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llvm-6502/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
Shuxin Yang a1444219b2 1. Hoist minus sign as high as possible in an attempt to reveal 
some optimization opportunities (in the enclosing supper-expressions).

   rule 1. (-0.0 - X ) * Y => -0.0 - (X * Y)
     if expression "-0.0 - X" has only one reference.

   rule 2. (0.0 - X ) * Y => -0.0 - (X * Y)
     if expression "0.0 - X" has only one reference, and
        the instruction is marked "noSignedZero".

2. Eliminate negation (The compiler was already able to handle these
    opt if the 0.0s are replaced with -0.0.)

   rule 3: (0.0 - X) * (0.0 - Y) => X * Y
   rule 4: (0.0 - X) * C => X * -C
   if the expr is flagged "noSignedZero".

3. 
  Rule 5: (X*Y) * X => (X*X) * Y
   if X!=Y and the expression is flagged with "UnsafeAlgebra".

   The purpose of this transformation is two-fold:
    a) to form a power expression (of X).
    b) potentially shorten the critical path: After transformation, the
       latency of the instruction Y is amortized by the expression of X*X,
       and therefore Y is in a "less critical" position compared to what it
      was before the transformation. 

4. Remove the InstCombine code about simplifiying "X * select".
   
   The reasons are following:
    a) The "select" is somewhat architecture-dependent, therefore the
       higher level optimizers are not able to precisely predict if
       the simplification really yields any performance improvement
       or not.

    b) The "select" operator is bit complicate, and tends to obscure
       optimization opportunities. It is btter to keep it as low as
       possible in expr tree, and let CodeGen to tackle the optimization.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@172551 91177308-0d34-0410-b5e6-96231b3b80d8
2013-01-15 21:09:32 +00:00

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//===- InstCombineMulDivRem.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 visit functions for mul, fmul, sdiv, udiv, fdiv,
// srem, urem, frem.
//
//===----------------------------------------------------------------------===//
#include "InstCombine.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/PatternMatch.h"
using namespace llvm;
using namespace PatternMatch;
/// simplifyValueKnownNonZero - The specific integer value is used in a context
/// where it is known to be non-zero. If this allows us to simplify the
/// computation, do so and return the new operand, otherwise return null.
static Value *simplifyValueKnownNonZero(Value *V, InstCombiner &IC) {
// If V has multiple uses, then we would have to do more analysis to determine
// if this is safe. For example, the use could be in dynamically unreached
// code.
if (!V->hasOneUse()) return 0;
bool MadeChange = false;
// ((1 << A) >>u B) --> (1 << (A-B))
// Because V cannot be zero, we know that B is less than A.
Value *A = 0, *B = 0, *PowerOf2 = 0;
if (match(V, m_LShr(m_OneUse(m_Shl(m_Value(PowerOf2), m_Value(A))),
m_Value(B))) &&
// The "1" can be any value known to be a power of 2.
isKnownToBeAPowerOfTwo(PowerOf2)) {
A = IC.Builder->CreateSub(A, B);
return IC.Builder->CreateShl(PowerOf2, A);
}
// (PowerOfTwo >>u B) --> isExact since shifting out the result would make it
// inexact. Similarly for <<.
if (BinaryOperator *I = dyn_cast<BinaryOperator>(V))
if (I->isLogicalShift() && isKnownToBeAPowerOfTwo(I->getOperand(0))) {
// We know that this is an exact/nuw shift and that the input is a
// non-zero context as well.
if (Value *V2 = simplifyValueKnownNonZero(I->getOperand(0), IC)) {
I->setOperand(0, V2);
MadeChange = true;
}
if (I->getOpcode() == Instruction::LShr && !I->isExact()) {
I->setIsExact();
MadeChange = true;
}
if (I->getOpcode() == Instruction::Shl && !I->hasNoUnsignedWrap()) {
I->setHasNoUnsignedWrap();
MadeChange = true;
}
}
// TODO: Lots more we could do here:
// If V is a phi node, we can call this on each of its operands.
// "select cond, X, 0" can simplify to "X".
return MadeChange ? V : 0;
}
/// MultiplyOverflows - True if the multiply can not be expressed in an int
/// this size.
