[cfe-users] AST Recursive Visitor- Statements (Stmt *)
Ayush Mittal via cfe-users
cfe-users at lists.llvm.org
Wed Aug 7 14:28:24 PDT 2019
Sure, Not a problem.
What's the way to get the declarations such as *ptr and &bar as it is
inside the *DeclRefExpr *block*. *
*Example: *
void foo(){
int bar=1;
int **ptr;
**ptr = &bar;* // this line
}
*If I query like this way:*
if (const ValueDecl *VD = dyn_cast<ValueDecl>(DRE->getDecl())){
OS << VD->getType() //returns the original type of that declaration,
not the one that was used.
}
Thanks and Regards.
On Tue, Aug 6, 2019 at 7:41 PM Richard Trieu <rtrieu at google.com> wrote:
> RecursiveASTVisitor should have an ASTContext available. ASTContext has a
> getParents function, which may be of some use. Unfortunately, I haven't
> used this part of the ASTContext before, so I can't give any more concrete
> advice. As you've seen, it's easier to traverse down the AST than up it.
>
> On Tue, Aug 6, 2019 at 11:56 AM Ayush Mittal <bellavistaghome at gmail.com>
> wrote:
>
>> Thanks Richard for the explanation!
>>
>> | | | |-IfStmt 0x78b6d90 <line:82:13, line:89:13>
>> | | | | |-<<<NULL>>>
>> | | | | |-<<<NULL>>>
>> | | | | |-BinaryOperator 0x78b5f08 <line:82:17, col:34> 'int' '=='
>> | | | | | |-ImplicitCastExpr 0x78b5eb0 <col:17, col:23> 'int'
>> <IntegralCast>
>> | | | | | | `-ImplicitCastExpr 0x78b5e58 <col:17, col:23>
>> 'example_tree':'enum example_tree_type_' <LValueToRValue>
>> | | | | | | `-MemberExpr 0x78b5d78 <col:17, col:23>
>> 'example_tree':'enum example_tree_type_' lvalue ->*bal* 0x75a3ab0
>> | | | | | | `-ImplicitCastExpr 0x78b5d20 <col:17>
>> 'example_tree_node *' <LValueToRValue>
>> | | | | | | `-*DeclRefExpr* 0x78b5cb8 <col:17>
>> 'example_tree_node *' lvalue Var 0x78b1d48 'left' 'example_tree_node *'
>>
>>
>> Is there a way to get an access to the MemberExpr and ImplicitCastExpr
>> from VisitDeclRefExpr.
>>
>> Thanks for the help!
>>
>> Reagrds.
>>
>> On Thu, Aug 1, 2019 at 8:14 PM Richard Trieu <rtrieu at google.com> wrote:
>>
>>> Adding back the mailing list. Please reply all to keep the discussion
>>> on the mailing list.
>>>
>>> On Thu, Aug 1, 2019 at 2:47 PM Ayush Mittal <bellavistaghome at gmail.com>
>>> wrote:
>>>
>>>> Thanks Richard for the explanation. Really appreciate it.
>>>> One quick question, Within VisitStmt (BinaryOperator) how could I get
>>>> an access to DeclRefExpr class.
>>>>
>>>
>>> You should be defining a VisitBinaryOperator(BinaryOperator*) function.
>>> VisitStmt(BinaryOperator) won't be called because the base visitor class
>>> doesn't know about it.
>>>
>>>>
>>>> For example,
>>>> *-IfStmt* 0x88b5698 <line:13:3, line:16:12>
>>>> | |-<<<NULL>>>
>>>> | |-<<<NULL>>>
>>>> | |-BinaryOperator 0x88b54a0 <line:13:7, col:13> 'int' '=='
>>>> | | |-ImplicitCastExpr 0x88b5420 <col:7> 'int' <LValueToRValue>
>>>> | | | `-*DeclRefExpr* 0x88b5358 <col:7> 'int' lvalue ParmVar
>>>> 0x88604b0 'argc' 'int'
>>>>
>>>> BinaryOperator has two methods, getLHS() and getRHS() which get the
>>> left-hand side and right-hand side expressions. Given your BinaryOperator,
>>> getLHS() will return the ImplicitCastExpr. The Expr class has several
>>> methods to remove nodes in the AST. Expr::IgnoreImpCasts() is probably
>>> what you want here*. Then you need to check the final Expr if it is
>>> DeclRefExpr and use that.
