From: Nathaniel Shead <nathanieloshead@gmail.com>
Date: Wed, 12 Feb 2025 12:07:43 +0000 (+1100)
Subject: c++: Constrain visibility for CNTTPs with internal types [PR118849]
X-Git-Tag: basepoints/gcc-16~2049
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0e485b8c85c31856b9f7c91015ac94874b100bd4;p=thirdparty%2Fgcc.git

c++: Constrain visibility for CNTTPs with internal types [PR118849]

While looking into PR118846 I noticed that we don't currently constrain
the linkage of functions involving CNTTPs of internal-linkage types.  It
seems to me that this would be sensible to do.

	PR c++/118849

gcc/cp/ChangeLog:

	* decl2.cc (min_vis_expr_r): Constrain visibility according to
	the type of decl_constant_var_p decls.

gcc/testsuite/ChangeLog:

	* g++.dg/template/linkage6.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
---

diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index 593dcaa4e2d..aa9ebca12f8 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -2814,7 +2814,9 @@ min_vis_expr_r (tree *tp, int */*walk_subtrees*/, void *data)
 	/* The ODR allows definitions in different TUs to refer to distinct
 	   constant variables with internal or no linkage, so such a reference
 	   shouldn't affect visibility (PR110323).  FIXME but only if the
-	   lvalue-rvalue conversion is applied.  */;
+	   lvalue-rvalue conversion is applied.  We still want to restrict
+	   visibility according to the type of the declaration however.  */
+	tpvis = type_visibility (TREE_TYPE (t));
       else if (! TREE_PUBLIC (t))
 	tpvis = VISIBILITY_ANON;
       else
diff --git a/gcc/testsuite/g++.dg/template/linkage6.C b/gcc/testsuite/g++.dg/template/linkage6.C
new file mode 100644
index 00000000000..b86c986568f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/linkage6.C
@@ -0,0 +1,13 @@
+// PR c++/118849
+// { dg-do compile { target c++20 } }
+// { dg-final { scan-assembler-not "(weak|glob)\[^\n\]*_Z" { xfail powerpc-*-aix* } } }
+
+namespace {
+  struct A {};
+}
+
+template <auto Q> void f() { }
+
+int main() {
+  f<A{}>();
+}