How to generate programs with loops unrolled?

Question

I am trying to generate multiple programs from a given C/C++ program with loops unrolled. For example, I would like to convert something like this:

i = 0;
while (i < 5) {
    printf("Hello");
    i++;
}

to this:

i = 0;
printf("Hello");
i++;
while (i < 5) {
    printf("Hello");
    i++;
}

In the above example, I'd like to generate 5 programs each with a different number of loops unrolled. The compiler flags that I have looked at so far don't seem to generate a program but just optimize it. Is there any straightforward automated way of doing this?

Edit: I don't understand why this is being downvoted. The question linked as being a duplicate isn't relevant.

@NickyC My question asks for generating C programs, I don't see how the question you linked is relevant. — Amit Rege, Oct 22 '18 at 04:01
@bolov I'm trying to create a synthetic dataset of programs (which do the same task) for my research. — Amit Rege, Oct 22 '18 at 04:12
@AmitRege please note "the same thing" can be only defined in terms of [as-if rule](https://stackoverflow.com/questions/15718262/what-exactly-is-the-as-if-rule) — Antti Haapala -- Слава Україні, Oct 22 '18 at 07:15
I don't know any tool that can generate this kind of code for you. Just write some simple script (bash, python, whatever you like) that will generate n files with your C code from one provided C source file. — pptaszni, Oct 22 '18 at 15:39

score 0 · Answer 1 · answered Oct 22 '18 at 04:07

0

Is there any straightforward automated way of doing this?

This is an unusual requirement, as such I think you will have a really difficult time to find a tool that does this.

Without knowing what you are trying to achieve, what problem you are trying to resolve we can't give you a solution, other than manual unroll:

printf("Hello");
printf("Hello");
printf("Hello");
printf("Hello");
printf("Hello");

answered Oct 22 '18 at 04:07

bolov

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I think you misunderstood. I want to generate a program from a given program with only loops unrolled. – Amit Rege Oct 22 '18 at 04:15
@AmitRege I understood. The example is the loop you showed unrolled. – bolov Oct 22 '18 at 04:16
In that case shouldn't it be printf("Hello"); i++; 5 times? – Amit Rege Oct 22 '18 at 04:19
@AmitRege no, `i` is used for the loop logic. It goes the same way `i < 5` goes. Anyway, depends on what you want to do with this. – bolov Oct 22 '18 at 04:25

score 0 · Answer 2 · answered Oct 22 '18 at 04:09

If the programs you want to change are all written by yourself and you know they're structure is simple, you may get along witha little magic of regular expressions.

For modifying arbitrary programs reliably, you must use a proper parser, detect constant for loops in the abstract syntax tree and then write back the modified syntax tree.

How to generate programs with loops unrolled?

2 Answers2