static bool MultiplyOverflows(ConstantInt *C1, ConstantInt *C2, bool sign) {
uint32_t W = C1->getBitWidth();
APInt LHSExt = C1->getValue(), RHSExt = C2->getValue();
if (sign) {
LHSExt = LHSExt.sext(W * 2);
RHSExt = RHSExt.sext(W * 2);
} else {
LHSExt = LHSExt.zext(W * 2);
RHSExt = RHSExt.zext(W * 2);
}
APInt MulExt = LHSExt * RHSExt;
if (!sign)
return MulExt.ugt(APInt::getLowBitsSet(W * 2, W));
APInt Min = APInt::getSignedMinValue(W).sext(W * 2);
APInt Max = APInt::getSignedMaxValue(W).sext(W * 2);
return MulExt.slt(Min) || MulExt.sgt(Max);
}
Instruction *InstCombiner::visitMul(BinaryOperator &I) {
bool Changed = SimplifyAssociativeOrCommutative(I);
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (Value *V = SimplifyMulInst(Op0, Op1, TD))
return ReplaceInstUsesWith(I, V);
if (Value *V = SimplifyUsingDistributiveLaws(I))
return ReplaceInstUsesWith(I, V);
if (match(Op1, m_AllOnes())) // X * -1 == 0 - X
return BinaryOperator::CreateNeg(Op0, I.getName());
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
// ((X << C1)*C2) == (X * (C2 << C1))
if (BinaryOperator *SI = dyn_cast<BinaryOperator>(Op0))
if (SI->getOpcode() == Instruction::Shl)
if (Constant *ShOp = dyn_cast<Constant>(SI->getOperand(1)))
return BinaryOperator::CreateMul(SI->getOperand(0),
ConstantExpr::getShl(CI, ShOp));
const APInt &Val = CI->getValue();
if (Val.isPowerOf2()) { // Replace X*(2^C) with X << C
Constant *NewCst = ConstantInt::get(Op0->getType(), Val.logBase2());
BinaryOperator *Shl = BinaryOperator::CreateShl(Op0, NewCst);
if (I.hasNoSignedWrap()) Shl->setHasNoSignedWrap();
if (I.hasNoUnsignedWrap()) Shl->setHasNoUnsignedWrap();
return Shl;
}
// Canonicalize (X+C1)*CI -> X*CI+C1*CI.
{ Value *X; ConstantInt *C1;
if (Op0->hasOneUse() &&
match(Op0, m_Add(m_Value(X), m_ConstantInt(C1)))) {
Value *Add = Builder->CreateMul(X, CI);
return BinaryOperator::CreateAdd(Add, Builder->CreateMul(C1, CI));
}
}
// (Y - X) * (-(2**n)) -> (X - Y) * (2**n), for positive nonzero n
// (Y + const) * (-(2**n)) -> (-constY) * (2**n), for positive nonzero n
// The "* (2**n)" thus becomes a potential shifting opportunity.
{
const APInt & Val = CI->getValue();
const APInt &PosVal = Val.abs();
if (Val.isNegative() && PosVal.isPowerOf2()) {
Value *X = 0, *Y = 0;
if (Op0->hasOneUse()) {
ConstantInt *C1;
Value *Sub = 0;
if (match(Op0, m_Sub(m_Value(Y), m_Value(X))))
Sub = Builder->CreateSub(X, Y, "suba");
else if (match(Op0, m_Add(m_Value(Y), m_ConstantInt(C1))))
Sub = Builder->CreateSub(Builder->CreateNeg(C1), Y, "subc");
if (Sub)
return
BinaryOperator::CreateMul(Sub,
ConstantInt::get(Y->getType(), PosVal));
}
}
}
}
// Simplify mul instructions with a constant RHS.
if (isa<Constant>(Op1)) {
// Try to fold constant mul 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;
}
if (Value *Op0v = dyn_castNegVal(Op0)) // -X * -Y = X*Y
if (Value *Op1v = dyn_castNegVal(Op1))
return BinaryOperator::CreateMul(Op0v, Op1v);
// (X / Y) * Y = X - (X % Y)
// (X / Y) * -Y = (X % Y) - X
{
Value *Op1C = Op1;
BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0);
if (!BO ||
(BO->getOpcode() != Instruction::UDiv &&
BO->getOpcode() != Instruction::SDiv)) {
Op1C = Op0;
BO = dyn_cast<BinaryOperator>(Op1);
}
Value *Neg = dyn_castNegVal(Op1C);
if (BO && BO->hasOneUse() &&
(BO->getOperand(1) == Op1C || BO->getOperand(1) == Neg) &&
(BO->getOpcode() == Instruction::UDiv ||
BO->getOpcode() == Instruction::SDiv)) {
Value *Op0BO = BO->getOperand(0), *Op1BO = BO->getOperand(1);
// If the division is exact, X % Y is zero, so we end up with X or -X.
if (PossiblyExactOperator *SDiv = dyn_cast<PossiblyExactOperator>(BO))
if (SDiv->isExact()) {
if (Op1BO == Op1C)
return ReplaceInstUsesWith(I, Op0BO);
return BinaryOperator::CreateNeg(Op0BO);
}
Value *Rem;
if (BO->getOpcode() == Instruction::UDiv)
Rem = Builder->CreateURem(Op0BO, Op1BO);
else
Rem = Builder->CreateSRem(Op0BO, Op1BO);
Rem->takeName(BO);
if (Op1BO == Op1C)
return BinaryOperator::CreateSub(Op0BO, Rem);
return BinaryOperator::CreateSub(Rem, Op0BO);
}
}
/// i1 mul -> i1 and.
