[PATCH] Avoid assuming valid_constant_size_p argument is a constant expression (PR 89294)

[Martin Sebor <msebor at gmail dot com>]

The attached patch removes the assumption introduced earlier today
in my fix for bug 87996 that the valid_constant_size_p argument is
a constant expression.  I couldn't come up with a C/C++ test case
where this isn't true but apparently it can happen in Ada which I
inadvertently didn't build.  I still haven't figured out what
I have to do to build it on my Fedora 29 machine so I tested
this change by hand (besides bootstrapping w/o Ada).

The first set of instructions Google gives me don't seem to do
it:

  https://fedoraproject.org/wiki/Features/Ada_developer_tools

and neither does dnf install gcc-gnat as explained on our Wiki:

  https://gcc.gnu.org/wiki/GNAT

If someone knows the magic chant I would be grateful (it might
be helpful to also update the Wiki page -- the last change to
it was made in 2012; I volunteer to do that).

Martin

PR middle-end/89294 - ICE in valid_constant_size_p

gcc/c-family/ChangeLog:

	PR middle-end/89294
	* c-common.c (invalid_array_size_error): Handle cst_size_not_constant.

gcc/ChangeLog:

	PR middle-end/89294
	* tree.c (valid_constant_size_p): Avoid assuming size is a constant
	expression.
	* tree.h (cst_size_error): Add the cst_size_not_constant enumerator.

Index: gcc/c-family/c-common.c
===================================================================
--- gcc/c-family/c-common.c	(revision 268783)
+++ gcc/c-family/c-common.c	(working copy)
@@ -8241,6 +8241,13 @@ invalid_array_size_error (location_t loc, cst_size
   tree maxsize = max_object_size ();
   switch (error)
     {
+    case cst_size_not_constant:
+      if (name)
+	error_at (loc, "size of array %qE is not a constant expression",
+		  name);
+      else
+	error_at (loc, "size of array is not a constant expression");
+      break;
     case cst_size_negative:
       if (name)
 	error_at (loc, "size %qE of array %qE is negative",
Index: gcc/tree.c
===================================================================
--- gcc/tree.c	(revision 268783)
+++ gcc/tree.c	(working copy)
@@ -7521,8 +7521,14 @@ valid_constant_size_p (const_tree size, cst_size_e
   if (!perr)
     perr = &error;
 
-  if (TREE_OVERFLOW (size))
+  if (TREE_CODE (size) != INTEGER_CST)
     {
+      *perr = cst_size_not_constant;
+      return false;
+    }
+
+  if (TREE_OVERFLOW_P (size))
+    {
       *perr = cst_size_overflow;
       return false;
     }
Index: gcc/tree.h
===================================================================
--- gcc/tree.h	(revision 268783)
+++ gcc/tree.h	(working copy)
@@ -4352,6 +4352,7 @@ extern tree excess_precision_type (tree);
    is not a valid size.  */
 enum cst_size_error {
   cst_size_ok,
+  cst_size_not_constant,
   cst_size_negative,
   cst_size_too_big,
   cst_size_overflow