Re: [Sablevm-developer] pc++ to skip preparation address in (GET|PUT)(FIELD|STATIC)

[Grzegorz B. P. <ga...@de...>]

W liście z pon, 26-01-2004, godz. 23:34, Chris Pickett pisze: 
> Hi Greg,
> 
> I'm almost done merging staging into my tree (should be done tomorrow if 
> not tonight).
Nice.

> I notice that instructions.m4.c in staging@r1503 no longer has a pc++ to 
> skip the preparation address at the beginning of (GET|PUT)(FIELD|STATIC).
Right.

> How does this address get skipped in the switch interpreter without 
> inlinability testing?
> 
> You have a some _svmf_no_inlining_increment_pc() function, but it's only 
> turned on / defined for inlinability testing.
> 
> The other instructions like INVOKE<X> still have the pc++ at the 
> beginning.  I checked in prepare_code.c and the preparation address is 
> still being used, I'm just wondering where it gets skipped ...
First see two_modes.list - it list all two-mode instructions.

Then see instructions_preparation.m4.c - there's all logic (or magic)
there. See m4svm_mark_start_and_skip macro which has two versions.
You're mainly interested in m4svm_mark_start_and_skip_normal.

For any two-modes bytecode it generates this code:

  if (SVM_INLINEABLE_$1 != SVM_INTRP_FLAG_INLINEABLE) pc++; 

Note, that the result of the comparison is known at comile time
as both values are #defines so no real conditional here.
Also note, that it depends on the value of SVM_INLINEABLE_$1 of
certain bytecode for certain architecture so we don't hardcode
pc++ usage in two_modes.list.

And for non-inlined engines it does pc++ for all two-modes instructions.

HTH

				Grzegorz B. Prokopski

-- 
Grzegorz B. Prokopski <ga...@de...>
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