Hi!

We ICE during error-recovery on the following testcase, compute_array_index_type
checks size for error_operand_p early (and it is not error operand; it is
<indirect_ref <var_decl c>> where c is of reference type with
error_mark_node DECL_INITIAL), then calls mark_rvalue_use (which returns 
error_mark_node), but we let it go
through maybe_constant_size etc. and because error_mark_node is
!TREE_CONSTANT, set it back to the original size.  Unfortunatley later on
that results in ICE, because
9662            itype = cp_build_binary_op (input_location,
9663                                        MINUS_EXPR,
9664                                        cp_convert (ssizetype, size, 
complain),
9665                                        cp_convert (ssizetype, 
integer_one_node,
9666                                                    complain),
9667                                        complain);
errors on it the second time:
error: use of local variable with automatic storage from containing function
(the first error was during mark_rvalue_use) and nothing gives up anymore,
so we build a domain with error_mark_node as maximum.
Fixed by giving up earlier if mark_rvalue_use fails.

Initially I had the second error_operand_p check before the
if (!TREE_CONSTANT (size)) check, but that unfortunately doesn't work,
it broke
FAIL: g++.dg/cpp0x/constexpr-47969.C  -std=c++11  (test for errors, line 11)
FAIL: g++.dg/cpp0x/constexpr-47969.C  -std=c++14  (test for errors, line 11)
FAIL: g++.dg/cpp0x/constexpr-ex2.C  -std=c++11  (test for errors, line 21)
FAIL: g++.dg/cpp0x/constexpr-ex2.C  -std=c++14  (test for errors, line 21)
FAIL: g++.dg/cpp0x/scoped_enum2.C  -std=c++11  (test for errors, line 7)
FAIL: g++.dg/cpp0x/scoped_enum2.C  -std=c++14  (test for errors, line 7)
FAIL: g++.dg/ext/stmtexpr15.C  -std=gnu++11  (test for errors, line 6)
FAIL: g++.dg/ext/stmtexpr15.C  -std=gnu++14  (test for errors, line 6)
FAIL: g++.dg/ext/stmtexpr15.C  -std=gnu++98  (test for errors, line 6)
FAIL: g++.dg/gomp/pr47963.C  -std=gnu++11 (test for excess errors)
FAIL: g++.dg/gomp/pr47963.C  -std=gnu++14 (test for excess errors)
FAIL: g++.dg/gomp/pr47963.C  -std=gnu++98 (test for excess errors)
where the errors weren't reported anymore.

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

2018-03-22  Jakub Jelinek  <ja...@redhat.com>

        PR c++/85015
        * decl.c (compute_array_index_type): Return error_mark_node if
        mark_rvalue_use or maybe_constant_value returns error_operand_p.

        * g++.dg/cpp0x/pr85015.C: New test.

--- gcc/cp/decl.c.jj    2018-03-21 22:47:16.642996454 +0100
+++ gcc/cp/decl.c       2018-03-22 19:37:10.039385428 +0100
@@ -9522,6 +9522,9 @@ compute_array_index_type (tree name, tre
     {
       size = mark_rvalue_use (size);
 
+      if (error_operand_p (size))
+       return error_mark_node;
+
       if (cxx_dialect < cxx11 && TREE_CODE (size) == NOP_EXPR
          && TREE_SIDE_EFFECTS (size))
        /* In C++98, we mark a non-constant array bound with a magic
@@ -9534,11 +9537,10 @@ compute_array_index_type (tree name, tre
 
          if (!TREE_CONSTANT (size))
            size = osize;
+         else if (error_operand_p (size))
+           return error_mark_node;
        }
 
-      if (error_operand_p (size))
-       return error_mark_node;
-
       /* The array bound must be an integer type.  */
       tree type = TREE_TYPE (size);
       if (!INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type))
--- gcc/testsuite/g++.dg/cpp0x/pr85015.C.jj     2018-03-22 19:27:12.856154008 
+0100
+++ gcc/testsuite/g++.dg/cpp0x/pr85015.C        2018-03-22 19:27:12.856154008 
+0100
@@ -0,0 +1,12 @@
+// PR c++/85015
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+void
+foo ()
+{
+  int &&c = v + 1;             // { dg-error "was not declared in this scope" }
+  struct S {                   // { dg-message "declared here" "" { target 
*-*-* } .-1 }
+    void bar () { int a[c]; }  // { dg-error "use of local variable with 
automatic storage from containing function" }
+  } e;
+}

        Jakub

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