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[Sema] SequenceChecker: Fix handling of operator ||, && and ?:
The current handling of the operators ||, && and ?: has a number of false
positive and false negative. The issues for operator || and && are:
1. We need to add sequencing regions for the LHS and RHS as is done for the
comma operator. Not doing so causes false positives in expressions like
`((a++, false) || (a++, false))` (from PR39779, see PR22197 for another
example).
2. In the current implementation when the evaluation of the LHS fails, the RHS
is added to a worklist to be processed later. This results in false negatives
in expressions like `(a && a++) + a`.
Fix these issues by introducing sequencing regions for the LHS and RHS, and by
not deferring the visitation of the RHS.
The issues with the ternary operator ?: are similar, with the added twist that
we should not warn on expressions like `(x ? y += 1 : y += 2)` since exactly
one of the 2nd and 3rd expression is going to be evaluated, but we should still
warn on expressions like `(x ? y += 1 : y += 2) = y`.
Differential Revision: https://reviews.llvm.org/D57747
Reviewed By: rsmith
This commit is contained in:
Bruno Ricci
parent
b6eba31292
commit
8a571538df
@ -12779,6 +12779,9 @@ public:
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SmallVectorImpl<const Expr *> &WorkList)
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: Base(S.Context), SemaRef(S), Region(Tree.root()), WorkList(WorkList) {
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Visit(E);
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// Silence a -Wunused-private-field since WorkList is now unused.
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// TODO: Evaluate if it can be used, and if not remove it.
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(void)this->WorkList;
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}
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void VisitStmt(const Stmt *S) {
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@ -12908,64 +12911,126 @@ public:
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notePostMod(O, UO, UK_ModAsSideEffect);
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}
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/// Don't visit the RHS of '&&' or '||' if it might not be evaluated.
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void VisitBinLOr(const BinaryOperator *BO) {
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// The side-effects of the LHS of an '&&' are sequenced before the
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// value computation of the RHS, and hence before the value computation
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// of the '&&' itself, unless the LHS evaluates to zero. We treat them
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// as if they were unconditionally sequenced.
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// C++11 [expr.log.or]p2:
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// If the second expression is evaluated, every value computation and
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// side effect associated with the first expression is sequenced before
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// every value computation and side effect associated with the
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// second expression.
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SequenceTree::Seq LHSRegion = Tree.allocate(Region);
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SequenceTree::Seq RHSRegion = Tree.allocate(Region);
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SequenceTree::Seq OldRegion = Region;
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EvaluationTracker Eval(*this);
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{
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SequencedSubexpression Sequenced(*this);
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Region = LHSRegion;
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Visit(BO->getLHS());
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}
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bool Result;
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if (Eval.evaluate(BO->getLHS(), Result)) {
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if (!Result)
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Visit(BO->getRHS());
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} else {
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// Check for unsequenced operations in the RHS, treating it as an
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// entirely separate evaluation.
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//
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// FIXME: If there are operations in the RHS which are unsequenced
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// with respect to operations outside the RHS, and those operations
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// are unconditionally evaluated, diagnose them.
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WorkList.push_back(BO->getRHS());
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// C++11 [expr.log.or]p1:
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// [...] the second operand is not evaluated if the first operand
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// evaluates to true.
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bool EvalResult = false;
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bool EvalOK = Eval.evaluate(BO->getLHS(), EvalResult);
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bool ShouldVisitRHS = !EvalOK || (EvalOK && !EvalResult);
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if (ShouldVisitRHS) {
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Region = RHSRegion;
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Visit(BO->getRHS());
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}
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Region = OldRegion;
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Tree.merge(LHSRegion);
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Tree.merge(RHSRegion);
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}
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void VisitBinLAnd(const BinaryOperator *BO) {
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// C++11 [expr.log.and]p2:
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// If the second expression is evaluated, every value computation and
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// side effect associated with the first expression is sequenced before
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// every value computation and side effect associated with the
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// second expression.
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SequenceTree::Seq LHSRegion = Tree.allocate(Region);
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SequenceTree::Seq RHSRegion = Tree.allocate(Region);
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SequenceTree::Seq OldRegion = Region;
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EvaluationTracker Eval(*this);
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{
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SequencedSubexpression Sequenced(*this);
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Region = LHSRegion;
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Visit(BO->getLHS());
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}
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bool Result;
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if (Eval.evaluate(BO->getLHS(), Result)) {
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if (Result)
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Visit(BO->getRHS());
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} else {
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WorkList.push_back(BO->getRHS());
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// C++11 [expr.log.and]p1:
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// [...] the second operand is not evaluated if the first operand is false.
