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Re: [Qemu-arm] [Qemu-devel] [PATCH 5/7] target-arm: Add isread parameter

From: Peter Maydell
Subject: Re: [Qemu-arm] [Qemu-devel] [PATCH 5/7] target-arm: Add isread parameter to CPAccessFns
Date: Fri, 5 Feb 2016 16:27:14 +0000

On 5 February 2016 at 16:17, Alex Bennée <address@hidden> wrote:
> Peter Maydell <address@hidden> writes:
>> I haven't measured, no, but since there are only 3 arguments the
>> third argument is going to be in a register on any host architecture
>> we care about, which means the overhead is just going to be a single
>> "load constant 0 or 1 into register before the call". I think that's
>> going to be lost in the noise compared to actually having to make
>> the function call at all, the work the function call does, and then
>> the second function call later to do the read or write.
> I was thinking of knock on effects on spilling other registers in the
> TCG code. I guess this depends on how complex the code is around system
> register access.

The register in question is going to be caller-saves anyway, so no
effect on spilling in the TCG code I think.

-- PMM

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