On Nov 26, 2013, at 11:03 AM, Joern Rennecke <joern.renne...@embecosm.com>
wrote:
> On 26 November 2013 15:55, Paul Koning <paulkon...@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
