llvm-6502/lib/Analysis/ValueNumbering.cpp
Matthijs Kooijman 845f524c25 Update comments and documentation to reflect that GCSE and ValueNumbering are
deprecated by the GVN and GVNPRE passes.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51983 91177308-0d34-0410-b5e6-96231b3b80d8
2008-06-05 07:55:49 +00:00

287 lines
11 KiB
C++

//===- ValueNumbering.cpp - Value #'ing Implementation ----------*- C++ -*-===//
//
// 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 non-abstract Value Numbering methods as well as a
// default implementation for the analysis group.
//
// The ValueNumbering analysis pass is mostly deprecated. It is only used by the
// Global Common Subexpression Elimination pass, which is deprecated by the
// Global Value Numbering pass (which does its value numbering on its own).
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/ValueNumbering.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/BasicBlock.h"
#include "llvm/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Type.h"
#include "llvm/Support/Compiler.h"
using namespace llvm;
char ValueNumbering::ID = 0;
// Register the ValueNumbering interface, providing a nice name to refer to.
static RegisterAnalysisGroup<ValueNumbering> V("Value Numbering");
/// ValueNumbering destructor: DO NOT move this to the header file for
/// ValueNumbering or else clients of the ValueNumbering class may not depend on
/// the ValueNumbering.o file in the current .a file, causing alias analysis
/// support to not be included in the tool correctly!
///
ValueNumbering::~ValueNumbering() {}
//===----------------------------------------------------------------------===//
// Basic ValueNumbering Pass Implementation
//===----------------------------------------------------------------------===//
//
// Because of the way .a files work, the implementation of the BasicVN class
// MUST be in the ValueNumbering file itself, or else we run the risk of
// ValueNumbering being used, but the default implementation not being linked
// into the tool that uses it. As such, we register and implement the class
// here.
//
namespace {
/// BasicVN - This class is the default implementation of the ValueNumbering
/// interface. It walks the SSA def-use chains to trivially identify
/// lexically identical expressions. This does not require any ahead of time
/// analysis, so it is a very fast default implementation.
///
struct VISIBILITY_HIDDEN BasicVN
: public ImmutablePass, public ValueNumbering {
static char ID; // Class identification, replacement for typeinfo
BasicVN() : ImmutablePass((intptr_t)&ID) {}
/// getEqualNumberNodes - Return nodes with the same value number as the
/// specified Value. This fills in the argument vector with any equal
/// values.
///
/// This is where our implementation is.
///
virtual void getEqualNumberNodes(Value *V1,
std::vector<Value*> &RetVals) const;
};
}
char BasicVN::ID = 0;
// Register this pass...
static RegisterPass<BasicVN>
X("basicvn", "Basic Value Numbering (default GVN impl)", false, true);
// Declare that we implement the ValueNumbering interface
static RegisterAnalysisGroup<ValueNumbering, true> Y(X);
namespace {
/// BVNImpl - Implement BasicVN in terms of a visitor class that
/// handles the different types of instructions as appropriate.
///
struct VISIBILITY_HIDDEN BVNImpl : public InstVisitor<BVNImpl> {
std::vector<Value*> &RetVals;
explicit BVNImpl(std::vector<Value*> &RV) : RetVals(RV) {}
void visitCastInst(CastInst &I);
void visitGetElementPtrInst(GetElementPtrInst &I);
void visitCmpInst(CmpInst &I);
void handleBinaryInst(Instruction &I);
void visitBinaryOperator(Instruction &I) { handleBinaryInst(I); }
void visitShiftInst(Instruction &I) { handleBinaryInst(I); }
void visitExtractElementInst(Instruction &I) { handleBinaryInst(I); }
void handleTernaryInst(Instruction &I);
void visitSelectInst(Instruction &I) { handleTernaryInst(I); }
void visitInsertElementInst(Instruction &I) { handleTernaryInst(I); }
void visitShuffleVectorInst(Instruction &I) { handleTernaryInst(I); }
void visitInstruction(Instruction &) {
// Cannot value number calls or terminator instructions.
}
};
}
ImmutablePass *llvm::createBasicVNPass() { return new BasicVN(); }
// getEqualNumberNodes - Return nodes with the same value number as the
// specified Value. This fills in the argument vector with any equal values.
//
void BasicVN::getEqualNumberNodes(Value *V, std::vector<Value*> &RetVals) const{
assert(V->getType() != Type::VoidTy &&
"Can only value number non-void values!");
// We can only handle the case where I is an instruction!
if (Instruction *I = dyn_cast<Instruction>(V))
BVNImpl(RetVals).visit(I);
}
void BVNImpl::visitCastInst(CastInst &CI) {
Instruction &I = (Instruction&)CI;
Value *Op = I.getOperand(0);
Function *F = I.getParent()->getParent();
for (Value::use_iterator UI = Op->use_begin(), UE = Op->use_end();
UI != UE; ++UI)
if (CastInst *Other = dyn_cast<CastInst>(*UI))
// Check that the opcode is the same
if (Other->getOpcode() == Instruction::CastOps(I.getOpcode()) &&
// Check that the destination types are the same
Other->getType() == I.getType() &&
// Is it embedded in the same function? (This could be false if LHS
// is a constant or global!)
Other->getParent()->getParent() == F &&
// Check to see if this new cast is not I.
Other != &I) {
// These instructions are identical. Add to list...
