[gcc r13-5310] c++: result location and explicit inst [PR108496]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:4b125d01a5d5e601961419396332b74eea2219bb

commit r13-5310-g4b125d01a5d5e601961419396332b74eea2219bb
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jan 23 13:33:07 2023 -0500

    c++: result location and explicit inst [PR108496]
    
    In r13-4469 we started to build the RESULT_DECL in grokdeclarator, while we
    still know the location of the return type.  But in this testcase, we hit
    that code again when parsing the explicit instantiation, and clobber the
    DECL_RESULT that was previously used in parsing the function.  So, only set
    DECL_RESULT if it isn't already set.
    
            PR c++/108496
    
    gcc/cp/ChangeLog:
    
            * decl.cc (grokdeclarator): Check whether DECL_RESULT is already
            set.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/template/explicit-instantiation5.C: New test.

Diff:
---
 gcc/cp/decl.cc                                          |  6 +++++-
 gcc/testsuite/g++.dg/template/explicit-instantiation5.C | 15 +++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 75ddf8016b5..d606b31d7a7 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -14776,7 +14776,9 @@ grokdeclarator (const cp_declarator *declarator,
       {
 	/* If we saw a return type, record its location.  */
 	location_t loc = declspecs->locations[ds_type_spec];
-	if (loc != UNKNOWN_LOCATION)
+	if (loc == UNKNOWN_LOCATION)
+	  /* Build DECL_RESULT in start_preparsed_function.  */;
+	else if (!DECL_RESULT (decl))
 	  {
 	    tree restype = TREE_TYPE (TREE_TYPE (decl));
 	    tree resdecl = build_decl (loc, RESULT_DECL, 0, restype);
@@ -14784,6 +14786,8 @@ grokdeclarator (const cp_declarator *declarator,
 	    DECL_IGNORED_P (resdecl) = 1;
 	    DECL_RESULT (decl) = resdecl;
 	  }
+	else if (funcdef_flag)
+	  DECL_SOURCE_LOCATION (DECL_RESULT (decl)) = loc;
       }
 
     /* Record constancy and volatility on the DECL itself .  There's
diff --git a/gcc/testsuite/g++.dg/template/explicit-instantiation5.C b/gcc/testsuite/g++.dg/template/explicit-instantiation5.C
new file mode 100644
index 00000000000..7bc007c8107
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/explicit-instantiation5.C
@@ -0,0 +1,15 @@
+// PR c++/108496
+
+struct S { long a, b, c; } s;
+
+template <int, typename>
+S foo (S);
+
+template <>
+S
+foo <0, long> (S)
+{
+  return s;
+}
+
+template S foo <0, long> (S);