Hi!
On Mon, Sep 26, 2011 at 04:33:05PM +0200, Richard Guenther wrote:
> Btw, can you add a changes.html entry for this?
Like this?
--- htdocs/gcc-4.7/changes.html 27 Sep 2011 18:42:56 -0000 1.38
+++ htdocs/gcc-4.7/changes.html 29 Sep 2011 12:56:42 -0000
@@ -124,6 +124,48 @@ void bar (void)
possibly only by inlining all calls. Cloning causes a lot less code size
growth.</li>
</ul></li>
+
+ <li>String length optimization pass has been added. This pass attempts
+ to track string lengths and optimize various standard C string functions
+ like <code>strlen</code>, <code>strchr</code>, <code>strcpy</code>,
+ <code>strcat</code>, <code>stpcpy</code> and their
+ <code>_FORTIFY_SOURCE</code> counterparts into faster alternatives.
+ This pass is enabled by default at <code>-O2</code> or above, unless
+ optimizing for size, and can be disabled by
+ <code>-fno-optimize-strlen</code> option. The pass can e.g. optimize
+ <pre>
+char *bar (const char *a)
+{
+ size_t l = strlen (a) + 2;
+ char *p = malloc (l); if (p == NULL) return p;
+ strcpy (p, a); strcat (p, "/"); return p;
+}
+ </pre>
+ can be optimized into:
+ <pre>
+char *bar (const char *a)
+{
+ size_t tmp = strlen (a);
+ char *p = malloc (tmp + 2); if (p == NULL) return p;
+ memcpy (p, a, tmp); memcpy (p + tmp, "/", 2); return p;
+}
+ </pre>
+ or for hosted compilations where <code>stpcpy</code> is available in the
+ runtime and headers provide its prototype, e.g.
+ <pre>
+void foo (char *a, const char *b, const char *c, const char *d)
+{
+ strcpy (a, b); strcat (a, c); strcat (a, d);
+}
+ </pre>
+ into:
+ <pre>
+void foo (char *a, const char *b, const char *c, const char *d)
+{
+ strcpy (stpcpy (stpcpy (a, b), c), d);
+}
+ </pre>
+ </li>
</ul>
<h2>New Languages and Language specific improvements</h2>
Jakub
