Count Optimized Assembly Instructions

After the preprocessor expands directives and macros (explored in the prerequisite challenge Inspect a Preprocessor Macro Expansion), source code reaches the second stage of the C compilation pipeline: the compiler itself. Here, the compiler parses high-level C code, analyzes its control flow, applies code optimizations, and emits target-specific assembly code. This challenge explores how compiler optimization flags alter the assembly instructions produced during this second phase.

The four stages of the C compilation pipeline. This challenge focuses on the second one (compilation to assembly).

Optimization flags radically change what the generated assembly looks like. A loop that looks straightforward in C can disappear entirely when the optimizer evaluates constant expressions at compile time.

Your task is to:

1. Create a workspace directory named ~/exercise.
2. Inside ~/exercise, create a C file named loop.c (or main.c) containing a program that sums the first 1000 integers (from 1 to 1000) and prints the result:

#include <stdio.h>

int main(void) {
    int sum = 0;
    for (int i = 1; i <= 1000; i++) {
        sum += i;
    }
    printf("%d\n", sum);
    return 0;
}

3. Change into ~/exercise and compile the program to assembly using gcc -O2 -S loop.c.
4. Inspect the generated loop.s file and count the number of add instructions.