if (I.getType()->isIntegerTy(1))
return BinaryOperator::CreateAnd(Op0, Op1);
// X*(1 << Y) --> X << Y
// (1 << Y)*X --> X << Y
{
Value *Y;
if (match(Op0, m_Shl(m_One(), m_Value(Y))))
return BinaryOperator::CreateShl(Op1, Y);
if (match(Op1, m_Shl(m_One(), m_Value(Y))))
return BinaryOperator::CreateShl(Op0, Y);
}
// If one of the operands of the multiply is a cast from a boolean value, then
// we know the bool is either zero or one, so this is a 'masking' multiply.
// X * Y (where Y is 0 or 1) -> X & (0-Y)
if (!I.getType()->isVectorTy()) {
// -2 is "-1 << 1" so it is all bits set except the low one.
APInt Negative2(I.getType()->getPrimitiveSizeInBits(), (uint64_t)-2, true);
Value *BoolCast = 0, *OtherOp = 0;
if (MaskedValueIsZero(Op0, Negative2))
BoolCast = Op0, OtherOp = Op1;
else if (MaskedValueIsZero(Op1, Negative2))
BoolCast = Op1, OtherOp = Op0;
if (BoolCast) {
Value *V = Builder->CreateSub(Constant::getNullValue(I.getType()),
BoolCast);
return BinaryOperator::CreateAnd(V, OtherOp);
}
}
return Changed ? &I : 0;
}
//
// Detect pattern:
//
// log2(Y*0.5)
//
// And check for corresponding fast math flags
//
static void detectLog2OfHalf(Value *&Op, Value *&Y, IntrinsicInst *&Log2) {
if (!Op->hasOneUse())
return;
IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op);
if (!II)
return;
if (II->getIntrinsicID() != Intrinsic::log2 || !II->hasUnsafeAlgebra())
return;
Log2 = II;
Value *OpLog2Of = II->getArgOperand(0);
if (!OpLog2Of->hasOneUse())
return;
Instruction *I = dyn_cast<Instruction>(OpLog2Of);
if (!I)
return;
if (I->getOpcode() != Instruction::FMul || !I->hasUnsafeAlgebra())
return;
ConstantFP *CFP = dyn_cast<ConstantFP>(I->getOperand(0));
if (CFP && CFP->isExactlyValue(0.5)) {
Y = I->getOperand(1);
return;
}
CFP = dyn_cast<ConstantFP>(I->getOperand(1));
if (CFP && CFP->isExactlyValue(0.5))
Y = I->getOperand(0);
}
/// Helper function of InstCombiner::visitFMul(BinaryOperator(). It returns
/// true iff the given value is FMul or FDiv with one and only one operand
/// being a normal constant (i.e. not Zero/NaN/Infinity).
static bool isFMulOrFDivWithConstant(Value *V) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I || (I->getOpcode() != Instruction::FMul &&
I->getOpcode() != Instruction::FDiv))
return false;
ConstantFP *C0 = dyn_cast<ConstantFP>(I->getOperand(0));
ConstantFP *C1 = dyn_cast<ConstantFP>(I->getOperand(1));
if (C0 && C1)
return false;
return (C0 && C0->getValueAPF().isNormal()) ||
(C1 && C1->getValueAPF().isNormal());
}
static bool isNormalFp(const ConstantFP *C) {
const APFloat &Flt = C->getValueAPF();
return Flt.isNormal() && !Flt.isDenormal();
}
/// foldFMulConst() is a helper routine of InstCombiner::visitFMul().
/// The input \p FMulOrDiv is a FMul/FDiv with one and only one operand
/// being a constant (i.e. isFMulOrFDivWithConstant(FMulOrDiv) == true).
/// This function is to simplify "FMulOrDiv * C" and returns the
/// resulting expression. Note that this function could return NULL in
/// case the constants cannot be folded into a normal floating-point.
