[cfe-dev] VLA size in typedef

Eli Friedman via cfe-dev cfe-dev at lists.llvm.org
Fri Apr 3 12:23:16 PDT 2020

Not deeply familiar with the relevant analyzer code, but it looks like the analyzer just isn’t aware that it needs to evaluate typedefs.  Try comparing CFGBuilder::VisitDeclSubExpr to CodeGenFunction::EmitDecl/CodeGenFunction::EmitVariablyModifiedType.


From: cfe-dev <cfe-dev-bounces at lists.llvm.org> On Behalf Of Balázs Kéri via cfe-dev
Sent: Friday, April 3, 2020 3:55 AM
To: cfe-dev at lists.llvm.org
Subject: [EXT] [cfe-dev] VLA size in typedef

I want to extend the VLA size checker to recognize invalid conditions if the VLA is used through a typedef. But the typedef statement seems to be not evaluated, the VLA size value is not known by the analyzer.

The following code produces a warning:
void check_uninit_sized_VLA() {
  int x;
  int vla[x]; // expected-warning{{Declared variable-length array (VLA) uses a garbage value as its size}}

But the following does not:
void check_uninit_sized_VLA() {
  int x;
  typedef int VLA[x];
  VLA vla; // value of 'x' is Unknown here, why ?

The `checkPreStmt` with `Decl*` is not called for `TypedefDecl`.
Similarly, at a `sizeof(VLA)`  in the code above `x` is always Unknown.
How is it possible (if it is) to obtain value of `x` in these cases, or find a way to check validity of the VLA in the typedef (or a `sizeof` call)?

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