Steve Ellcey <sell...@imgtec.com> writes: > This patch changes the default processor for mips4 from the r8000 to > the > r10000. There are several reasons for this change, the main one > being the difference in the r8000 madd instruction and the rest of the > mips4 > family. The r8000 has a fused madd instruction (no truncation between > the > multiply and add) but the rest of the mips4 CPUs have unfused madd > instructions where truncation is done and the result is identical to > using > separate multiply and add instructions. > > I plan to submit a patch later to clean up MIPS handling of madd and > other > fma style instructions but to do that it is necessary to do different > things > for r8000 vs the other mips4 targets and that is easier if r8000 is not > the > default processor selected when -mips4 is used. > > I have also been told that very few r8000 machines were ever released > and > that the r10k/r12k/etc. series is probably the most common mips4 > machines > still out there and so would be a better default. > > This patch will have no affect on compiles where a specific processor > is > specified (i.e. -march=r80000, -march=r10000), but only when using the > more generic -mips4 or -march=mips4 flags. The only visible difference > in that case is that GCC will use the r10k instruction scheduler > instead > of the generic MIPS scheduler (there is no r8000 specific scheduler) > and > that should be a good thing for most mips4 machines. > > Tested with the mips-linux-gnu toolchain. > > OK for checkin? > > Steve Ellcey > sell...@imgtec.com > > > 2015-04-28 Steve Ellcey <sell...@imgtec.com> > > * config/mips/mips-cpus.def: (mips4): Change default processor > from PROCESSOR_R8000 to PROCESSOR_R10000.
Ok with me. I'd like Catherine to have the chance to raise any concerns though. Thanks, Matthew
