Advanced Computer Architecture Chapter Q: Prediction

Advanced Computer Architecture, Imperial College 2001

Instructions for predication

•Idea #1: conditional move instruction

–

if (fluid[i][j]==0) {

U[i][j] = U[i-1,j]+U[i,j-1];

} else {

U[I,j] = 0.0;

}

..R1 is address of fluid[i,j]

..R2 is address of U[i,j]

..R3 is address of U[i-1,j]

..F4 is 0.0

LW R4, (R1)

LD F1, (R3)

LD F2, -1(R2)

ADDD F3, F1, F2

CMOVE F5, F3, F4, R4

SD (R2), F5

CMOVE F5, F3, F4, R4

If R4=0, move F3 to F5, else move F4 to F5