#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*/ strcat(char *, char *);
int /*<<< orphan*/ strcpy(char *, char *);
int strlen(char *);
char *mergestr(char *s1, char *s2) {
  char *s;
  int len = strlen(s1) + strlen(s2);
  s = malloc((len + 1) * sizeof(char));
  if (s == NULL)
    return NULL;
  strcpy(s, s1);
  strcat(s, s2);
  return s;
}


x86 assembly (clang, -O0):
<mergestr>:
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,-0x28(%rbp)
mov    -0x18(%rbp),%rdi
call   1040 <strlen@plt>
mov    %eax,%ecx
mov    -0x28(%rbp),%eax
add    %ecx,%eax
mov    %eax,-0x24(%rbp)
mov    -0x24(%rbp),%eax
add    $0x1,%eax
cltq
shl    $0x0,%rax
mov    %eax,%edi
call   1050 <malloc@plt>
mov    %rax,-0x20(%rbp)
cmpq   $0x0,-0x20(%rbp)
jne    119e <mergestr+0x5e>
movq   $0x0,-0x8(%rbp)
jmp    11c0 <mergestr+0x80>
mov    -0x20(%rbp),%rdi
mov    -0x10(%rbp),%rsi
call   1030 <strcpy@plt>
mov    -0x20(%rbp),%rdi
mov    -0x18(%rbp),%rsi
call   1060 <strcat@plt>
mov    -0x20(%rbp),%rax
mov    %rax,-0x8(%rbp)
mov    -0x8(%rbp),%rax
add    $0x30,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<mergestr>:
push   %r15
push   %r14
push   %rbx
mov    %rsi,%r14
mov    %rdi,%r15
call   1040 <strlen@plt>
mov    %eax,%ebx
mov    %r14,%rdi
call   1040 <strlen@plt>
lea    (%rbx,%rax,1),%edi
add    $0x1,%edi
call   1050 <malloc@plt>
mov    %rax,%rbx
test   %rax,%rax
je     1183 <mergestr+0x43>
mov    %rbx,%rdi
mov    %r15,%rsi
call   1030 <strcpy@plt>
mov    %rbx,%rdi
mov    %r14,%rsi
call   1060 <strcat@plt>
mov    %rbx,%rax
pop    %rbx
pop    %r14
pop    %r15
ret

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

LLVM IR (-O2):
define i8* @mergestr(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 %12, label %9
9: ; preds = %2
%10 = tail call i32 @strcpy(i8* %7, i8* %0)
%11 = tail call i32 @strcat(i8* %7, i8* %1)
br label %12
12: ; preds = %2, %9
ret i8* %7
}