Afterthought: maybe that's done this way to prevent local overheating EAX cpu cirquitry?

avoiding access to the same register by subsequent instructions (very simplified explanation!) may let you gain something in terms of performance.

... modern CPUs do register renaming ... avoiding access to the same register by subsequent instructions (very simplified explanation!) may let you gain something in terms of performance.

DimonSoft wrote:

... modern CPUs do register renaming ... avoiding access to the same register by subsequent instructions (very simplified explanation!) may let you gain something in terms of performance.

Erm, are you talking about dependency chain length? Because manually reordering instructions to trying and interleave dependency chains it tricky and can be confusing. In most cases letting the OOO engine do its job will be just fine. And of course testing in the final app will tell you if it makes any difference at runtime.

As usual it all depends upon what you are doing. Different situations will yield different results.

; Case 1
mov     ecx, [Value1]
mov     edx, [Value2]
inc     ecx
dec     edx
add     ecx, [Value3]
imul    edx, [Value4]
add     edx, ecx
mov     [Result1], ecx
mov     [Result2], edx

; Case 2
mov     ecx, [Value1]
inc     ecx
add     ecx, [Value3]
mov     edx, [Value2]
dec     edx
imul    edx, [Value4]
add     edx, ecx
mov     [Result1], ecx
mov     [Result2], edx    

Thanks Dimon!

DimonSoft wrote:

avoiding access to the same register by subsequent instructions (very simplified explanation!) may let you gain something in terms of performance.

Can you give a more comprehensive explanation or drop a link where I can read more about it?
(Either in English or in Russian)

Question #2
I'm wracking my brains around the http://wiki.osdev.org/Uefi.inc and can't figure out why on earth the guy needed all those bells and whistles with redefining data types and structures

struct EFI_SYSTEM_TABLE
  Hdr                   EFI_TABLE_HEADER
  FirmwareVendor        rq 1
  FirmwareRevision      rd 1
                        rd 1  ; alignment for the next qword
  ConsoleInHandle       rq 1
  ConIn                 rq 1
  ConsoleOutHandle      rq 1
  ConOut                rq 1
  StandardErrorHandle   rq 1
  StdErr                rq 1
  RuntimeServices       rq 1
  BootServices          rq 1
  NumberOfTableEntries  rq 1
  ConfigurationTable    rq 1
ends    

; Code

;->> Copying Actual tables SystemTable and SimpleTextOutput to local memory (gBS and tXT respectively)

; Something-something

lea eax,[string_to_print]
push eax
push [gBS.ConOut]
call [tXT.OutputString]
add esp, 8

; Data
gBS  EFI_SYSTEM_TABLE
tXT SIMPLE_TEXT_OUTPUT
    

  mov rcx, [r15 + EFI_SYSTEM_TABLE.ConOut]
  call [rcx + EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL.OutputString]