PR bootstrap/86621 - 'alloca' bound is unknown in tree-vect-slp.c:1437:16

gcc/ChangeLog:
	* gcc/gimple-ssa-warn-alloca.c (alloca_call_type_by_arg): Avoid
	diagnosing calls with unknown arguments unless -Walloca-larger-than
	is restricted to less than PTRDIFF_MAX bytes.

From-SVN: r262923

gcc/ChangeLog

+2018-07-22  Martin Sebor  <msebor@redhat.com>
+
+	PR bootstrap/86621
+	* gcc/gimple-ssa-warn-alloca.c (alloca_call_type_by_arg): Avoid
+	diagnosing calls with unknown arguments unless -Walloca-larger-than
+	is restricted to less than PTRDIFF_MAX bytes.
+
 2018-07-22  Gerald Pfeifer  <gerald@pfeifer.com>
 
 	* doc/gcov.texi (Invoking Gcov): Editorial changes.

gcc/gimple-ssa-warn-alloca.c

@@ -214,7 +214,15 @@ alloca_call_type_by_arg (tree arg, tree arg_casted, edge e,
 	    }
 	}
       else
-	return alloca_type_and_limit (ALLOCA_BOUND_UNKNOWN);
+	{
+	  /* Analogous to ALLOCA_UNBOUNDED, when MAX_SIZE is greater
+	     than or equal to PTRDIFF_MAX, treat allocations with
+	     an unknown bound as OK.  */
+	  alloca_type unknown_result
+	    = (max_size < maxobjsize.to_uhwi ()
+	       ? ALLOCA_BOUND_UNKNOWN : ALLOCA_OK);
+	  return alloca_type_and_limit (unknown_result);
+	}
     }
 
   // Similarly, but check for a comparison with an unknown LIMIT.