[cfe-dev] behaviour of EvaluatedExprVisitor vs. StmtVisitor

[Caitlin Sadowski]

Ted,

Ok, that makes sense.

 Here is my impression: For example,if I want to be sure to visit each
DeclRefExpr inside of a CFGBlock, I can just iterate over the CFGStmts
making up the block and use the (nonrecursive) StmtVisitor to visit
DeclRefExprs (as in the code above). Is this true, or are there any
corner cases I should be concerned about? I am a bit confused by the
"AlwaysAdd" vs. "NotAlwaysAdd" enum in AddStmtChoice in CFG.cpp.

Cheers,

Caitlin

On Tue, Aug 16, 2011 at 4:24 PM, Ted Kremenek <kremenek at apple.com> wrote:
> EvaluatedExprVisitor does a recursive visit of an expression:
>
> /// \begin Given a potentially-evaluated expression, this visitor visits all
> /// of its potentially-evaluated subexpressions, recursively.
>
> The CFG is linearized, which means every expression appears in the CFG.   There are three expressions in the CFG: the reference to 'y', and implicit lvalue-to-rvalue cast around 'y', and the initialization of 'x'.  The latter two have the reference to 'y' as a nested expression.  This means if you visit each one, you will see 'y' three times.
>
> On Aug 16, 2011, at 4:11 PM, Caitlin Sadowski wrote:
>
>> I am trying to visit each expression inside of a CFGBlock exactly
>> once. To do this, I iterate through the statements in a block, and
>> then call a visitor on each statement.
>>
>>    for (CFGBlock::const_iterator I = CurrBlock->begin(), E = CurrBlock->end();
>>         I != E; ++I) {
>>      if (const CFGStmt *CfgStmt = dyn_cast<CFGStmt>(&*I)) {
>>        MyVisitor.Visit(CfgStmt->getStmt());
>>      }
>>    }
>>
>> However, I have been having some strange behaviour. When MyVisitor is
>> a subclass of EvaluatedExprVisitor<MyVisitor>, I end up seeing some
>> DeclRefExprs multiple times. In contrast, when MyVisitor is a subclass
>> of StmtVisitor<MyVisitor>, I see the DeclRefExprs just once. Is this
>> expected behaviour?
>>
>> For a more specific example, it looks like when visiting the CFGBlocks
>> inside this function:
>>
>> void myFunction() {
>>  int x = y;
>> }
>>
>> with EvaluatedExprVisitor<MyVisitor>, I visit the DeclRefExpr for y three times.
>>
>> Cheers,
>>
>> Caitlin
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>
>