[cfe-dev] [analyzer] VisitIncDecOp store

Artem Dergachev via cfe-dev cfe-dev at lists.llvm.org
Sat Apr 7 16:12:19 PDT 2018

Looks like a bug, yeah. Though it's probable that some checkers have 
already "adapted" to it.

That said, a non-pointer prvalue expression that has a value of 
loc::ConcreteInt kind sounds like a bigger bug (regardless of whether 
it's the expression that we're looking for). Is it the value that was 
supplied in the callback, or is it the actual value of the unary 
operator expression (i.e. `State->getSVal(UnaryOp, LCtx)`)?

On 4/6/18 4:56 AM, Rafael·Stahl via cfe-dev wrote:
> Hi,
> While developing a checker I have noticed that in the checkLocation 
> callback I received an unexpected Expr. It was an UnaryOperator of 
> non-pointer type and its SVal was a loc::ConcreteInt which doesn't 
> really make sense in my opinion.
> When looking into this in ExprEngineC.cpp 
> ExprEngine::VisitIncrementDecrementOperator I noticed that the calls 
> to evalStore pass the whole UnaryOperator Expr as third argument 
> LocationE. This LocationE is documented as "The location expression 
> that is stored to". I would have understood this as the sub-expression 
> of the UnaryOp instead of the Op itself.
> In particular:
> -evalStore(Dst3, U, U, ...);
> +evalStore(Dst3, U, Ex, ...);
> Example:
> volatile int *p;
> (*p)++;
> UnaryOperator 0x1bad960 'int' postfix '++'
> `-ParenExpr 0x1bad940 'volatile int' lvalue
>   `-UnaryOperator 0x1bad920 'volatile int' lvalue prefix '*' cannot 
> overflow
>     `-ImplicitCastExpr 0x1bad908 'volatile int *' <LValueToRValue>
>       `-DeclRefExpr 0x1bad8e0 'volatile int *' lvalue Var 0x1bad320 
> 'p' 'volatile int *'
> Here the outer UnaryOp is passed as SVal in checkLocation instead of 
> the inner one.
> Is my understanding correct? In that case I'm able to submit a patch.
> Best regards
> Rafael
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