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Re: [RL78] Questions about code-generation
- From: DJ Delorie <dj at redhat dot com>
- To: Richard Hulme <peper03 at yahoo dot com>
- Cc: gcc at gcc dot gnu dot org
- Date: Mon, 10 Mar 2014 20:17:30 -0400
- Subject: Re: [RL78] Questions about code-generation
- Authentication-results: sourceware.org; auth=none
- References: <1394465260 dot 82407 dot YahooMailNeo at web125603 dot mail dot ne1 dot yahoo dot com> <201403102137 dot s2ALbDMw016198 at greed dot delorie dot com> <531E49CD dot 1040000 at yahoo dot com>
> Ah, that certainly explains a lot. How exactly would the fixing be
> done? Is there an example I could look at for one of the other processors?
No, RL78 is the first that uses this scheme.
> I calculated a week or two ago that we could make a code-saving of
> around 8% by using near or relative branches and near calls instead of
> always generating far calls. I changed rl78-real.md to use near
> addressing and got about 5%. That's probably about right. I tried to
> generate relative branches too but I'm guessing that the 'length'
> attribute needs to be set for all instructions to get that working properly.
Or the linker could be taught to optimize branches once it knows the
full displacement, but that can be even trickier to get right.