On Wed, Oct 27, 2004 at 07:45:40PM +0200, Thiemo Seufer wrote: > Daniel Jacobowitz wrote: > [snip] > > > > IIRC, likely branches are deprecated in the latest MIPS ISAs; we > > > > shouldn't be introducing more of them. I don't know what silicon bug > > > > you're working around, though, so I don't know if there's a better way. > > > > > > R10000 before revision 2.6 fail to handle ll/sc atomically under > > > somewhat obscure circumstances connected to the branch prediction > > > mechanism and the pipeline length (Erratum #6). The branch likely > > > avoids that specific bug. IRIX uses the same workaround, the Erratum > > > suggests IIRC a much less efficient workaround. > > > > Hmm. I'm not sure what to do with this. I don't want to add them to > > libstdc++ since MIPS is threatening to remove them... > > Well, libstdc++ has no means to detect the CPU type, so it's hard to > conditionalize it. OTOH, those instructions might be useless on CPUs > with advanced branch prediction, but removing them breaks backward > compatibility and provides little gain, so MIPS probably isn't too > hasty to remove them. > > At least so far, MIPS was careful to extend successor ISAs to a > proper superset of the predecessor WRT non-privileged instructions.
Fine by me then. Want to run this by the MIPS maintainers upstream first? -- Daniel Jacobowitz
