#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 */
int strlen(char *);
char *strcat(char *destination, const char *s) {
  char *d = (destination + strlen(destination));
  for (; *s != '\0'; *d++ = *s++)
    ;
  *d = '\0';
  return destination;
}


x86 assembly (clang, -O0):
<strcat>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x8(%rbp),%rax
mov    %rax,-0x20(%rbp)
mov    -0x8(%rbp),%rdi
call   1030 <strlen@plt>
mov    %eax,%ecx
mov    -0x20(%rbp),%rax
movslq %ecx,%rcx
add    %rcx,%rax
mov    %rax,-0x18(%rbp)
mov    -0x10(%rbp),%rax
movsbl (%rax),%eax
cmp    $0x0,%eax
je     117d <strcat+0x6d>
jmp    1156 <strcat+0x46>
mov    -0x10(%rbp),%rax
mov    %rax,%rcx
add    $0x1,%rcx
mov    %rcx,-0x10(%rbp)
mov    (%rax),%cl
mov    -0x18(%rbp),%rax
mov    %rax,%rdx
add    $0x1,%rdx
mov    %rdx,-0x18(%rbp)
mov    %cl,(%rax)
jmp    1141 <strcat+0x31>
mov    -0x18(%rbp),%rax
movb   $0x0,(%rax)
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>
cltq
add    %r14,%rax
mov    (%rbx),%cl
test   %cl,%cl
je     1141 <strcat+0x31>
add    $0x1,%rbx
xchg   %ax,%ax
mov    %cl,(%rax)
add    $0x1,%rax
movzbl (%rbx),%ecx
add    $0x1,%rbx
test   %cl,%cl
jne    1130 <strcat+0x20>
movb   $0x0,(%rax)
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 i8*
store i8* %0, i8** %3
store i8* %1, i8** %4
%6 = load i8*, i8** %3
%7 = load i8*, i8** %3
%8 = call i32 @strlen(i8* %7)
%9 = sext i32 %8 to i64
%10 = getelementptr inbounds i8, i8* %6, i64 %9
store i8* %10, i8** %5
br label %11
11: ; preds = %17, %2
%12 = load i8*, i8** %4
%13 = load i8, i8* %12
%14 = sext i8 %13 to i32
%15 = icmp ne i32 %14, 0
br i1 %15, label %16, label %23
16: ; preds = %11
br label %17
17: ; preds = %16
%18 = load i8*, i8** %4
%19 = getelementptr inbounds i8, i8* %18, i32 1
store i8* %19, i8** %4
%20 = load i8, i8* %18
%21 = load i8*, i8** %5
%22 = getelementptr inbounds i8, i8* %21, i32 1
store i8* %22, i8** %5
store i8 %20, i8* %21
br label %11
23: ; preds = %11
%24 = load i8*, i8** %5
store i8 0, i8* %24
%25 = load i8*, i8** %3
ret i8* %25
}

LLVM IR (-O2):
define i8* @strcat(i8* returned %0, i8* nocapture %1) {
%3 = tail call i32 @strlen(i8* %0)
%4 = sext i32 %3 to i64
%5 = getelementptr inbounds i8, i8* %0, i64 %4
%6 = load i8, i8* %1
%7 = icmp eq i8 %6, 0
br i1 %7, label %16, label %8
8: ; preds = %2, %8
%9 = phi i8 [ %14, %8 ], [ %6, %2 ]
%10 = phi i8* [ %13, %8 ], [ %5, %2 ]
%11 = phi i8* [ %12, %8 ], [ %1, %2 ]
%12 = getelementptr inbounds i8, i8* %11, i64 1
%13 = getelementptr inbounds i8, i8* %10, i64 1
store i8 %9, i8* %10
%14 = load i8, i8* %12
%15 = icmp eq i8 %14, 0
br i1 %15, label %16, label %8
16: ; preds = %8, %2
%17 = phi i8* [ %5, %2 ], [ %13, %8 ]
store i8 0, i8* %17
ret i8* %0
}