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Re: [PATCH] Fix DCE REG_LIBCALL note moving from noop move insns (PR rtl-optimization/33644)


On 10/14/07, Eric Botcazou <ebotcazou@libertysurf.fr> wrote:
> > For the record, REG_LIBCALL_ID also has very clear semantics.
> > REG_LIBCALL_ID signifies the current instruction is part of a libcall
> > sequence. All insns that are part of the same libcall share the same
> > ID number.
>
> I understand, but we now have 2 concurrent semantics for libcall sequences.
>
> > Why make DCE slower instead of fixing the bug?
>
> Because I think it's only the tip of the iceberg.  All RTL passes would need
> to be fixed to make them preserve both the old and the new semantics.


As more passes use libcall_id, you simply fix those that are messing
it up behind it.

This is exactly how we've made every other far reaching change in the
backend in the past year.
Start somewhere, and slowly expand the reach of it until it is done
throughout the entire backend.


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