On Tue, Nov 29, 2022 at 11:05:33PM +0100, Jakub Jelinek wrote:
> On Tue, Nov 29, 2022 at 04:38:50PM -0500, Jason Merrill wrote:
> > > --- gcc/testsuite/g++.dg/gomp/for-21.C.jj 2020-01-12 11:54:37.178401867
> > > +0100
> > > +++ gcc/testsuite/g++.dg/gomp/for-21.C 2022-11-29 13:06:59.038410557
> > > +0100
> > > @@ -54,9 +54,9 @@ void
> > > f6 (S (&a)[10])
> > > {
> > > #pragma omp for collapse (2)
> > > - for (auto [i, j, k] : a) // { dg-error "use of
> > > 'i' before deduction of 'auto'" "" { target *-*-* } .-1 }
> > > + for (auto [i, j, k] : a) // { dg-error "use of
> > > 'i' before deduction of 'auto'" }
> > > for (int l = i; l < j; l += k) // { dg-error "use of
> > > 'j' before deduction of 'auto'" }
> > > - ; // { dg-error "use of
> > > 'k' before deduction of 'auto'" "" { target *-*-* } .-3 }
> > > + ; // { dg-error "use of
> > > 'k' before deduction of 'auto'" "" { target *-*-* } .-1 }
> >
> > Hmm, this error is surprising: since the initializer is non-dependent, we
> > should have deduced immediately. I'd expect the same error as in the
> > non-structured-binding cases, "* expression refers to iteration variable".
>
> The reason was just to be consistent what is (unfortunately) emitted
> in the other cases (!processing_template_decl or type dependent).
> I guess I could try how much work would it be to deduce it sooner, but
> generally it is pretty corner case, people rarely do this in OpenMP code.
I had a look at that today, but it would be pretty hard. The thing is
we must emit all the associated code for all the range for loops in
OpenMP loops at a different spot. So, the only possibility I see would
be if we during parsing of a range for loop inside of the OpenMP loop nest
we don't do the cp_finish_omp_range_for stuff to avoid e.g. cp_finish_decl,
but instead
build_x_indirect_ref (input_location, begin, RO_UNARY_STAR,
NULL_TREE, tf_none)
and if that gives a non-dependent type, temporarily overwrite TREE_TYPE
of the decl and if it is structured binding, temporarily
++processing_template_decl and cp_finish_decomp, then after parsing all the
associated loop headers we revert that (and ditto for instantiation of
OpenMP loops).
Jakub
