Hi!
The following testcase ICEs during expansion, because cfun->returns_struct
wasn't cleared, despite auto being deduced to int.
The problem is that check_return_type -> apply_deduced_return_type
is called when parsing the expansion stmt body, at that time
processing_template_decl is non-zero and apply_deduced_return_type
in that case doesn't do the
if (function *fun = DECL_STRUCT_FUNCTION (fco))
{
bool aggr = aggregate_value_p (result, fco);
#ifdef PCC_STATIC_STRUCT_RETURN
fun->returns_pcc_struct = aggr;
#endif
fun->returns_struct = aggr;
}
My assumption is that !processing_template_decl in that case
is used in the sense "the fco function is not a function template",
for function templates no reason to bother with fun->returns*struct,
nothing will care about that.
When returning a type dependent expression in the expansion stmt
body, apply_deduced_return_type just won't be called during parsing,
but when instantiating the body and all will be fine. But when
returning a non-type-dependent expression, while check_return_type
will be called again during instantiation of the body, as the return
type is no longer auto in that case apply_deduced_return_type will not
be called again and so nothing will fix up fun->returns*struct.
The following patch fixes that by testing DECL_TEMPLATE_INFO, dunno
what else would be more appropriate for this function is a template,
maybe decl_dependent_p?
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Or some other test?
2025-08-25 Jakub Jelinek <[email protected]>
PR c++/121583
* semantics.cc (apply_deduced_return_type): Adjust
fun->returns*_struct even if processing_template_decl if
in_expansion_stmt and fco is not a template.
* g++.dg/cpp26/expansion-stmt23.C: New test.
* g++.dg/cpp26/expansion-stmt24.C: New test.
--- gcc/cp/semantics.cc.jj 2025-08-15 22:38:28.907872033 +0200
+++ gcc/cp/semantics.cc 2025-08-23 18:02:09.130079505 +0200
@@ -14213,7 +14213,8 @@ apply_deduced_return_type (tree fco, tre
result);
DECL_RESULT (fco) = result;
- if (!processing_template_decl)
+ if (!processing_template_decl
+ || (in_expansion_stmt && !DECL_TEMPLATE_INFO (fco)))
if (function *fun = DECL_STRUCT_FUNCTION (fco))
{
bool aggr = aggregate_value_p (result, fco);
--- gcc/testsuite/g++.dg/cpp26/expansion-stmt23.C.jj 2025-08-23
17:49:13.816155626 +0200
+++ gcc/testsuite/g++.dg/cpp26/expansion-stmt23.C 2025-08-23
18:08:32.125064559 +0200
@@ -0,0 +1,17 @@
+// PR c++/121583
+// { dg-do compile { target c++14 } }
+// { dg-options "" }
+
+auto
+foo ()
+{
+ template for (int i : { 0 }) // { dg-warning "'template for' only
available with" "" { target c++23_down } }
+ return i;
+}
+
+auto
+bar ()
+{
+ template for (auto i : { 0 }) // { dg-warning "'template for'
only available with" "" { target c++23_down } }
+ return i;
+}
--- gcc/testsuite/g++.dg/cpp26/expansion-stmt24.C.jj 2025-08-23
18:08:46.988868108 +0200
+++ gcc/testsuite/g++.dg/cpp26/expansion-stmt24.C 2025-08-23
18:12:46.856697841 +0200
@@ -0,0 +1,10 @@
+// PR c++/121583
+// { dg-do compile { target c++14 } }
+// { dg-options "" }
+
+auto
+foo ()
+{
+ template for (auto i : { 0, 1, 2LL }) // { dg-warning
"'template for' only available with" "" { target c++23_down } }
+ return i; // { dg-error "inconsistent
deduction for auto return type: 'int' and then 'long long int'" }
+}
Jakub
