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//=- LiveVariables.cpp - Live Variable Analysis for Source CFGs -*- 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 Live Variables analysis for source-level CFGs.
//
//===----------------------------------------------------------------------===//
#include "clang/Analysis/Analyses/LiveVariables.h"
#include "clang/Basic/SourceManager.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Expr.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/Visitors/CFGRecStmtDeclVisitor.h"
#include "clang/Analysis/FlowSensitive/DataflowSolver.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/raw_ostream.h"
using namespace clang;
//===----------------------------------------------------------------------===//
// Useful constants.
//===----------------------------------------------------------------------===//
static const bool Alive = true;
static const bool Dead = false;
//===----------------------------------------------------------------------===//
// Dataflow initialization logic.
//===----------------------------------------------------------------------===//
namespace {
class VISIBILITY_HIDDEN RegisterDecls
: public CFGRecStmtDeclVisitor<RegisterDecls> {
LiveVariables::AnalysisDataTy& AD;
typedef llvm::SmallVector<VarDecl*, 20> AlwaysLiveTy;
AlwaysLiveTy AlwaysLive;
public:
RegisterDecls(LiveVariables::AnalysisDataTy& ad) : AD(ad) {}
~RegisterDecls() {
AD.AlwaysLive.resetValues(AD);
for (AlwaysLiveTy::iterator I = AlwaysLive.begin(), E = AlwaysLive.end();
I != E; ++ I)
AD.AlwaysLive(*I, AD) = Alive;
}
void VisitImplicitParamDecl(ImplicitParamDecl* IPD) {
// Register the VarDecl for tracking.
AD.Register(IPD);
}
void VisitVarDecl(VarDecl* VD) {
// Register the VarDecl for tracking.
AD.Register(VD);
// Does the variable have global storage? If so, it is always live.
if (VD->hasGlobalStorage())
AlwaysLive.push_back(VD);
}
CFG& getCFG() { return AD.getCFG(); }
};
} // end anonymous namespace
LiveVariables::LiveVariables(ASTContext& Ctx, CFG& cfg) {
// Register all referenced VarDecls.
getAnalysisData().setCFG(cfg);
getAnalysisData().setContext(Ctx);
RegisterDecls R(getAnalysisData());
cfg.VisitBlockStmts(R);
}
//===----------------------------------------------------------------------===//
// Transfer functions.
//===----------------------------------------------------------------------===//
namespace {
class VISIBILITY_HIDDEN TransferFuncs : public CFGRecStmtVisitor<TransferFuncs>{
LiveVariables::AnalysisDataTy& AD;
LiveVariables::ValTy LiveState;
public:
TransferFuncs(LiveVariables::AnalysisDataTy& ad) : AD(ad) {}
LiveVariables::ValTy& getVal() { return LiveState; }
CFG& getCFG() { return AD.getCFG(); }
void VisitDeclRefExpr(DeclRefExpr* DR);
void VisitBinaryOperator(BinaryOperator* B);
void VisitAssign(BinaryOperator* B);
void VisitDeclStmt(DeclStmt* DS);
void BlockStmt_VisitObjCForCollectionStmt(ObjCForCollectionStmt* S);
void VisitUnaryOperator(UnaryOperator* U);
void Visit(Stmt *S);
void VisitTerminator(CFGBlock* B);
void SetTopValue(LiveVariables::ValTy& V) {
V = AD.AlwaysLive;
}
};
void TransferFuncs::Visit(Stmt *S) {
if (S == getCurrentBlkStmt()) {
if (AD.Observer)
AD.Observer->ObserveStmt(S,AD,LiveState);
if (getCFG().isBlkExpr(S)) LiveState(S,AD) = Dead;
StmtVisitor<TransferFuncs,void>::Visit(S);
}
else if (!getCFG().isBlkExpr(S)) {
if (AD.Observer)
AD.Observer->ObserveStmt(S,AD,LiveState);
StmtVisitor<TransferFuncs,void>::Visit(S);
}
else {
// For block-level expressions, mark that they are live.
LiveState(S,AD) = Alive;
}
}
void TransferFuncs::VisitTerminator(CFGBlock* B) {
const Stmt* E = B->getTerminatorCondition();
if (!E)
return;
assert (getCFG().isBlkExpr(E));
LiveState(E, AD) = Alive;
}
void TransferFuncs::VisitDeclRefExpr(DeclRefExpr* DR) {
if (VarDecl* V = dyn_cast<VarDecl>(DR->getDecl()))
LiveState(V,AD) = Alive;
}
void TransferFuncs::VisitBinaryOperator(BinaryOperator* B) {
if (B->isAssignmentOp()) VisitAssign(B);
else VisitStmt(B);
}
void
TransferFuncs::BlockStmt_VisitObjCForCollectionStmt(ObjCForCollectionStmt* S) {
// This is a block-level expression. Its value is 'dead' before this point.
LiveState(S, AD) = Dead;
// This represents a 'use' of the collection.
Visit(S->getCollection());
// This represents a 'kill' for the variable.
