From: "Emilio G. Cota" <cota@braap.org>
To: Richard Henderson <rth@twiddle.net>
Cc: qemu-devel@nongnu.org, Peter Maydell <peter.maydell@linaro.org>,
Eduardo Habkost <ehabkost@redhat.com>,
Peter Crosthwaite <crosthwaite.peter@gmail.com>,
Stefan Weil <sw@weilnetz.de>, Alexander Graf <agraf@suse.de>,
alex.bennee@linaro.org, qemu-arm@nongnu.org,
Pranith Kumar <bobby.prani+qemu@gmail.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Aurelien Jarno <aurelien@aurel32.net>
Subject: Re: [Qemu-devel] [PATCH 05/10] tcg: add jr opcode
Date: Sun, 16 Apr 2017 14:28:43 -0400 [thread overview]
Message-ID: <20170416182843.GA30160@flamenco> (raw)
In-Reply-To: <73257eb8-edfd-ae0b-a5fa-b1194de568d8@twiddle.net>
On Sat, Apr 15, 2017 at 04:40:35 -0700, Richard Henderson wrote:
> On 04/11/2017 06:17 PM, Emilio G. Cota wrote:
> >This will be used by TCG targets to implement a fast path
> >for indirect branches.
> >
> >I only have implemented and tested this on an i386 host, so
> >make this opcode optional and mark it as not implemented by
> >other TCG backends.
>
> I don't think this is quite the right abstraction. In particular, if we can
> always return a valid address from the helper, we can eliminate a
> conditional branch.
>
> I think this should work as follows:
(snip)
Yes that's much better. In fact in the cover letter I forgot to
mention that the code by the paper authors does something similar
to avoid the branch.
I went with the design with a branch because (1) I wasn't sure that
exporting tb_ret_addr would get your approval and (2) my knowledge
of TCG backend code is shamefully poor.
Will work on a v2. Thanks for the feedback!
Emilio
next prev parent reply other threads:[~2017-04-16 18:28 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-12 1:17 [Qemu-devel] [PATCH 00/10] TCG optimizations for 2.10 Emilio G. Cota
2017-04-12 1:17 ` [Qemu-devel] [PATCH 01/10] exec-all: add tb_from_jmp_cache Emilio G. Cota
2017-04-12 1:17 ` [Qemu-devel] [PATCH 02/10] exec-all: inline tb_from_jmp_cache Emilio G. Cota
2017-04-12 1:17 ` [Qemu-devel] [PATCH 03/10] target/arm: optimize cross-page block chaining in softmmu Emilio G. Cota
2017-04-15 11:24 ` Richard Henderson
2017-04-12 1:17 ` [Qemu-devel] [PATCH 04/10] target/i386: " Emilio G. Cota
2017-04-12 1:17 ` [Qemu-devel] [PATCH 05/10] tcg: add jr opcode Emilio G. Cota
2017-04-13 5:09 ` Paolo Bonzini
2017-04-15 11:40 ` Richard Henderson
2017-04-16 18:28 ` Emilio G. Cota [this message]
2017-04-12 1:17 ` [Qemu-devel] [PATCH 06/10] tcg: add brcondi_ptr Emilio G. Cota
2017-04-12 1:17 ` [Qemu-devel] [PATCH 07/10] tcg: add tcg_temp_local_new_ptr Emilio G. Cota
2017-04-12 1:17 ` [Qemu-devel] [PATCH 08/10] target/arm: optimize indirect branches with TCG's jr op Emilio G. Cota
2017-04-12 1:17 ` [Qemu-devel] [PATCH 09/10] target/i386: " Emilio G. Cota
2017-04-12 3:43 ` Paolo Bonzini
2017-04-13 1:46 ` Emilio G. Cota
2017-04-14 5:17 ` Paolo Bonzini
2017-04-12 1:17 ` [Qemu-devel] [PATCH 10/10] tb-hash: improve tb_jmp_cache hash function in user mode Emilio G. Cota
2017-04-12 3:46 ` Paolo Bonzini
2017-04-12 5:07 ` Emilio G. Cota
2017-04-12 10:03 ` [Qemu-devel] [PATCH 00/10] TCG optimizations for 2.10 Alex Bennée
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