#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 *string_cat(const char *l, const char *r) {
  size_t lSz = strlen(l);
  size_t rSz = strlen(r);
  char *newString = malloc(lSz + rSz + 1);
  strncpy(newString, l, lSz + rSz);
  strncpy(newString + lSz, r, rSz);
  newString[lSz + rSz] = '\0';
  return newString;
}


x86 assembly (clang, -O0):
<string_cat>:
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),%rdi
add    -0x20(%rbp),%rdi
add    $0x1,%rdi
call   1050 <malloc@plt>
mov    %rax,-0x28(%rbp)
mov    -0x28(%rbp),%rdi
mov    -0x8(%rbp),%rsi
mov    -0x18(%rbp),%rdx
add    -0x20(%rbp),%rdx
call   1030 <strncpy@plt>
mov    -0x28(%rbp),%rdi
add    -0x18(%rbp),%rdi
mov    -0x10(%rbp),%rsi
mov    -0x20(%rbp),%rdx
call   1030 <strncpy@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_cat>:
push   %rbp
push   %r15
push   %r14
push   %r13
push   %r12
push   %rbx
push   %rax
mov    %rsi,%r14
mov    %rdi,%r15
call   1040 <strlen@plt>
mov    %rax,%rbx
mov    %r14,%rdi
call   1040 <strlen@plt>
mov    %rax,%r12
lea    (%rax,%rbx,1),%r13
lea    (%rax,%rbx,1),%rdi
add    $0x1,%rdi
call   1050 <malloc@plt>
mov    %rax,%rbp
mov    %rax,%rdi
mov    %r15,%rsi
mov    %r13,%rdx
call   1030 <strncpy@plt>
add    %rbp,%rbx
mov    %rbx,%rdi
mov    %r14,%rsi
mov    %r12,%rdx
call   1030 <strncpy@plt>
movb   $0x0,0x0(%rbp,%r13,1)
mov    %rbp,%rax
add    $0x8,%rsp
pop    %rbx
pop    %r12
pop    %r13
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 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 i64, i64* %5
%13 = load i64, i64* %6
%14 = add i64 %12, %13
%15 = add i64 %14, 1
%16 = call i8* @malloc(i64 %15)
store i8* %16, i8** %7
%17 = load i8*, i8** %7
%18 = load i8*, i8** %3
%19 = load i64, i64* %5
%20 = load i64, i64* %6
%21 = add i64 %19, %20
%22 = call i32 @strncpy(i8* %17, i8* %18, i64 %21)
%23 = load i8*, i8** %7
%24 = load i64, i64* %5
%25 = getelementptr inbounds i8, i8* %23, i64 %24
%26 = load i8*, i8** %4
%27 = load i64, i64* %6
%28 = call i32 @strncpy(i8* %25, i8* %26, i64 %27)
%29 = load i8*, i8** %7
%30 = load i64, i64* %5
%31 = load i64, i64* %6
%32 = add i64 %30, %31
%33 = getelementptr inbounds i8, i8* %29, i64 %32
store i8 0, i8* %33
%34 = load i8*, i8** %7
ret i8* %34
}

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