test.c

#include <stdio.h>

int fib(int n) {
	if (n == 0 || n == 1) {
		return 1;
	}
	return fib(n-1) + fib(n-2);
}

int main() {
	printf("%d\n", fib(6));
}

test.ll

; ModuleID = 'test.c'
source_filename = "test.c"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"

@.str = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1

; Function Attrs: noinline nounwind optnone sspstrong uwtable
define dso_local i32 @fib(i32 %0) #0 {
  %2 = alloca i32, align 4
  %3 = alloca i32, align 4
  store i32 %0, i32* %3, align 4
  %4 = load i32, i32* %3, align 4
  %5 = icmp eq i32 %4, 0
  br i1 %5, label %9, label %6

6:                                                ; preds = %1
  %7 = load i32, i32* %3, align 4
  %8 = icmp eq i32 %7, 1
  br i1 %8, label %9, label %10

9:                                                ; preds = %6, %1
  store i32 1, i32* %2, align 4
  br label %18

10:                                               ; preds = %6
  %11 = load i32, i32* %3, align 4
  %12 = sub nsw i32 %11, 1
  %13 = call i32 @fib(i32 %12)
  %14 = load i32, i32* %3, align 4
  %15 = sub nsw i32 %14, 2
  %16 = call i32 @fib(i32 %15)
  %17 = add nsw i32 %13, %16
  store i32 %17, i32* %2, align 4
  br label %18

18:                                               ; preds = %10, %9
  %19 = load i32, i32* %2, align 4
  ret i32 %19
}

; Function Attrs: noinline nounwind optnone sspstrong uwtable
define dso_local i32 @main() #0 {
  %1 = call i32 @fib(i32 6)
  %2 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str, i64 0, i64 0), i32 %1)
  ret i32 0
}

declare i32 @printf(i8*, ...) #1

attributes #0 = { noinline nounwind optnone sspstrong uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.module.flags = !{!0, !1, !2}
!llvm.ident = !{!3}

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 7, !"PIC Level", i32 2}
!2 = !{i32 7, !"PIE Level", i32 2}
!3 = !{!"clang version 11.0.1"}

test.s

	.text
	.file	"test.c"
	.globl	fib                             # -- Begin function fib
	.p2align	4, 0x90
	.type	fib,@function
fib:                                    # @fib
	.cfi_startproc
# %bb.0:
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset %rbp, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register %rbp
	subq	$16, %rsp
	movl	%edi, -8(%rbp)
	cmpl	$0, -8(%rbp)
	je	.LBB0_2
# %bb.1:
	cmpl	$1, -8(%rbp)
	jne	.LBB0_3
.LBB0_2:
	movl	$1, -4(%rbp)
	jmp	.LBB0_4
.LBB0_3:
	movl	-8(%rbp), %eax
	subl	$1, %eax
	movl	%eax, %edi
	callq	fib
	movl	-8(%rbp), %ecx
	subl	$2, %ecx
	movl	%ecx, %edi
	movl	%eax, -12(%rbp)                 # 4-byte Spill
	callq	fib
	movl	-12(%rbp), %ecx                 # 4-byte Reload
	addl	%eax, %ecx
	movl	%ecx, -4(%rbp)
.LBB0_4:
	movl	-4(%rbp), %eax
	addq	$16, %rsp
	popq	%rbp
	.cfi_def_cfa %rsp, 8
	retq
.Lfunc_end0:
	.size	fib, .Lfunc_end0-fib
	.cfi_endproc
                                        # -- End function
	.globl	main                            # -- Begin function main
	.p2align	4, 0x90
	.type	main,@function
main:                                   # @main
	.cfi_startproc
# %bb.0:
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset %rbp, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register %rbp
	subq	$16, %rsp
	movl	$6, %edi
	callq	fib
	leaq	.L.str(%rip), %rdi
	movl	%eax, %esi
	movb	$0, %al
	callq	printf@PLT
	xorl	%ecx, %ecx
	movl	%eax, -4(%rbp)                  # 4-byte Spill
	movl	%ecx, %eax
	addq	$16, %rsp
	popq	%rbp
	.cfi_def_cfa %rsp, 8
	retq
.Lfunc_end1:
	.size	main, .Lfunc_end1-main
	.cfi_endproc
                                        # -- End function
	.type	.L.str,@object                  # @.str
	.section	.rodata.str1.1,"aMS",@progbits,1
.L.str:
	.asciz	"%d\n"
	.size	.L.str, 4

	.ident	"clang version 11.0.1"
	.section	".note.GNU-stack","",@progbits
	.addrsig
	.addrsig_sym fib
	.addrsig_sym printf