Справочник Пользователя для AMD 250

25112

Rev. 3.06

September 2005

Manually extract common subexpressions where C compilers may be unable to extract them from 
floating-point expressions due to the guarantee against reordering of such expressions in the ANSI 
standard. 

This optimization applies to:

•

32-bit software

•

64-bit software

Specifically, the compiler cannot rearrange the computation according to algebraic equivalencies 
before extracting common subexpressions. Rearranging the expression may give different 
computational results due to the lack of associativity of floating-point operations, but the results 
usually differ in only the least-significant bits.

double a, b, c, d, e, f;

e = b * c / d;

f = b / d * a;

double a, b, c, d, e, f, t;

t = b / d;

e = c * t;

f = a * t;

double a, b, c, e, f;

e = a / c;

f = b / c;