9.30.2.2 Register Names
General purpose registers (GPR)
There are 32 32-bit general purpose registers $r0 to $r31.
Accumulators d0 and d1
64-bit accumulators: $d0.hi, $d0.lo, $d1.hi, and $d1.lo.
Assembler reserved register $ta
Register $ta ($r15) is reserved for assembler using.
Operating system reserved registers $p0 and $p1
Registers $p0 ($r26) and $p1 ($r27) are used by operating system as scratch registers.
Frame pointer $fp
Register $r28 is regarded as the frame pointer.
Global pointer
Register $r29 is regarded as the global pointer.
Link pointer
Register $r30 is regarded as the link pointer.
Stack pointer
Register $r31 is regarded as the stack pointer.