Stmt* Element = S->getElement();
DeclRefExpr* DR = 0;
VarDecl* VD = 0;
if (DeclStmt* DS = dyn_cast<DeclStmt>(Element))
VD = cast<VarDecl>(DS->getSingleDecl());
else {
Expr* ElemExpr = cast<Expr>(Element)->IgnoreParens();
if ((DR = dyn_cast<DeclRefExpr>(ElemExpr)))
VD = cast<VarDecl>(DR->getDecl());
else {
Visit(ElemExpr);
return;
}
}
if (VD) {
LiveState(VD, AD) = Dead;
if (AD.Observer && DR) { AD.Observer->ObserverKill(DR); }
}
}
void TransferFuncs::VisitUnaryOperator(UnaryOperator* U) {
Expr *E = U->getSubExpr();
switch (U->getOpcode()) {
case UnaryOperator::PostInc:
case UnaryOperator::PostDec:
case UnaryOperator::PreInc:
case UnaryOperator::PreDec:
// Walk through the subexpressions, blasting through ParenExprs
// until we either find a DeclRefExpr or some non-DeclRefExpr
// expression.
if (DeclRefExpr* DR = dyn_cast<DeclRefExpr>(E->IgnoreParens()))
if (VarDecl* VD = dyn_cast<VarDecl>(DR->getDecl())) {
// Treat the --/++ operator as a kill.
if (AD.Observer) { AD.Observer->ObserverKill(DR); }
LiveState(VD, AD) = Alive;
return VisitDeclRefExpr(DR);
}
// Fall-through.
default:
return Visit(E);
}
}
void TransferFuncs::VisitAssign(BinaryOperator* B) {
Expr* LHS = B->getLHS();
// Assigning to a variable?
if (DeclRefExpr* DR = dyn_cast<DeclRefExpr>(LHS->IgnoreParens())) {
// Update liveness inforamtion.
unsigned bit = AD.getIdx(DR->getDecl());
LiveState.getDeclBit(bit) = Dead | AD.AlwaysLive.getDeclBit(bit);
if (AD.Observer) { AD.Observer->ObserverKill(DR); }
// Handle things like +=, etc., which also generate "uses"
// of a variable. Do this just by visiting the subexpression.
if (B->getOpcode() != BinaryOperator::Assign)
VisitDeclRefExpr(DR);
}
else // Not assigning to a variable. Process LHS as usual.
Visit(LHS);
Visit(B->getRHS());
}
void TransferFuncs::VisitDeclStmt(DeclStmt* DS) {
// Declarations effectively "kill" a variable since they cannot
// possibly be live before they are declared.
for (DeclStmt::decl_iterator DI=DS->decl_begin(), DE = DS->decl_end();
DI != DE; ++DI)
if (VarDecl* VD = dyn_cast<VarDecl>(*DI)) {
// The initializer is evaluated after the variable comes into scope.
// Since this is a reverse dataflow analysis, we must evaluate the
// transfer function for this expression first.
if (Expr* Init = VD->getInit())
Visit(Init);
if (const VariableArrayType* VT =
AD.getContext().getAsVariableArrayType(VD->getType())) {
StmtIterator I(const_cast<VariableArrayType*>(VT));
StmtIterator E;
for (; I != E; ++I) Visit(*I);
}
// Update liveness information by killing the VarDecl.
unsigned bit = AD.getIdx(VD);
LiveState.getDeclBit(bit) = Dead | AD.AlwaysLive.getDeclBit(bit);
}
}
} // end anonymous namespace
//===----------------------------------------------------------------------===//
// Merge operator: if something is live on any successor block, it is live
// in the current block (a set union).
//===----------------------------------------------------------------------===//
namespace {
struct Merge {
typedef StmtDeclBitVector_Types::ValTy ValTy;
void operator()(ValTy& Dst, const ValTy& Src) {
Dst.OrDeclBits(Src);
Dst.OrBlkExprBits(Src);
}
};
typedef DataflowSolver<LiveVariables, TransferFuncs, Merge> Solver;
} // end anonymous namespace
//===----------------------------------------------------------------------===//
// External interface to run Liveness analysis.
//===----------------------------------------------------------------------===//
void LiveVariables::runOnCFG(CFG& cfg) {
Solver S(*this);
S.runOnCFG(cfg);
}
void LiveVariables::runOnAllBlocks(const CFG& cfg,
LiveVariables::ObserverTy* Obs,
bool recordStmtValues) {
Solver S(*this);
ObserverTy* OldObserver = getAnalysisData().Observer;
getAnalysisData().Observer = Obs;
S.runOnAllBlocks(cfg, recordStmtValues);
getAnalysisData().Observer = OldObserver;
}
//===----------------------------------------------------------------------===//
// liveness queries
//
bool LiveVariables::isLive(const CFGBlock* B, const VarDecl* D) const {
DeclBitVector_Types::Idx i = getAnalysisData().getIdx(D);
return i.isValid() ? getBlockData(B).getBit(i) : false;
}
bool LiveVariables::isLive(const ValTy& Live, const VarDecl* D) const {
DeclBitVector_Types::Idx i = getAnalysisData().getIdx(D);
return i.isValid() ? Live.getBit(i) : false;
}
bool LiveVariables::isLive(const Stmt* Loc, const Stmt* StmtVal) const {
return getStmtData(Loc)(StmtVal,getAnalysisData());
}
bool LiveVariables::isLive(const Stmt* Loc, const VarDecl* D) const {
return getStmtData(Loc)(D,getAnalysisData());
}
//===----------------------------------------------------------------------===//
// printing liveness state for debugging
//
void LiveVariables::dumpLiveness(const ValTy& V, SourceManager& SM) const {
const AnalysisDataTy& AD = getAnalysisData();
for (AnalysisDataTy::decl_iterator I = AD.begin_decl(),
E = AD.end_decl(); I!=E; ++I)
if (V.getDeclBit(I->second)) {
llvm::errs() << " " << I->first->getIdentifier()->getName() << " <";
I->first->getLocation().dump(SM);
llvm::errs() << ">\n";
}
}
void LiveVariables::dumpBlockLiveness(SourceManager& M) const {
for (BlockDataMapTy::iterator I = getBlockDataMap().begin(),
E = getBlockDataMap().end(); I!=E; ++I) {
llvm::errs() << "\n[ B" << I->first->getBlockID()
<< " (live variables at block exit) ]\n";
dumpLiveness(I->second,M);
}
llvm::errs() << "\n";
}
|