#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 */
size_t strlen(char *);
char *strcat(char *dest, const char *src) {
  size_t i;
  for (i = strlen(dest); src[i] != '\0'; i++) {
    dest[i] = src[i];
  }
  dest[i] = '\0';
  return dest;
}


x86 assembly (clang, -O0):
<strcat>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x8(%rbp),%rdi
call   1030 <strlen@plt>
mov    %rax,-0x18(%rbp)
mov    -0x10(%rbp),%rax
mov    -0x18(%rbp),%rcx
movsbl (%rax,%rcx,1),%eax
cmp    $0x0,%eax
je     1169 <strcat+0x59>
mov    -0x10(%rbp),%rax
mov    -0x18(%rbp),%rcx
mov    (%rax,%rcx,1),%dl
mov    -0x8(%rbp),%rax
mov    -0x18(%rbp),%rcx
mov    %dl,(%rax,%rcx,1)
mov    -0x18(%rbp),%rax
add    $0x1,%rax
mov    %rax,-0x18(%rbp)
jmp    112d <strcat+0x1d>
mov    -0x8(%rbp),%rax
mov    -0x18(%rbp),%rcx
movb   $0x0,(%rax,%rcx,1)
mov    -0x8(%rbp),%rax
add    $0x20,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<strcat>:
push   %r14
push   %rbx
push   %rax
mov    %rsi,%rbx
mov    %rdi,%r14
call   1030 <strlen@plt>
mov    (%rbx,%rax,1),%cl
test   %cl,%cl
je     1141 <strcat+0x31>
cs nopw 0x0(%rax,%rax,1)
mov    %cl,(%r14,%rax,1)
movzbl 0x1(%rbx,%rax,1),%ecx
add    $0x1,%rax
test   %cl,%cl
jne    1130 <strcat+0x20>
movb   $0x0,(%r14,%rax,1)
mov    %r14,%rax
add    $0x8,%rsp
pop    %rbx
pop    %r14
ret

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

LLVM IR (-O2):
define i8* @strcat(i8* returned %0, i8* nocapture %1) {
%3 = tail call i64 @strlen(i8* dereferenceable(1) %0)
%4 = getelementptr inbounds i8, i8* %1, i64 %3
%5 = load i8, i8* %4
%6 = icmp eq i8 %5, 0
br i1 %6, label %15, label %7
7: ; preds = %2, %7
%8 = phi i8 [ %13, %7 ], [ %5, %2 ]
%9 = phi i64 [ %11, %7 ], [ %3, %2 ]
%10 = getelementptr inbounds i8, i8* %0, i64 %9
store i8 %8, i8* %10
%11 = add i64 %9, 1
%12 = getelementptr inbounds i8, i8* %1, i64 %11
%13 = load i8, i8* %12
%14 = icmp eq i8 %13, 0
br i1 %14, label %15, label %7
15: ; preds = %7, %2
%16 = phi i64 [ %3, %2 ], [ %11, %7 ]
%17 = getelementptr inbounds i8, i8* %0, i64 %16
store i8 0, i8* %17
ret i8* %0
}