Справочник Пользователя для AMD 250

25112

Rev. 3.06

September 2005

Sort local variables according to their type sizes, declaring those with larger type sizes ahead of those 
with smaller type sizes.

This optimization applies to:

•

32-bit software

•

64-bit software

It can be helpful to presort local variables, if your compiler allocates local variables in the same order 
in which they are declared in the source code. If the first variable is allocated for natural alignment, all 
other variables are allocated contiguously in the order they are declared and are naturally aligned 
without padding.

Some compilers do not allocate variables in the order they are declared. In these cases, the compiler 
should automatically allocate variables that are naturally aligned with the minimum amount of 
padding. In addition, some compilers do not guarantee that the stack is aligned suitably for the largest 
type (that is, they do not guarantee quadword alignment), so that quadword operands might be 
misaligned, even if this technique is used and the compiler does allocate variables in the order they 
are declared.

Avoid local variable declarations, when the variables are not declared in order of their type sizes:

short   ga, gu, gi;

long    foo, bar;

double  x, y, z[3];

char    a, b;

float   baz;

Instead, sort the declarations according to their type sizes (largest to smallest):

double  z[3];

double  x, y;

long    foo, bar;

float   baz;

short   ga, gu, gi;