///
Value *InstCombiner::foldFMulConst(Instruction *FMulOrDiv, ConstantFP *C,
Instruction *InsertBefore) {
assert(isFMulOrFDivWithConstant(FMulOrDiv) && "V is invalid");
Value *Opnd0 = FMulOrDiv->getOperand(0);
Value *Opnd1 = FMulOrDiv->getOperand(1);
ConstantFP *C0 = dyn_cast<ConstantFP>(Opnd0);
ConstantFP *C1 = dyn_cast<ConstantFP>(Opnd1);
BinaryOperator *R = 0;
// (X * C0) * C => X * (C0*C)
if (FMulOrDiv->getOpcode() == Instruction::FMul) {
Constant *F = ConstantExpr::getFMul(C1 ? C1 : C0, C);
if (isNormalFp(cast<ConstantFP>(F)))
R = BinaryOperator::CreateFMul(C1 ? Opnd0 : Opnd1, F);
} else {
if (C0) {
// (C0 / X) * C => (C0 * C) / X
ConstantFP *F = cast<ConstantFP>(ConstantExpr::getFMul(C0, C));
if (isNormalFp(F))
R = BinaryOperator::CreateFDiv(F, Opnd1);
} else {
// (X / C1) * C => X * (C/C1) if C/C1 is not a denormal
ConstantFP *F = cast<ConstantFP>(ConstantExpr::getFDiv(C, C1));
if (isNormalFp(F)) {
R = BinaryOperator::CreateFMul(Opnd0, F);
} else {
// (X / C1) * C => X / (C1/C)
Constant *F = ConstantExpr::getFDiv(C1, C);
if (isNormalFp(cast<ConstantFP>(F)))
R = BinaryOperator::CreateFDiv(Opnd0, F);
}
}
}
if (R) {
R->setHasUnsafeAlgebra(true);
InsertNewInstWith(R, *InsertBefore);
}
return R;
}
Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
bool Changed = SimplifyAssociativeOrCommutative(I);
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (isa<Constant>(Op0))
std::swap(Op0, Op1);
if (Value *V = SimplifyFMulInst(Op0, Op1, I.getFastMathFlags(), TD))
return ReplaceInstUsesWith(I, V);
bool AllowReassociate = I.hasUnsafeAlgebra();
// Simplify mul instructions with a constant RHS.
if (isa<Constant>(Op1)) {
// Try to fold constant mul 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;
ConstantFP *C = dyn_cast<ConstantFP>(Op1);
if (C && AllowReassociate && C->getValueAPF().isNormal()) {
// Let MDC denote an expression in one of these forms:
// X * C, C/X, X/C, where C is a constant.
//
// Try to simplify "MDC * Constant"
if (isFMulOrFDivWithConstant(Op0)) {
Value *V = foldFMulConst(cast<Instruction>(Op0), C, &I);
if (V)
return ReplaceInstUsesWith(I, V);
}
// (MDC +/- C1) * C2 => (MDC * C2) +/- (C1 * C2)
Instruction *FAddSub = dyn_cast<Instruction>(Op0);
if (FAddSub &&
(FAddSub->getOpcode() == Instruction::FAdd ||
FAddSub->getOpcode() == Instruction::FSub)) {
Value *Opnd0 = FAddSub->getOperand(0);
Value *Opnd1 = FAddSub->getOperand(1);
ConstantFP *C0 = dyn_cast<ConstantFP>(Opnd0);
ConstantFP *C1 = dyn_cast<ConstantFP>(Opnd1);
bool Swap = false;
if (C0) {
std::swap(C0, C1);
std::swap(Opnd0, Opnd1);
Swap = true;
}
if (C1 && C1->getValueAPF().isNormal() &&
isFMulOrFDivWithConstant(Opnd0)) {
Value *M0 = ConstantExpr::getFMul(C1, C);
Value *M1 = isNormalFp(cast<ConstantFP>(M0)) ?
foldFMulConst(cast<Instruction>(Opnd0), C, &I) :
0;
if (M0 && M1) {
if (Swap && FAddSub->getOpcode() == Instruction::FSub)
std::swap(M0, M1);
Value *R = (FAddSub->getOpcode() == Instruction::FAdd) ?
BinaryOperator::CreateFAdd(M0, M1) :
BinaryOperator::CreateFSub(M0, M1);
Instruction *RI = cast<Instruction>(R);
RI->copyFastMathFlags(&I);
return RI;
}
}
}
}
}
// Under unsafe algebra do:
// X * log2(0.5*Y) = X*log2(Y) - X
if (I.hasUnsafeAlgebra()) {
Value *OpX = NULL;
Value *OpY = NULL;
IntrinsicInst *Log2;
detectLog2OfHalf(Op0, OpY, Log2);
if (OpY) {
OpX = Op1;
} else {
detectLog2OfHalf(Op1, OpY, Log2);
if (OpY) {
OpX = Op0;
}
}
// if pattern detected emit alternate sequence
if (OpX && OpY) {
Log2->setArgOperand(0, OpY);
Value *FMulVal = Builder->CreateFMul(OpX, Log2);
Instruction *FMul = cast<Instruction>(FMulVal);
FMul->copyFastMathFlags(Log2);
Instruction *FSub = BinaryOperator::CreateFSub(FMulVal, OpX);
FSub->copyFastMathFlags(Log2);
return FSub;
}
}
// Handle symmetric situation in a 2-iteration loop
Value *Opnd0 = Op0;
Value *Opnd1 = Op1;
for (int i = 0; i < 2; i++) {
bool IgnoreZeroSign = I.hasNoSignedZeros();
if (BinaryOperator::isFNeg(Opnd0, IgnoreZeroSign)) {
Value *N0 = dyn_castFNegVal(Opnd0, IgnoreZeroSign);
Value *N1 = dyn_castFNegVal(Opnd1, IgnoreZeroSign);
// -X * -Y => X*Y
if (N1)
return BinaryOperator::CreateFMul(N0, N1);
if (Opnd0->hasOneUse()) {
// -X * Y => -(X*Y) (Promote negation as high as possible)
Value *T = Builder->CreateFMul(N0, Opnd1);
cast<Instruction>(T)->setDebugLoc(I.getDebugLoc());
Instruction *Neg = BinaryOperator::CreateFNeg(T);
if (I.getFastMathFlags().any()) {
cast<Instruction>(T)->copyFastMathFlags(&I);
Neg->copyFastMathFlags(&I);
}
return Neg;
}
}
// (X*Y) * X => (X*X) * Y where Y != X
// The purpose is two-fold:
// 1) to form a power expression (of X).
