Re: DECstation 2100 floating point

> -O
> -O -march=r2000
> -O -mtune=r2000
> -O -march=r2000 -mtune=r2000
> 
> And all four produced exactly the same binary.

Per src/gnu/dist/gcc4/gcc/config/mips/mips.c,
-march=r2000 is the same as r3000.

As mentioned in gcc(1) man page, -O enables following options:
>>         -O turns on the following optimization flags: -fdefer-pop
>>         -fdelayed-branch -fguess-branch-probability -fcprop-registers
>>         -floop-optimize -fif-conversion -fif-conversion2 -ftree-ccp
>>         -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-ter -ftree-lrs
>>         -ftree-sra -ftree-copyrename -ftree-fre -ftree-ch -funit-at-a-time
>>         -fmerge-constants

It might help to disable each options (by -fno-delayed-branch etc)
and which one causes the errors.

Probably we should also check R2000/R2010 errata.
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Izumi Tsutsui