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Re: VM jump table address kept in a register
From: |
Ludovic Courtès |
Subject: |
Re: VM jump table address kept in a register |
Date: |
Thu, 07 Jul 2011 15:42:11 +0200 |
User-agent: |
Gnus/5.110017 (No Gnus v0.17) Emacs/24.0.50 (gnu/linux) |
Hi,
Andy Wingo <address@hidden> skribis:
> I looked at specifying registers for the IP, SP, and FP as well. I got
> positive improvements with IP and FP but not (oddly) with SP. Should we
> try this?
>
> #define IP_REG asm ("r13")
> #define FP_REG asm ("r14")
I tried, and it’s noticeably worse than letting it choose %rbp and
%rbx.
I don’t have any explanation, though. It could be that loads to/from
r13/r14 are longer to decode, or that it is stressing GCC’s register
allocator in a bad way.
Thanks,
Ludo’.