A single pass compiler generates intermediate code
Answer: C
Actions emit instructions as productions are reduced or procedures return. Forward references are handled by backpatching, since the destination may not yet be known. Nothing can be revisited once the parser has moved past it.
Please log in or register to report this question.
Consider the following statements about three address code.
1. Each instruction names at most three addresses.
2. Temporaries are introduced for intermediate results.
3. The form is tied to a particular target instruction set.
Answer: D
Correct answer: 1 and 2 only
Statements 1 and 2 give the form correctly: at most three addresses per instruction, with temporaries introduced for intermediate results. Statement 3 denies the whole purpose of the representation - it is deliberately machine independent, which is what allows one optimiser and many back ends.
Please log in or register to report this question.
The chief advantage of three address code over a syntax tree for a back end is
Answer: A
Instruction selection and scheduling work on a sequence. A tree must be linearised first, which is one of the tasks the intermediate code generator performs. Flattening also fixes the evaluation order, which the tree left open.
Please log in or register to report this question.
Source level transformations such as loop interchange are performed on a tree rather than on three address code because
Answer: B
Rewriting a construct means rearranging nodes rather than renumbering instructions. Source level transformations are therefore normally done before the program is flattened. Loop interchange and unrolling are far easier to express on a tree.
Please log in or register to report this question.
A compiler emitting intermediate code for an expression with side effects must
Answer: C
Correct answer: fix the order in which the operands are evaluated
Once an operand has a side effect, the order in which the operands are evaluated changes what the program does. Generating code fixes that order, so the compiler must choose one consistent with whatever the language guarantees - and where the language leaves it unspecified, two conforming compilers may legitimately differ.
Please log in or register to report this question.
Generating intermediate code before optimisation rather than after is
Answer: D
There is nothing to optimise until the representation exists. Machine independent optimisation sits between generation and code generation for exactly this reason. Each phase operates on the representation best suited to what it does.
Please log in or register to report this question.
