I was reading: https://llvm.org/docs/LangRef.html#getelementptr-instruction
From what I can understand LLVM has infinite registers which raises the question, why we need store and load commands at all and when should we use them.
Why can't we keep everything in registers?
To make things clear, can you kindly refer to which commands are used in every line:
void example_func(int x) {
int y;
int z = 3;
int a = x;
a = 3;
x = 2;
}
You asked why we need loads and stores and I will give you one reason why. Say your goal is to compile a program that has 32 registers but you want to have more than 32 variables live at a time. Well now you can see there is a need to load and store with memory.
Consider the following scenario:
int f(int a) {
return a == 0 ? 0 : f(a-1);
return f(a-1);
}
f(50);
If you consider the call tree, you will realize that there is an a for every call to f, and there are more than 32 calls to f, hence the need for loads and stores.
void foo(int *p) { *p = 123; }. In your example, you don't need anything at all, the function might as well be empty unless you make a debug build. See Why does clang produce inefficient asm with -O0 (for this simple floating point sum)? , and for making functions that compile to something interesting to look at, see How to remove "noise" from GCC/clang assembly output? (take args and return a value, e.g.return (x + z)*2 - 3*a;)