[cfe-users] AST Recursive Visitor- Statements (Stmt *)
Richard Trieu via cfe-users
cfe-users at lists.llvm.org
Wed Aug 7 14:56:33 PDT 2019
The declarations are "ptr" and "bar". "*ptr" and "&bar" are expressions
since * and & are C++ operators. If you want the type of "*ptr" or "&bar",
then you need to get the associated UnaryOperator (a sub-class of Expr) and
call getType() on it.
On Wed, Aug 7, 2019 at 2:28 PM Ayush Mittal <bellavistaghome at gmail.com>
wrote:
> 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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