mirror of
https://github.com/c64scene-ar/llvm-6502.git
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de9f5452d3
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106707 91177308-0d34-0410-b5e6-96231b3b80d8
464 lines
19 KiB
C++
464 lines
19 KiB
C++
//===- InstCombineShifts.cpp ----------------------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the visitShl, visitLShr, and visitAShr functions.
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//
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//===----------------------------------------------------------------------===//
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#include "InstCombine.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Support/PatternMatch.h"
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using namespace llvm;
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using namespace PatternMatch;
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Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
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assert(I.getOperand(1)->getType() == I.getOperand(0)->getType());
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Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
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// shl X, 0 == X and shr X, 0 == X
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// shl 0, X == 0 and shr 0, X == 0
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if (Op1 == Constant::getNullValue(Op1->getType()) ||
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Op0 == Constant::getNullValue(Op0->getType()))
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return ReplaceInstUsesWith(I, Op0);
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if (isa<UndefValue>(Op0)) {
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if (I.getOpcode() == Instruction::AShr) // undef >>s X -> undef
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return ReplaceInstUsesWith(I, Op0);
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else // undef << X -> 0, undef >>u X -> 0
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return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
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}
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if (isa<UndefValue>(Op1)) {
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if (I.getOpcode() == Instruction::AShr) // X >>s undef -> X
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return ReplaceInstUsesWith(I, Op0);
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else // X << undef, X >>u undef -> 0
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return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
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}
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// See if we can fold away this shift.
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if (SimplifyDemandedInstructionBits(I))
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return &I;
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// Try to fold constant and into select arguments.
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if (isa<Constant>(Op0))
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if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
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if (Instruction *R = FoldOpIntoSelect(I, SI))
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return R;
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if (ConstantInt *CUI = dyn_cast<ConstantInt>(Op1))
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if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I))
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return Res;
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return 0;
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}
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Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
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BinaryOperator &I) {
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bool isLeftShift = I.getOpcode() == Instruction::Shl;
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// See if we can simplify any instructions used by the instruction whose sole
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// purpose is to compute bits we don't care about.
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uint32_t TypeBits = Op0->getType()->getScalarSizeInBits();
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// shl i32 X, 32 = 0 and srl i8 Y, 9 = 0, ... just don't eliminate
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// a signed shift.
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//
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if (Op1->uge(TypeBits)) {
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if (I.getOpcode() != Instruction::AShr)
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return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
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// ashr i32 X, 32 --> ashr i32 X, 31
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I.setOperand(1, ConstantInt::get(I.getType(), TypeBits-1));
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return &I;
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}
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// ((X*C1) << C2) == (X * (C1 << C2))
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if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0))
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if (BO->getOpcode() == Instruction::Mul && isLeftShift)
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if (Constant *BOOp = dyn_cast<Constant>(BO->getOperand(1)))
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return BinaryOperator::CreateMul(BO->getOperand(0),
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ConstantExpr::getShl(BOOp, Op1));
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// Try to fold constant and into select arguments.
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if (SelectInst *SI = dyn_cast<SelectInst>(Op0))
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if (Instruction *R = FoldOpIntoSelect(I, SI))
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return R;
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if (isa<PHINode>(Op0))
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if (Instruction *NV = FoldOpIntoPhi(I))
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return NV;
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// Fold shift2(trunc(shift1(x,c1)), c2) -> trunc(shift2(shift1(x,c1),c2))
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if (TruncInst *TI = dyn_cast<TruncInst>(Op0)) {
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Instruction *TrOp = dyn_cast<Instruction>(TI->getOperand(0));
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// If 'shift2' is an ashr, we would have to get the sign bit into a funny
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// place. Don't try to do this transformation in this case. Also, we
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// require that the input operand is a shift-by-constant so that we have
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// confidence that the shifts will get folded together. We could do this
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// xform in more cases, but it is unlikely to be profitable.
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if (TrOp && I.isLogicalShift() && TrOp->isShift() &&
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isa<ConstantInt>(TrOp->getOperand(1))) {
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// Okay, we'll do this xform. Make the shift of shift.
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Constant *ShAmt = ConstantExpr::getZExt(Op1, TrOp->getType());
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// (shift2 (shift1 & 0x00FF), c2)
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Value *NSh = Builder->CreateBinOp(I.getOpcode(), TrOp, ShAmt,I.getName());
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// For logical shifts, the truncation has the effect of making the high
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// part of the register be zeros. Emulate this by inserting an AND to
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// clear the top bits as needed. This 'and' will usually be zapped by
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// other xforms later if dead.
