CS606 GDB 1 Solution and Discussion

[laiba javed]

Re: CS606 GDB 1 Solution and Discussion

Total Marks 5
Starting Date Monday, February 15, 2021
Closing Date Tuesday, February 16, 2021
Status Open
Question Title Intermediate Code Generation
Question Description
CS606 GDB Fall 2020

Compilers are used to translate the source code in to machine code but there is an intermediate code is generated before the target machine code. Compilers can be developed to translate directly without generating machine code.

Do you think intermediate code generation is extra and time consuming step while translating or it is necessary or beneficial in some way?

Give your comments in favor or against it with proper reasons.

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[Ozair]

@zaasmi said in CS606 GDB 1 Solution and Discussion:

ntermediate code generation

As expected the input to the code generator is the output of the intermediate code generator. We assume that all syntactic and semantic error checks have been done by the front end. Also, all needed type conversions are already done and any type errors have been detected.

We are using three address instructions for our intermediate language. These instructions have several representations, quads, triples, indirect triples, etc. In this chapter I will tend to use the term quad (for brevity) when I should really say three-address instruction, since the representation doesn’t matter.

[Uzma noor]

@laiba-javed said in CS606 GDB 1 Solution and Discussion:

Do you think intermediate code generation is extra and time consuming step while translating or it is necessary or beneficial in some way?

Stack Allocation
We now need to access the ARs from the stack. The key distinction is that the location of the current AR is not known at compile time. Instead a pointer to the stack must be maintained dynamically.

We dedicate a register, call it SP, for this purpose. In this chapter we let SP point to the bottom of the current AR, that is the entire AR is above the SP. Since we are not supporting varargs, there is no advantage to having SP point to the middle of the AR as in the previous chapter.

The main procedure (or the run-time library code called before any user-written procedure) must initialize SP with
LD SP, #stackStart
where stackStart is a known-at-compile-time constant.

The caller increments SP (which now points to the beginning of its AR) to point to the beginning of the callee’s AR. This requires an increment by the size of the caller’s AR, which of course the caller knows.

Is this size a compile-time constant?

The book treats it as a constant. The only part that is not known at compile time is the size of the dynamic arrays. Strictly speaking this is not part of the AR, but it must be skipped over since the callee’s AR starts after the caller’s dynamic arrays.

Perhaps for simplicity we are assuming that there are no dynamic arrays being stored on the stack. If there are arrays, their size must be included in some way.