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. Stefan
