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Re: [PATCH]: Stack alignment
- From: "John David Anglin" <dave at hiauly1 dot hia dot nrc dot ca>
- To: geoffk at geoffk dot org (Geoff Keating)
- Cc: gcc at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
- Date: Mon, 17 Feb 2003 17:12:50 -0500 (EST)
- Subject: Re: [PATCH]: Stack alignment
> > Reload aligns the stack in each iteration. It uses a default alignment
> > value of BIGGEST_ALIGNMENT. If STARTING_FRAME_OFFSET % BIGGEST_ALIGNMENT
> > is not zero, the rounding in assign_stack_temp_for_type will cause the
> > frame size to be non-zero. As a result, you will never have a non-empty
> > frame and code for doing the stack adjustments needs to be emitted in
> > the prologue and epilogue.
>
> Right. This is because you need to keep the stack aligned, so you can
> never have an empty frame. Which brings us back to a variant of the
> previous poster's question: is the stack pointer supposed to be
> aligned, or not?
Yes, the stack pointer is supposed to aligned. Your question
implies that the value specified in STARTING_FRAME_OFFSET affects
the stack alignment. However, the frame sizes on the PA are
always rounded in compute_frame_size. The STARTING_FRAME_OFFSET
is just one of a number of items that make up the final frame size.
STARTING_FRAME_OFFSET is not added into the total if the size
returned by get_frame_size () is zero. That's why we don't want
assign_stack_local_1 to artificially create a frame.
Dave
--
J. David Anglin dave.anglin@nrc-cnrc.gc.ca
National Research Council of Canada (613) 990-0752 (FAX: 952-6605)