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unsigned SrcSize = TrOp->getType()->getScalarSizeInBits();
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unsigned DstSize = TI->getType()->getScalarSizeInBits();
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APInt MaskV(APInt::getLowBitsSet(SrcSize, DstSize));
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// The mask we constructed says what the trunc would do if occurring
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// between the shifts. We want to know the effect *after* the second
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// shift. We know that it is a logical shift by a constant, so adjust the
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// mask as appropriate.
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if (I.getOpcode() == Instruction::Shl)
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MaskV <<= Op1->getZExtValue();
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else {
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assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift");
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MaskV = MaskV.lshr(Op1->getZExtValue());
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}
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// shift1 & 0x00FF
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Value *And = Builder->CreateAnd(NSh,
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ConstantInt::get(I.getContext(), MaskV),
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TI->getName());
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// Return the value truncated to the interesting size.
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return new TruncInst(And, I.getType());
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}
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}
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if (Op0->hasOneUse()) {
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if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) {
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// Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
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Value *V1, *V2;
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ConstantInt *CC;
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switch (Op0BO->getOpcode()) {
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default: break;
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case Instruction::Add:
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case Instruction::And:
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case Instruction::Or:
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case Instruction::Xor: {
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// These operators commute.
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// Turn (Y + (X >> C)) << C -> (X + (Y << C)) & (~0 << C)
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if (isLeftShift && Op0BO->getOperand(1)->hasOneUse() &&
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match(Op0BO->getOperand(1), m_Shr(m_Value(V1),
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m_Specific(Op1)))) {
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Value *YS = // (Y << C)
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Builder->CreateShl(Op0BO->getOperand(0), Op1, Op0BO->getName());
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// (X + (Y << C))
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Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), YS, V1,
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Op0BO->getOperand(1)->getName());
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uint32_t Op1Val = Op1->getLimitedValue(TypeBits);
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return BinaryOperator::CreateAnd(X, ConstantInt::get(I.getContext(),
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APInt::getHighBitsSet(TypeBits, TypeBits-Op1Val)));
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}
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// Turn (Y + ((X >> C) & CC)) << C -> ((X & (CC << C)) + (Y << C))
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Value *Op0BOOp1 = Op0BO->getOperand(1);
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if (isLeftShift && Op0BOOp1->hasOneUse() &&
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match(Op0BOOp1,
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m_And(m_Shr(m_Value(V1), m_Specific(Op1)),
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m_ConstantInt(CC))) &&
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cast<BinaryOperator>(Op0BOOp1)->getOperand(0)->hasOneUse()) {
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Value *YS = // (Y << C)
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Builder->CreateShl(Op0BO->getOperand(0), Op1,
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Op0BO->getName());
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// X & (CC << C)
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Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
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V1->getName()+".mask");
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return BinaryOperator::Create(Op0BO->getOpcode(), YS, XM);
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}
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}
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// FALL THROUGH.
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case Instruction::Sub: {
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// Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C)
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if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
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match(Op0BO->getOperand(0), m_Shr(m_Value(V1),
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m_Specific(Op1)))) {
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Value *YS = // (Y << C)
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Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
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// (X + (Y << C))
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Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), V1, YS,
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Op0BO->getOperand(0)->getName());
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uint32_t Op1Val = Op1->getLimitedValue(TypeBits);
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return BinaryOperator::CreateAnd(X, ConstantInt::get(I.getContext(),
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APInt::getHighBitsSet(TypeBits, TypeBits-Op1Val)));
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}
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// Turn (((X >> C)&CC) + Y) << C -> (X + (Y << C)) & (CC << C)
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if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() &&
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match(Op0BO->getOperand(0),
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m_And(m_Shr(m_Value(V1), m_Value(V2)),
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m_ConstantInt(CC))) && V2 == Op1 &&
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cast<BinaryOperator>(Op0BO->getOperand(0))
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->getOperand(0)->hasOneUse()) {
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Value *YS = // (Y << C)
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Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName());
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// X & (CC << C)
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Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1),
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V1->getName()+".mask");
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return BinaryOperator::Create(Op0BO->getOpcode(), XM, YS);
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}
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break;
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}
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}
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// If the operand is an bitwise operator with a constant RHS, and the
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// shift is the only use, we can pull it out of the shift.
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if (ConstantInt *Op0C = dyn_cast<ConstantInt>(Op0BO->getOperand(1))) {
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bool isValid = true; // Valid only for And, Or, Xor
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bool highBitSet = false; // Transform if high bit of constant set?
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switch (Op0BO->getOpcode()) {
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default: isValid = false; break; // Do not perform transform!
