#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 strlen(char const *);
int /*<<< orphan*/ strncpy(char *, char const *, int);
char *String_cat(const char *s1, const char *s2) {
  int l1 = strlen(s1);
  int l2 = strlen(s2);
  char *out = malloc(l1 + l2 + 1);
  strncpy(out, s1, l1);
  strncpy(out + l1, s2, l2 + 1);
  return out;
}


x86 assembly (clang, -O0):
<String_cat>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x8(%rbp),%rdi
call   1040 <strlen@plt>
mov    %eax,-0x14(%rbp)
mov    -0x10(%rbp),%rdi
call   1040 <strlen@plt>
mov    %eax,-0x18(%rbp)
mov    -0x14(%rbp),%edi
add    -0x18(%rbp),%edi
add    $0x1,%edi
call   1050 <malloc@plt>
mov    %rax,-0x20(%rbp)
mov    -0x20(%rbp),%rdi
mov    -0x8(%rbp),%rsi
mov    -0x14(%rbp),%edx
call   1030 <strncpy@plt>
mov    -0x20(%rbp),%rdi
movslq -0x14(%rbp),%rax
add    %rax,%rdi
mov    -0x10(%rbp),%rsi
mov    -0x18(%rbp),%edx
add    $0x1,%edx
call   1030 <strncpy@plt>
mov    -0x20(%rbp),%rax
add    $0x20,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<String_cat>:
push   %rbp
push   %r15
push   %r14
push   %r12
push   %rbx
mov    %rsi,%r14
mov    %rdi,%r15
call   1040 <strlen@plt>
mov    %eax,%ebx
mov    %r14,%rdi
call   1040 <strlen@plt>
lea    0x1(%rax),%r12d
lea    (%rax,%rbx,1),%edi
add    $0x1,%edi
call   1050 <malloc@plt>
mov    %rax,%rbp
mov    %rax,%rdi
mov    %r15,%rsi
mov    %ebx,%edx
call   1030 <strncpy@plt>
movslq %ebx,%rdi
add    %rbp,%rdi
mov    %r14,%rsi
mov    %r12d,%edx
call   1030 <strncpy@plt>
mov    %rbp,%rax
pop    %rbx
pop    %r12
pop    %r14
pop    %r15
pop    %rbp
ret

LLVM IR (-O0):
define i8* @String_cat(i8* %0, i8* %1) {
%3 = alloca i8*
%4 = alloca i8*
%5 = alloca i32
%6 = alloca i32
%7 = alloca i8*
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* %5
%10 = load i8*, i8** %4
%11 = call i32 @strlen(i8* %10)
store i32 %11, i32* %6
%12 = load i32, i32* %5
%13 = load i32, i32* %6
%14 = add nsw i32 %12, %13
%15 = add nsw i32 %14, 1
%16 = call i8* @malloc(i32 %15)
store i8* %16, i8** %7
%17 = load i8*, i8** %7
%18 = load i8*, i8** %3
%19 = load i32, i32* %5
%20 = call i32 @strncpy(i8* %17, i8* %18, i32 %19)
%21 = load i8*, i8** %7
%22 = load i32, i32* %5
%23 = sext i32 %22 to i64
%24 = getelementptr inbounds i8, i8* %21, i64 %23
%25 = load i8*, i8** %4
%26 = load i32, i32* %6
%27 = add nsw i32 %26, 1
%28 = call i32 @strncpy(i8* %24, i8* %25, i32 %27)
%29 = load i8*, i8** %7
ret i8* %29
}

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