int do_something(int argc, char *argv[]) {
  int i;
  printf("this is %s\n", __func__);
  for (i = 0; i < argc; i++)
    printf("argv[%d] = %s\n", i, argv[i]);
  return 0;
}


x86 assembly (clang, -O0):
<do_something>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
mov    %edi,-0x4(%rbp)
mov    %rsi,-0x10(%rbp)
lea    0xeda(%rip),%rdi
lea    0xedf(%rip),%rsi
mov    $0x0,%al
call   1030 <printf@plt>
movl   $0x0,-0x14(%rbp)
mov    -0x14(%rbp),%eax
cmp    -0x4(%rbp),%eax
jge    1172 <do_something+0x62>
mov    -0x14(%rbp),%esi
mov    -0x10(%rbp),%rax
movslq -0x14(%rbp),%rcx
mov    (%rax,%rcx,8),%rdx
lea    0xebc(%rip),%rdi
mov    $0x0,%al
call   1030 <printf@plt>
mov    -0x14(%rbp),%eax
add    $0x1,%eax
mov    %eax,-0x14(%rbp)
jmp    113b <do_something+0x2b>
xor    %eax,%eax
add    $0x20,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<do_something>:
push   %r15
push   %r14
push   %r12
push   %rbx
push   %rax
mov    %rsi,%r15
mov    %edi,%ebx
lea    0xedc(%rip),%rdi
lea    0xee1(%rip),%rsi
xor    %eax,%eax
call   1030 <printf@plt>
test   %ebx,%ebx
jle    1169 <do_something+0x59>
mov    %ebx,%r12d
lea    0xed9(%rip),%r14
xor    %ebx,%ebx
cs nopw 0x0(%rax,%rax,1)
nopl   0x0(%rax)
mov    (%r15,%rbx,8),%rdx
mov    %r14,%rdi
mov    %ebx,%esi
xor    %eax,%eax
call   1030 <printf@plt>
add    $0x1,%rbx
cmp    %rbx,%r12
jne    1150 <do_something+0x40>
xor    %eax,%eax
add    $0x8,%rsp
pop    %rbx
pop    %r12
pop    %r14
pop    %r15
ret

LLVM IR (-O0):
@.str = [12 x i8] c"this is %s\0A\00"
@__func__.do_something = [13 x i8] c"do_something\00"
@.str.1 = [15 x i8] c"argv[%d] = %s\0A\00"
define i32 @do_something(i32 %0, i8** %1) {
%3 = alloca i32
%4 = alloca i8**
%5 = alloca i32
store i32 %0, i32* %3
store i8** %1, i8*** %4
%6 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([12 x i8], [12 x i8]* @.str, i64 0, i64 0), i8* getelementptr inbounds ([13 x i8], [13 x i8]* @__func__.do_something, i64 0, i64 0))
store i32 0, i32* %5
br label %7
7: ; preds = %19, %2
%8 = load i32, i32* %5
%9 = load i32, i32* %3
%10 = icmp slt i32 %8, %9
br i1 %10, label %11, label %22
11: ; preds = %7
%12 = load i32, i32* %5
%13 = load i8**, i8*** %4
%14 = load i32, i32* %5
%15 = sext i32 %14 to i64
%16 = getelementptr inbounds i8*, i8** %13, i64 %15
%17 = load i8*, i8** %16
%18 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([15 x i8], [15 x i8]* @.str.1, i64 0, i64 0), i32 %12, i8* %17)
br label %19
19: ; preds = %11
%20 = load i32, i32* %5
%21 = add nsw i32 %20, 1
store i32 %21, i32* %5
br label %7
22: ; preds = %7
ret i32 0
}

LLVM IR (-O2):
@.str = [12 x i8] c"this is %s\0A\00"
@__func__.do_something = [13 x i8] c"do_something\00"
@.str.1 = [15 x i8] c"argv[%d] = %s\0A\00"
define i32 @do_something(i32 %0, i8** nocapture %1) {
%3 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([12 x i8], [12 x i8]* @.str, i64 0, i64 0), i8* getelementptr inbounds ([13 x i8], [13 x i8]* @__func__.do_something, i64 0, i64 0))
%4 = icmp sgt i32 %0, 0
br i1 %4, label %5, label %15
5: ; preds = %2
%6 = zext i32 %0 to i64
br label %7
7: ; preds = %5, %7
%8 = phi i64 [ 0, %5 ], [ %13, %7 ]
%9 = getelementptr inbounds i8*, i8** %1, i64 %8
%10 = load i8*, i8** %9
%11 = trunc i64 %8 to i32
%12 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([15 x i8], [15 x i8]* @.str.1, i64 0, i64 0), i32 %11, i8* %10)
%13 = add nuw nsw i64 %8, 1
%14 = icmp eq i64 %13, %6
br i1 %14, label %15, label %7
15: ; preds = %7, %2
ret i32 0
}