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From: "klepikov.alex+bugs at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/54089] [SH] Refactor shift patterns
Date: Thu, 08 Jun 2023 12:07:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D54089

--- Comment #68 from Alexander Klepikov <klepikov.alex+bugs at gmail dot co=
m> ---
OK, I finished my patch. Let me remind you briefly, what it does.

First, it does not emit library call for ashrsi3 during expand pass. Instea=
d it
emits intermediate 'collapsed' libcall insn which is expanded later at spli=
t1
pass.

Consecutive right arithmetic shifts can be catched at combine pass
and converted to 'collapsed' libcall insn.

Then 'collapsed' insn splits whether to short sequnce of individual right
shifts
or to __ashiftrt_r4_N library call during split1 pass.

Finally, loop move invariants only pass executed right after split1 pass
to hoist library addresses that potentially were emitted during split pass.

I ran GCC testsuite and there were 1 new failed test that actually turned o=
ut
to be an optimization, and 3 tests that failed on clean GCC and passed on
patched. I could not set up my environment to test all little endian exec
tests, so for those I don't have results. Also I successfully compiled (but=
 not
linked due to not fully set environment) Linux kenel 6.1. My homemade
performance tests (I timed linux kernel build) showed a slowdown of less th=
en
3%.

To reduce slowdown it would be good to run loop move invariants pass only in
functions that have expanded libcall, but to do so it is necessary to mark =
such
funcnion when emitting insn and I'm not so sure if insn knows about in what
function it is located.=