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case Instruction::Add:
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isValid = isLeftShift;
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break;
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case Instruction::Or:
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case Instruction::Xor:
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highBitSet = false;
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break;
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case Instruction::And:
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highBitSet = true;
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break;
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}
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// If this is a signed shift right, and the high bit is modified
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// by the logical operation, do not perform the transformation.
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// The highBitSet boolean indicates the value of the high bit of
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// the constant which would cause it to be modified for this
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// operation.
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//
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if (isValid && I.getOpcode() == Instruction::AShr)
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isValid = Op0C->getValue()[TypeBits-1] == highBitSet;
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if (isValid) {
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Constant *NewRHS = ConstantExpr::get(I.getOpcode(), Op0C, Op1);
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Value *NewShift =
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Builder->CreateBinOp(I.getOpcode(), Op0BO->getOperand(0), Op1);
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NewShift->takeName(Op0BO);
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return BinaryOperator::Create(Op0BO->getOpcode(), NewShift,
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NewRHS);
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}
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}
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}
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}
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// Find out if this is a shift of a shift by a constant.
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BinaryOperator *ShiftOp = dyn_cast<BinaryOperator>(Op0);
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if (ShiftOp && !ShiftOp->isShift())
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ShiftOp = 0;
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if (ShiftOp && isa<ConstantInt>(ShiftOp->getOperand(1))) {
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ConstantInt *ShiftAmt1C = cast<ConstantInt>(ShiftOp->getOperand(1));
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uint32_t ShiftAmt1 = ShiftAmt1C->getLimitedValue(TypeBits);
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uint32_t ShiftAmt2 = Op1->getLimitedValue(TypeBits);
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assert(ShiftAmt2 != 0 && "Should have been simplified earlier");
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if (ShiftAmt1 == 0) return 0; // Will be simplified in the future.
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Value *X = ShiftOp->getOperand(0);
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uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift.
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const IntegerType *Ty = cast<IntegerType>(I.getType());
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// Check for (X << c1) << c2 and (X >> c1) >> c2
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if (I.getOpcode() == ShiftOp->getOpcode()) {
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// If this is oversized composite shift, then unsigned shifts get 0, ashr
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// saturates.
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if (AmtSum >= TypeBits) {
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if (I.getOpcode() != Instruction::AShr)
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return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
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AmtSum = TypeBits-1; // Saturate to 31 for i32 ashr.
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}
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return BinaryOperator::Create(I.getOpcode(), X,
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ConstantInt::get(Ty, AmtSum));
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}
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if (ShiftOp->getOpcode() == Instruction::LShr &&
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I.getOpcode() == Instruction::AShr) {
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if (AmtSum >= TypeBits)
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return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
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// ((X >>u C1) >>s C2) -> (X >>u (C1+C2)) since C1 != 0.
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return BinaryOperator::CreateLShr(X, ConstantInt::get(Ty, AmtSum));
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}
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if (ShiftOp->getOpcode() == Instruction::AShr &&
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I.getOpcode() == Instruction::LShr) {
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// ((X >>s C1) >>u C2) -> ((X >>s (C1+C2)) & mask) since C1 != 0.
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if (AmtSum >= TypeBits)
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AmtSum = TypeBits-1;
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Value *Shift = Builder->CreateAShr(X, ConstantInt::get(Ty, AmtSum));
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APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
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return BinaryOperator::CreateAnd(Shift,
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ConstantInt::get(I.getContext(), Mask));
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}
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// Okay, if we get here, one shift must be left, and the other shift must be
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// right. See if the amounts are equal.
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if (ShiftAmt1 == ShiftAmt2) {
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// If we have ((X >>? C) << C), turn this into X & (-1 << C).
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if (I.getOpcode() == Instruction::Shl) {
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APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt1));
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return BinaryOperator::CreateAnd(X,
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ConstantInt::get(I.getContext(),Mask));
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}
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// If we have ((X << C) >>u C), turn this into X & (-1 >>u C).
