, CxtI))
return true;
}
return false;
}
/// See if we can compute the specified value, but shifted
/// logically to the left or right by some number of bits. This should return
/// true if the expression can be computed for the same cost as the current
/// expression tree. This is used to eliminate extraneous shifting from things
/// like:
/// %C = shl i128 %A, 64
/// %D = shl i128 %B, 96
/// %E = or i128 %C, %D
/// %F = lshr i128 %E, 64
/// where the client will ask if E can be computed shifted right by 64-bits. If
/// this succeeds, the GetShiftedValue function will be called to produce the
/// value.
static bool CanEvaluateShifted(Value *V, unsigned NumBits, bool IsLeftShift,
InstCombiner &IC, Instruction *CxtI) {
// We can always evaluate constants shifted.
if (isa<Constant>(V))
return true;
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return false;
// If this is the opposite shift, we can directly reuse the input of the shift
// if the needed bits are already zero in the input. This allows us to reuse
// the value which means that we don't care if the shift has multiple uses.
// TODO: Handle opposite shift by exact value.
ConstantInt *CI = nullptr;
if ((IsLeftShift && match(I, m_LShr(m_Value(), m_ConstantInt(CI)))) ||
(!IsLeftShift && match(I, m_Shl(m_Value(), m_ConstantInt(CI))))) {
if (CI->getZExtValue() == NumBits) {
// TODO: Check that the input bits are already zero with MaskedValueIsZero
#if 0
// If this is a truncate of a logical shr, we can truncate it to a smaller
// lshr iff we know that the bits we would otherwise be shifting in are
// already zeros.
uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
uint32_t BitWidth = Ty->getScalarSizeInBits();
if (MaskedValueIsZero(I->getOperand(0),
APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
CI->getLimitedValue(BitWidth) < BitWidth) {
return CanEvaluateTruncated(I->getOperand(0), Ty);
}
#endif
}
}
// We can't mutate something that has multiple uses: doing so would
// require duplicating the instruction in general, which isn't profitable.
if (!I->hasOneUse()) return false;
switch (I->getOpcode()) {
default: return false;
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
// Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
return CanEvaluateShifted(I->getOperand(0), NumBits, IsLeftShift, IC, I) &&
CanEvaluateShifted(I->getOperand(1), NumBits, IsLeftShift, IC, I);
case Instruction::Shl:
case Instruction::LShr:
return canEvaluateShiftedShift(NumBits, IsLeftShift, I, IC, CxtI);
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(I);
Value *TrueVal = SI->getTrueValue();
Value *FalseVal = SI->getFalseValue();
return CanEvaluateShifted(TrueVal, NumBits, IsLeftShift, IC, SI) &&
CanEvaluateShifted(FalseVal, NumBits, IsLeftShift, IC, SI);
}
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
// get into trouble with cyclic PHIs here because we only consider
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
for (Value *IncValue : PN->incoming_values())
if (!CanEvaluateShifted(IncValue, NumBits, IsLeftShift, IC, PN))
return false;
return true;
}
}
}
/// When CanEvaluateShifted returned true for an expression,
/// this value inserts the new computation that produces the shifted value.
static Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift,
InstCombiner &IC, const DataLayout &DL) {
// We can always evaluate constants shifted.
if (Constant *C = dyn_cast<Constant>(V)) {
if (isLeftShift)
V = IC.Builder->CreateShl(C, NumBits);
else
V = IC.Builder->CreateLShr(C, NumBits);
// If we got a constantexpr back, try to simplify it with TD info.
if (auto *C = dyn_cast<Constant>(V))
if (auto *FoldedC =
ConstantFoldConstant(C, DL, &IC.getTargetLibraryInfo()))
V = FoldedC;
return V;
}
Instruction *I = cast<Instruction>(V);
IC.Worklist.Add(I);
switch (I->getOpcode()) {
default: llvm_unreachable("Inconsistency with CanEvaluateShifted");
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
// Bitwise operators can all arbitrarily be arbitrarily evaluated shifted.
