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

[Richard Sandiford]

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.

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

Richard


2019-10-11  Richard Sandiford  <richard.sandiford@arm.com>

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

Index: gcc/tree-ssa-strlen.c
===================================================================
--- gcc/tree-ssa-strlen.c	2019-10-11 15:43:51.127514545 +0100
+++ gcc/tree-ssa-strlen.c	2019-10-11 15:46:11.718524445 +0100
@@ -4026,10 +4026,10 @@ count_nonzero_bytes (tree exp, unsigned
 
       /* 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,