>>>
>>> BinaryOperator *BO = ...;
>>> Expr *E = BO->getLHS();
>>> E = E->IgnoreImpCasts();
>>> if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
>>> // Do your stuff here.
>>> }
>>>
>>> or just:
>>>
>>> BinaryOperator *BO = ...;
>>> if (DeclRefExpr *DRE =
>>> dyn_cast<DeclRefExpr>(E->getLHS()->IgnoreImpCasts())) {
>>> // Do your stuff here.
>>> }
>>>
>>> * There's several Expr::Ignore* functions that recursively strips aways
>>> different AST nodes from Expr's. In your examples, IgnoreImpCasts will
>>> strip away the LValue to RValue cast, but if there was something like
>>> integral cast between different int types, that would stripped away too.
>>> If you need more fine-grained control, you'll need to do the AST traversal
>>> yourself.
>>>
>>>>
>>>> Thanks and Regards.
>>>>
>>>> On Tue, Jul 30, 2019 at 9:11 PM Richard Trieu <rtrieu at google.com>
>>>> wrote:
>>>>
>>>>> Hi Ayush,
>>>>>
>>>>> First, you need to know the classes associated with each of your
>>>>> target AST nodes. These are IfStmt, WhileStmt, ForStmt, BinaryOperator,
>>>>> and UnaryOperator. Each of these are sub-classes of Stmt. IfStmt,
>>>>> WhileStmt, ForStmt and direct sub-classes while BinaryOperator and
>>>>> UnaryOperator are sub-classes of Expr, which is a sub-class of ValueStmt,
>>>>> which is a sub-class of Stmt. There's also two other related classes,
>>>>> CXXForRangeStmt and DoStmt, which represent ranged-based for-loops and
>>>>> do/while loops.
>>>>>
>>>>> Second, pointers can be changed between classes with the cast and
>>>>> dyn_cast functions and Stmt::getStmtClass() will tell the type of the
>>>>> Stmt. They are used as follows:
>>>>>
>>>>> void VisitStmt(Stmt *S) {
>>>>> if (BinaryOperator *BO = dyn_cast<BinaryOperator>(S)) {
>>>>> // Process BinaryOperator here
>>>>> } else if (UnaryOperator *UO = dyn_cast<UnaryOperator>(S)) {
>>>>> ...
>>>>> } // other checks here
>>>>> }
>>>>>
>>>>> void VisitStmt(Stmt *S) {
>>>>> switch (S->getStmtClass()) {
>>>>> case Stmt::BinaryOperatorClass: {
>>>>> BinaryOperator *BO = cast<BinaryOperator>(S);
>>>>> // Process BinaryOperator here
>>>>> }
>>>>> case Stmt::UnaryOperatorClass: {
>>>>> UnaryOperator *UO = cast<UnaryOperator>(S);
>>>>> }
>>>>> // Other cases here
>>>>> }
>>>>> }
>>>>>
>>>>> The difference between cast and dyn_cast is that cast expects the
>>>>> pointer is the correct type without checking while dyn_cast does check the
>>>>> target type and returns a null pointer on a type mismatch. Chains of
>>>>> dyn_cast's are used if the list of nodes is short while using a switch on
>>>>> Stmt::getStmtClass() is used when checking a lot of node types.
>>>>>
>>>>> There's also a third way. Since you are already using a visitor, the
>>>>> visitor will have a visit function for each AST node. Instead of writing
>>>>> just VisitStmt, you will write a VisitBinaryOperator(BinaryOperator *),
>>>>> VisitUnaryOperator(UnaryOperator *), and so on for each one you're
>>>>> interested in. Hope this is enough to get you started.
>>>>>
>>>>> On Tue, Jul 30, 2019 at 4:25 PM Ayush Mittal via cfe-users <
>>>>> cfe-users at lists.llvm.org> wrote:
>>>>>
>>>>>> Hello Clangers,
>>>>>>
>>>>>> I'm new to clang. I'm writing an AST Consumer plug-in to visit the
>>>>>> statements node and record the data in one of my table with line numbers.
>>>>>> I've this function callback ready: *VisitStmt(Stmt *S)*. My question
>>>>>> is how could I traverse If, while, for loop, boolean and Unary Operators-
>>>>>> inside this function.
>>>>>>
>>>>>> Thanks and Regards.
>>>>>> _______________________________________________
>>>>>> cfe-users mailing list
>>>>>> cfe-users at lists.llvm.org
>>>>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
>>>>>>
>>>>>
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