| Message ID | 20110929130217.GU2687@tyan-ft48-01.lab.bos.redhat.com |
|---|---|
| State | New |
| Headers | show |
On Thu, Sep 29, 2011 at 3:02 PM, Jakub Jelinek <jakub@redhat.com> wrote: > 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? Yes. Thanks, Richard. > --- 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 >
--- 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>
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? Jakub