[C++ PATCH] Fix cp_finish_decl error recovery (PR c++/85134)

[Jakub Jelinek]

Hi!

When we clear DECL_DECLARED_CONSTEXPR_P because the decl doesn't have
literal type, we returned immediately, which unfortunately breaks e.g.
OpenMP gimplification, as required DECL_EXPR is not emitted for VLA vars.

This patch instead of returning immediately just clears it and so that
we don't ICE on constexpr-ice19.C also clears init and DECL_EXTERNAL for
static data members (or should we return immediately for the static data
members like we used to do and only fall through for other decls)?

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2018-04-03  Jakub Jelinek  <ja...@redhat.com>

        PR c++/85134
        * decl.c (cp_finish_decl): If ensure_literal_type_for_constexpr_object
        fails, after clearing DECL_DECLARED_CONSTEXPR_P don't return early,
        instead for static data members clear init and set DECL_EXTERNAL.

        * g++.dg/gomp/pr85134.C: New test.
        * g++.dg/cpp0x/constexpr-ice19.C: Expect one further error.

--- gcc/cp/decl.c.jj    2018-03-27 12:54:48.049242949 +0200
+++ gcc/cp/decl.c       2018-04-03 11:48:40.396539609 +0200
@@ -6923,11 +6923,14 @@ cp_finish_decl (tree decl, tree init, bo
       cp_apply_type_quals_to_decl (cp_type_quals (type), decl);
     }
 
-  if (ensure_literal_type_for_constexpr_object (decl)
-      == error_mark_node)
+  if (ensure_literal_type_for_constexpr_object (decl) == error_mark_node)
     {
       DECL_DECLARED_CONSTEXPR_P (decl) = 0;
-      return;
+      if (VAR_P (decl) && DECL_CLASS_SCOPE_P (decl))
+       {
+         init = NULL_TREE;
+         DECL_EXTERNAL (decl) = 1;
+       }
     }
 
   if (VAR_P (decl)
--- gcc/testsuite/g++.dg/gomp/pr85134.C.jj      2018-04-03 11:06:22.533539818 
+0200
+++ gcc/testsuite/g++.dg/gomp/pr85134.C 2018-04-03 11:06:13.333540153 +0200
@@ -0,0 +1,11 @@
+// PR c++/85134
+// { dg-do compile }
+// { dg-options "-std=c++14 -fopenmp" }
+
+void
+foo (int i)
+{
+  constexpr int x[i] = {};     // { dg-error "'constexpr' variable 'x' has 
variably-modified type" }
+#pragma omp parallel shared(x)
+  ;
+}
--- gcc/testsuite/g++.dg/cpp0x/constexpr-ice19.C.jj     2018-01-17 
22:00:11.747228288 +0100
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-ice19.C        2018-04-03 
11:50:28.203541642 +0200
@@ -9,5 +9,5 @@ struct A
 
 struct B
 {
-  static constexpr A a {};  // { dg-error "not literal" }
+  static constexpr A a {};  // { dg-error "not literal|in-class 
initialization" }
 };

        Jakub