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bool EvalResult = false;
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bool EvalOK = Eval.evaluate(BO->getLHS(), EvalResult);
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bool ShouldVisitRHS = !EvalOK || (EvalOK && EvalResult);
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if (ShouldVisitRHS) {
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Region = RHSRegion;
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Visit(BO->getRHS());
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}
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Region = OldRegion;
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Tree.merge(LHSRegion);
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Tree.merge(RHSRegion);
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}
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// Only visit the condition, unless we can be sure which subexpression will
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// be chosen.
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void VisitAbstractConditionalOperator(const AbstractConditionalOperator *CO) {
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// C++11 [expr.cond]p1:
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// [...] Every value computation and side effect associated with the first
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// expression is sequenced before every value computation and side effect
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// associated with the second or third expression.
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SequenceTree::Seq ConditionRegion = Tree.allocate(Region);
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// No sequencing is specified between the true and false expression.
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// However since exactly one of both is going to be evaluated we can
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// consider them to be sequenced. This is needed to avoid warning on
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// something like "x ? y+= 1 : y += 2;" in the case where we will visit
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// both the true and false expressions because we can't evaluate x.
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// This will still allow us to detect an expression like (pre C++17)
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// "(x ? y += 1 : y += 2) = y".
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//
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// We don't wrap the visitation of the true and false expression with
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// SequencedSubexpression because we don't want to downgrade modifications
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// as side effect in the true and false expressions after the visition
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// is done. (for example in the expression "(x ? y++ : y++) + y" we should
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// not warn between the two "y++", but we should warn between the "y++"
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// and the "y".
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SequenceTree::Seq TrueRegion = Tree.allocate(Region);
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SequenceTree::Seq FalseRegion = Tree.allocate(Region);
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SequenceTree::Seq OldRegion = Region;
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EvaluationTracker Eval(*this);
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{
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SequencedSubexpression Sequenced(*this);
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Region = ConditionRegion;
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Visit(CO->getCond());
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}
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bool Result;
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if (Eval.evaluate(CO->getCond(), Result))
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Visit(Result ? CO->getTrueExpr() : CO->getFalseExpr());
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else {
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WorkList.push_back(CO->getTrueExpr());
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WorkList.push_back(CO->getFalseExpr());
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// C++11 [expr.cond]p1:
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// [...] The first expression is contextually converted to bool (Clause 4).
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// It is evaluated and if it is true, the result of the conditional
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// expression is the value of the second expression, otherwise that of the
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// third expression. Only one of the second and third expressions is
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// evaluated. [...]
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bool EvalResult = false;
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bool EvalOK = Eval.evaluate(CO->getCond(), EvalResult);
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bool ShouldVisitTrueExpr = !EvalOK || (EvalOK && EvalResult);
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bool ShouldVisitFalseExpr = !EvalOK || (EvalOK && !EvalResult);
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if (ShouldVisitTrueExpr) {
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Region = TrueRegion;
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Visit(CO->getTrueExpr());
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}
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if (ShouldVisitFalseExpr) {
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Region = FalseRegion;
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Visit(CO->getFalseExpr());
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}
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Region = OldRegion;
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Tree.merge(ConditionRegion);
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Tree.merge(TrueRegion);
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Tree.merge(FalseRegion);
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}
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void VisitCallExpr(const CallExpr *CE) {
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@ -40,18 +40,18 @@ void test() {
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A agg1 = { a++, a++ }; // expected-warning {{multiple unsequenced modifications}}
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A agg2 = { a++ + a, a++ }; // expected-warning {{unsequenced modification and access}}
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(xs[2] && (a = 0)) + a; // ok
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(xs[2] && (a = 0)) + a; // expected-warning {{unsequenced modification and access to 'a'}}
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(0 && (a = 0)) + a; // ok
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(1 && (a = 0)) + a; // expected-warning {{unsequenced modification and access}}
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(xs[3] || (a = 0)) + a; // ok
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(xs[3] || (a = 0)) + a; // expected-warning {{unsequenced modification and access to 'a'}}
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(0 || (a = 0)) + a; // expected-warning {{unsequenced modification and access}}
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(1 || (a = 0)) + a; // ok
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(xs[4] ? a : ++a) + a; // ok
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(xs[4] ? a : ++a) + a; // expected-warning {{unsequenced modification and access to 'a'}}
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(0 ? a : ++a) + a; // expected-warning {{unsequenced modification and access}}
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(1 ? a : ++a) + a; // ok
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(xs[5] ? ++a : ++a) + a; // FIXME: warn here
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(xs[5] ? ++a : ++a) + a; // expected-warning {{unsequenced modification and access to 'a'}}
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(++a, xs[6] ? ++a : 0) + a; // expected-warning {{unsequenced modification and access}}
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@ -73,10 +73,11 @@ void test() {
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// unconditional.
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a = a++ && f(a, a);
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// This has undefined behavior if a != 0. FIXME: We should diagnose this.
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(a && a++) + a;
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// This has undefined behavior if a != 0.
