[PATCH] D106681: [analyzer][NFCI] Move a block from `getBindingForElement` to separate functions

[Denys Petrov via Phabricator via cfe-commits]

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}}
+}
----------------
ASDenysPetrov wrote:
> 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.
> And in that case, you use dump() yet you get Unknown as a result. But the issue remains the same.
I just realized that I was confused as well :) The `dump` returns a symbolic value like `reg_$0<int Element{glob_arr_no_init,2 S64b,int}>`, **not** `Unknown`. So my intention of using `eval` was deliberate. Anyway we should improve this to produce `FALSE` instead of `UNKNOWN`, since it has a //static storage//.


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https://reviews.llvm.org/D106681