Re: [PATCH] abg-reader: optimize if construction

[Dodji Seketeli <dodji@seketeli.org>]

Hello Xiaole,

Xiaole He via Libabigail <libabigail@sourceware.org> a écrit:

> In 'build_enum_type_decl' function of 'src/abg-reader.cc', the
> 'for loop' walk through all the child nodes of the '<enum-decl>' for
> seeking '<underlying-type>' and '<enumerator>':
>
> /* original src/abg-reader.cc begin */
> static enum_type_decl_sptr
> build_enum_type_decl(read_context& ctxt,
>              const xmlNodePtr node,
>              bool add_to_current_scope)
> {
>   ...
>   for (xmlNodePtr n = xmlFirstElementChild(node);
>        n;
>        n = xmlNextElementSibling(n))
>     {
>       if (xmlStrEqual(n->name, BAD_CAST("underlying-type")))
>       {
>          ...
>       }
>
>       if (xmlStrEqual(n->name, BAD_CAST("enumerator")))
>       {
>          ...
>       }
>     }
>   ...
> }
> /* original src/abg-reader.cc end */
>
> Here uses 2 separate 'if' statements for seeking, that is, for any
> child node of the '<enum-decl>', there involves 2 'if' comparations.
> Because the child node of the '<enum-decl>' is either
> '<underlying-type>' or '<enumerator>', there would be a slight
> optimization when use 'if-else if' construction instead, like below:
>
> /* optimized src/abg-reader.cc begin */
> for (xmlNodePtr n = xmlFirstElementChild(node);
>      n;
>      n = xmlNextElementSibling(n))
>   {
>     if (xmlStrEqual(n->name, BAD_CAST("underlying-type")))
>     {
>        ...
>     }
>     else if (xmlStrEqual(n->name, BAD_CAST("enumerator")))
>     {
>        ...
>     }
>   }
> /* optimized src/abg-reader.cc end */
>
> Supposing there has the test case:
>
> /* test case begin */
> <abi-instr version='1.0'>
>   <enum-decl name='E' filepath='../../abitests/test-enum0-v0.cc' line='1' column='6' id='type-id-2'>
>     <underlying-type type-id='type-id-1'/>
>     <enumerator name='e0' value='0'/>
>     <enumerator name='e2' value='1'/>
>   </enum-decl>
> </abi-instr>
> /* test case end */
>
> When parsing the '<underlying-type>' xml tag, for the original
> 'src/abg-reader.cc', there involves 2 'if' comparations. But involves
> only 1 'if' comparation for the optimized 'src/abg-reader.cc'.
>
> Signed-off-by: Xiaole He <hexiaole@kylinos.cn>
> Tested-by: Xiaole He <hexiaole@kylinos.cn>

Applied to the master branch.

Cheers,

-- 
		Dodji