Instances of Variable Usage (SSA form)

Clang Frontend
1

Hi,
   I want to use clang to find out all the instances of a variable usage.
e.g. I want to find out every place where the variable 'x' was used? I know
that, in theory, this problem can be solved using the SSA form. How can I do
this in clang?

Regards,
Adil

2

You could search for all DeclRefExprs that refer to the particular variable declaration (by doing an AST walk).

Note that this will find only syntactic references to a particular variable, but will not trace the data flow. For example,
int x = 0;
int y = x;
use(y); // This will not be a use of x.

(SSA form just guarantees that there is only a single assignment for each variable.)

Anna.

3

Thank you. This is exactly what I was looking for. I have a small issue though. I’ve used a CompilerInvocation and CompilerInstance to set up clang. Then I use parseAST to parse the clang AST. My program can’t find standard C++ headers like and <stdio.h>. How do I make clang automatically find system include directories (e.g. /usr/include etc).

Regards,
Adil

4

Thank you. This is exactly what I was looking for. I have a small issue
though. I've used a CompilerInvocation and CompilerInstance to set up
clang. Then I use parseAST to parse the clang AST. My program can't find
standard C++ headers like <string> and <stdio.h>. How do I make clang
automatically find system include directories (e.g. /usr/include etc).

The easiest way is to not code your own Clang setup, and use either
- a clang plugin (Clang Plugins — Clang 18.0.0git documentation)
- or LibTooling (LibTooling — Clang 18.0.0git documentation)

Cheers,
/Manuel