Re: [PATCH] add statistics counting to postreload, copy-rename, and math-opts

[Nathan Froyd <froydnj@codesourcery.com>]

On Tue, Apr 12, 2011 at 04:54:43PM +0200, Richard Guenther wrote:
> On Tue, Apr 12, 2011 at 4:51 PM, Nathan Froyd <froydnj@codesourcery.com> wrote:
> > True, but maybe those testcases should be adjusted--per-pass flags,
> > rather than blindly assuming -O2 includes them.  And it's not clear to
> 
> It's easier to add things to GCC than to argue removing things ...

And sometimes not even easy to argue for adding things. :)

> > me that the statistics_counter_event infrastructure really helps
> > catching do-nothing passes, since it doesn't record stats that increment
> > by zero...
> 
> Well, if the overall count is zero then nothing was done.

Granted, but that fact should still be recorded.  The situation we have
today, for something like:

func1: statistic for "statx" was 0
  - nothing is recorded in the statistics table
func2: statistic for "statx" was 0
  - nothing is recorded in the statistics table
func3: statistic for "statx" was 0
  - nothing is recorded in the statistics table
...

and so forth, is that at the end of the day, the dump file won't even
include any information about "statx".  If you had some func7387 where
"statx" was non-zero, you could infer that nothing else happened in the
previous 7386 functions.  For the case where a pass is truly useless on
a TU, it's hard to figure out from the statistics dump alone.  And I'd
argue that it's useful to see explicitly that the pass only helped in 1
out of 7387 functions, rather than trying to infer it from missing data.

-Nathan