I->setOperand(
0, GetShiftedValue(I->getOperand(0), NumBits, isLeftShift, IC, DL));
I->setOperand(
1, GetShiftedValue(I->getOperand(1), NumBits, isLeftShift, IC, DL));
return I;
case Instruction::Shl: {
BinaryOperator *BO = cast<BinaryOperator>(I);
unsigned TypeWidth = BO->getType()->getScalarSizeInBits();
// We only accept shifts-by-a-constant in CanEvaluateShifted.
ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));
// We can always fold shl(c1)+shl(c2) -> shl(c1+c2).
if (isLeftShift) {
// If this is oversized composite shift, then unsigned shifts get 0.
unsigned NewShAmt = NumBits+CI->getZExtValue();
if (NewShAmt >= TypeWidth)
return Constant::getNullValue(I->getType());
BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));
BO->setHasNoUnsignedWrap(false);
BO->setHasNoSignedWrap(false);
return I;
}
// We turn shl(c)+lshr(c) -> and(c2) if the input doesn't already have
// zeros.
if (CI->getValue() == NumBits) {
APInt Mask(APInt::getLowBitsSet(TypeWidth, TypeWidth - NumBits));
V = IC.Builder->CreateAnd(BO->getOperand(0),
ConstantInt::get(BO->getContext(), Mask));
if (Instruction *VI = dyn_cast<Instruction>(V)) {
VI->moveBefore(BO);
VI->takeName(BO);
}
return V;
}
// We turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but only when we know that
// the and won't be needed.
assert(CI->getZExtValue() > NumBits);
BO->setOperand(1, ConstantInt::get(BO->getType(),
CI->getZExtValue() - NumBits));
BO->setHasNoUnsignedWrap(false);
BO->setHasNoSignedWrap(false);
return BO;
}
// FIXME: This is almost identical to the SHL case. Refactor both cases into
// a helper function.
case Instruction::LShr: {
BinaryOperator *BO = cast<BinaryOperator>(I);
unsigned TypeWidth = BO->getType()->getScalarSizeInBits();
// We only accept shifts-by-a-constant in CanEvaluateShifted.
ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));
// We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2).
if (!isLeftShift) {
// If this is oversized composite shift, then unsigned shifts get 0.
unsigned NewShAmt = NumBits+CI->getZExtValue();
if (NewShAmt >= TypeWidth)
return Constant::getNullValue(BO->getType());
BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt));
BO->setIsExact(false);
return I;
}
// We turn lshr(c)+shl(c) -> and(c2) if the input doesn't already have
// zeros.
if (CI->getValue() == NumBits) {
APInt Mask(APInt::getHighBitsSet(TypeWidth, TypeWidth - NumBits));
V = IC.Builder->CreateAnd(I->getOperand(0),
ConstantInt::get(BO->getContext(), Mask));
if (Instruction *VI = dyn_cast<Instruction>(V)) {
VI->moveBefore(I);
VI->takeName(I);
}
return V;
}
// We turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but only when we know that
// the and won't be needed.
assert(CI->getZExtValue() > NumBits);
BO->setOperand(1, ConstantInt::get(BO->getType(),
CI->getZExtValue() - NumBits));
BO->setIsExact(false);
return BO;
}
case Instruction::Select:
I->setOperand(
1, GetShiftedValue(I->getOperand(1), NumBits, isLeftShift, IC, DL));
I->setOperand(
2, GetShiftedValue(I->getOperand(2), NumBits, isLeftShift, IC, DL));
return I;
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
// get into trouble with cyclic PHIs here because we only consider
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
PN->setIncomingValue(i, GetShiftedValue(PN->getIncomingValue(i), NumBits,
isLeftShift, IC, DL));
return PN;
}
}
}
Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
BinaryOperator &I) {
bool isLeftShift = I.getOpcode() == Instruction::Shl;
ConstantInt *COp1 = nullptr;
if (ConstantDataVector *CV = dyn_cast<ConstantDataVector>(Op1))
COp1 = dyn_cast_or_null<ConstantInt>(CV->getSplatValue());
else if (ConstantVector *CV = dyn_cast<ConstantVector>(Op1))
COp1 = dyn_cast_or_null<ConstantInt>(CV->getSplatValue());
else
COp1 = dyn_cast<ConstantInt>(Op1);
if (!COp1)
return nullptr;
// See if we can propagate this shift into the input, this covers the trivial
// cast of lshr(shl(x,c1),c2) as well as other more complex cases.
