[Spice-devel] [PATCH spice-server 3/6] spicevmc: Avoid computing some variable value if not necessary

[Frediano Ziglio]

> 
> On Thu, Jan 26, 2017 at 10:56:45AM +0000, Frediano Ziglio wrote:
> > Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> > ---
> >  server/spicevmc.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/server/spicevmc.c b/server/spicevmc.c
> > index a92ec7f..23e60b3 100644
> > --- a/server/spicevmc.c
> > +++ b/server/spicevmc.c
> > @@ -585,12 +585,13 @@ static uint8_t
> > *spicevmc_red_channel_alloc_msg_rcv_buf(RedChannelClient *rcc,
> >                                                         uint32_t size)
> >  {
> >      RedVmcChannel *channel;
> > -    RedClient *client = red_channel_client_get_client(rcc);
> > -
> > -    channel = RED_VMC_CHANNEL(red_channel_client_get_channel(rcc));
> > +    RedClient *client;
> >  
> >      switch (type) {
> >      case SPICE_MSGC_SPICEVMC_DATA:
> > +        client = red_channel_client_get_client(rcc);
> > +        channel = RED_VMC_CHANNEL(red_channel_client_get_channel(rcc));
> > +
> >          assert(!channel->recv_from_client_buf);
> >  
> >          channel->recv_from_client_buf =
> >          red_char_device_write_buffer_get(channel->chardev,
> > @@ -615,10 +616,9 @@ static void
> > spicevmc_red_channel_release_msg_rcv_buf(RedChannelClient *rcc,
> >  {
> >      RedVmcChannel *channel;
> >  
> > -    channel = RED_VMC_CHANNEL(red_channel_client_get_channel(rcc));
> > -
> >      switch (type) {
> >      case SPICE_MSGC_SPICEVMC_DATA:
> > +        channel = RED_VMC_CHANNEL(red_channel_client_get_channel(rcc));
> >          /* buffer wasn't pushed to device */
> >          red_char_device_write_buffer_release(channel->chardev,
> >          &channel->recv_from_client_buf);
> >          break;
> 
> This is something that I'd just let the compiler handle if needed. Note
> that this also change some variables from being always initialized to
> sometimes being initialized, which is in my opinion is not necessarily a
> good move.
> 
> Christophe
> 

In this case the compiler cannot do it. How can it know that not calling
a function does not make any difference?
If you are going to use channel not initialized the compiler will
warn you so it's not a big deal.

Frediano