435 lines
14 KiB
C++
435 lines
14 KiB
C++
//===- InstructionSimplify.cpp - Fold instruction operands ----------------===//
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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 routines for folding instructions into simpler forms
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// that do not require creating new instructions. For example, this does
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// constant folding, and can handle identities like (X&0)->0.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Support/ValueHandle.h"
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#include "llvm/Instructions.h"
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#include "llvm/Support/PatternMatch.h"
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using namespace llvm;
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using namespace llvm::PatternMatch;
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/// SimplifyAddInst - Given operands for an Add, see if we can
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/// fold the result. If not, this returns null.
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Value *llvm::SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
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const TargetData *TD) {
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if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
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if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
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Constant *Ops[] = { CLHS, CRHS };
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return ConstantFoldInstOperands(Instruction::Add, CLHS->getType(),
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Ops, 2, TD);
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}
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// Canonicalize the constant to the RHS.
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std::swap(Op0, Op1);
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}
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if (Constant *Op1C = dyn_cast<Constant>(Op1)) {
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// X + undef -> undef
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if (isa<UndefValue>(Op1C))
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return Op1C;
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// X + 0 --> X
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if (Op1C->isNullValue())
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return Op0;
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}
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// FIXME: Could pull several more out of instcombine.
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return 0;
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}
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/// SimplifyAndInst - Given operands for an And, see if we can
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/// fold the result. If not, this returns null.
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Value *llvm::SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD) {
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if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
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if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
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Constant *Ops[] = { CLHS, CRHS };
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return ConstantFoldInstOperands(Instruction::And, CLHS->getType(),
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Ops, 2, TD);
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}
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// Canonicalize the constant to the RHS.
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std::swap(Op0, Op1);
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}
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// X & undef -> 0
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if (isa<UndefValue>(Op1))
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return Constant::getNullValue(Op0->getType());
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// X & X = X
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if (Op0 == Op1)
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return Op0;
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// X & <0,0> = <0,0>
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if (isa<ConstantAggregateZero>(Op1))
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return Op1;
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// X & <-1,-1> = X
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if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
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if (CP->isAllOnesValue())
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return Op0;
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if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
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// X & 0 = 0
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if (Op1CI->isZero())
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return Op1CI;
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// X & -1 = X
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if (Op1CI->isAllOnesValue())
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return Op0;
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}
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// A & ~A = ~A & A = 0
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Value *A, *B;
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if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
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(match(Op1, m_Not(m_Value(A))) && A == Op0))
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return Constant::getNullValue(Op0->getType());
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// (A | ?) & A = A
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if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
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(A == Op1 || B == Op1))
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return Op1;
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// A & (A | ?) = A
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if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
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(A == Op0 || B == Op0))
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return Op0;
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return 0;
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}
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/// SimplifyOrInst - Given operands for an Or, see if we can
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/// fold the result. If not, this returns null.
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Value *llvm::SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD) {
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if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
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if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
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Constant *Ops[] = { CLHS, CRHS };
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return ConstantFoldInstOperands(Instruction::Or, CLHS->getType(),
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Ops, 2, TD);
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}
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// Canonicalize the constant to the RHS.
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std::swap(Op0, Op1);
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}
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// X | undef -> -1
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if (isa<UndefValue>(Op1))
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return Constant::getAllOnesValue(Op0->getType());
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// X | X = X
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if (Op0 == Op1)
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return Op0;
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// X | <0,0> = X
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if (isa<ConstantAggregateZero>(Op1))
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return Op0;
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// X | <-1,-1> = <-1,-1>
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if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
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if (CP->isAllOnesValue())
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return Op1;
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if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
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// X | 0 = X
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if (Op1CI->isZero())
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return Op0;
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// X | -1 = -1
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if (Op1CI->isAllOnesValue())
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return Op1CI;
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}
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// A | ~A = ~A | A = -1
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Value *A, *B;
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if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
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(match(Op1, m_Not(m_Value(A))) && A == Op0))
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return Constant::getAllOnesValue(Op0->getType());
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// (A & ?) | A = A
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if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
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(A == Op1 || B == Op1))
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return Op1;
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// A | (A & ?) = A
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if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
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(A == Op0 || B == Op0))
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return Op0;
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return 0;
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}
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static const Type *GetCompareTy(Value *Op) {
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return CmpInst::makeCmpResultType(Op->getType());
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}
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/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
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/// fold the result. If not, this returns null.
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Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
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const TargetData *TD) {
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CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
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assert(CmpInst::isIntPredicate(Pred) && "Not an integer compare!");
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if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
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if (Constant *CRHS = dyn_cast<Constant>(RHS))
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return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
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// If we have a constant, make sure it is on the RHS.
