main(argc, argv, envp) int argc;
char *argv[], **envp;
{
  if (argc != 2) {
    printf("usage:  factorial <number>\n");
    return 1;
  } else {
    printf("%d\n", factorial(atoi(argv[1])));
  }
  return 0;
}


x86 assembly (clang, -O0):
<main>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
movl   $0x0,-0x4(%rbp)
mov    %edi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    %rdx,-0x18(%rbp)
cmpl   $0x2,-0x8(%rbp)
je     116e <main+0x3e>
lea    0xea5(%rip),%rdi
mov    $0x0,%al
call   1040 <printf@plt>
movl   $0x1,-0x4(%rbp)
jmp    119d <main+0x6d>
mov    -0x10(%rbp),%rax
mov    0x8(%rax),%rdi
mov    $0x0,%al
call   1050 <atoi@plt>
mov    %eax,%edi
mov    $0x0,%al
call   1030 <factorial@plt>
mov    %eax,%esi
lea    0xe8d(%rip),%rdi
mov    $0x0,%al
call   1040 <printf@plt>
movl   $0x0,-0x4(%rbp)
mov    -0x4(%rbp),%eax
add    $0x20,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<main>:
push   %rbx
cmp    $0x2,%edi
jne    116e <main+0x2e>
mov    0x8(%rsi),%rdi
xor    %ebx,%ebx
xor    %eax,%eax
call   1060 <atoi@plt>
mov    %eax,%edi
xor    %eax,%eax
call   1040 <factorial@plt>
lea    0xe9d(%rip),%rdi
mov    %eax,%esi
xor    %eax,%eax
call   1050 <printf@plt>
jmp    117f <main+0x3f>
lea    0xe8f(%rip),%rdi
call   1030 <puts@plt>
mov    $0x1,%ebx
mov    %ebx,%eax
pop    %rbx
ret

LLVM IR (-O0):
@.str = [28 x i8] c"usage: factorial <number>\0A\00"
@.str.1 = [4 x i8] c"%d\0A\00"
define i32 @main(i32 %0, i8** %1, i8** %2) {
%4 = alloca i32
%5 = alloca i32
%6 = alloca i8**
%7 = alloca i8**
store i32 0, i32* %4
store i32 %0, i32* %5
store i8** %1, i8*** %6
store i8** %2, i8*** %7
%8 = load i32, i32* %5
%9 = icmp ne i32 %8, 2
br i1 %9, label %10, label %12
10: ; preds = %3
%11 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([28 x i8], [28 x i8]* @.str, i64 0, i64 0))
store i32 1, i32* %4
br label %20
12: ; preds = %3
%13 = load i8**, i8*** %6
%14 = getelementptr inbounds i8*, i8** %13, i64 1
%15 = load i8*, i8** %14
%16 = call i32 (i8*, ...) bitcast (i32 (...)* @atoi to i32 (i8*, ...)*)(i8* %15)
%17 = call i32 (i32, ...) bitcast (i32 (...)* @factorial to i32 (i32, ...)*)(i32 %16)
%18 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0), i32 %17)
br label %19
19: ; preds = %12
store i32 0, i32* %4
br label %20
20: ; preds = %19, %10
%21 = load i32, i32* %4
ret i32 %21
}

LLVM IR (-O2):
@.str.1 = [4 x i8] c"%d\0A\00"
@str = [27 x i8] c"usage: factorial <number>\00"
define i32 @main(i32 %0, i8** nocapture %1, i8** nocapture readnone %2) {
%4 = icmp eq i32 %0, 2
br i1 %4, label %7, label %5
5: ; preds = %3
%6 = tail call i32 @puts(i8* dereferenceable(1) getelementptr inbounds ([27 x i8], [27 x i8]* @str, i64 0, i64 0))
br label %13
7: ; preds = %3
%8 = getelementptr inbounds i8*, i8** %1, i64 1
%9 = load i8*, i8** %8
%10 = tail call i32 (i8*, ...) bitcast (i32 (...)* @atoi to i32 (i8*, ...)*)(i8* %9)
%11 = tail call i32 (i32, ...) bitcast (i32 (...)* @factorial to i32 (i32, ...)*)(i32 %10)
%12 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0), i32 %11)
br label %13
13: ; preds = %7, %5
%14 = phi i32 [ 1, %5 ], [ 0, %7 ]
ret i32 %14
}