[cfe-dev] VLA size in typedef

[Aaron Ballman via cfe-dev]

On Fri, Apr 3, 2020 at 3:24 PM Eli Friedman via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
>
> 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.

I'm guessing the analyzer is similarly unaware of evaluations within
typically unevaluated contexts like sizeof.

~Aaron

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> -Eli
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> 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
>
>
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> 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.
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> The following code produces a warning:
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> void check_uninit_sized_VLA() {
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>   int x;
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>   int vla[x]; // expected-warning{{Declared variable-length array (VLA) uses a garbage value as its size}}
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> }
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> But the following does not:
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> void check_uninit_sized_VLA() {
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>   int x;
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>   typedef int VLA[x];
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>   VLA vla; // value of 'x' is Unknown here, why ?
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> }
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> The `checkPreStmt` with `Decl*` is not called for `TypedefDecl`.
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> Similarly, at a `sizeof(VLA)`  in the code above `x` is always Unknown.
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> 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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