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std::swap(LHS, RHS);
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Pred = CmpInst::getSwappedPredicate(Pred);
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}
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// ITy - This is the return type of the compare we're considering.
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const Type *ITy = GetCompareTy(LHS);
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// icmp X, X -> true/false
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// X icmp undef -> true/false. For example, icmp ugt %X, undef -> false
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// because X could be 0.
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if (LHS == RHS || isa<UndefValue>(RHS))
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return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
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// icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
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// addresses never equal each other! We already know that Op0 != Op1.
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if ((isa<GlobalValue>(LHS) || isa<AllocaInst>(LHS) ||
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isa<ConstantPointerNull>(LHS)) &&
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(isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
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isa<ConstantPointerNull>(RHS)))
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return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
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// See if we are doing a comparison with a constant.
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if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
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// If we have an icmp le or icmp ge instruction, turn it into the
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// appropriate icmp lt or icmp gt instruction. This allows us to rely on
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// them being folded in the code below.
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switch (Pred) {
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default: break;
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case ICmpInst::ICMP_ULE:
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if (CI->isMaxValue(false)) // A <=u MAX -> TRUE
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return ConstantInt::getTrue(CI->getContext());
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break;
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case ICmpInst::ICMP_SLE:
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if (CI->isMaxValue(true)) // A <=s MAX -> TRUE
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return ConstantInt::getTrue(CI->getContext());
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break;
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case ICmpInst::ICMP_UGE:
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if (CI->isMinValue(false)) // A >=u MIN -> TRUE
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return ConstantInt::getTrue(CI->getContext());
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break;
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case ICmpInst::ICMP_SGE:
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if (CI->isMinValue(true)) // A >=s MIN -> TRUE
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return ConstantInt::getTrue(CI->getContext());
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break;
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}
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}
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return 0;
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}
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/// SimplifyFCmpInst - Given operands for an FCmpInst, see if we can
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/// fold the result. If not, this returns null.
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Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
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const TargetData *TD) {
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CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
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assert(CmpInst::isFPPredicate(Pred) && "Not an FP compare!");
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if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
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if (Constant *CRHS = dyn_cast<Constant>(RHS))
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return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
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// If we have a constant, make sure it is on the RHS.
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std::swap(LHS, RHS);
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Pred = CmpInst::getSwappedPredicate(Pred);
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}
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// Fold trivial predicates.
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if (Pred == FCmpInst::FCMP_FALSE)
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return ConstantInt::get(GetCompareTy(LHS), 0);
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if (Pred == FCmpInst::FCMP_TRUE)
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return ConstantInt::get(GetCompareTy(LHS), 1);
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if (isa<UndefValue>(RHS)) // fcmp pred X, undef -> undef
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return UndefValue::get(GetCompareTy(LHS));
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// fcmp x,x -> true/false. Not all compares are foldable.
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if (LHS == RHS) {
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if (CmpInst::isTrueWhenEqual(Pred))
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return ConstantInt::get(GetCompareTy(LHS), 1);
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if (CmpInst::isFalseWhenEqual(Pred))
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return ConstantInt::get(GetCompareTy(LHS), 0);
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}
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// Handle fcmp with constant RHS
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if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
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// If the constant is a nan, see if we can fold the comparison based on it.
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if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
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if (CFP->getValueAPF().isNaN()) {
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if (FCmpInst::isOrdered(Pred)) // True "if ordered and foo"
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return ConstantInt::getFalse(CFP->getContext());
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assert(FCmpInst::isUnordered(Pred) &&
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"Comparison must be either ordered or unordered!");
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// True if unordered.
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return ConstantInt::getTrue(CFP->getContext());
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}
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// Check whether the constant is an infinity.
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if (CFP->getValueAPF().isInfinity()) {
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if (CFP->getValueAPF().isNegative()) {
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switch (Pred) {
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case FCmpInst::FCMP_OLT:
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// No value is ordered and less than negative infinity.
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return ConstantInt::getFalse(CFP->getContext());
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case FCmpInst::FCMP_UGE:
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// All values are unordered with or at least negative infinity.
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return ConstantInt::getTrue(CFP->getContext());
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default:
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break;
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}
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} else {
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switch (Pred) {
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case FCmpInst::FCMP_OGT:
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// No value is ordered and greater than infinity.
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return ConstantInt::getFalse(CFP->getContext());
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case FCmpInst::FCMP_ULE:
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// All values are unordered with and at most infinity.