if (I.getOpcode() != Instruction::AShr &&
CanEvaluateShifted(Op0, COp1->getZExtValue(), isLeftShift, *this, &I)) {
DEBUG(dbgs() << "ICE: GetShiftedValue propagating shift through expression"
" to eliminate shift:\n IN: " << *Op0 << "\n SH: " << I <<"\n");
return replaceInstUsesWith(
I, GetShiftedValue(Op0, COp1->getZExtValue(), isLeftShift, *this, DL));
}
// See if we can simplify any instructions used by the instruction whose sole
// purpose is to compute bits we don't care about.
uint32_t TypeBits = Op0->getType()->getScalarSizeInBits();
assert(!COp1->uge(TypeBits) &&
"Shift over the type width should have been removed already");
// ((X*C1) << C2) == (X * (C1 << C2))
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0))
if (BO->getOpcode() == Instruction::Mul && isLeftShift)
if (Constant *BOOp = dyn_cast<Constant>(BO->getOperand(1)))
return BinaryOperator::CreateMul(BO->getOperand(0),
ConstantExpr::getShl(BOOp, Op1));
// Try to fold constant and into select arguments.
if (SelectInst *SI = dyn_cast<SelectInst>(Op0))
if (Instruction *R = FoldOpIntoSelect(I, SI))
return R;
if (isa<PHINode>(Op0))
if (Instruction *NV = FoldOpIntoPhi(I))
return NV;
// Fold shift2(trunc(shift1(x,c1)), c2) -> trunc(shift2(shift1(x,c1),c2))
if (TruncInst *TI = dyn_cast<TruncInst>(Op0)) {
Instruction *TrOp = dyn_cast<Instruction>(TI->getOperand(0));
// If 'shift2' is an ashr, we would have to get the sign bit into a funny
// place. Don't try to do this transformation in this case. Also, we
// require that the input operand is a shift-by-constant so that we have
// confidence that the shifts will get folded together. We could do this
// xform in more cases, but it is unlikely to be profitable.
if (TrOp && I.isLogicalShift() && TrOp->isShift() &&
isa<ConstantInt>(TrOp->getOperand(1))) {
// Okay, we'll do this xform. Make the shift of shift.
Constant *ShAmt = ConstantExpr::getZExt(COp1, TrOp->getType());
// (shift2 (shift1 & 0x00FF), c2)
Value *NSh = Builder->CreateBinOp(I.getOpcode(), TrOp, ShAmt,I.getName());
// For logical shifts, the truncation has the effect of making the high
// part of the register be zeros. Emulate this by inserting an AND to
// clear the top bits as needed. This 'and' will usually be zapped by
// other xforms later if dead.
unsigned SrcSize = TrOp->getType()->getScalarSizeInBits();
unsigned DstSize = TI->getType()->getScalarSizeInBits();
APInt MaskV(APInt::getLowBitsSet(SrcSize, DstSize));
// The mask we constructed says what the trunc would do if occurring
// between the shifts. We want to know the effect *after* the second
// shift. We know that it is a logical shift by a constant, so adjust the
// mask as appropriate.
if (I.getOpcode() == Instruction::Shl)
MaskV <<= COp1->getZExtValue();
else {
assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift");
MaskV = MaskV.lshr(COp1->getZExtValue());
}
// shift1 & 0x00FF
Value *And = Builder->CreateAnd(NSh,
ConstantInt::get(I.getContext(), MaskV),
TI->getName());
// Return the value truncated to the interesting size.
return new TruncInst(And, I.getType());
}
}
if (Op0->hasOneUse()) {
if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) {
// Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
Value *V1, *V2;
ConstantInt *CC;
switch (Op0BO->getOpcode()) {
default: break;
case Instruction::Add:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor: {
// These operators commute.
