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PR16467: Teach -Wunsequenced that in C11 (unlike C++11), an assignment's

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side-effect is not sequenced before its value computation. Also fix a
mishandling of ?: expressions where the condition is constant that was
exposed by the tests for this.

llvm-svn: 185035
This commit is contained in:
Richard Smith
2013-06-26 23:16:51 +00:00
parent b4e1d4c630
commit 83e37bee44
3 changed files with 102 additions and 5 deletions
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20
clang/lib/Sema/SemaChecking.cpp
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@@ -5347,7 +5347,7 @@ class SequenceChecker : public EvaluatedExprVisitor<SequenceChecker> {
/// A read of an object. Multiple unsequenced reads are OK.
UK_Use,
/// A modification of an object which is sequenced before the value
/// computation of the expression, such as ++n.
/// computation of the expression, such as ++n in C++.
UK_ModAsValue,
/// A modification of an object which is not sequenced before the value
/// computation of the expression, such as n++.
@@ -5597,7 +5597,12 @@ public:
Visit(BO->getRHS());
notePostMod(O, BO, UK_ModAsValue);
// C++11 [expr.ass]p1:
// the assignment is sequenced [...] before the value computation of the
// assignment expression.
// C11 6.5.16/3 has no such rule.
notePostMod(O, BO, SemaRef.getLangOpts().CPlusPlus ? UK_ModAsValue
: UK_ModAsSideEffect);
}
void VisitCompoundAssignOperator(CompoundAssignOperator *CAO) {
VisitBinAssign(CAO);
@@ -5612,7 +5617,10 @@ public:
notePreMod(O, UO);
Visit(UO->getSubExpr());
notePostMod(O, UO, UK_ModAsValue);
// C++11 [expr.pre.incr]p1:
// the expression ++x is equivalent to x+=1
notePostMod(O, UO, SemaRef.getLangOpts().CPlusPlus ? UK_ModAsValue
: UK_ModAsSideEffect);
}
void VisitUnaryPostInc(UnaryOperator *UO) { VisitUnaryPostIncDec(UO); }
@@ -5673,8 +5681,10 @@ public:
// be chosen.
void VisitAbstractConditionalOperator(AbstractConditionalOperator *CO) {
EvaluationTracker Eval(*this);
SequencedSubexpression Sequenced(*this);
Visit(CO->getCond());
{
SequencedSubexpression Sequenced(*this);
Visit(CO->getCond());
}
bool Result;
if (Eval.evaluate(CO->getCond(), Result))