// 2) potentially shorten the critical path: After transformation, the
// latency of the instruction Y is amortized by the expression of X*X,
// and therefore Y is in a "less critical" position compared to what it
// was before the transformation.
//
if (AllowReassociate) {
Value *Opnd0_0, *Opnd0_1;
if (Opnd0->hasOneUse() &&
match(Opnd0, m_FMul(m_Value(Opnd0_0), m_Value(Opnd0_1)))) {
Value *Y = 0;
if (Opnd0_0 == Opnd1 && Opnd0_1 != Opnd1)
Y = Opnd0_1;
else if (Opnd0_1 == Opnd1 && Opnd0_0 != Opnd1)
Y = Opnd0_0;
if (Y) {
Instruction *T = cast<Instruction>(Builder->CreateFMul(Opnd1, Opnd1));
T->copyFastMathFlags(&I);
T->setDebugLoc(I.getDebugLoc());
Instruction *R = BinaryOperator::CreateFMul(T, Y);
R->copyFastMathFlags(&I);
return R;
}
}
}
if (!isa<Constant>(Op1))
std::swap(Opnd0, Opnd1);
else
break;
}
return Changed ? &I : 0;
}
/// SimplifyDivRemOfSelect - Try to fold a divide or remainder of a select
/// instruction.
bool InstCombiner::SimplifyDivRemOfSelect(BinaryOperator &I) {
SelectInst *SI = cast<SelectInst>(I.getOperand(1));
// div/rem X, (Cond ? 0 : Y) -> div/rem X, Y
int NonNullOperand = -1;
if (Constant *ST = dyn_cast<Constant>(SI->getOperand(1)))
if (ST->isNullValue())
NonNullOperand = 2;
// div/rem X, (Cond ? Y : 0) -> div/rem X, Y
if (Constant *ST = dyn_cast<Constant>(SI->getOperand(2)))
if (ST->isNullValue())
NonNullOperand = 1;
if (NonNullOperand == -1)
return false;
Value *SelectCond = SI->getOperand(0);
// Change the div/rem to use 'Y' instead of the select.
I.setOperand(1, SI->getOperand(NonNullOperand));
// Okay, we know we replace the operand of the div/rem with 'Y' with no
// problem. However, the select, or the condition of the select may have
// multiple uses. Based on our knowledge that the operand must be non-zero,
// propagate the known value for the select into other uses of it, and
// propagate a known value of the condition into its other users.
// If the select and condition only have a single use, don't bother with this,
// early exit.
if (SI->use_empty() && SelectCond->hasOneUse())
return true;
// Scan the current block backward, looking for other uses of SI.
BasicBlock::iterator BBI = &I, BBFront = I.getParent()->begin();
while (BBI != BBFront) {
--BBI;
// If we found a call to a function, we can't assume it will return, so
// information from below it cannot be propagated above it.
if (isa<CallInst>(BBI) && !isa<IntrinsicInst>(BBI))
break;
// Replace uses of the select or its condition with the known values.
for (Instruction::op_iterator I = BBI->op_begin(), E = BBI->op_end();
I != E; ++I) {
if (*I == SI) {
*I = SI->getOperand(NonNullOperand);
Worklist.Add(BBI);
} else if (*I == SelectCond) {
*I = NonNullOperand == 1 ? ConstantInt::getTrue(BBI->getContext()) :
ConstantInt::getFalse(BBI->getContext());
Worklist.Add(BBI);
}
}
// If we past the instruction, quit looking for it.
if (&*BBI == SI)
SI = 0;
if (&*BBI == SelectCond)
SelectCond = 0;
// If we ran out of things to eliminate, break out of the loop.
if (SelectCond == 0 && SI == 0)
break;
}
return true;
}
/// This function implements the transforms common to both integer division
/// instructions (udiv and sdiv). It is called by the visitors to those integer
/// division instructions.
