On Fri, Sep 10, 2010 at 03:32:14PM +0200, Stefan Sperling wrote: > On Thu, Sep 09, 2010 at 10:58:06PM -0000, stef...@apache.org wrote: > > Author: stefan2 > > Date: Thu Sep 9 22:58:06 2010 > > New Revision: 995603 > > > > URL: http://svn.apache.org/viewvc?rev=995603&view=rev > > Log: > > Try really hard to help the compiler generate good code > > for this frequently called function. > > > > * subversion/libsvn_subr/svn_string.c > > (svn_stringbuf_appendbyte): reformulate > > > > Modified: > > subversion/branches/performance/subversion/libsvn_subr/svn_string.c > > > > Modified: > > subversion/branches/performance/subversion/libsvn_subr/svn_string.c > > URL: > > http://svn.apache.org/viewvc/subversion/branches/performance/subversion/libsvn_subr/svn_string.c?rev=995603&r1=995602&r2=995603&view=diff > > ============================================================================== > > --- subversion/branches/performance/subversion/libsvn_subr/svn_string.c > > (original) > > +++ subversion/branches/performance/subversion/libsvn_subr/svn_string.c Thu > > Sep 9 22:58:06 2010 > > @@ -403,8 +403,11 @@ svn_stringbuf_appendbyte(svn_stringbuf_t > > apr_size_t old_len = str->len; > > if (str->blocksize > old_len + 1) > > { > > - str->data[old_len] = byte; > > - str->data[old_len+1] = '\0'; > > + char *dest = str->data; > > + > > + dest[old_len] = byte; > > + dest[old_len+1] = '\0'; > > + > > str->len = old_len+1; > > } > > else > > @@ -412,7 +415,8 @@ svn_stringbuf_appendbyte(svn_stringbuf_t > > /* we need to re-allocate the string buffer > > * -> let the more generic implementation take care of that part > > */ > > - svn_stringbuf_appendbytes(str, &byte, 1); > > + char b = byte; > > + svn_stringbuf_appendbytes(str, &b, 1); > > } > > } > > > > > > If you're expecting this function to stay written as it now, > you need to add a comment explaining why it is laid out the way it is. > Otherwise people might change it, and the resulting generated code will > be less optimal again. > > That said, I have my doubts whether tweaking C code in order to tune the > output of certain compilers in certain versions is a useful thing to do. > Will this still work as expected when new compiler versions are released? > It seems you'd rather want to fix the optimizer of the compiler.
This has been merged into trunk now, so I'm bumping this thread to repeat my question above. Stefan
