Fix PR77880

Fix PR77880

[Bernd Schmidt]

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When encountering a memcmp with something like ULONG_MAX for the size, a 
calculation can overflow in by_pieces_ninsns because it uses int rather 
than HOST_WIDE_INT.

Bootstrapped & tested on x86_64-linux, committed as obvious.


Bernd


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Index: gcc/ChangeLog
===================================================================
--- gcc/ChangeLog	(revision 240861)
+++ gcc/ChangeLog	(working copy)
@@ -1,3 +1,9 @@
+2016-10-07  Bernd Schmidt  <bschmidt@redhat.com>
+
+	PR tree-optimization/77880
+	* expr.c (by_pieces_ninsns): Use unsigned HOST_WIDE_INT where
+	necessary.
+
 2016-10-07  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/77803
Index: gcc/expr.c
===================================================================
--- gcc/expr.c	(revision 240861)
+++ gcc/expr.c	(working copy)
@@ -785,7 +785,7 @@ by_pieces_ninsns (unsigned HOST_WIDE_INT
 	    case COMPARE_BY_PIECES:
 	      int batch = targetm.compare_by_pieces_branch_ratio (mode);
 	      int batch_ops = 4 * batch - 1;
-	      int full = n_pieces / batch;
+	      unsigned HOST_WIDE_INT full = n_pieces / batch;
 	      n_insns += full * batch_ops;
 	      if (n_pieces % batch != 0)
 		n_insns++;