/// @brief Common integer divide transforms
Instruction *InstCombiner::commonIDivTransforms(BinaryOperator &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
// The RHS is known non-zero.
if (Value *V = simplifyValueKnownNonZero(I.getOperand(1), *this)) {
I.setOperand(1, V);
return &I;
}
// Handle cases involving: [su]div X, (select Cond, Y, Z)
// This does not apply for fdiv.
if (isa<SelectInst>(Op1) && SimplifyDivRemOfSelect(I))
return &I;
if (ConstantInt *RHS = dyn_cast<ConstantInt>(Op1)) {
// (X / C1) / C2 -> X / (C1*C2)
if (Instruction *LHS = dyn_cast<Instruction>(Op0))
if (Instruction::BinaryOps(LHS->getOpcode()) == I.getOpcode())
if (ConstantInt *LHSRHS = dyn_cast<ConstantInt>(LHS->getOperand(1))) {
if (MultiplyOverflows(RHS, LHSRHS,
I.getOpcode()==Instruction::SDiv))
return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
return BinaryOperator::Create(I.getOpcode(), LHS->getOperand(0),
ConstantExpr::getMul(RHS, LHSRHS));
}
if (!RHS->isZero()) { // avoid X udiv 0
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;
}
}
// See if we can fold away this div instruction.
if (SimplifyDemandedInstructionBits(I))
return &I;
// (X - (X rem Y)) / Y -> X / Y; usually originates as ((X / Y) * Y) / Y
Value *X = 0, *Z = 0;
if (match(Op0, m_Sub(m_Value(X), m_Value(Z)))) { // (X - Z) / Y; Y = Op1
bool isSigned = I.getOpcode() == Instruction::SDiv;
if ((isSigned && match(Z, m_SRem(m_Specific(X), m_Specific(Op1)))) ||
(!isSigned && match(Z, m_URem(m_Specific(X), m_Specific(Op1)))))
return BinaryOperator::Create(I.getOpcode(), X, Op1);
}
return 0;
}
/// dyn_castZExtVal - Checks if V is a zext or constant that can
/// be truncated to Ty without losing bits.
static Value *dyn_castZExtVal(Value *V, Type *Ty) {
if (ZExtInst *Z = dyn_cast<ZExtInst>(V)) {
if (Z->getSrcTy() == Ty)
return Z->getOperand(0);
} else if (ConstantInt *C = dyn_cast<ConstantInt>(V)) {
if (C->getValue().getActiveBits() <= cast<IntegerType>(Ty)->getBitWidth())
return ConstantExpr::getTrunc(C, Ty);
}
return 0;
}
Instruction *InstCombiner::visitUDiv(BinaryOperator &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (Value *V = SimplifyUDivInst(Op0, Op1, TD))
return ReplaceInstUsesWith(I, V);
// Handle the integer div common cases
if (Instruction *Common = commonIDivTransforms(I))
return Common;
{
// X udiv 2^C -> X >> C
// Check to see if this is an unsigned division with an exact power of 2,
// if so, convert to a right shift.
const APInt *C;
if (match(Op1, m_Power2(C))) {
BinaryOperator *LShr =
BinaryOperator::CreateLShr(Op0,
ConstantInt::get(Op0->getType(),
C->logBase2()));
if (I.isExact()) LShr->setIsExact();
return LShr;
}
}
if (ConstantInt *C = dyn_cast<ConstantInt>(Op1)) {
// X udiv C, where C >= signbit
if (C->getValue().isNegative()) {
Value *IC = Builder->CreateICmpULT(Op0, C);
return SelectInst::Create(IC, Constant::getNullValue(I.getType()),
ConstantInt::get(I.getType(), 1));
}
}
// (x lshr C1) udiv C2 --> x udiv (C2 << C1)
if (ConstantInt *C2 = dyn_cast<ConstantInt>(Op1)) {
Value *X;
ConstantInt *C1;
if (match(Op0, m_LShr(m_Value(X), m_ConstantInt(C1)))) {
APInt NC = C2->getValue().shl(C1->getLimitedValue(C1->getBitWidth()-1));
return BinaryOperator::CreateUDiv(X, Builder->getInt(NC));
}
}
// X udiv (C1 << N), where C1 is "1<<C2" --> X >> (N+C2)
{ const APInt *CI; Value *N;
if (match(Op1, m_Shl(m_Power2(CI), m_Value(N))) ||
match(Op1, m_ZExt(m_Shl(m_Power2(CI), m_Value(N))))) {
if (*CI != 1)
N = Builder->CreateAdd(N,
ConstantInt::get(N->getType(), CI->logBase2()));
if (ZExtInst *Z = dyn_cast<ZExtInst>(Op1))
N = Builder->CreateZExt(N, Z->getDestTy());
if (I.isExact())
return BinaryOperator::CreateExactLShr(Op0, N);
return BinaryOperator::CreateLShr(Op0, N);
}
}
// udiv X, (Select Cond, C1, C2) --> Select Cond, (shr X, C1), (shr X, C2)
// where C1&C2 are powers of two.