RetVals.push_back(Other);
}
}
void BVNImpl::visitCmpInst(CmpInst &CI1) {
Value *LHS = CI1.getOperand(0);
for (Value::use_iterator UI = LHS->use_begin(), UE = LHS->use_end();
UI != UE; ++UI)
if (CmpInst *CI2 = dyn_cast<CmpInst>(*UI))
// Check to see if this compare instruction is not CI, but same opcode,
// same predicate, and in the same function.
if (CI2 != &CI1 && CI2->getOpcode() == CI1.getOpcode() &&
CI2->getPredicate() == CI1.getPredicate() &&
CI2->getParent()->getParent() == CI1.getParent()->getParent())
// If the operands are the same
if ((CI2->getOperand(0) == CI1.getOperand(0) &&
CI2->getOperand(1) == CI1.getOperand(1)) ||
// Or the compare is commutative and the operands are reversed
(CI1.isCommutative() &&
CI2->getOperand(0) == CI1.getOperand(1) &&
CI2->getOperand(1) == CI1.getOperand(0)))
// Then the instructiosn are identical, add to list.
RetVals.push_back(CI2);
}
// isIdenticalBinaryInst - Return true if the two binary instructions are
// identical.
//
static inline bool isIdenticalBinaryInst(const Instruction &I1,
const Instruction *I2) {
// Is it embedded in the same function? (This could be false if LHS
// is a constant or global!)
if (I1.getOpcode() != I2->getOpcode() ||
I1.getParent()->getParent() != I2->getParent()->getParent())
return false;
// If they are CmpInst instructions, check their predicates
if (CmpInst *CI1 = dyn_cast<CmpInst>(&const_cast<Instruction&>(I1)))
if (CI1->getPredicate() != cast<CmpInst>(I2)->getPredicate())
return false;
// They are identical if both operands are the same!
if (I1.getOperand(0) == I2->getOperand(0) &&
I1.getOperand(1) == I2->getOperand(1))
return true;
// If the instruction is commutative, the instruction can match if the
// operands are swapped!
//
if ((I1.getOperand(0) == I2->getOperand(1) &&
I1.getOperand(1) == I2->getOperand(0)) &&
I1.isCommutative())
return true;
return false;
}
// isIdenticalTernaryInst - Return true if the two ternary instructions are
// identical.
//
static inline bool isIdenticalTernaryInst(const Instruction &I1,
const Instruction *I2) {
// Is it embedded in the same function? (This could be false if LHS
// is a constant or global!)
if (I1.getParent()->getParent() != I2->getParent()->getParent())
return false;
// They are identical if all operands are the same!
return I1.getOperand(0) == I2->getOperand(0) &&
I1.getOperand(1) == I2->getOperand(1) &&
I1.getOperand(2) == I2->getOperand(2);
}
void BVNImpl::handleBinaryInst(Instruction &I) {
Value *LHS = I.getOperand(0);
for (Value::use_iterator UI = LHS->use_begin(), UE = LHS->use_end();
UI != UE; ++UI)
if (Instruction *Other = dyn_cast<Instruction>(*UI))
// Check to see if this new binary operator is not I, but same operand...
if (Other != &I && isIdenticalBinaryInst(I, Other)) {
// These instructions are identical. Handle the situation.
RetVals.push_back(Other);
}
}
// IdenticalComplexInst - Return true if the two instructions are the same, by
// using a brute force comparison. This is useful for instructions with an
// arbitrary number of arguments.
//
static inline bool IdenticalComplexInst(const Instruction *I1,
const Instruction *I2) {
assert(I1->getOpcode() == I2->getOpcode());
// Equal if they are in the same function...
return I1->getParent()->getParent() == I2->getParent()->getParent() &&
// And return the same type...
I1->getType() == I2->getType() &&
// And have the same number of operands...
I1->getNumOperands() == I2->getNumOperands() &&
// And all of the operands are equal.
std::equal(I1->op_begin(), I1->op_end(), I2->op_begin());
}
void BVNImpl::visitGetElementPtrInst(GetElementPtrInst &I) {
Value *Op = I.getOperand(0);
// Try to pick a local operand if possible instead of a constant or a global
// that might have a lot of uses.
for (User::op_iterator i = I.op_begin() + 1, e = I.op_end(); i != e; ++i)
if (isa<Instruction>(*i) || isa<Argument>(*i)) {
Op = *i;
break;
}
for (Value::use_iterator UI = Op->use_begin(), UE = Op->use_end();
UI != UE; ++UI)
if (GetElementPtrInst *Other = dyn_cast<GetElementPtrInst>(*UI))
// Check to see if this new getelementptr is not I, but same operand...
if (Other != &I && IdenticalComplexInst(&I, Other)) {
// These instructions are identical. Handle the situation.
RetVals.push_back(Other);
}
}
void BVNImpl::handleTernaryInst(Instruction &I) {
Value *Op0 = I.getOperand(0);
Instruction *OtherInst;
for (Value::use_iterator UI = Op0->use_begin(), UE = Op0->use_end();
UI != UE; ++UI)
if ((OtherInst = dyn_cast<Instruction>(*UI)) &&
OtherInst->getOpcode() == I.getOpcode()) {
// Check to see if this new select is not I, but has the same operands.
if (OtherInst != &I && isIdenticalTernaryInst(I, OtherInst)) {
// These instructions are identical. Handle the situation.
RetVals.push_back(OtherInst);
}
}
}
// Ensure that users of ValueNumbering.h will link with this file
DEFINING_FILE_FOR(BasicValueNumbering)