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Subject: [Bug middle-end/99797] accessing uninitialized automatic variables
Date: Mon, 19 Apr 2021 18:57:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99797

--- Comment #11 from Martin Uecker <muecker at gwdg dot de> ---
(In reply to Ivan Sorokin from comment #10)

...
> > is a bug if this choice is unreasonable and does not serve its users we=
ll.
>=20
> Do you have some specific proposal in mind?
>=20
> Currently a user has these 5 options:
> 1. Using -O0 suppressing optimizations.
> 2. Using -fno-tree-ccp suppressing this specific optimization.

Optimizations are important, so this is not really an option.

> 3. Using -Wall and relying on warnings.

It is not clear to me that this fully addresses the problem. GCC does not w=
arn
about all possible accesses to uninitialized variables.

> 4. (in theory) Using static analyzer -fanalyzer. It doesn't detect this e=
rror
>    at the moment, but I believe can be taught detecting this.

This may be helpful.

> 5. Using dynamic analyzer like valgrind.

This is too expensive for production and also only useful for limited testi=
ng.

> It seems that you find existing options insufficient and want another one.

I want the optimizer to assume that uninitialized variables have an unknown=
 but
fixed value. Then one could still optimize almost as well *and* get analyza=
ble
and more benign behavior even when uninitialized variables are accessed.
Optimizers already know how to deal with variables of unknown content, so t=
his
should be fairly easy to implement (maybe I will try).

I would also like something such as -fsanitize=3Dundefined which detects for
uninitialized variables at run-time.

Best,
Martin=