#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);
char *realloc(char const *, size_t);
size_t strlen(char const *);
const char *string_append(const char *str0, const char *str1) {
  size_t s0 = strlen(str0);
  size_t s1 = strlen(str1);
  char *out = realloc(str0, s0 + s1 + 1);
  memcpy(out + s0, str1, s1);
  out[s0 + s1] = '\0';
  return out;
}


x86 assembly (clang, -O0):
<string_append>:
push   %rbp
mov    %rsp,%rbp
sub    $0x30,%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   1050 <realloc@plt>
mov    %rax,-0x28(%rbp)
mov    -0x28(%rbp),%rdi
add    -0x18(%rbp),%rdi
mov    -0x10(%rbp),%rsi
mov    -0x20(%rbp),%rdx
call   1040 <memcpy@plt>
mov    -0x28(%rbp),%rax
mov    -0x18(%rbp),%rcx
add    -0x20(%rbp),%rcx
movb   $0x0,(%rax,%rcx,1)
mov    -0x28(%rbp),%rax
add    $0x30,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<string_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   1050 <realloc@plt>
mov    %rax,%r15
add    %rax,%rbx
mov    %rbx,%rdi
mov    %r14,%rsi
mov    %r12,%rdx
call   1040 <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* @string_append(i8* %0, i8* %1) {
%3 = alloca i8*
%4 = alloca i8*
%5 = alloca i64
%6 = alloca i64
%7 = alloca i8*
store i8* %0, i8** %3
store i8* %1, i8** %4
%8 = load i8*, i8** %3
%9 = call i64 @strlen(i8* %8)
store i64 %9, i64* %5
%10 = load i8*, i8** %4
%11 = call i64 @strlen(i8* %10)
store i64 %11, i64* %6
%12 = load i8*, i8** %3
%13 = load i64, i64* %5
%14 = load i64, i64* %6
%15 = add i64 %13, %14
%16 = add i64 %15, 1
%17 = call i8* @realloc(i8* %12, i64 %16)
store i8* %17, i8** %7
%18 = load i8*, i8** %7
%19 = load i64, i64* %5
%20 = getelementptr inbounds i8, i8* %18, i64 %19
%21 = load i8*, i8** %4
%22 = load i64, i64* %6
%23 = call i32 @memcpy(i8* %20, i8* %21, i64 %22)
%24 = load i8*, i8** %7
%25 = load i64, i64* %5
%26 = load i64, i64* %6
%27 = add i64 %25, %26
%28 = getelementptr inbounds i8, i8* %24, i64 %27
store i8 0, i8* %28
%29 = load i8*, i8** %7
ret i8* %29
}

LLVM IR (-O2):
define i8* @string_append(i8* nocapture %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* @realloc(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
}