AMD Typewriter x86 사용자 설명서

22007E/0—November 1999

I f   t h e   f o l l o w i n g   c o n d i t i o n s   a r e   p r e s e n t ,   t h e re   i s   a
narrow-to-wide store-buffer data forwarding restriction:

■

The operand size of the store data is smaller than the
operand size of the load data.

■

The range of addresses spanned by the store data covers
some sub-region of range of addresses spanned by the load
data.

Avoid the type of code shown in the following two examples.

MOV EAX, 10h
MOV WORD PTR [EAX], BX

;word store

...
MOV ECX, DWORD PTR [EAX]

;doubleword load
;cannot forward upper
; byte from store buffer

MOV EAX, 10h
MOV BYTE PTR [EAX + 3], BL ;byte store
...
MOV ECX, DWORD PTR [EAX]   ;doubleword load

  

;cannot forward upper byte

  

; from store buffer

I f   t h e   f o l l o w i n g   c o n d i t i o n s   a r e   p r e s e n t ,   t h e re   i s   a
wide-to-narrow store-buffer data forwarding restriction:

■

The operand size of the store data is greater than the
operand size of the load data.

■

The start address of the store data does not match the start
address of the load.

MOV EAX, 10h
ADD DWORD PTR [EAX], EBX 

;doubleword store

MOV CX, WORD PTR [EAX + 2] ;word load-cannot forward high

; word from store buffer

Use example 5 instead of example 4.

MOVQ       [foo], MM1    ;store upper and lower half
...
ADD        EAX, [foo]    ;fine
ADD        EDX, [foo+4]  ;uh-oh!