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return ConstantInt::getTrue(CFP->getContext());
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default:
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break;
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}
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}
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}
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}
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}
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return 0;
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}
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/// SimplifyGEPInst - Given operands for an GetElementPtrInst, see if we can
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/// fold the result. If not, this returns null.
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Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
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const TargetData *TD) {
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// getelementptr P -> P.
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if (NumOps == 1)
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return Ops[0];
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// TODO.
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//if (isa<UndefValue>(Ops[0]))
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// return UndefValue::get(GEP.getType());
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// getelementptr P, 0 -> P.
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if (NumOps == 2)
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if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
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if (C->isZero())
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return Ops[0];
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// Check to see if this is constant foldable.
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for (unsigned i = 0; i != NumOps; ++i)
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if (!isa<Constant>(Ops[i]))
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return 0;
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return ConstantExpr::getGetElementPtr(cast<Constant>(Ops[0]),
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(Constant *const*)Ops+1, NumOps-1);
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}
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//=== Helper functions for higher up the class hierarchy.
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/// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
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/// fold the result. If not, this returns null.
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Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
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const TargetData *TD) {
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switch (Opcode) {
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case Instruction::And: return SimplifyAndInst(LHS, RHS, TD);
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case Instruction::Or: return SimplifyOrInst(LHS, RHS, TD);
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default:
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if (Constant *CLHS = dyn_cast<Constant>(LHS))
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if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
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Constant *COps[] = {CLHS, CRHS};
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return ConstantFoldInstOperands(Opcode, LHS->getType(), COps, 2, TD);
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}
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return 0;
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}
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}
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/// SimplifyCmpInst - Given operands for a CmpInst, see if we can
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/// fold the result.
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Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
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const TargetData *TD) {
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if (CmpInst::isIntPredicate((CmpInst::Predicate)Predicate))
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return SimplifyICmpInst(Predicate, LHS, RHS, TD);
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return SimplifyFCmpInst(Predicate, LHS, RHS, TD);
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}
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/// SimplifyInstruction - See if we can compute a simplified version of this
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/// instruction. If not, this returns null.
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Value *llvm::SimplifyInstruction(Instruction *I, const TargetData *TD) {
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switch (I->getOpcode()) {
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default:
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return ConstantFoldInstruction(I, TD);
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case Instruction::Add:
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return SimplifyAddInst(I->getOperand(0), I->getOperand(1),
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cast<BinaryOperator>(I)->hasNoSignedWrap(),
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cast<BinaryOperator>(I)->hasNoUnsignedWrap(), TD);
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case Instruction::And:
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return SimplifyAndInst(I->getOperand(0), I->getOperand(1), TD);
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case Instruction::Or:
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return SimplifyOrInst(I->getOperand(0), I->getOperand(1), TD);
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case Instruction::ICmp:
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return SimplifyICmpInst(cast<ICmpInst>(I)->getPredicate(),
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I->getOperand(0), I->getOperand(1), TD);
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case Instruction::FCmp:
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return SimplifyFCmpInst(cast<FCmpInst>(I)->getPredicate(),
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I->getOperand(0), I->getOperand(1), TD);
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case Instruction::GetElementPtr: {
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SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
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return SimplifyGEPInst(&Ops[0], Ops.size(), TD);
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}
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}
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}
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/// ReplaceAndSimplifyAllUses - Perform From->replaceAllUsesWith(To) and then
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/// delete the From instruction. In addition to a basic RAUW, this does a
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/// recursive simplification of the newly formed instructions. This catches
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/// things where one simplification exposes other opportunities. This only
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/// simplifies and deletes scalar operations, it does not change the CFG.
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///
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void llvm::ReplaceAndSimplifyAllUses(Instruction *From, Value *To,
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const TargetData *TD) {
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assert(From != To && "ReplaceAndSimplifyAllUses(X,X) is not valid!");
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// FromHandle - This keeps a weakvh on the from value so that we can know if
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// it gets deleted out from under us in a recursive simplification.
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WeakVH FromHandle(From);
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while (!From->use_empty()) {
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// Update the instruction to use the new value.
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Use &U = From->use_begin().getUse();
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Instruction *User = cast<Instruction>(U.getUser());
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U = To;
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// See if we can simplify it.
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if (Value *V = SimplifyInstruction(User, TD)) {
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// Recursively simplify this.
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ReplaceAndSimplifyAllUses(User, V, TD);
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// If the recursive simplification ended up revisiting and deleting 'From'
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// then we're done.
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if (FromHandle == 0)
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return;
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}
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}
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From->eraseFromParent();
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}
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