#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(size_t);
size_t strlen(char const *);
int /*<<< orphan*/ strncpy(char *, char const *, size_t);
char *str_concat(const char *s1, const char *s2) {
  size_t l1 = strlen(s1), l2 = strlen(s2);
  size_t len = l1 + l2 + 1;
  char *s = malloc(len * sizeof(char));
  if (s) {
    strncpy(s, s1, l1);
    strncpy(s + l1, s2, l2 + 1);
  }
  return s;
}


x86 assembly (clang, -O0):
<str_concat>:
push   %rbp
mov    %rsp,%rbp
sub    $0x30,%rsp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x8(%rbp),%rdi
call   1040 <strlen@plt>
mov    %rax,-0x18(%rbp)
mov    -0x10(%rbp),%rdi
call   1040 <strlen@plt>
mov    %rax,-0x20(%rbp)
mov    -0x18(%rbp),%rax
add    -0x20(%rbp),%rax
add    $0x1,%rax
mov    %rax,-0x28(%rbp)
mov    -0x28(%rbp),%rdi
shl    $0x0,%rdi
call   1050 <malloc@plt>
mov    %rax,-0x30(%rbp)
cmpq   $0x0,-0x30(%rbp)
je     11b0 <str_concat+0x80>
mov    -0x30(%rbp),%rdi
mov    -0x8(%rbp),%rsi
mov    -0x18(%rbp),%rdx
call   1030 <strncpy@plt>
mov    -0x30(%rbp),%rdi
add    -0x18(%rbp),%rdi
mov    -0x10(%rbp),%rsi
mov    -0x20(%rbp),%rdx
add    $0x1,%rdx
call   1030 <strncpy@plt>
mov    -0x30(%rbp),%rax
add    $0x30,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<str_concat>:
push   %r15
push   %r14
push   %r13
push   %r12
push   %rbx
mov    %rsi,%r14
mov    %rdi,%r15
call   1040 <strlen@plt>
mov    %rax,%r12
mov    %r14,%rdi
call   1040 <strlen@plt>
mov    %rax,%r13
lea    (%rax,%r12,1),%rdi
add    $0x1,%rdi
call   1050 <malloc@plt>
mov    %rax,%rbx
test   %rax,%rax
je     118a <str_concat+0x5a>
add    $0x1,%r13
mov    %rbx,%rdi
mov    %r15,%rsi
mov    %r12,%rdx
call   1030 <strncpy@plt>
mov    %rbx,%rdi
add    %r12,%rdi
mov    %r14,%rsi
mov    %r13,%rdx
call   1030 <strncpy@plt>
mov    %rbx,%rax
pop    %rbx
pop    %r12
pop    %r13
pop    %r14
pop    %r15
ret

LLVM IR (-O0):
define i8* @str_concat(i8* %0, i8* %1) {
%3 = alloca i8*
%4 = alloca i8*
%5 = alloca i64
%6 = alloca i64
%7 = alloca i64
%8 = alloca i8*
store i8* %0, i8** %3
store i8* %1, i8** %4
%9 = load i8*, i8** %3
%10 = call i64 @strlen(i8* %9)
store i64 %10, i64* %5
%11 = load i8*, i8** %4
%12 = call i64 @strlen(i8* %11)
store i64 %12, i64* %6
%13 = load i64, i64* %5
%14 = load i64, i64* %6
%15 = add i64 %13, %14
%16 = add i64 %15, 1
store i64 %16, i64* %7
%17 = load i64, i64* %7
%18 = mul i64 %17, 1
%19 = call i8* @malloc(i64 %18)
store i8* %19, i8** %8
%20 = load i8*, i8** %8
%21 = icmp ne i8* %20, null
br i1 %21, label %22, label %34
22: ; preds = %2
%23 = load i8*, i8** %8
%24 = load i8*, i8** %3
%25 = load i64, i64* %5
%26 = call i32 @strncpy(i8* %23, i8* %24, i64 %25)
%27 = load i8*, i8** %8
%28 = load i64, i64* %5
%29 = getelementptr inbounds i8, i8* %27, i64 %28
%30 = load i8*, i8** %4
%31 = load i64, i64* %6
%32 = add i64 %31, 1
%33 = call i32 @strncpy(i8* %29, i8* %30, i64 %32)
br label %34
34: ; preds = %22, %2
%35 = load i8*, i8** %8
ret i8* %35
}

LLVM IR (-O2):
define i8* @str_concat(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, 1
%6 = add i64 %5, %3
%7 = tail call i8* @malloc(i64 %6)
%8 = icmp eq i8* %7, null
br i1 %8, label %13, label %9
9: ; preds = %2
%10 = tail call i32 @strncpy(i8* %7, i8* %0, i64 %3)
%11 = getelementptr inbounds i8, i8* %7, i64 %3
%12 = tail call i32 @strncpy(i8* %11, i8* %1, i64 %5)
br label %13
13: ; preds = %9, %2
ret i8* %7
}