[PATCH] [analyzer] Refactor conditional expression evaluating code
Manuel Klimek
klimek at google.com
Wed Aug 14 21:06:31 PDT 2013
On Thu, Aug 15, 2013 at 2:12 AM, Ted Kremenek <kremenek at apple.com> wrote:
> Hi Pavel,
>
> Sorry for not getting to this sooner. It looks like Jordan has been
> carefully reviewing this. Since I’m the author of this code it’s probably
> worth me taking a pass of your patch as well. I’ll try and take a careful
> look at it tonight and cross-reference my feedback with any Jordan has
> already provided.
>
> Can you provide some context on what problem you are trying to solve?
> Your original patch includes no test case which indicates the behavioral
> change (if any) you are trying to capture. Although your later email
> indicates you don’t expect a behavioral change, I also don’t understand the
> motivation behind the patch. The second patch includes a test case, but I
> doubt it is for the original motivation of this patch. Is this purely a
> functional refactoring, or something else? I can better evaluate this
> change if I understand the motivation. Otherwise I cannot see approving
> this change unless there is some genuine benefit as it touches some fairly
> sensitive parts of the analyzer. Specifically, what problem are you trying
> to solve?
>
See http://llvm-reviews.chandlerc.com/D1259 (WIP Fix for temporary
destructors in conditionals), which this patch afaik enables.
>
> Thanks,
> Ted
>
> On Aug 9, 2013, at 5:39 AM, Pavel Labath <labath at google.com> wrote:
>
> Hi jordan_rose,
>
> Instead of digging through the ExplodedGraph, to figure out which edge
> brought
> us here, I compute the value of conditional expression by looking at the
> sub-expression values.
>
> To do this, I needed to change the liveness algorithm a bit -- now, the
> full
> conditional expression depends on all atomic sub-expressions, not only the
> outermost ones.
>
> http://llvm-reviews.chandlerc.com/D1340
>
> Files:
> lib/Analysis/LiveVariables.cpp
> lib/StaticAnalyzer/Core/ExprEngineC.cpp
>
> Index: lib/Analysis/LiveVariables.cpp
> ===================================================================
> --- lib/Analysis/LiveVariables.cpp
> +++ lib/Analysis/LiveVariables.cpp
> @@ -212,6 +212,8 @@
> LiveVariables::LivenessValues &val;
> LiveVariables::Observer *observer;
> const CFGBlock *currentBlock;
> +
> + void MarkLogicalOpsLive(const Expr *E);
> public:
> TransferFunctions(LiveVariablesImpl &im,
> LiveVariables::LivenessValues &Val,
> @@ -368,9 +370,28 @@
> if (observer)
> observer->observerKill(DR);
> }
> + } else {
> + // All logical sub-operations are live until we reach the outermost
> + // operator. Static analyzer relies on this behaviour.
> + MarkLogicalOpsLive(B);
> }
> }
>
> +void TransferFunctions::MarkLogicalOpsLive(const Expr *E) {
> + const BinaryOperator *BO = dyn_cast<BinaryOperator>(E);
> + if (!BO || !BO->isLogicalOp())
> + return;
> +
> + const Expr *LHS = BO->getLHS()->IgnoreParens();
> + const Expr *RHS = BO->getRHS()->IgnoreParens();
> +
> + val.liveStmts = LV.SSetFact.add(val.liveStmts, LHS);
> + val.liveStmts = LV.SSetFact.add(val.liveStmts, RHS);
> +
> + MarkLogicalOpsLive(LHS);
> + MarkLogicalOpsLive(RHS);
> +}
> +
> void TransferFunctions::VisitBlockExpr(BlockExpr *BE) {
> AnalysisDeclContext::referenced_decls_iterator I, E;
> llvm::tie(I, E) =
> Index: lib/StaticAnalyzer/Core/ExprEngineC.cpp
> ===================================================================
> --- lib/StaticAnalyzer/Core/ExprEngineC.cpp
> +++ lib/StaticAnalyzer/Core/ExprEngineC.cpp
> @@ -501,72 +501,64 @@
> }
> }
>
> +static ProgramStateRef EvaluateLogicalExpression(const Expr *E,
> + const LocationContext
> *LC,
> + ProgramStateRef State) {
> + SVal X = State->getSVal(E, LC);
> + if (! X.isUnknown())
> + return State;
> +
> + const BinaryOperator *B =
> cast_or_null<BinaryOperator>(E->IgnoreParens());
> + if (!B || (B->getOpcode() != BO_LAnd && B->getOpcode() != BO_LOr))
> + return State;
> +
> + State = EvaluateLogicalExpression(B->getLHS(), LC, State);
> + X = State->getSVal(B->getLHS(), LC);
> + QualType XType = B->getLHS()->getType();