{ Value *Cond; const APInt *C1, *C2;
if (match(Op1, m_Select(m_Value(Cond), m_Power2(C1), m_Power2(C2)))) {
// Construct the "on true" case of the select
Value *TSI = Builder->CreateLShr(Op0, C1->logBase2(), Op1->getName()+".t",
I.isExact());
// Construct the "on false" case of the select
Value *FSI = Builder->CreateLShr(Op0, C2->logBase2(), Op1->getName()+".f",
I.isExact());
// construct the select instruction and return it.
return SelectInst::Create(Cond, TSI, FSI);
}
}
// (zext A) udiv (zext B) --> zext (A udiv B)
if (ZExtInst *ZOp0 = dyn_cast<ZExtInst>(Op0))
if (Value *ZOp1 = dyn_castZExtVal(Op1, ZOp0->getSrcTy()))
return new ZExtInst(Builder->CreateUDiv(ZOp0->getOperand(0), ZOp1, "div",
I.isExact()),
I.getType());
return 0;
}
Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (Value *V = SimplifySDivInst(Op0, Op1, TD))
return ReplaceInstUsesWith(I, V);
// Handle the integer div common cases
if (Instruction *Common = commonIDivTransforms(I))
return Common;
if (ConstantInt *RHS = dyn_cast<ConstantInt>(Op1)) {
// sdiv X, -1 == -X
if (RHS->isAllOnesValue())
return BinaryOperator::CreateNeg(Op0);
// sdiv X, C --> ashr exact X, log2(C)
if (I.isExact() && RHS->getValue().isNonNegative() &&
RHS->getValue().isPowerOf2()) {
Value *ShAmt = llvm::ConstantInt::get(RHS->getType(),
RHS->getValue().exactLogBase2());
return BinaryOperator::CreateExactAShr(Op0, ShAmt, I.getName());
}
// -X/C --> X/-C provided the negation doesn't overflow.
if (SubOperator *Sub = dyn_cast<SubOperator>(Op0))
if (match(Sub->getOperand(0), m_Zero()) && Sub->hasNoSignedWrap())
return BinaryOperator::CreateSDiv(Sub->getOperand(1),
ConstantExpr::getNeg(RHS));
}
// If the sign bits of both operands are zero (i.e. we can prove they are
// unsigned inputs), turn this into a udiv.
if (I.getType()->isIntegerTy()) {
APInt Mask(APInt::getSignBit(I.getType()->getPrimitiveSizeInBits()));
if (MaskedValueIsZero(Op0, Mask)) {
if (MaskedValueIsZero(Op1, Mask)) {
// X sdiv Y -> X udiv Y, iff X and Y don't have sign bit set
return BinaryOperator::CreateUDiv(Op0, Op1, I.getName());
}
if (match(Op1, m_Shl(m_Power2(), m_Value()))) {
// X sdiv (1 << Y) -> X udiv (1 << Y) ( -> X u>> Y)
// Safe because the only negative value (1 << Y) can take on is
// INT_MIN, and X sdiv INT_MIN == X udiv INT_MIN == 0 if X doesn't have
// the sign bit set.
return BinaryOperator::CreateUDiv(Op0, Op1, I.getName());
}
}
}
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);
bool AllowReassociate = I.hasUnsafeAlgebra();
bool AllowReciprocal = I.hasAllowReciprocal();
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;
}
}
return 0;
}
/// This function implements the transforms common to both integer remainder
/// instructions (urem and srem). It is called by the visitors to those integer
/// remainder instructions.
/// @brief Common integer remainder transforms
Instruction *InstCombiner::commonIRemTransforms(BinaryOperator &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
// The RHS is known non-zero.
if (Value *V = simplifyValueKnownNonZero(I.getOperand(1), *this)) {
I.setOperand(1, V);
return &I;
}
// Handle cases involving: rem X, (select Cond, Y, Z)
if (isa<SelectInst>(Op1) && SimplifyDivRemOfSelect(I))
return &I;
if (isa<ConstantInt>(Op1)) {
if (Instruction *Op0I = dyn_cast<Instruction>(Op0)) {
if (SelectInst *SI = dyn_cast<SelectInst>(Op0I)) {
if (Instruction *R = FoldOpIntoSelect(I, SI))
return R;
} else if (isa<PHINode>(Op0I)) {
if (Instruction *NV = FoldOpIntoPhi(I))
return NV;
}
// See if we can fold away this rem instruction.