// Turn (Y + (X >> C)) << C -> (X + (Y << C)) & (~0 << C)
if (isLeftShift && Op0BO->getOperand(1)->hasOneUse() &&
match(Op0BO->getOperand(1), m_Shr(m_Value(V1),
m_Specific(Op1)))) {
Value *YS = // (Y << C)
Builder->CreateShl(Op0BO->getOperand(0), Op1, Op0BO->getName());
// (X + (Y << C))
Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), YS, V1,
Op0BO->getOperand(1)->getName());
uint32_t Op1Val = COp1->getLimitedValue(TypeBits);
APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val);
Constant *Mask = ConstantInt::get(I.getContext(), Bits);
if (VectorType *VT = dyn_cast<VectorType>(X->getType()))
Mask = ConstantVector::getSplat(VT->getNumElements(), Mask);
return BinaryOperator::CreateAnd(X, Mask);
}
// Turn (Y + ((X >> C) & CC)) << C -> ((X & (CC << C)) + (Y << C))
Value *Op0BOOp1 = Op0BO->getOperand(1);
if (isLeftShift && Op0BOOp1->hasOneUse() &&
match(Op0BOOp1,
m_And(m_OneUse(m_Shr(m_Value(V1), m_Specific(Op1))),
m_ConstantInt(CC)))) {
Value *YS = // (Y << C)
Builder->CreateShl(Op0BO->getOperand(0), Op1,
Op0BO->getName());
// X & (CC << C)
Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
V1->getName()+".mask");
return BinaryOperator::Create(Op0BO->getOpcode(), YS, XM);
}
LLVM_FALLTHROUGH;
}
case Instruction::Sub: {
// Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
match(Op0BO->getOperand(0), m_Shr(m_Value(V1),
m_Specific(Op1)))) {
Value *YS = // (Y << C)
Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
// (X + (Y << C))
Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), V1, YS,
Op0BO->getOperand(0)->getName());
uint32_t Op1Val = COp1->getLimitedValue(TypeBits);
APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val);
Constant *Mask = ConstantInt::get(I.getContext(), Bits);
if (VectorType *VT = dyn_cast<VectorType>(X->getType()))
Mask = ConstantVector::getSplat(VT->getNumElements(), Mask);
return BinaryOperator::CreateAnd(X, Mask);
}
// Turn (((X >> C)&CC) + Y) << C -> (X + (Y << C)) & (CC << C)
if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
match(Op0BO->getOperand(0),
m_And(m_OneUse(m_Shr(m_Value(V1), m_Value(V2))),
m_ConstantInt(CC))) && V2 == Op1) {
Value *YS = // (Y << C)
Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
// X & (CC << C)
Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
V1->getName()+".mask");
return BinaryOperator::Create(Op0BO->getOpcode(), XM, YS);
}
break;
}
}
// If the operand is a bitwise operator with a constant RHS, and the
// shift is the only use, we can pull it out of the shift.
if (ConstantInt *Op0C = dyn_cast<ConstantInt>(Op0BO->getOperand(1))) {
bool isValid = true; // Valid only for And, Or, Xor
bool highBitSet = false; // Transform if high bit of constant set?
switch (Op0BO->getOpcode()) {
default: isValid = false; break; // Do not perform transform!
case Instruction::Add:
isValid = isLeftShift;
break;
case Instruction::Or:
case Instruction::Xor:
highBitSet = false;
break;
case Instruction::And:
highBitSet = true;
break;
}
// If this is a signed shift right, and the high bit is modified
// by the logical operation, do not perform the transformation.
// The highBitSet boolean indicates the value of the high bit of
// the constant which would cause it to be modified for this
// operation.
