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Consider the grammar rule E → E1 – E2 for arithmetic expressions. The code generated is targeted to a CPU having a single user register. The subtraction operation requires the first operand to be in the register. If E1 and E2 do not have any common sub-expression, in order to get shortest possible code.
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- E1 should be evaluated first
- E2 should be evaluated first
- Evaluation of E1 and E2 should necessarily be interleaved
- Order to evaluation of E1 and E2 is of no consequence
- E1 should be evaluated first
Correct Option: B
E1 is to be kept in accumulator & accumulator is required for operations to evaluate E2 also. So E2 should be evaluated first & then E1, so finally E1 will be in accumulator, otherwise need to use move & load instructions.
Hence (b) is correct option.
