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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: Tue, 23 May 2023 19:05:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D49263

--- Comment #34 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Alexander Klepikov from comment #33)
> Created attachment 55142 [details]
> Disable dynamic shift instructions patch

First of all, thanks for digging into this.  This issue has been a can of
worms, due to all sorts of reasons.

As you have discovered, some code patterns take the shift instruction route,
which is basically decided earlier by the various middle-end optimizations.=
=20
There have also been some changes to those parts recently, but I haven't be=
en
watching what it does for SH.

> unsigned int f(char v){
>     return (v & FLAG) =3D=3D FLAG;
> }

Bit-tests of char and unsigned char should be covered by the test-suite and
should work -- at least originally.  However, what might be triggering this
problem is the '=3D=3D FLAG' comparison.  When I was working on this issue =
I only
used '=3D=3D 0' or '!=3D 0' comparison.  I can imagine that your test code =
triggers
some other middle end optimizations and hence we get this.

Can you try to rewrite your test code to something like this?

unsigned int f(char v){
    return (v & FLAG) !=3D 0;
}

... and see if it generates the tst instruction as expected?


> I also compiled my project with '-m2e' and new '-mdisable-dynshift'
> options and tested it in SH-2E mone on Renesas's emulator that comes
> with High-performance Embedded Workshop and all unit tests run as expecte=
d.

I'm not sure what the purpose of the '-mdisable-dynshift' option would be h=
ere
though.  For '-m2e' TARGET_DYNSHIFT is already 'false'.  So the option seems
misnamed.=