//
if (isValid && I.getOpcode() == Instruction::AShr)
isValid = Op0C->getValue()[TypeBits-1] == highBitSet;
if (isValid) {
Constant *NewRHS = ConstantExpr::get(I.getOpcode(), Op0C, Op1);
Value *NewShift =
Builder->CreateBinOp(I.getOpcode(), Op0BO->getOperand(0), Op1);
NewShift->takeName(Op0BO);
return BinaryOperator::Create(Op0BO->getOpcode(), NewShift,
NewRHS);
}
}
}
}
// Find out if this is a shift of a shift by a constant.
BinaryOperator *ShiftOp = dyn_cast<BinaryOperator>(Op0);
if (ShiftOp && !ShiftOp->isShift())
ShiftOp = nullptr;
if (ShiftOp && isa<ConstantInt>(ShiftOp->getOperand(1))) {
// This is a constant shift of a constant shift. Be careful about hiding
// shl instructions behind bit masks. They are used to represent multiplies
// by a constant, and it is important that simple arithmetic expressions
// are still recognizable by scalar evolution.
//
// The transforms applied to shl are very similar to the transforms applied
// to mul by constant. We can be more aggressive about optimizing right
// shifts.
//
// Combinations of right and left shifts will still be optimized in
// DAGCombine where scalar evolution no longer applies.
ConstantInt *ShiftAmt1C = cast<ConstantInt>(ShiftOp->getOperand(1));
uint32_t ShiftAmt1 = ShiftAmt1C->getLimitedValue(TypeBits);
uint32_t ShiftAmt2 = COp1->getLimitedValue(TypeBits);
assert(ShiftAmt2 != 0 && "Should have been simplified earlier");
if (ShiftAmt1 == 0) return nullptr; // Will be simplified in the future.
Value *X = ShiftOp->getOperand(0);
IntegerType *Ty = cast<IntegerType>(I.getType());
// Check for (X << c1) << c2 and (X >> c1) >> c2
if (I.getOpcode() == ShiftOp->getOpcode()) {
uint32_t AmtSum = ShiftAmt1 + ShiftAmt2; // Fold into one big shift.
// If this is an oversized composite shift, then unsigned shifts become
// zero (handled in InstSimplify) and ashr saturates.
if (AmtSum >= TypeBits) {
if (I.getOpcode() != Instruction::AShr)
return nullptr;
AmtSum = TypeBits - 1; // Saturate to 31 for i32 ashr.
}
return BinaryOperator::Create(I.getOpcode(), X,
ConstantInt::get(Ty, AmtSum));
}
if (ShiftAmt1 == ShiftAmt2) {
// If we have ((X << C) >>u C), turn this into X & (-1 >>u C).
if (I.getOpcode() == Instruction::LShr &&
ShiftOp->getOpcode() == Instruction::Shl) {
APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt1));
return BinaryOperator::CreateAnd(X,
ConstantInt::get(I.getContext(), Mask));
}
} else if (ShiftAmt1 < ShiftAmt2) {
uint32_t ShiftDiff = ShiftAmt2-ShiftAmt1;
// (X >>?,exact C1) << C2 --> X << (C2-C1)
// The inexact version is deferred to DAGCombine so we don't hide shl
// behind a bit mask.
if (I.getOpcode() == Instruction::Shl &&
ShiftOp->getOpcode() != Instruction::Shl &&
ShiftOp->isExact()) {
assert(ShiftOp->getOpcode() == Instruction::LShr ||
ShiftOp->getOpcode() == Instruction::AShr);
ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl,
X, ShiftDiffCst);
NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
NewShl->setHasNoSignedWrap(I.hasNoSignedWrap());
return NewShl;
}
// (X << C1) >>u C2 --> X >>u (C2-C1) & (-1 >> C2)
if (I.getOpcode() == Instruction::LShr &&
ShiftOp->getOpcode() == Instruction::Shl) {
ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
// (X <<nuw C1) >>u C2 --> X >>u (C2-C1)
if (ShiftOp->hasNoUnsignedWrap()) {
BinaryOperator *NewLShr = BinaryOperator::Create(Instruction::LShr,
X, ShiftDiffCst);
NewLShr->setIsExact(I.isExact());
return NewLShr;
}
Value *Shift = Builder->CreateLShr(X, ShiftDiffCst);
APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
return BinaryOperator::CreateAnd(Shift,
ConstantInt::get(I.getContext(),Mask));
}
// We can't handle (X << C1) >>s C2, it shifts arbitrary bits in. However,
// we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits.
