#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(int);
int /*<<< orphan*/ strcpy(char *, char const *);
int strlen(char const *);
char *concat(const char *str1, const char *str2) {
  char *newstr;
  int str1_length = strlen(str1);
  newstr = malloc(str1_length + strlen(str2) + 1);
  if (newstr == 0)
    return 0;
  strcpy(newstr, str1);
  strcpy(newstr + str1_length, str2);
  return newstr;
}


x86 assembly (clang, -O0):
<concat>:
push   %rbp
mov    %rsp,%rbp
sub    $0x30,%rsp
mov    %rdi,-0x10(%rbp)
mov    %rsi,-0x18(%rbp)
mov    -0x10(%rbp),%rdi
call   1040 <strlen@plt>
mov    %eax,-0x24(%rbp)
mov    -0x24(%rbp),%eax
mov    %eax,-0x28(%rbp)
mov    -0x18(%rbp),%rdi
call   1040 <strlen@plt>
mov    -0x28(%rbp),%edi
add    %eax,%edi
add    $0x1,%edi
call   1050 <malloc@plt>
mov    %rax,-0x20(%rbp)
cmpq   $0x0,-0x20(%rbp)
jne    1184 <concat+0x54>
movq   $0x0,-0x8(%rbp)
jmp    11ad <concat+0x7d>
mov    -0x20(%rbp),%rdi
mov    -0x10(%rbp),%rsi
call   1030 <strcpy@plt>
mov    -0x20(%rbp),%rdi
movslq -0x24(%rbp),%rax
add    %rax,%rdi
mov    -0x18(%rbp),%rsi
call   1030 <strcpy@plt>
mov    -0x20(%rbp),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
add    $0x30,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<concat>:
push   %r15
push   %r14
push   %r12
push   %rbx
push   %rax
mov    %rsi,%r14
mov    %rdi,%r15
call   1040 <strlen@plt>
mov    %eax,%r12d
mov    %r14,%rdi
call   1040 <strlen@plt>
lea    (%r12,%rax,1),%edi
add    $0x1,%edi
call   1050 <malloc@plt>
mov    %rax,%rbx
test   %rax,%rax
je     117e <concat+0x4e>
mov    %rbx,%rdi
mov    %r15,%rsi
call   1030 <strcpy@plt>
movslq %r12d,%rax
mov    %rbx,%rdi
add    %rax,%rdi
mov    %r14,%rsi
call   1030 <strcpy@plt>
mov    %rbx,%rax
add    $0x8,%rsp
pop    %rbx
pop    %r12
pop    %r14
pop    %r15
ret

LLVM IR (-O0):
define i8* @concat(i8* %0, i8* %1) {
%3 = alloca i8*
%4 = alloca i8*
%5 = alloca i8*
%6 = alloca i8*
%7 = alloca i32
store i8* %0, i8** %4
store i8* %1, i8** %5
%8 = load i8*, i8** %4
%9 = call i32 @strlen(i8* %8)
store i32 %9, i32* %7
%10 = load i32, i32* %7
%11 = load i8*, i8** %5
%12 = call i32 @strlen(i8* %11)
%13 = add nsw i32 %10, %12
%14 = add nsw i32 %13, 1
%15 = call i8* @malloc(i32 %14)
store i8* %15, i8** %6
%16 = load i8*, i8** %6
%17 = icmp eq i8* %16, null
br i1 %17, label %18, label %19
18: ; preds = %2
store i8* null, i8** %3
br label %30
19: ; preds = %2
%20 = load i8*, i8** %6
%21 = load i8*, i8** %4
%22 = call i32 @strcpy(i8* %20, i8* %21)
%23 = load i8*, i8** %6
%24 = load i32, i32* %7
%25 = sext i32 %24 to i64
%26 = getelementptr inbounds i8, i8* %23, i64 %25
%27 = load i8*, i8** %5
%28 = call i32 @strcpy(i8* %26, i8* %27)
%29 = load i8*, i8** %6
store i8* %29, i8** %3
br label %30
30: ; preds = %19, %18
%31 = load i8*, i8** %3
ret i8* %31
}

LLVM IR (-O2):
define i8* @concat(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 = icmp eq i8* %7, null
br i1 %8, label %14, label %9
9: ; preds = %2
%10 = tail call i32 @strcpy(i8* %7, i8* %0)
%11 = sext i32 %3 to i64
%12 = getelementptr inbounds i8, i8* %7, i64 %11
%13 = tail call i32 @strcpy(i8* %12, i8* %1)
br label %14
14: ; preds = %2, %9
ret i8* %7
}