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Re: [buildrobot] pdp11-aout
- From: Paul Koning <paulkoning at comcast dot net>
- To: Joern Rennecke <joern dot rennecke at embecosm dot com>
- Cc: Jan-Benedict Glaw <jbglaw at lug-owl dot de>, "gcc at gcc dot gnu dot org Development" <gcc at gcc dot gnu dot org>
- Date: Tue, 26 Nov 2013 11:47:20 -0500
- Subject: Re: [buildrobot] pdp11-aout
- Authentication-results: sourceware.org; auth=none
- References: <20131126032546 dot GX30563 at lug-owl dot de> <35F5B26B-B1E5-40E3-A598-F715571B9522 at comcast dot net> <CAMqJFCp1s7wrH2W3da3ccHnsm6CY0869NDfdEhw_crJW-1CXdg at mail dot gmail dot com>
On Nov 26, 2013, at 11:03 AM, Joern Rennecke <joern.rennecke@embecosm.com> wrote:
> On 26 November 2013 15:55, Paul Koning <paulkoning@comcast.net> wrote:
>
>> Is there a requirement that all targets must have branch cost that it, at least some of the time, 4 or greater?
>
> Not by design, although there seem to be a number of issues with
> supporting targets with a lower branch cost. E.g. consider
> LOGICAL_OP_NON_SHORT_CIRCUIT - the default of which also seems to
> assume superscalarity and a cheap flag-set operation - and its impact
> on/treatment by the test suite.
The doc says that the default branch cost is 1. So it seems reasonable for a target to have branch cost < 4 at all times, if the target doesn't have expensive branches or widely varying branch costs. Low speed processors with simple execution units are likely to be such targets (and indeed the pdp11 is a good example).
>
>> If so, why? If not, then I suppose cfgexpand.c could be changed to defeat this message
>
> I agree.
>
> , but how, or why?
>
> Changing this target macro into a target hook should do the trick.
Is there such a target hook in the current code?
paul