Hi!
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.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2025-08-25 Jakub Jelinek <ja...@redhat.com>
PR c++/121575
* pt.cc (tsubst_expr) <case PARM_DECL>: During expansion stmt body
instantiation outside of templates return t for PARM_DECLs without
local specialization.
* g++.dg/cpp26/expansion-stmt20.C: New test.
--- gcc/cp/pt.cc.jj 2025-08-23 15:00:04.262787988 +0200
+++ gcc/cp/pt.cc 2025-08-23 15:51:08.726081054 +0200
@@ -22321,6 +22321,13 @@ tsubst_expr (tree t, tree args, tsubst_f
if (DECL_NAME (t) == this_identifier && current_class_ptr)
RETURN (current_class_ptr);
+ /* Parameters during expansion stmt body instantiation outside
+ of templates map to themselves. */
+ if (current_tinst_level
+ && (TREE_CODE (current_tinst_level->tldcl)
+ == TEMPLATE_FOR_STMT))
+ 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. */
--- gcc/testsuite/g++.dg/cpp26/expansion-stmt20.C.jj 2025-08-23
16:13:06.881488788 +0200
+++ gcc/testsuite/g++.dg/cpp26/expansion-stmt20.C 2025-08-23
15:58:11.641445497 +0200
@@ -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 ();
+}
Jakub
