#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 */
int /*<<< orphan*/ memcpy(char *, char const *, size_t);
size_t strlen(char const *);
char *xrealloc(char *, size_t);
char *append(char *s1, const char *s2) {
  size_t z1 = strlen(s1);
  size_t z2 = strlen(s2);
  s1 = xrealloc(s1, z1 + z2 + 1);
  memcpy(s1 + z1, s2, z2);
  s1[z1 + z2] = '\0';
  return s1;
}


x86 assembly (clang, -O0):
<append>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x8(%rbp),%rdi
call   1030 <strlen@plt>
mov    %rax,-0x18(%rbp)
mov    -0x10(%rbp),%rdi
call   1030 <strlen@plt>
mov    %rax,-0x20(%rbp)
mov    -0x8(%rbp),%rdi
mov    -0x18(%rbp),%rsi
add    -0x20(%rbp),%rsi
add    $0x1,%rsi
call   1040 <xrealloc@plt>
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rdi
add    -0x18(%rbp),%rdi
mov    -0x10(%rbp),%rsi
mov    -0x20(%rbp),%rdx
call   1050 <memcpy@plt>
mov    -0x8(%rbp),%rax
mov    -0x18(%rbp),%rcx
add    -0x20(%rbp),%rcx
movb   $0x0,(%rax,%rcx,1)
mov    -0x8(%rbp),%rax
add    $0x20,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<append>:
push   %r15
push   %r14
push   %r13
push   %r12
push   %rbx
mov    %rsi,%r14
mov    %rdi,%r15
call   1030 <strlen@plt>
mov    %rax,%rbx
mov    %r14,%rdi
call   1030 <strlen@plt>
mov    %rax,%r12
lea    (%rax,%rbx,1),%r13
lea    (%rax,%rbx,1),%rsi
add    $0x1,%rsi
mov    %r15,%rdi
call   1040 <xrealloc@plt>
mov    %rax,%r15
add    %rax,%rbx
mov    %rbx,%rdi
mov    %r14,%rsi
mov    %r12,%rdx
call   1050 <memcpy@plt>
movb   $0x0,(%r15,%r13,1)
mov    %r15,%rax
pop    %rbx
pop    %r12
pop    %r13
pop    %r14
pop    %r15
ret

LLVM IR (-O0):
define i8* @append(i8* %0, i8* %1) {
%3 = alloca i8*
%4 = alloca i8*
%5 = alloca i64
%6 = alloca i64
store i8* %0, i8** %3
store i8* %1, i8** %4
%7 = load i8*, i8** %3
%8 = call i64 @strlen(i8* %7)
store i64 %8, i64* %5
%9 = load i8*, i8** %4
%10 = call i64 @strlen(i8* %9)
store i64 %10, i64* %6
%11 = load i8*, i8** %3
%12 = load i64, i64* %5
%13 = load i64, i64* %6
%14 = add i64 %12, %13
%15 = add i64 %14, 1
%16 = call i8* @xrealloc(i8* %11, i64 %15)
store i8* %16, i8** %3
%17 = load i8*, i8** %3
%18 = load i64, i64* %5
%19 = getelementptr inbounds i8, i8* %17, i64 %18
%20 = load i8*, i8** %4
%21 = load i64, i64* %6
%22 = call i32 @memcpy(i8* %19, i8* %20, i64 %21)
%23 = load i8*, i8** %3
%24 = load i64, i64* %5
%25 = load i64, i64* %6
%26 = add i64 %24, %25
%27 = getelementptr inbounds i8, i8* %23, i64 %26
store i8 0, i8* %27
%28 = load i8*, i8** %3
ret i8* %28
}

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 %4, %3
%6 = add i64 %5, 1
%7 = tail call i8* @xrealloc(i8* %0, i64 %6)
%8 = getelementptr inbounds i8, i8* %7, i64 %3
%9 = tail call i32 @memcpy(i8* %8, i8* %1, i64 %4)
%10 = getelementptr inbounds i8, i8* %7, i64 %5
store i8 0, i8* %10
ret i8* %7
}