[PATCH][ARM] Enable code hoisting with -Os (PR80155)

Wilco Dijkstra Wilco.Dijkstra@arm.com
Tue Sep 17 17:18:00 GMT 2019


Hi Richard,

> The issue with the bugzilla is that it lacked appropriate testcase(s) and thus
> it is now a mess.  There are clear testcases (maybe not in the benchmarks you

Agreed - it's not clear whether any of the proposed changes would actually
help the original issue. My patch absolutely does.

> care about) that benefit from code hoisting as enabler, mainly when control
> flow can be then converted to data flow.  Also note that "size optimizations"
> are important for all cases where followup transforms have size limits on the IL
> in place.

The gain from -fcode-hoisting is about 0.2% overall on Thumb-2. Ie. it's definitely
useful, but there are much larger gains to be had from other tweaks [1]. So we can
live without it until a better solution is found.

[1] https://gcc.gnu.org/ml/gcc-patches/2019-07/msg01739.html

Wilco


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