#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*/ free(char *);
char *malloc(int);
int /*<<< orphan*/ strcpy(char *, char *);
int strlen(char *);
char *append_string(char *old, char *new) {
  char *new_string;
  int old_length;
  int new_length;
  old_length = strlen(old);
  new_length = strlen(new);
  new_string = malloc(old_length + new_length + 1);
  strcpy(new_string, old);
  strcpy(new_string + old_length, new);
  free(old);
  return new_string;
}


x86 assembly (clang, -O0):
<append_string>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x8(%rbp),%rdi
call   1050 <strlen@plt>
mov    %eax,-0x1c(%rbp)
mov    -0x10(%rbp),%rdi
call   1050 <strlen@plt>
mov    %eax,-0x20(%rbp)
mov    -0x1c(%rbp),%edi
add    -0x20(%rbp),%edi
add    $0x1,%edi
call   1060 <malloc@plt>
mov    %rax,-0x18(%rbp)
mov    -0x18(%rbp),%rdi
mov    -0x8(%rbp),%rsi
call   1040 <strcpy@plt>
mov    -0x18(%rbp),%rdi
movslq -0x1c(%rbp),%rax
add    %rax,%rdi
mov    -0x10(%rbp),%rsi
call   1040 <strcpy@plt>
mov    -0x8(%rbp),%rdi
call   1030 <free@plt>
mov    -0x18(%rbp),%rax
add    $0x20,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<append_string>:
push   %r15
push   %r14
push   %r12
push   %rbx
push   %rax
mov    %rsi,%r14
mov    %rdi,%r12
call   1050 <strlen@plt>
mov    %eax,%r15d
mov    %r14,%rdi
call   1050 <strlen@plt>
lea    (%r15,%rax,1),%edi
add    $0x1,%edi
call   1060 <malloc@plt>
mov    %rax,%rbx
mov    %rax,%rdi
mov    %r12,%rsi
call   1040 <strcpy@plt>
movslq %r15d,%rdi
add    %rbx,%rdi
mov    %r14,%rsi
call   1040 <strcpy@plt>
mov    %r12,%rdi
call   1030 <free@plt>
mov    %rbx,%rax
add    $0x8,%rsp
pop    %rbx
pop    %r12
pop    %r14
pop    %r15
ret

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

LLVM IR (-O2):
define i8* @append_string(i8* %0, i8* %1) {
%3 = tail call i32 @strlen(i8* %0)
%4 = tail call i32 @strlen(i8* %1)
%5 = add i32 %3, 1
%6 = add i32 %5, %4
%7 = tail call i8* @malloc(i32 %6)
%8 = tail call i32 @strcpy(i8* %7, i8* %0)
%9 = sext i32 %3 to i64
%10 = getelementptr inbounds i8, i8* %7, i64 %9
%11 = tail call i32 @strcpy(i8* %10, i8* %1)
%12 = tail call i32 @free(i8* %0)
ret i8* %7
}