int isassign(s)
register char *s;
{
  if (!letter(*s))
    return (0);
  for (; *s != '='; s++)
    if (*s == 0 || !letnum(*s))
      return (0);
  return (1);
}


x86 assembly (clang, -O0):
<isassign>:
push   %rbp
mov    %rsp,%rbp
sub    $0x10,%rsp
mov    %rdi,-0x10(%rbp)
mov    -0x10(%rbp),%rax
movsbl (%rax),%edi
mov    $0x0,%al
call   1040 <letter@plt>
cmp    $0x0,%eax
jne    114f <isassign+0x2f>
movl   $0x0,-0x4(%rbp)
jmp    11b4 <isassign+0x94>
jmp    1154 <isassign+0x34>
mov    -0x10(%rbp),%rax
movsbl (%rax),%eax
cmp    $0x3d,%eax
je     11ad <isassign+0x8d>
mov    -0x10(%rbp),%rax
movsbl (%rax),%eax
cmp    $0x0,%eax
je     118b <isassign+0x6b>
mov    -0x10(%rbp),%rax
movsbl (%rax),%edi
mov    $0x0,%al
call   1030 <letnum@plt>
cmp    $0x0,%eax
jne    1197 <isassign+0x77>
movl   $0x0,-0x4(%rbp)
jmp    11b4 <isassign+0x94>
jmp    119c <isassign+0x7c>
mov    -0x10(%rbp),%rax
add    $0x1,%rax
mov    %rax,-0x10(%rbp)
jmp    1154 <isassign+0x34>
movl   $0x1,-0x4(%rbp)
mov    -0x4(%rbp),%eax
add    $0x10,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<isassign>:
push   %rbp
push   %rbx
push   %rax
mov    %rdi,%rbx
movsbl (%rdi),%edi
xor    %eax,%eax
call   1040 <letter@plt>
xor    %ebp,%ebp
test   %eax,%eax
je     1167 <isassign+0x47>
cs nopw 0x0(%rax,%rax,1)
movsbl (%rbx),%edi
test   %edi,%edi
je     115e <isassign+0x3e>
cmp    $0x3d,%dil
je     1162 <isassign+0x42>
xor    %eax,%eax
call   1030 <letnum@plt>
add    $0x1,%rbx
test   %eax,%eax
jne    1140 <isassign+0x20>
jmp    1167 <isassign+0x47>
xor    %ebp,%ebp
jmp    1167 <isassign+0x47>
mov    $0x1,%ebp
mov    %ebp,%eax
add    $0x8,%rsp
pop    %rbx
pop    %rbp
ret

LLVM IR (-O0):
define i32 @isassign(i8* %0) {
%2 = alloca i32
%3 = alloca i8*
store i8* %0, i8** %3
%4 = load i8*, i8** %3
%5 = load i8, i8* %4
%6 = sext i8 %5 to i32
%7 = call i32 (i32, ...) bitcast (i32 (...)* @letter to i32 (i32, ...)*)(i32 %6)
%8 = icmp ne i32 %7, 0
br i1 %8, label %10, label %9
9: ; preds = %1
store i32 0, i32* %2
br label %33
10: ; preds = %1
br label %11
11: ; preds = %29, %10
%12 = load i8*, i8** %3
%13 = load i8, i8* %12
%14 = sext i8 %13 to i32
%15 = icmp ne i32 %14, 61
br i1 %15, label %16, label %32
16: ; preds = %11
%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 %27, label %21
21: ; preds = %16
%22 = load i8*, i8** %3
%23 = load i8, i8* %22
%24 = sext i8 %23 to i32
%25 = call i32 (i32, ...) bitcast (i32 (...)* @letnum to i32 (i32, ...)*)(i32 %24)
%26 = icmp ne i32 %25, 0
br i1 %26, label %28, label %27
27: ; preds = %21, %16
store i32 0, i32* %2
br label %33
28: ; preds = %21
br label %29
29: ; preds = %28
%30 = load i8*, i8** %3
%31 = getelementptr inbounds i8, i8* %30, i32 1
store i8* %31, i8** %3
br label %11
32: ; preds = %11
store i32 1, i32* %2
br label %33
33: ; preds = %32, %27, %9
%34 = load i32, i32* %2
ret i32 %34
}

LLVM IR (-O2):
define i32 @isassign(i8* nocapture %0) {
%2 = load i8, i8* %0
%3 = sext i8 %2 to i32
%4 = tail call i32 (i32, ...) bitcast (i32 (...)* @letter to i32 (i32, ...)*)(i32 %3)
%5 = icmp eq i32 %4, 0
br i1 %5, label %15, label %6
6: ; preds = %1, %9
%7 = phi i8* [ %13, %9 ], [ %0, %1 ]
%8 = load i8, i8* %7
switch i8 %8, label %9 [
i8 61, label %15
i8 0, label %14
]
9: ; preds = %6
%10 = sext i8 %8 to i32
%11 = tail call i32 (i32, ...) bitcast (i32 (...)* @letnum to i32 (i32, ...)*)(i32 %10)
%12 = icmp eq i32 %11, 0
%13 = getelementptr inbounds i8, i8* %7, i64 1
br i1 %12, label %14, label %6
14: ; preds = %6, %9
br label %15
15: ; preds = %6, %14, %1
%16 = phi i32 [ 0, %1 ], [ 0, %14 ], [ 1, %6 ]
ret i32 %16
}