[RFA] Fix PR 598 and PR 776

[Neil Booth]

Since at least as far back as 2.95.x, GCC ICEs if an object of
sufficiently large size is allocated on the stack.

This is because assign_stack_temp_for_type expects a size of -1
(returned indirectly from int_size_for_type) to mean an object of
unknown size has been allocated on the stack, an ICE condition.

However, in fact -1 has an overloaded meaning: it also means object
too large (larger than the positive range of HOST_WIDE_INT).

This patch + testcase catches such cases before
assign_stack_temp_for_type sees -1, emits an error, and allocates a
small object instead to allow the compilation to continue.

Bootstrapping x86 Linux.  OK to commit?

Neil.

	* function.c (assign_temp): Recover gracefully when stack
	objects are too large.
	* testsuite/gcc.dg/largeobj.c: New test.

Index: function.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/function.c,v
retrieving revision 1.319
diff -u -p -r1.319 function.c
--- function.c	2001/10/23 22:59:15	1.319
+++ function.c	2001/10/26 21:58:34
@@ -849,14 +849,23 @@ assign_temp (type, keep, memory_required
       if (size == 0)
 	size = 1;
 
-      /* Unfortunately, we don't yet know how to allocate variable-sized
-	 temporaries.  However, sometimes we have a fixed upper limit on
-	 the size (which is stored in TYPE_ARRAY_MAX_SIZE) and can use that
-	 instead.  This is the case for Chill variable-sized strings.  */
-      if (size == -1 && TREE_CODE (type) == ARRAY_TYPE
-	  && TYPE_ARRAY_MAX_SIZE (type) != NULL_TREE
-	  && host_integerp (TYPE_ARRAY_MAX_SIZE (type), 1))
-	size = tree_low_cst (TYPE_ARRAY_MAX_SIZE (type), 1);
+      if (size == -1)
+	{
+	  if (TYPE_SIZE_UNIT (TYPE_MAIN_VARIANT (type)) != 0)
+	    {
+	      error ("object too large for the stack");
+	      size = 1;
+	    }
+	  /* Unfortunately, we don't yet know how to allocate
+	     variable-sized temporaries.  However, sometimes we have a
+	     fixed upper limit on the size (which is stored in
+	     TYPE_ARRAY_MAX_SIZE) and can use that instead.  This is
+	     the case for Chill variable-sized strings.  */
+	  else if (TREE_CODE (type) == ARRAY_TYPE
+		   && TYPE_ARRAY_MAX_SIZE (type) != NULL_TREE
+		   && host_integerp (TYPE_ARRAY_MAX_SIZE (type), 1))
+	    size = tree_low_cst (TYPE_ARRAY_MAX_SIZE (type), 1);
+	}
 
       tmp = assign_stack_temp_for_type (mode, size, keep, type);
       return tmp;
Index: testsuite/gcc.dg/largeobj.c
===================================================================
RCS file: largeobj.c
diff -N largeobj.c
--- /dev/null	Tue May  5 13:32:27 1998
+++ largeobj.c	Fri Oct 26 14:58:34 2001
@@ -0,0 +1,11 @@
+/* PRs 598 and 776 - ICE when declaring large objects on the stack.  */
+
+/* Because we need to pick a definite size for the array, this test
+   only overflows "properly" on 32-bit machines.  */
+
+/* { dg-do compile { target i?86-*-* } } */
+
+int main()
+{
+  int a[540000000];		/* { dg-error "too large" } */
+}