Re: [PATCH] tcg: Introduce tcg_remove_ops_after

[Peter Maydell <peter.maydell@linaro.org>]

On Fri, 4 Jun 2021 at 22:27, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Introduce a function to remove everything emitted
> since a given point.
>
> Cc: Peter Maydell <peter.maydell@linaro.org>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  include/tcg/tcg.h |  1 +
>  tcg/tcg.c         | 13 +++++++++++++
>  2 files changed, 14 insertions(+)
>
> diff --git a/include/tcg/tcg.h b/include/tcg/tcg.h
> index 74cb345308..6895246fab 100644
> --- a/include/tcg/tcg.h
> +++ b/include/tcg/tcg.h
> @@ -1081,6 +1081,7 @@ TCGOp *tcg_emit_op(TCGOpcode opc);
>  void tcg_op_remove(TCGContext *s, TCGOp *op);
>  TCGOp *tcg_op_insert_before(TCGContext *s, TCGOp *op, TCGOpcode opc);
>  TCGOp *tcg_op_insert_after(TCGContext *s, TCGOp *op, TCGOpcode opc);
> +void tcg_remove_ops_after(TCGOp *op);

A doc comment would be nice.

>  void tcg_optimize(TCGContext *s);
>
> diff --git a/tcg/tcg.c b/tcg/tcg.c
> index 0dc271aac9..262dbba1fd 100644
> --- a/tcg/tcg.c
> +++ b/tcg/tcg.c
> @@ -2649,6 +2649,19 @@ void tcg_op_remove(TCGContext *s, TCGOp *op)
>  #endif
>  }
>
> +void tcg_remove_ops_after(TCGOp *op)
> +{
> +    TCGContext *s = tcg_ctx;
> +
> +    while (true) {
> +        TCGOp *last = tcg_last_op();
> +        if (last == op) {
> +            return;
> +        }
> +        tcg_op_remove(s, last);
> +    }
> +}

This looks OK as far as TCG proper goes, but is it going to confuse
the TCG plugin infrastructure if a frontend generates a bunch of
TCG IR and then winds back the insn stream and generates something
else instead ? I see some calls from tcg/ into plugin related
functions, so I'm not sure...

thanks
-- PMM