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[CFG] Cache boolean evaluations of expressions to avoid multiple re-evaluations 

during construction of branches for chained logical operators.

This makes -fsyntax-only for test/Sema/many-logical-ops.c about 32x times faster.

With measuring SemaExpr.cpp I see differences below the noise level.

llvm-svn: 153297
This commit is contained in:
Argyrios Kyrtzidis 2012-03-23 00:59:17 +00:00
parent c7c66e4db4
commit 5f172a3301
1 changed files with 66 additions and 7 deletions
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73
clang/lib/Analysis/CFG.cpp
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@ -286,6 +286,10 @@ class CFGBuilder {
CFG::BuildOptions::ForcedBlkExprs::value_type *cachedEntry;
const Stmt *lastLookup;
// Caches boolean evaluations of expressions to avoid multiple re-evaluations
// during construction of branches for chained logical operators.
llvm::DenseMap<Expr *, TryResult> CachedBoolEvals;
public:
explicit CFGBuilder(ASTContext *astContext,
const CFG::BuildOptions &buildOpts)
@ -439,12 +443,65 @@ private:
/// tryEvaluateBool - Try and evaluate the Stmt and return 0 or 1
/// if we can evaluate to a known value, otherwise return -1.
TryResult tryEvaluateBool(Expr *S) {
bool Result;
if (!BuildOpts.PruneTriviallyFalseEdges ||
S->isTypeDependent() || S->isValueDependent() ||
!S->EvaluateAsBooleanCondition(Result, *Context))
S->isTypeDependent() || S->isValueDependent())
return TryResult();
return Result;
if (BinaryOperator *Bop = dyn_cast<BinaryOperator>(S)) {
if (Bop->isLogicalOp()) {
// Check the cache first.
typedef llvm::DenseMap<Expr *, TryResult>::iterator eval_iterator;
eval_iterator I;
bool Inserted;
llvm::tie(I, Inserted) =
CachedBoolEvals.insert(std::make_pair(S, TryResult()));
if (!Inserted)
return I->second; // already in map;
return (I->second = evaluateAsBooleanConditionNoCache(S));
}
}
return evaluateAsBooleanConditionNoCache(S);
}
/// \brief Evaluate as boolean \param E without using the cache.
TryResult evaluateAsBooleanConditionNoCache(Expr *E) {
if (BinaryOperator *Bop = dyn_cast<BinaryOperator>(E)) {
if (Bop->isLogicalOp()) {
TryResult LHS = tryEvaluateBool(Bop->getLHS());
if (LHS.isKnown()) {
// We were able to evaluate the LHS, see if we can get away with not
// evaluating the RHS: 0 && X -> 0, 1 || X -> 1
if (LHS.isTrue() == (Bop->getOpcode() == BO_LOr))
return LHS.isTrue();
TryResult RHS = tryEvaluateBool(Bop->getRHS());
if (RHS.isKnown()) {
if (Bop->getOpcode() == BO_LOr)
return LHS.isTrue() || RHS.isTrue();
else
return LHS.isTrue() && RHS.isTrue();
}
} else {
TryResult RHS = tryEvaluateBool(Bop->getRHS());
if (RHS.isKnown()) {
// We can't evaluate the LHS; however, sometimes the result
// is determined by the RHS: X && 0 -> 0, X || 1 -> 1.
if (RHS.isTrue() == (Bop->getOpcode() == BO_LOr))
return RHS.isTrue();
}
}
return TryResult();
}
}
bool Result;
if (E->EvaluateAsBooleanCondition(Result, *Context))
return Result;
return TryResult();
}
};
@ -1127,6 +1184,10 @@ CFGBlock *CFGBuilder::VisitBinaryOperator(BinaryOperator *B,
RHSBlock = createBlock();
}
// Generate the blocks for evaluating the LHS.
Block = LHSBlock;
CFGBlock *EntryLHSBlock = addStmt(B->getLHS());
// See if this is a known constant.
TryResult KnownVal = tryEvaluateBool(B->getLHS());
if (KnownVal.isKnown() && (B->getOpcode() == BO_LOr))
@ -1142,9 +1203,7 @@ CFGBlock *CFGBuilder::VisitBinaryOperator(BinaryOperator *B,
addSuccessor(LHSBlock, KnownVal.isTrue() ? NULL : ConfluenceBlock);
}
// Generate the blocks for evaluating the LHS.
Block = LHSBlock;
return addStmt(B->getLHS());
return EntryLHSBlock;
}
if (B->getOpcode() == BO_Comma) { // ,