[gcc r13-6813] c++: array bound partial ordering [PR108390]

[Jason Merrill]

https://gcc.gnu.org/g:5a1717fbdfd1242a5beb3ac8300766a3534d3f88

commit r13-6813-g5a1717fbdfd1242a5beb3ac8300766a3534d3f88
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Mar 22 11:12:57 2023 -0400

    c++: array bound partial ordering [PR108390]
    
    fold_convert doesn't work with a dependent argument, and problematically
    differed from the corresponding fold+build_nop further down in the
    function.  So change it to match.
    
            PR c++/108390
    
    gcc/cp/ChangeLog:
    
            * pt.cc (unify): Use fold of build_nop instead of fold_convert.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/template/partial-order3.C: New test.

Diff:
---
 gcc/cp/pt.cc                                   | 8 +++++---
 gcc/testsuite/g++.dg/template/partial-order3.C | 6 ++++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 056b8c7abad..90bcaa78701 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -24635,8 +24635,9 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
 	  if ((strict & UNIFY_ALLOW_INTEGER)
 	      && TREE_TYPE (targ) && TREE_TYPE (arg)
 	      && CP_INTEGRAL_TYPE_P (TREE_TYPE (targ)))
-	    /* We're deducing from an array bound, the type doesn't matter.  */
-	    arg = fold_convert (TREE_TYPE (targ), arg);
+	    /* We're deducing from an array bound, the type doesn't matter.
+	       This conversion should match the one below.  */
+	    arg = fold (build_nop (TREE_TYPE (targ), arg));
 	  int x = !cp_tree_equal (targ, arg);
 	  if (x)
 	    unify_inconsistency (explain_p, parm, targ, arg);
@@ -24684,7 +24685,8 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
 	       && CP_INTEGRAL_TYPE_P (tparm))
 	/* Convert the ARG to the type of PARM; the deduced non-type
 	   template argument must exactly match the types of the
-	   corresponding parameter.  */
+	   corresponding parameter.  This conversion should match the
+	   one above.  */
 	arg = fold (build_nop (tparm, arg));
       else if (uses_template_parms (tparm))
 	{
diff --git a/gcc/testsuite/g++.dg/template/partial-order3.C b/gcc/testsuite/g++.dg/template/partial-order3.C
new file mode 100644
index 00000000000..154505321bf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/partial-order3.C
@@ -0,0 +1,6 @@
+// PR c++/108390
+// { dg-do compile { target c++11 } }
+
+template<class T, T t>  long f(int(*)[t], T(*)[t]);
+template<class T, int i> int f(int(*)[i], T(*)[i]) = delete;
+int n = f<int, 2>(0, 0);