if (I.getOpcode() == Instruction::AShr &&
ShiftOp->getOpcode() == Instruction::Shl) {
if (ShiftOp->hasNoSignedWrap()) {
// (X <<nsw C1) >>s C2 --> X >>s (C2-C1)
ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
BinaryOperator *NewAShr = BinaryOperator::Create(Instruction::AShr,
X, ShiftDiffCst);
NewAShr->setIsExact(I.isExact());
return NewAShr;
}
}
} else {
assert(ShiftAmt2 < ShiftAmt1);
uint32_t ShiftDiff = ShiftAmt1-ShiftAmt2;
// (X >>?exact C1) << C2 --> X >>?exact (C1-C2)
// The inexact version is deferred to DAGCombine so we don't hide shl
// behind a bit mask.
if (I.getOpcode() == Instruction::Shl &&
ShiftOp->getOpcode() != Instruction::Shl &&
ShiftOp->isExact()) {
ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
BinaryOperator *NewShr = BinaryOperator::Create(ShiftOp->getOpcode(),
X, ShiftDiffCst);
NewShr->setIsExact(true);
return NewShr;
}
// (X << C1) >>u C2 --> X << (C1-C2) & (-1 >> C2)
if (I.getOpcode() == Instruction::LShr &&
ShiftOp->getOpcode() == Instruction::Shl) {
ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
if (ShiftOp->hasNoUnsignedWrap()) {
// (X <<nuw C1) >>u C2 --> X <<nuw (C1-C2)
BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl,
X, ShiftDiffCst);
NewShl->setHasNoUnsignedWrap(true);
return NewShl;
}
Value *Shift = Builder->CreateShl(X, ShiftDiffCst);
APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
return BinaryOperator::CreateAnd(Shift,
ConstantInt::get(I.getContext(),Mask));
}
// We can't handle (X << C1) >>s C2, it shifts arbitrary bits in. However,
// we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits.
if (I.getOpcode() == Instruction::AShr &&
ShiftOp->getOpcode() == Instruction::Shl) {
if (ShiftOp->hasNoSignedWrap()) {
// (X <<nsw C1) >>s C2 --> X <<nsw (C1-C2)
ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl,
X, ShiftDiffCst);
NewShl->setHasNoSignedWrap(true);
return NewShl;
}
}
}
}
return nullptr;
}
Instruction *InstCombiner::visitShl(BinaryOperator &I) {
if (Value *V = SimplifyVectorOp(I))
return replaceInstUsesWith(I, V);
if (Value *V =
SimplifyShlInst(I.getOperand(0), I.getOperand(1), I.hasNoSignedWrap(),
I.hasNoUnsignedWrap(), DL, &TLI, &DT, &AC))
return replaceInstUsesWith(I, V);
if (Instruction *V = commonShiftTransforms(I))
return V;
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(I.getOperand(1))) {
unsigned ShAmt = Op1C->getZExtValue();
// If the shifted-out value is known-zero, then this is a NUW shift.
if (!I.hasNoUnsignedWrap() &&
MaskedValueIsZero(I.getOperand(0),
APInt::getHighBitsSet(Op1C->getBitWidth(), ShAmt), 0,
&I)) {
I.setHasNoUnsignedWrap();
return &I;
}
// If the shifted out value is all signbits, this is a NSW shift.
