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Re: [Qemu-devel] [PATCH] ppc: Convert op_440_dlmzb to TCG


From: Andreas Färber
Subject: Re: [Qemu-devel] [PATCH] ppc: Convert op_440_dlmzb to TCG
Date: Sun, 30 Nov 2008 19:03:14 +0100


Am 30.11.2008 um 18:40 schrieb Laurent Desnogues:

On Sun, Nov 30, 2008 at 6:25 PM, Andreas Färber <address@hidden > wrote:

Am 30.11.2008 um 17:31 schrieb Aurélien Jarno:

Doing loops with TCG is a bad idea as it is very inefficient.

Did you read the code? There is no loop in TCG here, that's exactly what I
was saying.
The labels are for conditionals only and for exiting the non-loop.

If you have a better suggestion, please say so as this is one of the dyngen
ops that keep me from working on the conversion on my own system.

Going for a helper might be better for larger sequences of TCG ops;
Fabrice mentions a threshold of about 20 ops.  And your replacement
is certainly larger than 20 ops :-) Plus given it uses brcond, it would
prevent TCG liveness analysis from doing its job in the basic block
containing that instruction.

Thanks for the explanation!

So, if I encounter a dyngen op that calls a helper, then in general I should convert it to TCG code calling the helper?

My next problem is op_440_tlbre, which does call a helper, but with a PARAM1 argument. Any hint how to translate that?

Andreas



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