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Re: [Qemu-devel] [RFC 20/28] target-xtensa: implement windowed registers
From: |
Richard Henderson |
Subject: |
Re: [Qemu-devel] [RFC 20/28] target-xtensa: implement windowed registers |
Date: |
Wed, 04 May 2011 13:07:32 -0700 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc14 Thunderbird/3.1.10 |
On 05/04/2011 12:35 PM, Blue Swirl wrote:
> On Wed, May 4, 2011 at 3:59 AM, Max Filippov <address@hidden> wrote:
>> See ISA, 4.7.1 for details.
>>
>> Physical registers and currently visible window are separate fields in
>> CPUEnv. Only current window is accessible to TCG. On operations that
>> change window base helpers copy current window to and from physical
>> registers.
>
> I'm not sure how the register windows work, but maybe you could use
> the same trick used for Sparc. There is a pool of registers
> (env->regbase[]), a register window pointer (env->regwptr,
> cpu_regwptr) tracks which are the currently accessible ones. The
> advantage is to avoid copying (not entirely for Sparc due to the
> window overlap).
Sparc loses out on some TCG optimizations because of that, although
to be fair the most effective of these are still in Aurlien's trees.
That said, I still would not recommend a new port to follow suit.
r~
- [Qemu-devel] [RFC 18/28] target-xtensa: implement exceptions, (continued)
[Qemu-devel] [RFC 19/28] target-xtensa: implement RST2 group (32 bit mul/div/rem), Max Filippov, 2011/05/03
[Qemu-devel] [RFC 20/28] target-xtensa: implement windowed registers, Max Filippov, 2011/05/03
[Qemu-devel] [RFC 21/28] target-xtensa: implement loop option, Max Filippov, 2011/05/03
[Qemu-devel] [RFC 22/28] target-xtensa: implement extended L32R, Max Filippov, 2011/05/03
[Qemu-devel] [RFC 23/28] target-xtensa: implement unaligned exception option, Max Filippov, 2011/05/03
[Qemu-devel] [RFC 24/28] target-xtensa: implement SIMCALL, Max Filippov, 2011/05/03
[Qemu-devel] [RFC 25/28] target-xtensa: implement interrupt option, Max Filippov, 2011/05/03
[Qemu-devel] [RFC 26/28] target-xtensa: implement accurate window check, Max Filippov, 2011/05/03