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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/49263] SH Target: underutilized "TST #imm, R0"
 instruction
Date: Fri, 26 May 2023 12:03:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D49263

--- Comment #41 from Alexander Klepikov <klepikov.alex+bugs at gmail dot co=
m> ---
> > It looks like with optimization enabled it converts bitwise AND to right
> > shift and then optimizes again. But SH4 has 'shad' and 'shad' can be
> > optimized to 'tst'. And SH2E has libcall instead of dynamic shift and l=
ibcll
> > cannot be converted. It seems that very first optimization spoils thing=
s.
> >=20
> > But when we have numerous 'shar' instructions, optimization joins the g=
ame
> > again and converts them to 'tst'.
>=20
> Yes, something like this is what I remember happening there.  I'll try to
> look into the issue with your test cases and see if it's possible to add
> some patterns to catch those.

Thank you! I have an idea. If it's impossible to defer initial optimization,
maybe it's possible to emit some intermediate insn and catch it and optimize
later?

> BTW, have you tried it on a more recent GCC?  There have also been some
> optimizations in the middle-end (a bit more backend independent) for this
> kind of thing.

I tried 13.1 about week or two ago with the same result.

> Have you tried to use whole program optimization via -flto and
> -ffunction-sections? It  should be able to strip out all unnecessary libr=
ary
> functions.

Thank you for advice, I'll take a try.=