xp(a) unsigned char *a;
{
  int i;
  for (i = 0; i < 8; i++)
    printf("%02X", a[i]);
  printf("\n");
}


x86 assembly (clang, -O0):
<xp>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
mov    %rdi,-0x10(%rbp)
movl   $0x0,-0x14(%rbp)
cmpl   $0x8,-0x14(%rbp)
jge    1155 <xp+0x45>
mov    -0x10(%rbp),%rax
movslq -0x14(%rbp),%rcx
movzbl (%rax,%rcx,1),%esi
lea    0xec0(%rip),%rdi
mov    $0x0,%al
call   1030 <printf@plt>
mov    -0x14(%rbp),%eax
add    $0x1,%eax
mov    %eax,-0x14(%rbp)
jmp    1123 <xp+0x13>
lea    0xea9(%rip),%rdi
mov    $0x0,%al
call   1030 <printf@plt>
mov    -0x4(%rbp),%eax
add    $0x20,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<xp>:
push   %r14
push   %rbx
push   %rax
mov    %rdi,%rbx
movzbl (%rdi),%esi
lea    0xecf(%rip),%r14
mov    %r14,%rdi
xor    %eax,%eax
call   1040 <printf@plt>
movzbl 0x1(%rbx),%esi
mov    %r14,%rdi
xor    %eax,%eax
call   1040 <printf@plt>
movzbl 0x2(%rbx),%esi
mov    %r14,%rdi
xor    %eax,%eax
call   1040 <printf@plt>
movzbl 0x3(%rbx),%esi
mov    %r14,%rdi
xor    %eax,%eax
call   1040 <printf@plt>
movzbl 0x4(%rbx),%esi
mov    %r14,%rdi
xor    %eax,%eax
call   1040 <printf@plt>
movzbl 0x5(%rbx),%esi
mov    %r14,%rdi
xor    %eax,%eax
call   1040 <printf@plt>
movzbl 0x6(%rbx),%esi
mov    %r14,%rdi
xor    %eax,%eax
call   1040 <printf@plt>
movzbl 0x7(%rbx),%esi
mov    %r14,%rdi
xor    %eax,%eax
call   1040 <printf@plt>
mov    $0xa,%edi
add    $0x8,%rsp
pop    %rbx
pop    %r14
jmp    1030 <putchar@plt>

LLVM IR (-O0):
@.str = [5 x i8] c"%02X\00"
@.str.1 = [2 x i8] c"\0A\00"
define i32 @xp(i8* %0) {
%2 = alloca i32
%3 = alloca i8*
%4 = alloca i32
store i8* %0, i8** %3
store i32 0, i32* %4
br label %5
5: ; preds = %16, %1
%6 = load i32, i32* %4
%7 = icmp slt i32 %6, 8
br i1 %7, label %8, label %19
8: ; preds = %5
%9 = load i8*, i8** %3
%10 = load i32, i32* %4
%11 = sext i32 %10 to i64
%12 = getelementptr inbounds i8, i8* %9, i64 %11
%13 = load i8, i8* %12
%14 = zext i8 %13 to i32
%15 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 %14)
br label %16
16: ; preds = %8
%17 = load i32, i32* %4
%18 = add nsw i32 %17, 1
store i32 %18, i32* %4
br label %5
19: ; preds = %5
%20 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([2 x i8], [2 x i8]* @.str.1, i64 0, i64 0))
%21 = load i32, i32* %2
ret i32 %21
}

LLVM IR (-O2):
@.str = [5 x i8] c"%02X\00"
define i32 @xp(i8* nocapture %0) {
%2 = load i8, i8* %0
%3 = zext i8 %2 to i32
%4 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 %3)
%5 = getelementptr inbounds i8, i8* %0, i64 1
%6 = load i8, i8* %5
%7 = zext i8 %6 to i32
%8 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 %7)
%9 = getelementptr inbounds i8, i8* %0, i64 2
%10 = load i8, i8* %9
%11 = zext i8 %10 to i32
%12 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 %11)
%13 = getelementptr inbounds i8, i8* %0, i64 3
%14 = load i8, i8* %13
%15 = zext i8 %14 to i32
%16 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 %15)
%17 = getelementptr inbounds i8, i8* %0, i64 4
%18 = load i8, i8* %17
%19 = zext i8 %18 to i32
%20 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 %19)
%21 = getelementptr inbounds i8, i8* %0, i64 5
%22 = load i8, i8* %21
%23 = zext i8 %22 to i32
%24 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 %23)
%25 = getelementptr inbounds i8, i8* %0, i64 6
%26 = load i8, i8* %25
%27 = zext i8 %26 to i32
%28 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 %27)
%29 = getelementptr inbounds i8, i8* %0, i64 7
%30 = load i8, i8* %29
%31 = zext i8 %30 to i32
%32 = tail call i32 (i8*, ...) @printf(i8* dereferenceable(1) getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 %31)
%33 = tail call i32 @putchar(i32 10)
ret i32 undef
}