[PATCH][PR target/80358][7 regression] Fix boundary check error in expand_block_compare

[Aaron Sawdey]

Turns out we get passed const -1 for the length arg from this code.
ROUND_UP adds load_mode_size to that resulting in a small positive
number, hilarity ensues. Fixed by computing a sensible limit and using
IN_RANGE instead, which won't overflow in this way.

OK for trunk if bootstrap/regtest in progress passes?

2017-04-07  Aaron Sawdey  <acsawdey@linux.vnet.ibm.com>

	PR target/80358
	* config/rs6000/rs6000.c (expand_block_compare): Fix boundary check.

Index: gcc/config/rs6000/rs6000.c
===================================================================
--- gcc/config/rs6000/rs6000.c  (revision 246771)
+++ gcc/config/rs6000/rs6000.c  (working copy)
@@ -19672,8 +19672,9 @@
   unsigned int load_mode_size = GET_MODE_SIZE (load_mode);
 
   /* We don't want to generate too much code.  */
-  if (ROUND_UP (bytes, load_mode_size) / load_mode_size
-      > (unsigned HOST_WIDE_INT) rs6000_block_compare_inline_limit)
+  unsigned HOST_WIDE_INT max_bytes =
+    load_mode_size * (unsigned HOST_WIDE_INT) rs6000_block_compare_inline_limit;
+  if (!IN_RANGE (bytes, 1, max_bytes))
     return false;
 
   bool generate_6432_conversion = false;
-- 
Aaron Sawdey, Ph.D.  acsawdey@linux.vnet.ibm.com
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