Re: [PATCH] Tree SRA and atomicity/volatility

[Eric Botcazou <ebotcazou at adacore dot com>]

> > Exactly.  Gigi makes sure that a full-word load is always possible, but
> > it relies on the side-effectness for keeping it together.
>
> I don't see where the tree-ssa part of the middle-end guarantees this and
> also expand does not seem to honor this as then we'd get a full load
> for every component load.  It looks to me that for a component write
> you then need a read-modify-write cycle as we get for targets that
> don't support sub-word loads/stores and/or strict-alignment targets.

I'm not sure I understand, maybe my wording was ambiguous.  Gigi has all the 
magic to support atomicity (type wrapping, alignment tweaking, countermeasure 
for problematic targets, e.g. Alpha, and so on) and generates the full-word 
access on its own.  The only requirement is for the middle-end to fully honor 
the TREE_THIS_VOLATILE and TREE_SIDE_EFFECTS flags.

-- 
Eric Botcazou