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From: "Alex Bennée" <alex.bennee@linaro.org>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Richard Henderson <richard.henderson@linaro.org>,
	qemu-devel@nongnu.org,
	"Catherine A. Frederick" <agrecascino123@gmail.com>
Subject: Re: [RFC] Various questions about TCG implementation, DRM patches dealing with pointers over guest-host barrier.
Date: Mon, 18 May 2020 11:52:15 +0100	[thread overview]
Message-ID: <877dx9ldls.fsf@linaro.org> (raw)
In-Reply-To: <CAFEAcA-yTm7h_EGZ4_iKVGJ0GMFinWOyQXyKsYgs8s933Bnn1Q@mail.gmail.com>


Peter Maydell <peter.maydell@linaro.org> writes:

> On Mon, 18 May 2020 at 00:23, Catherine A. Frederick
> <agrecascino123@gmail.com> wrote:
>> Hi, I've been patching TCG for my own purposes recently and I was
>> wondering a few things. That being:
>>
<snip>
>> - I've been implementing an instruction scheduler(list scheduler, with
>> priority given to most successors) for TCG and currently if I replace
>> instructions in s->ops(the TCG context) I get a crash later in
>> tcg_reg_alloc_op, even if the instruction stream is identical. Is there
>> anything else I need to move when I do this?
>
> This one's out of my field of knowledge; Richard might know.

I'm a little unclear in what is happening here. For TCG plugins we
insert dummy ops into the stream so they can be replaced or removed at a
later phase in the translation.

>> - Is insn_start necessary to have in order(and what does it do?)? These
>> currently are serializing instructions in my scheduler and significantly
>> limit my reordering as they create lots of dependencies every few
>> instructions.
>
> The primary purpose of insn_start is to save information about the
> current instruction in a metadata
<snip>
> Finally, I haven't checked, but I suspect the new TCG plugin APIs
> implicitly assume that code for each insn is generated serially,
> ie that a plugin can do "for each instruction" type work on a
> callback that hangs off the insn_start op.

Spoiler alert: Yes it does ;-)

-- 
Alex Bennée


  reply	other threads:[~2020-05-18 10:53 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-17 23:05 [RFC] Various questions about TCG implementation, DRM patches dealing with pointers over guest-host barrier Catherine A. Frederick
2020-05-18 10:21 ` Peter Maydell
2020-05-18 10:52   ` Alex Bennée [this message]
2020-05-19 14:51 ` Richard Henderson

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