Re: Question about direct block chaining

[Richard Henderson]

On 4/18/22 07:54, Taylor Simpson wrote:
> I implemented both approaches for inner loops and didn't see speedup in my 
> benchmark.  So, I have a couple of questions
> 1) What are the pros and cons of the two approaches (lookup_and_goto_ptr and 
> goto_tb + exit_tb)?

goto_tb can only be used within a single page (plus other restrictions, see 
translator_use_goto_tb).  In addition, as documented, the change in cpu state must be 
constant, beginning with a direct jump.

lookup_and_goto_ptr can handle any change in cpu state, including indirect 
jumps.


> 2) How can I verify that direct block chaining is working properly?
>        With -d exec, I see lines like the following with goto_tb + exit_tb but 
> NOT lookup_and_goto_ptr
>        Linking TBs 0x7fda44172e00 [0050ac38] index 1 -> 0x7fda44173b40 
> [0050ac6c]

Well, that's one way.  I would have also suggested simply looking at -d op output, for the 
various branchy cases you're considering, to see that all of the exits are as expected.


r~