#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 tolower(char const);
int strcasecmp(const char *s1, const char *s2) {
  int result;
  while (1) {
    result = tolower(*s1) - tolower(*s2);
    if (result != 0 || *s1 == '\0')
      break;
    ++s1;
    ++s2;
  }
  return result;
}


x86 assembly (clang, -O0):
<strcasecmp>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
mov    %rdi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
mov    -0x8(%rbp),%rax
movsbl (%rax),%edi
call   1030 <tolower@plt>
mov    %eax,-0x18(%rbp)
mov    -0x10(%rbp),%rax
movsbl (%rax),%edi
call   1030 <tolower@plt>
mov    %eax,%ecx
mov    -0x18(%rbp),%eax
sub    %ecx,%eax
mov    %eax,-0x14(%rbp)
cmpl   $0x0,-0x14(%rbp)
jne    115f <strcasecmp+0x4f>
mov    -0x8(%rbp),%rax
movsbl (%rax),%eax
cmp    $0x0,%eax
jne    1164 <strcasecmp+0x54>
jmp    1181 <strcasecmp+0x71>
mov    -0x8(%rbp),%rax
add    $0x1,%rax
mov    %rax,-0x8(%rbp)
mov    -0x10(%rbp),%rax
add    $0x1,%rax
mov    %rax,-0x10(%rbp)
jmp    1120 <strcasecmp+0x10>
mov    -0x14(%rbp),%eax
add    $0x20,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<strcasecmp>:
push   %rbp
push   %r15
push   %r14
push   %rbx
push   %rax
mov    %rsi,%r14
mov    %rdi,%r15
movsbl (%rdi),%edi
call   1030 <tolower@plt>
mov    %eax,%ebp
movsbl (%r14),%edi
call   1030 <tolower@plt>
sub    %eax,%ebp
jne    116a <strcasecmp+0x5a>
mov    $0x1,%ebx
nopl   0x0(%rax)
cmpb   $0x0,-0x1(%r15,%rbx,1)
je     1168 <strcasecmp+0x58>
movsbl (%r15,%rbx,1),%edi
call   1030 <tolower@plt>
mov    %eax,%ebp
movsbl (%r14,%rbx,1),%edi
call   1030 <tolower@plt>
add    $0x1,%rbx
sub    %eax,%ebp
je     1140 <strcasecmp+0x30>
jmp    116a <strcasecmp+0x5a>
xor    %ebp,%ebp
mov    %ebp,%eax
add    $0x8,%rsp
pop    %rbx
pop    %r14
pop    %r15
pop    %rbp
ret

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

LLVM IR (-O2):
define i32 @strcasecmp(i8* nocapture %0, i8* nocapture %1) {
%3 = load i8, i8* %0
%4 = tail call i32 @tolower(i8 signext %3)
%5 = load i8, i8* %1
%6 = tail call i32 @tolower(i8 signext %5)
%7 = sub nsw i32 %4, %6
%8 = icmp eq i32 %7, 0
br i1 %8, label %9, label %23
9: ; preds = %2, %14
%10 = phi i8* [ %15, %14 ], [ %0, %2 ]
%11 = phi i8* [ %16, %14 ], [ %1, %2 ]
%12 = load i8, i8* %10
%13 = icmp eq i8 %12, 0
br i1 %13, label %23, label %14
14: ; preds = %9
%15 = getelementptr inbounds i8, i8* %10, i64 1
%16 = getelementptr inbounds i8, i8* %11, i64 1
%17 = load i8, i8* %15
%18 = tail call i32 @tolower(i8 signext %17)
%19 = load i8, i8* %16
%20 = tail call i32 @tolower(i8 signext %19)
%21 = sub nsw i32 %18, %20
%22 = icmp eq i32 %21, 0
br i1 %22, label %9, label %23
23: ; preds = %9, %14, %2
%24 = phi i32 [ %7, %2 ], [ %21, %14 ], [ 0, %9 ]
ret i32 %24
}