On Wed, May 15, 2013 at 07:20:03PM +0200, Jakub Jelinek wrote:
> Well, if si->length is known constant != 0 (note, it is enough to
> test that it is non-zero and probably the code above this has
> tested that already?) and we are storing non-zero, then that
> should mean we are overwriting a non-zero value with another (or same)
> non-zero value. Such operation shouldn't change the length of any strings
> at all, not just the ones related to the current strinfo.
Right. Adjusted.
> That is either just setting all current strinfos to dont_invalidate, or
> perhaps faster doing gsi_next (gsi); return false; (that means the caller
> won't call maybe_invalidate - of course in that case you must not set
> any dont_invalidate on any strinfo on that stmt) and the caller of
> strlen_optimize_stmt will not do gsi_next (&gsi) - that is why you need
> to do it instead.
Cool, I took the gsi_next approach; seems to work nicely. So, updated
version (it still doesn't handle p[1], p[2], etc.).
Regtested/bootstrapped on x86_64-linux.
2013-05-16 Marek Polacek <pola...@redhat.com>
* tree-ssa-strlen.c (handle_char_store): Don't invalidate
cached length when doing non-zero store.
* gcc.dg/strlenopt-25.c: New test.
--- gcc/tree-ssa-strlen.c.mp 2013-05-15 14:11:20.079707492 +0200
+++ gcc/tree-ssa-strlen.c 2013-05-16 14:44:06.496545662 +0200
@@ -1717,6 +1717,13 @@ handle_char_store (gimple_stmt_iterator
si->endptr = ssaname;
si->dont_invalidate = true;
}
+ else if (si != NULL && si->length != NULL_TREE
+ && TREE_CODE (si->length) == INTEGER_CST
+ && integer_nonzerop (gimple_assign_rhs1 (stmt)))
+ {
+ gsi_next (gsi);
+ return false;
+ }
}
else if (idx == 0 && initializer_zerop (gimple_assign_rhs1 (stmt)))
{
--- gcc/testsuite/gcc.dg/strlenopt-25.c.mp 2013-05-15 17:15:18.702118637
+0200
+++ gcc/testsuite/gcc.dg/strlenopt-25.c 2013-05-15 18:26:27.881030317 +0200
@@ -0,0 +1,18 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fdump-tree-strlen" } */
+
+#include "strlenopt.h"
+
+int
+main ()
+{
+ char p[] = "foobar";
+ int len, len2;
+ len = strlen (p);
+ p[0] = 'O';
+ len2 = strlen (p);
+ return len - len2;
+}
+
+/* { dg-final { scan-tree-dump-times "strlen \\(" 0 "strlen" } } */
+/* { dg-final { cleanup-tree-dump "strlen" } } */
Marek
