On Fri, 22 Apr 2016, Paul Burton wrote: > > In that case however it looks to me like these `-mcompact-branches=' > > options (all the three we support) need to be wrapped into `$(call > > cc-option,...)'. > > An alternative that it could be argued better fits the principle of > least surprise is to add an extra option to the Kconfig choice that > simply leaves -mcompact-branches unspecified. I just submitted a patch > to do so [1].
Hmm, good idea in principle, but given that -- as you say -- this is a debug option I have a further suggestion I'll reply to your patch submission with. > > They do not affect any functionality and they are an > > optimisation choice only anyway (and therefore I wonder why they've been > > placed in arch/mips/Kconfig.debug rather than arch/mips/Kconfig). > > They're in Kconfig.debug because debug is exactly what they've been > useful for - given that compact branches are new to R6 it's been useful > in debugging systems, both hardware & simulators, to sometimes not use > them. It's also been useful to force their use attempting to work around > the compiler bug that [2] works around differently (bug 2179 on DMZ > bugzilla). On the other hand I can't think of a reason we'd want to > specify compact branch policy that isn't for debug - I'd expect for > performance optimisation we're more likely to rely upon the toolchain > using a sensible policy if the kernel is built for a specific CPU (eg. > perhaps -mcpu=p6600 prefers non-compact branches & -mcpu=m6250 prefers > all compact branches, or similar). Good point, it should indeed be the compiler making the right choice for the `-mtune=' setting selected with the default branch policy rather the user fiddling with `-mcompact-branches=' manually unless, as you say, for debugging. Thanks for the patience to educate me. Maciej
