On Wed, Aug 24, 2011 at 9:00 PM, Ian Lance Taylor <i...@google.com> wrote: > Tom de Vries <vr...@codesourcery.com> writes: > >> Do you have a moment to give a second look to a gimple CFG optimization? The >> optimization removes duplicate basic blocks and reduces code size by 1-2%. >> >> The latest patch is posted at >> http://gcc.gnu.org/ml/gcc-patches/2011-08/msg01602.html. > > > I'm not really the best person to look at this patch, since it applies > to areas of the compiler with which I am less familiar.. However, since > you ask, I did read through the patch, and it looks OK to me. Since > Richi OK'ed it, this patch is OK with the following changes. > > >> +typedef struct same_succ *same_succ_t; >> +typedef const struct same_succ *const_same_succ_t; > > Don't name new types ending with "_t". POSIX reserves names ending with > "_t" when <sys/types.h> is #included. Name these something else. > >> +typedef struct bb_cluster *bb_cluster_t; >> +typedef const struct bb_cluster *const_bb_cluster_t; > > Same here. > > >> +@item -ftree-tail-merge >> +Merges identical blocks with same successors. This flag is enabled by >> default >> +at @option{-O2} and higher. The run time of this pass can be limited using >> +@option{max-tail-merge-comparisons} parameter. > > I think this text can be improved to be more meaningful to compiler > users. I suggest something like: > > Look for identical code sequences. When found, replace one with a > jump to the other. This optimization is known as tail merging or > cross jumping. This flag is enabled [now same as above]
Can you also add a --param for the maximum number of iterations you perform (16 sounds quite high for GCC bootstrap), I'd default it to 2 which seems to catch 99% of all cases. If you already committed the patch just do it as a followup please. Thanks, Richard. > > Thanks. > > Ian >
