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Re: subreg rtl documentation
- From: Jeff Law <law at redhat dot com>
- To: Kenneth Zadeck <zadeck at naturalbridge dot com>
- Cc: Jim Wilson <wilson at tuliptree dot org>, Kenneth dot Zadeck at naturalbridge dot com, gcc-patches at gcc dot gnu dot org, "Bonzini\, Paolo" <bonzini at gnu dot org>, Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>, Bernd Schmidt <bernds_cb1 at t-online dot de>, "Joseph S. Myers" <joseph at codesourcery dot com>, Joern Rennecke <joernr at arc dot com>, rsandifo at nildram dot co dot uk
- Date: Mon, 07 Apr 2008 12:50:55 -0600
- Subject: Re: subreg rtl documentation
- References: <87wsnda8bu.fsf@moria.site> <87ej9l8tad.fsf@firetop.home> <47FA40CC.5070503@naturalbridge.com> <87skxxabop.fsf@firetop.home> <47FA61D3.70504@tuliptree.org> <47FA6A4E.4090208@naturalbridge.com>
Kenneth Zadeck wrote:
I think that the big picture thinking was that richard and i had not
only vetted the text with the community, but that unlike the many things
that get vetted on the mailing list, this one did not turn into a flame
war, so it was easy to put together a document that reflected the
feelings of those that contributed. Given that at least two of the
people that participated in that were gwm's who were instrumental in
developing the parts of the compiler that used subregs, i think that
david felt that it had been vetted enough and that this was not just a
rouge change to the documents to reflect one person's perspective.
The issue with the mem subregs did not come up in the previous
discussions and as you point out does seem to have been dropped by us.
Going back and reading the text that was dropped and what you say here,
gives me the feeling that there is yet another complex use of subregs
that was underdocumented in the original text that is certainly
deserving of some enhancement. Unlike the area of subregs of hardregs,
where the consensus opinion was that these should go away, there was
just not much said about subregs of mems and it looks like the issue
fell between the cracks.
lets let the subregs of mem issue kick around for a few days and i will
propose a patch based on what people say and the currently committed
code that supports subregs of mem.
If you want to understand some of the (subreg (mem)) issues, look in
combine.c. Anywhere you find LOAD_EXTEND_OP is probably worth reading.
Painful, painful memories...
Jeff