https://gcc.gnu.org/g:cc85998ba7984e43c1d89d47dfbfc219c142fddf
commit r16-3429-gcc85998ba7984e43c1d89d47dfbfc219c142fddf
Author: Jakub Jelinek <ja...@redhat.com>
Date: Thu Aug 28 10:46:51 2025 +0200
c++: Fix ICE with parameter uses in expansion stmts [PR121575]
The following testcase shows an ICE when a parameter of a non-template
function is referenced in expansion stmt body.
tsubst_expr in that case assumes that either the PARM_DECL has registered
local specialization, or is this argument or it is in unevaluated context.
Parameters are always defined outside of the expansion statement
for-range-declaration or body, so for the instantiation of the body
outside of templates should always map to themselves.
It could be fixed by registering local self-specializations for all the
function parameters, but just handling it in tsubst_expr seems to be easier
and less costly.
Some PARM_DECLs, e.g. from concepts, have NULL DECL_CONTEXT, those are
handled like before (and assert it is unevaluated operand), for others
this checks if the PARM_DECL is from a non-template and in that case it
will just return t.
2025-08-28 Jakub Jelinek <ja...@redhat.com>
Jason Merrill <ja...@redhat.com>
PR c++/121575
* pt.cc (tsubst_expr) <case PARM_DECL>: If DECL_CONTEXT (t) isn't a
template return t for PARM_DECLs without local specialization.
* g++.dg/cpp26/expansion-stmt20.C: New test.
Diff:
---
gcc/cp/pt.cc | 5 +++
gcc/testsuite/g++.dg/cpp26/expansion-stmt20.C | 59 +++++++++++++++++++++++++++
2 files changed, 64 insertions(+)
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index d628744dbfd1..9b79267d16b3 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -22321,6 +22321,11 @@ tsubst_expr (tree t, tree args, tsubst_flags_t
complain, tree in_decl)
if (DECL_NAME (t) == this_identifier && current_class_ptr)
RETURN (current_class_ptr);
+ /* Parameters of non-templates map to themselves (e.g. in
+ expansion statement body). */
+ if (DECL_CONTEXT (t) && !uses_template_parms (DECL_CONTEXT (t)))
+ RETURN (t);
+
/* This can happen for a parameter name used later in a function
declaration (such as in a late-specified return type). Just
make a dummy decl, since it's only used for its type. */
diff --git a/gcc/testsuite/g++.dg/cpp26/expansion-stmt20.C
b/gcc/testsuite/g++.dg/cpp26/expansion-stmt20.C
new file mode 100644
index 000000000000..4cc0b3853819
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/expansion-stmt20.C
@@ -0,0 +1,59 @@
+// PR c++/121575
+// { dg-do run { target c++11 } }
+// { dg-options "" }
+
+struct A { int x, y; };
+int c;
+
+void
+qux (A p)
+{
+ if (p.x != 1 || p.y != 3)
+ __builtin_abort ();
+ ++c;
+}
+
+void
+foo ()
+{
+ A p { 1, 3 };
+ template for (auto _ : {}) // { dg-warning "'template for'
only available with" "" { target c++23_down } }
+ qux (p);
+ template for (auto _ : { 0 }) // { dg-warning
"'template for' only available with" "" { target c++23_down } }
+ qux (p);
+}
+
+void
+bar (A p)
+{
+ template for (auto _ : {}) // { dg-warning "'template for'
only available with" "" { target c++23_down } }
+ qux (p);
+ template for (auto _ : { 0, 1 }) // { dg-warning "'template for'
only available with" "" { target c++23_down } }
+ qux (p);
+}
+
+A
+baz ()
+{
+ A p { 1, 3 };
+ template for (auto _ : {}) // { dg-warning "'template for'
only available with" "" { target c++23_down } }
+ qux (p);
+ template for (auto _ : { 0, 1, 2 }) // { dg-warning "'template for'
only available with" "" { target c++23_down } }
+ qux (p);
+ return p;
+}
+
+int
+main ()
+{
+ foo ();
+ if (c != 1)
+ __builtin_abort ();
+ bar ({ 1, 3 });
+ if (c != 3)
+ __builtin_abort ();
+ if (baz ().x != 1 || baz ().y != 3)
+ __builtin_abort ();
+ if (c != 9)
+ __builtin_abort ();
+}
