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22007E/0—November 1999 AMD Athlon™ Processor x86 Code Optimization
Memory Size and Alignment Issues 45
5
Cache and Memory
Optimizations
This chapter describes code optimization techniques that take
advantage of the large L1 caches and high-bandwidth buses of
the AMD Athlon™ processor. Guidelines are listed in order of
importance.
Memory Size and Alignment Issues
Avoid Memory Size Mismatches
Avoid memory size mismatches when instructions operate on
the same data. For instructions that store and reload the same
data, keep operands aligned and keep the loads/stores of each
operand the same size. The following code examples result in a
store-to-load-forwarding (STLF) stall:
Example 1 (Avoid):
MOV DWORD PTR [FOO], EAX
MOV DWORD PTR [FOO+4], EDX
FLD QWORD PTR [FOO]
Avoid large-to-small mismatches, as shown in the following
code:
Example 2 (Avoid):
FST QWORD PTR [FOO]
MOV EAX, DWORD PTR [FOO]
MOV EDX, DWORD PTR [FOO+4]
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