User's Manual

Avoid the Loop Instruction 65
22007E/0—November 1999 AMD Athlon™ Processor x86 Code Optimization
Avoid the Loop Instruction
The LOOP instruction in the AMD Athlon processor requires
eight cycles to execute. Use the preferred code shown below:
Example 1 (Avoid):
LOOP LABEL
Example 2 (Preferred):
DEC ECX
JNZ LABEL
Avoid Far Control Transfer Instructions
Avoid using far control transfer instructions. Far control
transfer branches can not be predicted by the branch target
buffer (BTB).