Re: [PATCH] tree-optimization/102943 - avoid (re-)computing dominance bitmap

[Jeff Law <jeffreyalaw@gmail.com>]

On 3/10/2022 4:50 AM, Richard Biener via Gcc-patches wrote:
> Currently back_propagate_equivalences tries to optimize dominance
> queries in a smart way but it fails to notice that when fast indexes
> are available the dominance query is fast (when called from DOM).
> It also re-computes the dominance bitmap for each equivalence recorded
> on an edge, which for FP are usually several.  Finally it fails to
> use the tree bitmap view for efficiency.  Overall this cuts 7
> seconds of compile-time from originally 77 in the slowest LTRANS
> unit when building 521.wrf_r.
>
> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
>
> Richard.
>
> 2022-03-10  Richard Biener  <rguenther@suse.de>
>
> 	PR tree-optimization/102943
> 	* tree-ssa-dom.cc (back_propagate_equivalences): Only
> 	populate the dominance bitmap if fast queries are not
> 	available.  Use a tree view bitmap.
> 	(record_temporary_equivalences): Cache the dominance bitmap
> 	across all equivalences on the edge.
Anything that helps WRF build times is a win in my book.    IIRC the 
worst module in there takes something like 27 minutes to cross compile 
for our target.  Annoying as hell when you have to do it multiple times 
a day.

jeff