Looping in llvm

Beginners
1

I have written a simple code in c using for loop.

void foo(int a, int n){
int i;
for (i=0;i<n;i = i+1){
    a = a+i;
}
return;
}

it will give the llvm ir like

define dso_local void @foo(i32 %0, i32 %1) #0 {
  %3 = alloca i32, align 4
  %4 = alloca i32, align 4
  %5 = alloca i32, align 4
  store i32 %0, i32* %3, align 4
  store i32 %1, i32* %4, align 4
  store i32 0, i32* %5, align 4
  br label %6

6:                                                ; preds = %14, %2
  %7 = load i32, i32* %5, align 4
  %8 = load i32, i32* %4, align 4
  %9 = icmp slt i32 %7, %8
  br i1 %9, label %10, label %17

10:                                               ; preds = %6
  %11 = load i32, i32* %3, align 4
  %12 = load i32, i32* %5, align 4
  %13 = add nsw i32 %11, %12
  store i32 %13, i32* %3, align 4
  br label %14

14:                                               ; preds = %10
  %15 = load i32, i32* %5, align 4
  %16 = add nsw i32 %15, 1
  store i32 %16, i32* %5, align 4
  br label %6

17:                                               ; preds = %6
  ret void
}

I want to write a module pass which will take LLVM IR as input and from llvm IR it will check if there is any loop present or not , if present then what are those initializations, conditions and increments and what are the body of that loop etc.

2

Hello - it might help if you read the Kaleidoscope tutorial - My First Language Frontend with LLVM Tutorial — LLVM 17.0.0git documentation. Chapter 5 covers control flow so you will learn how for loops are represented in the IR. Its kind of like assembly.

3

You can start with this page:
https://llvm.org/docs/LoopTerminology.html