[Bug tree-optimization/108696] querying relations is slow

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108696

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Macleod from comment #2)
> Created attachment 54437 [details]
> possible patch
> 
> This patch should successfully short circuit unnecessary checks. untested in
> compiler.i
> 
> Where did you get a 17% time in DOM?  when I run compiler.i I get
> dominator optimization             :  38.28 (  2%) 
> where most of the time is in
> machine dep reorg                  :1447.64 ( 60%) 
> 
> I'll check this patch for correctness and to see if it generally makes any
> time improvements that are measurable elsewhere.

It helps the callgrind profile but doesn't show any effect on the -ftime-report
or a perf profile.  For the testcase the bitmap operations in ranger are
definitely visible in a perf profile (with call traces), and with -O1 it's
mostly DOM and jump-threading that perform any ranger ops when diagnostics are
disabled.

That said, not allocating the self-relation bitmaps at query time is
definitely good (not 100% sure if the patch achieves that).