[gcc/devel/c++-modules] Concepts and local externs

[gcc/devel/c++-modules] Concepts and local externs

[Nathan Sidwell]

https://gcc.gnu.org/g:a1fed5312efcfedb047f51714a29370675b9af86

commit a1fed5312efcfedb047f51714a29370675b9af86
Author: Nathan Sidwell <nathan@acm.org>
Date:   Fri Sep 11 11:42:07 2020 -0700

    Concepts and local externs
    
            gcc/cp/
            * decl.c (grokfndecl): Don't attach to local extern.
            gcc/testsuite/
            * concepts/local-extern.C: New.

Diff:
---
 ChangeLog.modules                            |  6 +++++
 gcc/cp/decl.c                                | 13 +++++++---
 gcc/cp/module.cc                             |  5 ++++
 gcc/testsuite/g++.dg/concepts/local-extern.C | 39 ++++++++++++++++++++++++++++
 4 files changed, 59 insertions(+), 4 deletions(-)

diff --git a/ChangeLog.modules b/ChangeLog.modules
index 9801ec197a9..85798763a5f 100644
--- a/ChangeLog.modules
+++ b/ChangeLog.modules
@@ -1,5 +1,11 @@
 2020-09-11  Nathan Sidwell  <nathan@acm.org>
 
+	Concepts and local externs
+	gcc/cp/
+	* decl.c (grokfndecl): Don't attach to local extern.
+	gcc/testsuite/
+	* concepts/local-extern.C: New.
+
 	Local extern fns do not get template header
 	gcc/cp/
 	* module.cc (trees_out::chained_decls): Also mark local fns for
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 10dce3a13e2..4a8ebc121e8 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -9503,7 +9503,10 @@ grokfndecl (tree ctype,
     {
       tree tmpl_reqs = NULL_TREE;
       tree ctx = friendp ? current_class_type : ctype;
-      bool memtmpl = (processing_template_decl > template_class_depth (ctx));
+      bool block_local = TREE_CODE (current_scope ()) == FUNCTION_DECL;
+      bool memtmpl = (!block_local
+		      && (processing_template_decl
+			  > template_class_depth (ctx)));
       if (memtmpl)
         tmpl_reqs = TEMPLATE_PARMS_CONSTRAINTS (current_template_parms);
       tree ci = build_constraints (tmpl_reqs, decl_reqs);
@@ -9513,9 +9516,11 @@ grokfndecl (tree ctype,
           ci = NULL_TREE;
         }
       /* C++20 CA378: Remove non-templated constrained functions.  */
-      if (ci && !flag_concepts_ts
-	  && (!processing_template_decl
-	      || (friendp && !memtmpl && !funcdef_flag)))
+      if (ci
+	  && (block_local
+	      || (!flag_concepts_ts
+		  && (!processing_template_decl
+		      || (friendp && !memtmpl && !funcdef_flag)))))
 	{
 	  error_at (location, "constraints on a non-templated function");
 	  ci = NULL_TREE;
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index af13b45b0c7..cc529220026 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -9869,6 +9869,11 @@ trees_out::get_merge_kind (tree decl, depset *dep)
 	 out-of-class definition.  For instance a FIELD_DECL.  */
       tree ctx = CP_DECL_CONTEXT (decl);
       if (TREE_CODE (ctx) == FUNCTION_DECL)
+	// FIXME: This not right if DECL has a template header.  For
+	// those will have instantiations pointing at it.  I think the
+	// only case is class definitions inside templates (including
+	// lambdas).  At least those have an ABI-mandated
+	// disambiguation mechanism that we can leverage.
 	return MK_unique;
 
       if (TREE_CODE (decl) == TEMPLATE_DECL
diff --git a/gcc/testsuite/g++.dg/concepts/local-extern.C b/gcc/testsuite/g++.dg/concepts/local-extern.C
new file mode 100644
index 00000000000..69ecc2361c0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/local-extern.C
@@ -0,0 +1,39 @@
+// { dg-do compile { target c++17 } }
+// { dg-additional-options -fconcepts }
+
+// Don't attach constraints to block-scope fn-decls and ICE
+
+template<typename _Iter>
+    concept input_or_output_iterator
+      = requires(_Iter __i) { { *__i } ; };
+
+
+  template<input_or_output_iterator _It>
+  class common_iterator
+  {
+
+  public:
+    
+void
+      frob ()
+    {
+      if (__builtin_is_constant_evaluated())
+	{
+	  void __failed_assertion(); // ICEd
+	  if (!bool(_M_index == 0)) __failed_assertion();
+	}
+
+    }
+
+  private:
+    unsigned char _M_index;
+  };
+
+template <typename T> concept C = true;
+
+template<typename T>
+void F ()
+{
+  void bad () requires C<T>; // { dg-error "a non-templated function" }
+  
+}