Am Montag, den 02.08.2021, 16:19 +0200 schrieb Martin Uecker:
>
> Am Montag, den 02.08.2021, 16:05 +0200 schrieb Martin Uecker:
> > > On Sun, Aug 1, 2021 at 7:37 PM Uecker, Martin
> > > <martin.uec...@med.uni-goettingen.de> wrote:
> > > >
> > > > Here is an attempt to fix some old and annoying bugs related
> > > > to VLAs and statement expressions. In particulary, this seems
> > > > to fix the issues with variably-modified types which are
> > > > returned from statement expressions (which works on clang),
> > > > but there are still bugs remaining related to structs
> > > > with VLA members (which seems to be a FE bug).
> > > >
> > > > Of course, I might be doing something stupid...
> > >
> > > How's evaluation order of (f())[g()] defined (with f returning a
> > > pointer)?
> > > Isn't that just f() + g()*sizeof(int) and thus undefined?
> >
> > Yes, in C it is
> >
> > f() + g()
> >
> > and it is unsequenced. But the order of 'f' and 'g'
> > is not relevant here and also the patch does not change
> > it (the base expression is gimplified before the index).
> >
> > Essentially, we have
> >
> > ({ ... }) + g() * sizeof(X)
> >
> > where X refers to a declaration in the statement expression.
> > Without the patch the size expressions are gimplified before
> > the base expression and also before the index expression.
> > With the patch the ({ ... }) is gimplified also before the
> > size expression.
> >
> > > If it's undefined then I think the incoming GENERIC is ill-defined.
> >
> > I think it is OK because the arguments are evaluated
> > before the operation. Without the patch, parts of the
> > operation (the size expressions) are gimplified before
> > the arguments and this seems wrong to me.
>
> If I rewrite the ARRAY_REFs into *(f + g) in the test
> cases, they also works with unpatched GCC. So it is really
> the incorrect ordering in the gimplification of the
> ARRAY_REF which is the problem.
But there seem quite a few other bugs:
For
int foo2b(void)
{
return sizeof *({ int n = 20; struct { int x[n]; } x; x.x[12] = 1; &x; });
}
I get:
;; Function foo2b (null)
;; enabled by -tree-original
{
return (int) ((unsigned int) (sizetype) SAVE_EXPR <n> * 4);
}
Martin
