Re: [RFC] Various questions about TCG implementation, DRM patches dealing with pointers over guest-host barrier.

[Richard Henderson <richard.henderson@linaro.org>]

On 5/17/20 4:05 PM, Catherine A. Frederick wrote:
> - I've been implementing an instruction scheduler(list scheduler, with priority
> given to most successors) for TCG and currently if I replace instructions in
> s->ops(the TCG context) I get a crash later in tcg_reg_alloc_op, even if the
> instruction stream is identical. Is there anything else I need to move when I
> do this?

If you're getting a crash in tcg_reg_alloc_op, are you updating liveness info?
 Where are you inserting your scheduler in the list of passes?

> - Is insn_start necessary to have in order(and what does it do?)? These
> currently are serializing instructions in my scheduler and significantly limit
> my reordering as they create lots of dependencies every few instructions.

insn_start is required for unwinding from exceptions.  You can consider it a
barrier for call and qemu_ld/st.  Anything else cannot raise an exception and
can be moved.


r~