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From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/49263] SH Target: underutilized "TST #imm, R0"
 instruction
Date: Thu, 25 May 2023 21:32:35 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D49263

--- Comment #40 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Alexander Klepikov from comment #39)
>=20
> I'm sorry, but .md lang is too complicated for me.

Yeah, it looks alien at first sight.  But it's where a lot of things happen
w.r.t. instruction selection.

> 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 lib=
cll
> cannot be converted. It seems that very first optimization spoils things.
>=20
> But when we have numerous 'shar' instructions, optimization joins the game
> again and converts them to 'tst'.

Yes, something like this is what I remember happening there.  I'll try to l=
ook
into the issue with your test cases and see if it's possible to add some
patterns to catch those.

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 k=
ind
of thing.

> You are absolutely right, the code will be larger when we do right shifts.
> But there's situations when you can't use library. For exmple, SH7055 eng=
ine
> control unit can barely contain the program. The library just won't fit.

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