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202 lines
7.6 KiB
C++
202 lines
7.6 KiB
C++
//===- ValueNumbering.cpp - Value #'ing Implementation ----------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source 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 non-abstract Value Numbering methods as well as a
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// default implementation for the analysis group.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/Passes.h"
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#include "llvm/Analysis/ValueNumbering.h"
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#include "llvm/Support/InstVisitor.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Instructions.h"
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#include "llvm/Pass.h"
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#include "llvm/Type.h"
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using namespace llvm;
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// Register the ValueNumbering interface, providing a nice name to refer to.
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static RegisterAnalysisGroup<ValueNumbering> X("Value Numbering");
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/// ValueNumbering destructor: DO NOT move this to the header file for
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/// ValueNumbering or else clients of the ValueNumbering class may not depend on
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/// the ValueNumbering.o file in the current .a file, causing alias analysis
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/// support to not be included in the tool correctly!
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///
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ValueNumbering::~ValueNumbering() {}
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//===----------------------------------------------------------------------===//
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// Basic ValueNumbering Pass Implementation
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//===----------------------------------------------------------------------===//
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//
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// Because of the way .a files work, the implementation of the BasicVN class
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// MUST be in the ValueNumbering file itself, or else we run the risk of
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// ValueNumbering being used, but the default implementation not being linked
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// into the tool that uses it. As such, we register and implement the class
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// here.
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//
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namespace {
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/// BasicVN - This class is the default implementation of the ValueNumbering
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/// interface. It walks the SSA def-use chains to trivially identify
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/// lexically identical expressions. This does not require any ahead of time
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/// analysis, so it is a very fast default implementation.
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///
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struct BasicVN : public ImmutablePass, public ValueNumbering {
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/// getEqualNumberNodes - Return nodes with the same value number as the
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/// specified Value. This fills in the argument vector with any equal
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/// values.
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///
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/// This is where our implementation is.
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///
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virtual void getEqualNumberNodes(Value *V1,
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std::vector<Value*> &RetVals) const;
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};
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// Register this pass...
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RegisterOpt<BasicVN>
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X("basicvn", "Basic Value Numbering (default GVN impl)");
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// Declare that we implement the ValueNumbering interface
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RegisterAnalysisGroup<ValueNumbering, BasicVN, true> Y;
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/// BVNImpl - Implement BasicVN in terms of a visitor class that
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/// handles the different types of instructions as appropriate.
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///
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struct BVNImpl : public InstVisitor<BVNImpl> {
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std::vector<Value*> &RetVals;
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BVNImpl(std::vector<Value*> &RV) : RetVals(RV) {}
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void handleBinaryInst(Instruction &I);
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void visitBinaryOperator(BinaryOperator &I) {
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handleBinaryInst((Instruction&)I);
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}
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void visitGetElementPtrInst(GetElementPtrInst &I);
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void visitCastInst(CastInst &I);
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void visitShiftInst(ShiftInst &I) { handleBinaryInst((Instruction&)I); }
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void visitInstruction(Instruction &) {
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// Cannot value number calls or terminator instructions...
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}
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};
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}
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ImmutablePass *llvm::createBasicVNPass() { return new BasicVN(); }
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// getEqualNumberNodes - Return nodes with the same value number as the
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// specified Value. This fills in the argument vector with any equal values.
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//
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void BasicVN::getEqualNumberNodes(Value *V, std::vector<Value*> &RetVals) const{
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assert(V->getType() != Type::VoidTy &&
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"Can only value number non-void values!");
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// We can only handle the case where I is an instruction!
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if (Instruction *I = dyn_cast<Instruction>(V))
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BVNImpl(RetVals).visit(I);
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}
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void BVNImpl::visitCastInst(CastInst &CI) {
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Instruction &I = (Instruction&)CI;
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Value *Op = I.getOperand(0);
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Function *F = I.getParent()->getParent();
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for (Value::use_iterator UI = Op->use_begin(), UE = Op->use_end();
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UI != UE; ++UI)
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if (CastInst *Other = dyn_cast<CastInst>(*UI))
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// Check that the types are the same, since this code handles casts...
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if (Other->getType() == I.getType() &&
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// Is it embedded in the same function? (This could be false if LHS
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// is a constant or global!)
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Other->getParent()->getParent() == F &&
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// Check to see if this new cast is not I.
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Other != &I) {
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// These instructions are identical. Add to list...
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RetVals.push_back(Other);
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}
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}
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// isIdenticalBinaryInst - Return true if the two binary instructions are
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// identical.
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//
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static inline bool isIdenticalBinaryInst(const Instruction &I1,
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const Instruction *I2) {
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// Is it embedded in the same function? (This could be false if LHS
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// is a constant or global!)
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if (I1.getOpcode() != I2->getOpcode() ||
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I1.getParent()->getParent() != I2->getParent()->getParent())
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return false;
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// They are identical if both operands are the same!
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if (I1.getOperand(0) == I2->getOperand(0) &&
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I1.getOperand(1) == I2->getOperand(1))
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return true;
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// If the instruction is commutative, the instruction can match if the
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// operands are swapped!
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//
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if ((I1.getOperand(0) == I2->getOperand(1) &&
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I1.getOperand(1) == I2->getOperand(0)) &&
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I1.isCommutative())
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return true;
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return false;
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}
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void BVNImpl::handleBinaryInst(Instruction &I) {
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Value *LHS = I.getOperand(0);
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for (Value::use_iterator UI = LHS->use_begin(), UE = LHS->use_end();
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UI != UE; ++UI)
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if (Instruction *Other = dyn_cast<Instruction>(*UI))
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// Check to see if this new binary operator is not I, but same operand...
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if (Other != &I && isIdenticalBinaryInst(I, Other)) {
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// These instructions are identical. Handle the situation.
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RetVals.push_back(Other);
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}
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}
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// IdenticalComplexInst - Return true if the two instructions are the same, by
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// using a brute force comparison. This is useful for instructions with an
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// arbitrary number of arguments.
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//
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static inline bool IdenticalComplexInst(const Instruction *I1,
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const Instruction *I2) {
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assert(I1->getOpcode() == I2->getOpcode());
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// Equal if they are in the same function...
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return I1->getParent()->getParent() == I2->getParent()->getParent() &&
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// And return the same type...
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I1->getType() == I2->getType() &&
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// And have the same number of operands...
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I1->getNumOperands() == I2->getNumOperands() &&
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// And all of the operands are equal.
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std::equal(I1->op_begin(), I1->op_end(), I2->op_begin());
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}
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void BVNImpl::visitGetElementPtrInst(GetElementPtrInst &I) {
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Value *Op = I.getOperand(0);
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// Try to pick a local operand if possible instead of a constant or a global
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// that might have a lot of uses.
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for (unsigned i = 1, e = I.getNumOperands(); i != e; ++i)
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if (isa<Instruction>(I.getOperand(i)) || isa<Argument>(I.getOperand(i))) {
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Op = I.getOperand(i);
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break;
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}
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for (Value::use_iterator UI = Op->use_begin(), UE = Op->use_end();
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UI != UE; ++UI)
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if (GetElementPtrInst *Other = dyn_cast<GetElementPtrInst>(*UI))
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// Check to see if this new getelementptr is not I, but same operand...
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if (Other != &I && IdenticalComplexInst(&I, Other)) {
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// These instructions are identical. Handle the situation.
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RetVals.push_back(Other);
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}
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}
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void llvm::BasicValueNumberingStub() { }
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