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if (I.getOpcode() == Instruction::LShr) {
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APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt1));
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return BinaryOperator::CreateAnd(X,
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ConstantInt::get(I.getContext(), Mask));
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}
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} else if (ShiftAmt1 < ShiftAmt2) {
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uint32_t ShiftDiff = ShiftAmt2-ShiftAmt1;
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// (X >>? C1) << C2 --> X << (C2-C1) & (-1 << C2)
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if (I.getOpcode() == Instruction::Shl) {
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assert(ShiftOp->getOpcode() == Instruction::LShr ||
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ShiftOp->getOpcode() == Instruction::AShr);
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Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff));
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APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
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return BinaryOperator::CreateAnd(Shift,
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ConstantInt::get(I.getContext(),Mask));
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}
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// (X << C1) >>u C2 --> X >>u (C2-C1) & (-1 >> C2)
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if (I.getOpcode() == Instruction::LShr) {
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assert(ShiftOp->getOpcode() == Instruction::Shl);
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Value *Shift = Builder->CreateLShr(X, ConstantInt::get(Ty, ShiftDiff));
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APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
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return BinaryOperator::CreateAnd(Shift,
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ConstantInt::get(I.getContext(),Mask));
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}
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// We can't handle (X << C1) >>s C2, it shifts arbitrary bits in.
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} else {
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assert(ShiftAmt2 < ShiftAmt1);
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uint32_t ShiftDiff = ShiftAmt1-ShiftAmt2;
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// (X >>? C1) << C2 --> X >>? (C1-C2) & (-1 << C2)
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if (I.getOpcode() == Instruction::Shl) {
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assert(ShiftOp->getOpcode() == Instruction::LShr ||
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ShiftOp->getOpcode() == Instruction::AShr);
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Value *Shift = Builder->CreateBinOp(ShiftOp->getOpcode(), X,
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ConstantInt::get(Ty, ShiftDiff));
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APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
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return BinaryOperator::CreateAnd(Shift,
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ConstantInt::get(I.getContext(),Mask));
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}
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// (X << C1) >>u C2 --> X << (C1-C2) & (-1 >> C2)
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if (I.getOpcode() == Instruction::LShr) {
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assert(ShiftOp->getOpcode() == Instruction::Shl);
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Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff));
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APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
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return BinaryOperator::CreateAnd(Shift,
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ConstantInt::get(I.getContext(),Mask));
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}
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// We can't handle (X << C1) >>a C2, it shifts arbitrary bits in.
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}
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}
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return 0;
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}
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Instruction *InstCombiner::visitShl(BinaryOperator &I) {
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return commonShiftTransforms(I);
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}
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Instruction *InstCombiner::visitLShr(BinaryOperator &I) {
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if (Instruction *R = commonShiftTransforms(I))
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return R;
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Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
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if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1))
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if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0)) {
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unsigned BitWidth = Op0->getType()->getScalarSizeInBits();
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// ctlz.i32(x)>>5 --> zext(x == 0)
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// cttz.i32(x)>>5 --> zext(x == 0)
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// ctpop.i32(x)>>5 --> zext(x == -1)
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if ((II->getIntrinsicID() == Intrinsic::ctlz ||
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II->getIntrinsicID() == Intrinsic::cttz ||
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II->getIntrinsicID() == Intrinsic::ctpop) &&
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isPowerOf2_32(BitWidth) && Log2_32(BitWidth) == Op1C->getZExtValue()){
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bool isCtPop = II->getIntrinsicID() == Intrinsic::ctpop;
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Constant *RHS = ConstantInt::getSigned(Op0->getType(), isCtPop ? -1:0);
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Value *Cmp = Builder->CreateICmpEQ(II->getArgOperand(0), RHS);
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return new ZExtInst(Cmp, II->getType());
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}
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}
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return 0;
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}
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Instruction *InstCombiner::visitAShr(BinaryOperator &I) {
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if (Instruction *R = commonShiftTransforms(I))
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return R;
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Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
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if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0)) {
|
|
// ashr int -1, X = -1 (for any arithmetic shift rights of ~0)
|
|
if (CSI->isAllOnesValue())
|
|
return ReplaceInstUsesWith(I, CSI);
|
|
}
|
|
|
|
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
|
|
// 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 value is known to already be sign extended enough, delete
|
|
// the extension.
|
|
if (ComputeNumSignBits(X) > Op1C->getZExtValue())
|
|
return ReplaceInstUsesWith(I, X);
|
|
|
|
// 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());
|
|
}
|
|
}
|
|
}
|
|
|
|
// See if we can turn a signed shr into an unsigned shr.
|
|
if (MaskedValueIsZero(Op0,
|
|
APInt::getSignBit(I.getType()->getScalarSizeInBits())))
|
|
return BinaryOperator::CreateLShr(Op0, Op1);
|
|
|
|
// Arithmetic shifting an all-sign-bit value is a no-op.
|
|
unsigned NumSignBits = ComputeNumSignBits(Op0);
|
|
if (NumSignBits == Op0->getType()->getScalarSizeInBits())
|
|
return ReplaceInstUsesWith(I, Op0);
|
|
|
|
return 0;
|
|
}
|
|
|