if (SimplifyDemandedInstructionBits(I))
return &I;
}
}
return 0;
}
Instruction *InstCombiner::visitURem(BinaryOperator &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (Value *V = SimplifyURemInst(Op0, Op1, TD))
return ReplaceInstUsesWith(I, V);
if (Instruction *common = commonIRemTransforms(I))
return common;
// X urem C^2 -> X and C-1
{ const APInt *C;
if (match(Op1, m_Power2(C)))
return BinaryOperator::CreateAnd(Op0,
ConstantInt::get(I.getType(), *C-1));
}
// Turn A % (C << N), where C is 2^k, into A & ((C << N)-1)
if (match(Op1, m_Shl(m_Power2(), m_Value()))) {
Constant *N1 = Constant::getAllOnesValue(I.getType());
Value *Add = Builder->CreateAdd(Op1, N1);
return BinaryOperator::CreateAnd(Op0, Add);
}
// urem X, (select Cond, 2^C1, 2^C2) -->
// select Cond, (and X, C1-1), (and X, C2-1)
// when C1&C2 are powers of two.
{ Value *Cond; const APInt *C1, *C2;
if (match(Op1, m_Select(m_Value(Cond), m_Power2(C1), m_Power2(C2)))) {
Value *TrueAnd = Builder->CreateAnd(Op0, *C1-1, Op1->getName()+".t");
Value *FalseAnd = Builder->CreateAnd(Op0, *C2-1, Op1->getName()+".f");
return SelectInst::Create(Cond, TrueAnd, FalseAnd);
}
}
// (zext A) urem (zext B) --> zext (A urem B)
if (ZExtInst *ZOp0 = dyn_cast<ZExtInst>(Op0))
if (Value *ZOp1 = dyn_castZExtVal(Op1, ZOp0->getSrcTy()))
return new ZExtInst(Builder->CreateURem(ZOp0->getOperand(0), ZOp1),
I.getType());
return 0;
}
Instruction *InstCombiner::visitSRem(BinaryOperator &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (Value *V = SimplifySRemInst(Op0, Op1, TD))
return ReplaceInstUsesWith(I, V);
// Handle the integer rem common cases
if (Instruction *Common = commonIRemTransforms(I))
return Common;
if (Value *RHSNeg = dyn_castNegVal(Op1))
if (!isa<Constant>(RHSNeg) ||
(isa<ConstantInt>(RHSNeg) &&
cast<ConstantInt>(RHSNeg)->getValue().isStrictlyPositive())) {
// X % -Y -> X % Y
Worklist.AddValue(I.getOperand(1));
I.setOperand(1, RHSNeg);
return &I;
}
// If the sign bits of both operands are zero (i.e. we can prove they are
// unsigned inputs), turn this into a urem.
if (I.getType()->isIntegerTy()) {
APInt Mask(APInt::getSignBit(I.getType()->getPrimitiveSizeInBits()));
if (MaskedValueIsZero(Op1, Mask) && MaskedValueIsZero(Op0, Mask)) {
// X srem Y -> X urem Y, iff X and Y don't have sign bit set
return BinaryOperator::CreateURem(Op0, Op1, I.getName());
}
}
// If it's a constant vector, flip any negative values positive.
if (isa<ConstantVector>(Op1) || isa<ConstantDataVector>(Op1)) {
Constant *C = cast<Constant>(Op1);
unsigned VWidth = C->getType()->getVectorNumElements();
bool hasNegative = false;
bool hasMissing = false;
for (unsigned i = 0; i != VWidth; ++i) {
Constant *Elt = C->getAggregateElement(i);
if (Elt == 0) {
hasMissing = true;
break;
}
if (ConstantInt *RHS = dyn_cast<ConstantInt>(Elt))
if (RHS->isNegative())
hasNegative = true;
}
if (hasNegative && !hasMissing) {
SmallVector<Constant *, 16> Elts(VWidth);
for (unsigned i = 0; i != VWidth; ++i) {
Elts[i] = C->getAggregateElement(i); // Handle undef, etc.
if (ConstantInt *RHS = dyn_cast<ConstantInt>(Elts[i])) {
if (RHS->isNegative())
Elts[i] = cast<ConstantInt>(ConstantExpr::getNeg(RHS));
}
}
Constant *NewRHSV = ConstantVector::get(Elts);
if (NewRHSV != C) { // Don't loop on -MININT
Worklist.AddValue(I.getOperand(1));
I.setOperand(1, NewRHSV);
return &I;
}
}
}
return 0;
}
Instruction *InstCombiner::visitFRem(BinaryOperator &I) {
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
if (Value *V = SimplifyFRemInst(Op0, Op1, TD))
return ReplaceInstUsesWith(I, V);
// Handle cases involving: rem X, (select Cond, Y, Z)
if (isa<SelectInst>(Op1) && SimplifyDivRemOfSelect(I))
return &I;
return 0;
}
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