AMD Athlon Processor x86, Optimization Manual, Page: 23 / 256

22007E/0—November 1999
AMD Athlon™ Processor x86 Code Optimization
Top Optimizations 7
2
Top Optimizations
This chapter contains concise descriptions of the best
o p t i m i z a t i o n s fo r i m p rov i n g t h e p e r fo r m a n c e o f t h e
AMD Athlon™ processor. Subsequent chapters contain more
detailed descriptions of these and other optimizations. The
optimizations in this chapter are divided into two groups and
listed in order of importance.
Group I — Essential
Optimizations Group I contains essential optimizations. Users should follow
these critical guidelines closely. The optimizations in Group I
are as follows:
■
Memory Size and Alignment Issues—Avoid memory size
mismatches—Align data where possible
■
Use the 3DNow!™ PREFETCH and PREFETCHW
Instructions
■
Select DirectPath Over VectorPath Instructions
Group II — Secondary
Optimizations G r o u p I I c o n t a i n s s e c o n d a ry o p t i m i z a t i o n s t h a t c a n
significantly improve the performance of the AMD Athlon
processor. The optimizations in Group II are as follows:
■
Load-Execute Instruction Usage—Use Load-Execute
instructions—Avoid load-execute floating-point instructions
with integer operands
■
Take Advantage of Write Combining
■
Use 3DNow! Instructions
■
Avoid Branches Dependent on Random Data