user manual

22007E/0—November 1999 AMD Athlon™ Processor x86 Code Optimization
Top Optimizations 7
2
Top Optimizations
This chapter contains concise descriptions of the best
optimizations for improving the performance of the
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
Group II contains secondary optimizations that can
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