#define NULL ((void *)0)
typedef unsigned long size_t; // Customize by platform.
typedef long intptr_t;
typedef unsigned long uintptr_t;
typedef long scalar_t__; // Either arithmetic or pointer type.
/* By default, we understand bool (as a convenience). */
typedef int bool;
#define false 0
#define true 1

/* Forward declarations */

/* Type definitions */

/* Variables and functions */
char *malloc(scalar_t__);
int /*<<< orphan*/ strcat(char *, char *);
scalar_t__ strlen(char *);
char *append(char *head, char *tail) {
  char *final_str;
  if ((final_str = malloc(strlen(head) + strlen(tail) + 1)) != NULL) {
    final_str[0] = '\0';
    strcat(final_str, head);
    strcat(final_str, tail);
    return final_str;
  }
}


x86 assembly (clang, -O0):
<append>:
push   %rbp
mov    %rsp,%rbp
sub    $0x30,%rsp
mov    %rdi,-0x10(%rbp)
mov    %rsi,-0x18(%rbp)
mov    -0x10(%rbp),%rdi
call   1030 <strlen@plt>
mov    %rax,-0x28(%rbp)
mov    -0x18(%rbp),%rdi
call   1030 <strlen@plt>
mov    -0x28(%rbp),%rdi
add    %rax,%rdi
add    $0x1,%rdi
call   1040 <malloc@plt>
mov    %rax,-0x20(%rbp)
cmp    $0x0,%rax
je     119d <append+0x6d>
mov    -0x20(%rbp),%rax
movb   $0x0,(%rax)
mov    -0x20(%rbp),%rdi
mov    -0x10(%rbp),%rsi
call   1050 <strcat@plt>
mov    -0x20(%rbp),%rdi
mov    -0x18(%rbp),%rsi
call   1050 <strcat@plt>
mov    -0x20(%rbp),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
add    $0x30,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<append>:
push   %r15
push   %r14
push   %rbx
mov    %rsi,%r14
mov    %rdi,%r15
call   1030 <strlen@plt>
mov    %rax,%rbx
mov    %r14,%rdi
call   1030 <strlen@plt>
lea    (%rbx,%rax,1),%rdi
add    $0x1,%rdi
call   1040 <malloc@plt>
mov    %rax,%rbx
test   %rax,%rax
je     1179 <append+0x49>
movb   $0x0,(%rbx)
mov    %rbx,%rdi
mov    %r15,%rsi
call   1050 <strcat@plt>
mov    %rbx,%rdi
mov    %r14,%rsi
call   1050 <strcat@plt>
mov    %rbx,%rax
pop    %rbx
pop    %r14
pop    %r15
ret

LLVM IR (-O0):
define i8* @append(i8* %0, i8* %1) {
%3 = alloca i8*
%4 = alloca i8*
%5 = alloca i8*
%6 = alloca i8*
store i8* %0, i8** %4
store i8* %1, i8** %5
%7 = load i8*, i8** %4
%8 = call i64 @strlen(i8* %7)
%9 = load i8*, i8** %5
%10 = call i64 @strlen(i8* %9)
%11 = add nsw i64 %8, %10
%12 = add nsw i64 %11, 1
%13 = call i8* @malloc(i64 %12)
store i8* %13, i8** %6
%14 = icmp ne i8* %13, null
br i1 %14, label %15, label %25
15: ; preds = %2
%16 = load i8*, i8** %6
%17 = getelementptr inbounds i8, i8* %16, i64 0
store i8 0, i8* %17
%18 = load i8*, i8** %6
%19 = load i8*, i8** %4
%20 = call i32 @strcat(i8* %18, i8* %19)
%21 = load i8*, i8** %6
%22 = load i8*, i8** %5
%23 = call i32 @strcat(i8* %21, i8* %22)
%24 = load i8*, i8** %6
store i8* %24, i8** %3
br label %25
25: ; preds = %15, %2
%26 = load i8*, i8** %3
ret i8* %26
}

LLVM IR (-O2):
define i8* @append(i8* %0, i8* %1) {
%3 = tail call i64 @strlen(i8* dereferenceable(1) %0)
%4 = tail call i64 @strlen(i8* dereferenceable(1) %1)
%5 = add i64 %3, 1
%6 = add i64 %5, %4
%7 = tail call i8* @malloc(i64 %6)
%8 = icmp eq i8* %7, null
br i1 %8, label %12, label %9
9: ; preds = %2
store i8 0, i8* %7
%10 = tail call i32 @strcat(i8* %7, i8* %0)
%11 = tail call i32 @strcat(i8* %7, i8* %1)
br label %12
12: ; preds = %2, %9
ret i8* %7
}