Fix unguarded uses of tree_to_uhwi

[Richard Sandiford]

This patch uses tree_fits_uhwi_p to protect a previously unguarded
use of tree_to_uhwi.  Without this we would ICE for variable-sized types.

Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64le-linus-gnu.
OK to install?

Richard


2017-09-20  Richard Sandiford  <richard.sandif...@linaro.org>
            Alan Hayward  <alan.hayw...@arm.com>
            David Sherwood  <david.sherw...@arm.com>

gcc/
        * tree.c (find_atomic_core_type): Check tree_fits_uhwi_p before
        calling tree_to_uhwi.

Index: gcc/tree.c
===================================================================
--- gcc/tree.c  2017-09-14 16:45:44.199522746 +0100
+++ gcc/tree.c  2017-09-20 13:13:43.953534150 +0100
@@ -5821,11 +5821,10 @@ find_atomic_core_type (tree type)
   tree base_atomic_type;
 
   /* Only handle complete types.  */
-  if (TYPE_SIZE (type) == NULL_TREE)
+  if (!tree_fits_uhwi_p (TYPE_SIZE (type)))
     return NULL_TREE;
 
-  HOST_WIDE_INT type_size = tree_to_uhwi (TYPE_SIZE (type));
-  switch (type_size)
+  switch (tree_to_uhwi (TYPE_SIZE (type)))
     {
     case 8:
       base_atomic_type = atomicQI_type_node;