Since many people have asked about this and I haven't seen a complete list posted, this is how the registers from the ee-gcc toolchain map to the registers in the psp-gcc chain
#define zero $0
#define v0 $2
#define v1 $3
#define a0 $4
#define a1 $5
#define a2 $6
#define a3 $7
#define t0 $8
#define t1 $9
#define t2 $10
#define t3 $11
#define t4 $12
#define t5 $13
#define t6 $14
#define t7 $15
#define s0 $16
#define s1 $17
#define s2 $18
#define s3 $19
#define s4 $20
#define s5 $21
#define s6 $22
#define s7 $23
#define t8 $24
#define t9 $25
#define k0 $26
#define k1 $27
#define gp $gp
#define sp $sp
#define s8 $30
#define ra $31
#define pc $pc
Maybe someone should sticky this?