Re: [Qemu-devel] [PATCH v1 2/3] tcg-runtime: light re-factor of lookup_tb_ptr

[Richard Henderson <rth@twiddle.net>]

On 06/14/2017 07:02 AM, Alex Bennée wrote:
> Just a little precursor re-factoring before I was going to add a trace
> point:
> 
>    - single return point, defaulting to tcg_ctx.code_gen_epilogue

Why?  Any if you're going to do that, why not init ret = epilogue and avoid the 
null test at the end?

>    - move cs_base, pc and flags inside the jump cache hit scope

Funny story.  While looking at this again, I notice that there's no reason to 
avoid, and every reason not to avoid, calling tb_htable_lookup when 
tb_jmp_cache is empty.  So I'm now doing

     tb = atomic_rcu_read(...);
     cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);

     if (!(tb && tb->pc == addr && ...)) {
         tb = tb_htable_lookup(...);
         ...

>    - calculate the tb_jmp_cache hash once

I did look once and the compiler is doing the CSE.  But it does look cleaner.


r~