> + assert(!X.isUnknownOrUndef() && "Value should have already been
> computed.");
> +
> + ProgramStateRef StTrue, StFalse;
> + llvm::tie(StTrue, StFalse) =
> State->assume(X.castAs<DefinedOrUnknownSVal>());
> +
> + assert(!StTrue != !StFalse && "Value should be evaluate to true or
> false.");
> + if(!StFalse == (B->getOpcode() == BO_LAnd)) {
> + // LHS not sufficient, we need to check RHS as well
> + State = EvaluateLogicalExpression(B->getRHS(), LC, State);
> + X = State->getSVal(B->getRHS(), LC);
> + XType = B->getRHS()->getType();
> + }
> +
> + SValBuilder &SVB = State->getStateManager().getSValBuilder();
> + return State->BindExpr(E, LC, SVB.evalCast(X, B->getType(), XType));
> +}
> +
> void ExprEngine::VisitLogicalExpr(const BinaryOperator* B, ExplodedNode
> *Pred,
> ExplodedNodeSet &Dst) {
> assert(B->getOpcode() == BO_LAnd ||
> B->getOpcode() == BO_LOr);
>
> StmtNodeBuilder Bldr(Pred, Dst, *currBldrCtx);
> ProgramStateRef state = Pred->getState();
>
> - ExplodedNode *N = Pred;
> - while (!N->getLocation().getAs<BlockEntrance>()) {
> - ProgramPoint P = N->getLocation();
> - assert(P.getAs<PreStmt>()|| P.getAs<PreStmtPurgeDeadSymbols>());
> - (void) P;
> - assert(N->pred_size() == 1);
> - N = *N->pred_begin();
> - }
> - assert(N->pred_size() == 1);
> - N = *N->pred_begin();
> - BlockEdge BE = N->getLocation().castAs<BlockEdge>();
> - SVal X;
> -
> - // Determine the value of the expression by introspecting how we
> - // got this location in the CFG. This requires looking at the previous
> - // block we were in and what kind of control-flow transfer was involved.
> - const CFGBlock *SrcBlock = BE.getSrc();
> - // The only terminator (if there is one) that makes sense is a logical
> op.
> - CFGTerminator T = SrcBlock->getTerminator();
> - if (const BinaryOperator *Term =
> cast_or_null<BinaryOperator>(T.getStmt())) {
> - (void) Term;
> - assert(Term->isLogicalOp());
> - assert(SrcBlock->succ_size() == 2);
> - // Did we take the true or false branch?
> - unsigned constant = (*SrcBlock->succ_begin() == BE.getDst()) ? 1 : 0;
> - X = svalBuilder.makeIntVal(constant, B->getType());
> - }
> - else {
> - // If there is no terminator, by construction the last statement
> - // in SrcBlock is the value of the enclosing expression.
> - // However, we still need to constrain that value to be 0 or 1.
> - assert(!SrcBlock->empty());
> - CFGStmt Elem = SrcBlock->rbegin()->castAs<CFGStmt>();
> - const Expr *RHS = cast<Expr>(Elem.getStmt());
> - SVal RHSVal = N->getState()->getSVal(RHS, Pred->getLocationContext());
> -
> - if (RHSVal.isUndef()) {
> - X = RHSVal;
> - } else {
> - DefinedOrUnknownSVal DefinedRHS =
> RHSVal.castAs<DefinedOrUnknownSVal>();
> - ProgramStateRef StTrue, StFalse;
> - llvm::tie(StTrue, StFalse) = N->getState()->assume(DefinedRHS);
> - if (StTrue) {
> - if (StFalse) {
> - // We can't constrain the value to 0 or 1.
> - // The best we can do is a cast.
> - X = getSValBuilder().evalCast(RHSVal, B->getType(),
> RHS->getType());
> - } else {
> - // The value is known to be true.
> - X = getSValBuilder().makeIntVal(1, B->getType());
> - }
> - } else {
> - // The value is known to be false.
> - assert(StFalse && "Infeasible path!");
> - X = getSValBuilder().makeIntVal(0, B->getType());
> + state = EvaluateLogicalExpression(B, Pred->getLocationContext(), state);
> + SVal X = state->getSVal(B, Pred->getLocationContext());
> +
> + if (!X.isUndef()) {
> + DefinedOrUnknownSVal DefinedRHS = X.castAs<DefinedOrUnknownSVal>();
> + ProgramStateRef StTrue, StFalse;
> + llvm::tie(StTrue, StFalse) = state->assume(DefinedRHS);
> + if (StTrue) {
> + if (!StFalse) {
> + // The value is known to be true.
> + X = getSValBuilder().makeIntVal(1, B->getType());
> }
> + } else {
> + // The value is known to be false.
> + assert(StFalse && "Infeasible path!");
> + X = getSValBuilder().makeIntVal(0, B->getType());
> }
> }
> +
> Bldr.generateNode(B, Pred, state->BindExpr(B,
> Pred->getLocationContext(), X));
> }
> <D1340.1.patch>_______________________________________________
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