Advanced Computer Architecture Chapter Q: Prediction

Advanced Computer Architecture, Imperial College 2001

Instructions for predication

•Idea #2: predicated instructions

–

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

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

}

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

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

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

LW R4, (R1)

CMP P1, R4, 0

(P1) LD F1, (R3)

(P1) LD F2, -1(R2)

(P1) ADDD F3, F1, F2

(P1) SD (R2), F3

CMP P1, R4, 0

If R4=0, set predicate register P1 to true

(P1) LD F1, (R3)

If P1=true, execute load (F1=Mem[R3])