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(a && a++) + a; // expected-warning {{unsequenced modification and access to 'a'}}
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(xs[7] && ++a) * (!xs[7] && ++a); // ok
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// FIXME: Find a way to avoid warning here.
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(xs[7] && ++a) * (!xs[7] && ++a); // expected-warning {{multiple unsequenced modifications to 'a'}}
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xs[0] = (a = 1, a); // ok
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@ -4,6 +4,8 @@
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// RUN: -Wunsequenced -Wno-c++17-extensions -Wno-c++14-extensions %s
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int f(int, int = 0);
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int g1();
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int g2(int);
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struct A {
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int x, y;
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@ -79,24 +81,28 @@ void test() {
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A { ++a, a++ }.x + A { ++a, a++ }.y; // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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(xs[2] && (a = 0)) + a; // ok
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(xs[2] && (a = 0)) + a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(0 && (a = 0)) + a; // ok
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(1 && (a = 0)) + a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(xs[3] || (a = 0)) + a; // ok
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(xs[3] || (a = 0)) + a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(0 || (a = 0)) + a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(1 || (a = 0)) + a; // ok
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(xs[4] ? a : ++a) + a; // ok
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(xs[4] ? a : ++a) + a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(0 ? a : ++a) + a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(1 ? a : ++a) + a; // ok
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(0 ? a : a++) + a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(1 ? a : a++) + a; // ok
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(xs[5] ? ++a : ++a) + a; // FIXME: warn here
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(xs[5] ? ++a : ++a) + a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(++a, xs[6] ? ++a : 0) + a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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@ -122,10 +128,13 @@ void test() {
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// unconditional.
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a = a++ && f(a, a);
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// This has undefined behavior if a != 0. FIXME: We should diagnose this.
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(a && a++) + a;
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// This has undefined behavior if a != 0.
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(a && a++) + a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(xs[7] && ++a) * (!xs[7] && ++a); // ok
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// FIXME: Don't warn here.
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(xs[7] && ++a) * (!xs[7] && ++a); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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xs[0] = (a = 1, a); // ok
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(a -= 128) &= 128; // ok
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@ -135,13 +144,64 @@ void test() {
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// cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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xs[8] ? 0 : ++a + a++; // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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xs[8] ? ++a : a++; // ok
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xs[8] ? ++a : a++; // no-warning
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xs[8] ? a+=1 : a+= 2; // no-warning
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(xs[8] ? a+=1 : a+= 2) = a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// TODO cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(xs[8] ? a+=1 : a) = a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// TODO cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(xs[8] ? a : a+= 2) = a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// TODO cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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a = (xs[8] ? a+=1 : a+= 2); // no-warning
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a += (xs[8] ? a+=1 : a+= 2); // cxx11-warning {{unsequenced modification and access to 'a'}}
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// TODO cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(false ? a+=1 : a) = a; // no-warning
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(true ? a+=1 : a) = a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// TODO cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(false ? a : a+=2) = a; // cxx11-warning {{unsequenced modification and access to 'a'}}
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// TODO cxx17-warning@-1 {{unsequenced modification and access to 'a'}}
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(true ? a : a+=2) = a; // no-warning
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xs[8] && (++a + a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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xs[8] || (++a + a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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((a++, false) || (a++, false)); // no-warning PR39779
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((a++, true) && (a++, true)); // no-warning PR39779
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int i,j;
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(i = g1(), false) || (j = g2(i)); // no-warning PR22197
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(i = g1(), true) && (j = g2(i)); // no-warning PR22197
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(a++, false) || (a++, false) || (a++, false) || (a++, false); // no-warning
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(a++, true) || (a++, true) || (a++, true) || (a++, true); // no-warning
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a = ((a++, false) || (a++, false) || (a++, false) || (a++, false)); // no-warning
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a = ((a++, true) && (a++, true) && (a++, true) && (a++, true)); // no-warning
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a = ((a++, false) || (a++, false) || (a++, false) || a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// TODO cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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a = ((a++, true) && (a++, true) && (a++, true) && a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// TODO cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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a = ((a++, false) || (a++, false) || (a++, false) || (a + a, false)); // no-warning
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a = ((a++, true) && (a++, true) && (a++, true) && (a + a, true)); // no-warning
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a = (false && a++); // no-warning
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a = (true && a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// TODO cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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a = (true && ++a); // no-warning
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a = (true || a++); // no-warning
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a = (false || a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// TODO cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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a = (false || ++a); // no-warning
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(a++) | (a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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(a++) & (a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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(a++) ^ (a++); // cxx11-warning {{multiple unsequenced modifications to 'a'}}
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// cxx17-warning@-1 {{multiple unsequenced modifications to 'a'}}
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(__builtin_classify_type(++a) ? 1 : 0) + ++a; // ok
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(__builtin_constant_p(++a) ? 1 : 0) + ++a; // ok
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(__builtin_object_size(&(++a, a), 0) ? 1 : 0) + ++a; // ok
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