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Re: RFC: PATCH to gimplify_modify_expr_rhs to make return slotexplicit
- From: Daniel Berlin <dberlin at dberlin dot org>
- To: Diego Novillo <dnovillo at redhat dot com>
- Cc: Jason Merrill <jason at redhat dot com>, gcc-patches at gcc dot gnu dot org, Mark Mitchell <mark at codesourcery dot com>, "Frank Ch. Eigler" <fche at redhat dot com>, Richard Henderson <rth at redhat dot com>
- Date: Wed, 12 Jan 2005 21:59:34 -0500 (EST)
- Subject: Re: RFC: PATCH to gimplify_modify_expr_rhs to make return slotexplicit
- References: <xypvfa2giqj.fsf@miranda.boston.redhat.com> <41E5E276.60909@redhat.com>
On Wed, 12 Jan 2005, Diego Novillo wrote:
Jason Merrill wrote:
Any thoughts?
Not an objection to the patch, but this will also cause TBAA to introduce
more alias relations with the variable in the return slot. The aliasing code
will not only see it as an addressable variable, but will also consider it
call-clobbered.
I'm not sure how much of a problem this is, but it should be easy to measure
by checking the .alias dumps before/after the patch. We obviously need to
make the aliaser smarter (law and dberlin are working on enhancements that
should help, though they may not be ready for 4.0).
The stuff i'm working on is definitely not 4.0 material, though i'm about
to fix the remaining regressions.
I have no idea about Jeff's work (i assume it's a much smaller amount of
work, since he hasn't created a branch for it or anything of the sort).
Diego.