Re: [Qemu-devel] [PATCH 5/8] tcg: Add interpreter for bytecode

[Avi Kivity]

On 09/18/2011 10:22 AM, Paolo Bonzini wrote:
> On 09/18/2011 07:49 AM, Stefan Weil wrote:
> > Is there really any difference in the generated code?
> > gcc already uses a jump table internally to handle the
> > switch cases.
>
> You typically save something on range checks, and it enables a lot 
> more tricks for use later (e.g. using multiple jump tables to perform 
> simple peephole optimizations, or to divert code execution on 
> interrupts).

I think it also improves branch target prediction - if you have a tight 
loop of a few opcodes the predictor can guess where you're headed (since 
there is a separate lookup key for each opcode), whereas with the 
original code, there's a single key which cannot be used to predict the 
branch target.

--
error compiling committee.c: too many arguments to function