if (!I.hasNoSignedWrap() &&
ComputeNumSignBits(I.getOperand(0), 0, &I) > ShAmt) {
I.setHasNoSignedWrap();
return &I;
}
}
// (C1 << A) << C2 -> (C1 << C2) << A
Constant *C1, *C2;
Value *A;
if (match(I.getOperand(0), m_OneUse(m_Shl(m_Constant(C1), m_Value(A)))) &&
match(I.getOperand(1), m_Constant(C2)))
return BinaryOperator::CreateShl(ConstantExpr::getShl(C1, C2), A);
return nullptr;
}
Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
if (Value *V = SimplifyVectorOp(I))
return replaceInstUsesWith(I, V);
if (Value *V = SimplifyLShrInst(I.getOperand(0), I.getOperand(1), I.isExact(),
DL, &TLI, &DT, &AC))
return replaceInstUsesWith(I, V);
if (Instruction *R = commonShiftTransforms(I))
return R;
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
unsigned ShAmt = Op1C->getZExtValue();
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0)) {
unsigned BitWidth = Op0->getType()->getScalarSizeInBits();
// ctlz.i32(x)>>5 --> zext(x == 0)
// cttz.i32(x)>>5 --> zext(x == 0)
// ctpop.i32(x)>>5 --> zext(x == -1)
if ((II->getIntrinsicID() == Intrinsic::ctlz ||
II->getIntrinsicID() == Intrinsic::cttz ||
II->getIntrinsicID() == Intrinsic::ctpop) &&
isPowerOf2_32(BitWidth) && Log2_32(BitWidth) == ShAmt) {
bool isCtPop = II->getIntrinsicID() == Intrinsic::ctpop;
Constant *RHS = ConstantInt::getSigned(Op0->getType(), isCtPop ? -1:0);
Value *Cmp = Builder->CreateICmpEQ(II->getArgOperand(0), RHS);
return new ZExtInst(Cmp, II->getType());
}
}
// If the shifted-out value is known-zero, then this is an exact shift.
if (!I.isExact() &&
MaskedValueIsZero(Op0, APInt::getLowBitsSet(Op1C->getBitWidth(), ShAmt),
0, &I)){
I.setIsExact();
return &I;
}
}
return nullptr;
}
Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
if (Value *V = SimplifyVectorOp(I))
return replaceInstUsesWith(I, V);
if (Value *V = SimplifyAShrInst(I.getOperand(0), I.getOperand(1), I.isExact(),
DL, &TLI, &DT, &AC))
return replaceInstUsesWith(I, V);
if (Instruction *R = commonShiftTransforms(I))
return R;
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
unsigned ShAmt = Op1C->getZExtValue();
// If the input is a SHL by the same constant (ashr (shl X, C), C), then we
// have a sign-extend idiom.
Value *X;
if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1)))) {
// If the input is an extension from the shifted amount value, e.g.
// %x = zext i8 %A to i32
// %y = shl i32 %x, 24
// %z = ashr %y, 24
// then turn this into "z = sext i8 A to i32".
if (ZExtInst *ZI = dyn_cast<ZExtInst>(X)) {
uint32_t SrcBits = ZI->getOperand(0)->getType()->getScalarSizeInBits();
uint32_t DestBits = ZI->getType()->getScalarSizeInBits();
if (Op1C->getZExtValue() == DestBits-SrcBits)
return new SExtInst(ZI->getOperand(0), ZI->getType());
}
}
// If the shifted-out value is known-zero, then this is an exact shift.
if (!I.isExact() &&
MaskedValueIsZero(Op0, APInt::getLowBitsSet(Op1C->getBitWidth(), ShAmt),
0, &I)) {
I.setIsExact();
return &I;
}
}
// See if we can turn a signed shr into an unsigned shr.
if (MaskedValueIsZero(Op0,
APInt::getSignBit(I.getType()->getScalarSizeInBits()),
0, &I))
return BinaryOperator::CreateLShr(Op0, Op1);
return nullptr;
}
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