Re: Make max_issue honor issue_rate

[Maxim Kuvyrkov <maxim at codesourcery dot com>]

On 10/25/10 2:36 PM, Jie Zhang wrote:

> 4 units: a, b, c, d.
>
> insn 1 uses a, insn 2 uses b, insn 3 uses c, insn 4 uses d.
>
> and we set issue_rate to 3. In this case, we can only issue insn 1, 2, 3
> but not 4 although its unit is free.
>
> To extend this example a little, i.e. insn4 uses nothing, (it does not
> change the state, right? I'm not very sure), it still can not be issued.
>
> So I think we should use "top - choice_stack >= more_issue" instead of
> "top->n >= more_issue". Am I right?

I think the 'n' field was introduced for a reason.  DFA description has 
the "nothing" reservation that specifies that a particular instruction 
does not have a noticeable effect on a CPU (imagine a nop instruction 
that gets optimized out by decoder and does not get into the pipeline).

Regards,

--
Maxim Kuvyrkov
CodeSourcery
maxim@codesourcery.com
(650) 331-3385 x724