In a simplified computer, the instructions are
OP R_j, R_i – Performs R_j OP R_i and stores the result in register R_i .
OP m, R_j – Performs val OP R_i and stores the result in R_j. val denotes the content of memory location m.
MOV m, R_i – Moves the content of memory location m to register R_i.
MOV, R_i, m – Moves the content of the register R_i to memory location m.
The computer has only two registers, and OP is either ADD or SUB. Consider the following basic block:
t₁ = a + b
t₂ = c + d
t₃ = e – t₂
t₄ = t₁ – t₃
Assume that all operands are initially in memory. The final value of the computation should be in memory. What is the minimum number of MOV instructions in the code generated for this basic block?