ASDenysPetrov added inline comments.
================
Comment at: clang/test/Analysis/initialization.c:103
+void glob_arr_index4() {
+ clang_analyzer_eval(glob_arr_no_init[2]); // expected-warning{{UNKNOWN}}
+}
----------------
steakhal wrote:
> martong wrote:
> > ASDenysPetrov wrote:
> > > steakhal wrote:
> > > > I'm pretty sure we should not get `Unknown` for simply loading from a
> > > > global variable.
> > > > That would imply that loading two times subsequently we could not prove
> > > > that the value remained the same.
> > > > But that should remain the same, thus compare equal unless some other
> > > > code modifier that memory region.
> > > >
> > > > That could happen for two reasons:
> > > > 1) There is a racecondition, and another thread modified that location.
> > > > But that would be UB, so that could not happen.
> > > > 2) The global variable is //volatile//, so the hardware might changed
> > > > its content- but this global is not volatile so this does not apply.
> > > >
> > > > That being said, this load should have resulted in a //fresh// conjured
> > > > symbolic value instead of //unknown//.
> > > > Could you please check if it did result in //unknown// before your
> > > > patch, or you did introduce this behavior?
> > > I'm not sure I caught your thoughts.
> > > But I think the things is much simplier:
> > > `clang_analyzer_eval` can only produce `UNKNOWN` or `TRUE` or `FALSE`. If
> > > we know the constraint of `glob_arr_no_init[2]` we return `TRUE` or
> > > `FALSE`, and `UNKNOWN` otherwise.
> > > But in fact I should use `clang_analyzer_dump` here instead of
> > > `clang_analyzer_eval`. This is actually my fault. I'll update this.
> > > Could you please check if it did result in unknown before your patch, or
> > > you did introduce this behavior?
> >
> > I've just checked it, it was `Unknown` before this patch as well.
> > And actually, that is wrong because the array has static storage duration
> > and as such, we know that it is initialized with zeros according to the C
> > standard. But, that should be addressed in a follow-up patch (if someone
> > has the capacity).
> > https://stackoverflow.com/questions/32708161/value-of-uninitialized-elements-in-array-of-c-language/32708288
> Oh true. I was actually tricked by the `initialization.cpp:38`, where I
> actually caught this. And in that case, you use `dump()` yet you get
> `Unknown` as a result. But the issue remains the same.
C++ also states about zero-initialization for static storage lifetime duration:
http://eel.is/c++draft/basic.start.static#2
I think it will be among my next patches.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D106681/new/
https://reviews.llvm.org/D106681
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