Re: [Qemu-devel] [PATCH v3 05/25] tcg: Allow extra data to be attached to insn_start

[Kevin O'Connor]

On Tue, Sep 22, 2015 at 01:24:47PM -0700, Richard Henderson wrote:
> With an eye toward having this data replace the gen_opc_* arrays
> that each target collects in order to enable restore_state_from_tb.

Hi Richard,

Instead of having each architecture front-end determine the constants
to be restored on an exception, have you considered having the tcg
liveness pass automatically detect them?

What I was thinking was if:
- each front-end stored each constant on every instruction using
  regular "movi" ops
- tcg_liveness_analysis() tracked which global memory "sync" writes
  are purely due to an op that can raise an exception
- then tcg_liveness_analysis() could remove "movi" instructions with
  outputs that are needed only during an exception and place the
  constant directly in the compressed table itself.

I'm curious if this was considered and if there is a reason it
wouldn't work well.

-Kevin