Fix unchecked use of tree_to_uhwi in tree-ssa-strlen.c

r273783 introduced an unchecked use of tree_to_uhwi.  This is
tested by the SVE ACLE patches, but could potentially trigger
in non-SVE cases too.

2019-10-15  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-ssa-strlen.c (count_nonzero_bytes): Check tree_fits_uhwi_p
	before using tree_to_uhwi.

From-SVN: r276990

gcc/ChangeLog

+2019-10-15  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* tree-ssa-strlen.c (count_nonzero_bytes): Check tree_fits_uhwi_p
+	before using tree_to_uhwi.
+
 2019-10-15  Ilya Leoshkevich  <iii@linux.ibm.com>
 
 	* config/s390/s390.md: Run %a0:DI splitters only after reload.

gcc/tree-ssa-strlen.c

@@ -4026,10 +4026,10 @@ count_nonzero_bytes (tree exp, unsigned HOST_WIDE_INT offset,
 
       /* The size of the MEM_REF access determines the number of bytes.  */
       tree type = TREE_TYPE (exp);
-      if (tree typesize = TYPE_SIZE_UNIT (type))
-	nbytes = tree_to_uhwi (typesize);
-      else
+      tree typesize = TYPE_SIZE_UNIT (type);
+      if (!typesize || !tree_fits_uhwi_p (typesize))
 	return false;
+      nbytes = tree_to_uhwi (typesize);
 
       /* Handle MEM_REF = SSA_NAME types of assignments.  */
       return count_nonzero_bytes (arg, offset, nbytes, lenrange, nulterm,