On Tue, 19 Jan 2021, Jason Merrill wrote:
> On 1/18/21 12:31 AM, Patrick Palka wrote:
> > Here after resolving the address of a template-id inside decltype, we
> > end up instantiating the chosen specialization from the call to
> > mark_used in resolve_nondeduced_context, even though only its type is
> > needed.
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look for
> > trunk?
> >
> > gcc/cp/ChangeLog:
> >
> > PR c++/71879
> > * semantics.c (finish_decltype_type): Temporarily increment
> > cp_unevaluated_operand during call to resolve_nondeduced_context.
> >
> > gcc/testsuite/ChangeLog:
> >
> > PR c++/71879
> > * g++.dg/cpp0x/decltype-71879.C: New test.
> > ---
> > gcc/cp/semantics.c | 2 ++
> > gcc/testsuite/g++.dg/cpp0x/decltype-71879.C | 5 +++++
> > 2 files changed, 7 insertions(+)
> > create mode 100644 gcc/testsuite/g++.dg/cpp0x/decltype-71879.C
> >
> > diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
> > index c8a6283b120..cad55665ce8 100644
> > --- a/gcc/cp/semantics.c
> > +++ b/gcc/cp/semantics.c
> > @@ -10098,7 +10098,9 @@ finish_decltype_type (tree expr, bool
> > id_expression_or_member_access_p,
> > /* The type denoted by decltype(e) is defined as follows: */
> > + ++cp_unevaluated_operand;
> > expr = resolve_nondeduced_context (expr, complain);
> > + --cp_unevaluated_operand;
>
> Hmm, is there a reason not to have cp_unevaluated_operand set through the
> whole function? We might stick 'cp_unevaluated u;' at the top of the function
> and remove the existing messing with cp_unevaluated_operand. Or assert that
> it's set and fix the callers to leave it set longer.
That makes sense to me. AFAICT the only parts of finish_decltype_type
tha are sensitive to cp_unevaluated_operand are
resolve_nondeduced_context and instantiate_nondependent_expr_sfinae,
but it makes sense to have cp_unevaluated_operand set throughout the
function.
The following passes limited testing, does it look OK for trunk after a
full bootstrap+regtest?
-- >8 --
Subject: [PATCH] c++: Fix excessive instantiation inside decltype [PR71879]
Here after resolving the address of a template-id inside decltype, we
end up instantiating the chosen specialization (from the call to
mark_used in resolve_nondeduced_context), even though only its type is
needed.
This patch sets cp_unevaluated_operand throughout finish_decltype_type,
so that in particular it's set during the call to
resolve_nondeduced_context within.
gcc/cp/ChangeLog:
PR c++/71879
* semantics.c (finish_decltype_type): Set up a cp_unevaluated
sentinel at the start of the function. Remove a now-redundant
manual adjustment of cp_unevaluated_operand.
gcc/testsuite/ChangeLog:
PR c++/71879
* g++.dg/cpp0x/decltype-71879.C: New test.
---
gcc/cp/semantics.c | 5 +++--
gcc/testsuite/g++.dg/cpp0x/decltype-71879.C | 5 +++++
2 files changed, 8 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/decltype-71879.C
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 244fc70d02d..834885616db 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -10080,6 +10080,9 @@ finish_decltype_type (tree expr, bool
id_expression_or_member_access_p,
return error_mark_node;
}
+ /* The operand of decltype is an unevaluated expression. */
+ cp_unevaluated u;
+
/* Depending on the resolution of DR 1172, we may later need to distinguish
instantiation-dependent but not type-dependent expressions so that, say,
A<decltype(sizeof(T))>::U doesn't require 'typename'. */
@@ -10095,9 +10098,7 @@ finish_decltype_type (tree expr, bool
id_expression_or_member_access_p,
}
else if (processing_template_decl)
{
- ++cp_unevaluated_operand;
expr = instantiate_non_dependent_expr_sfinae (expr, complain);
- --cp_unevaluated_operand;
if (expr == error_mark_node)
return error_mark_node;
}
diff --git a/gcc/testsuite/g++.dg/cpp0x/decltype-71879.C
b/gcc/testsuite/g++.dg/cpp0x/decltype-71879.C
new file mode 100644
index 00000000000..9da4d40ca70
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/decltype-71879.C
@@ -0,0 +1,5 @@
+// PR c++/71879
+// { dg-do compile { target c++11 } }
+
+template <class T> void f(T x) { x.fail(); }
+using R = decltype(&f<int>);
--
2.30.0.155.g66e871b664
