编译器中间代码生成三个地址代码fjump

Question

What does FJUMP mean in this context ?

The following is a Three Address Code (TAC) Intermediate Representation for a register machine: it contains a function called foo , which takes an integer parameter n and a parameter a which is an array of integers. Write down the high-level language counterpart in Java-like pseudocode.

 label Foo: res = 1 i = 1 label BAR: t1 = i LEQ n a[1] = res i = i ADD 1 res = res MUL i JUMP BAR label BAZ: 

I thought a jump instruction in three address code is something like "if x goto L"?

Answer 1

The relevant excerpt is:

t1 = i LEQ n
FJUMP t1 BAZ

Which I take to mean "if i is less than or equal to n , jump to BAZ ". So FJUMP indeed does seem to denote a conditional jump (as you read it, feel free to insert the "if" and "goto" parts yourself!).

You have to understand that three-address code is not a language . It is a class of intermediate representations (languages) that have similar characteristics, not unlike the classes of object-oriented or functional languages. As a compiler developer, you get to design your three-address code, should you opt to use such an intermediate representation.

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On a side note, I have a feeling that students of compiler theory tend to read their textbooks too literally. If you look at a bunch of reasonably modern compilers, you are likely to find recurring patterns, but they tend to differ quite significantly in the details.