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Appendix E
SSE and SSE2 Optimizations
361
Software Optimization Guide for AMD64 Processors
25112
Rev. 3.06
September 2005
E.5
Saving and Restoring Registers of Unknown
Format
Format
Optimization
Use INT loads (MOVDQA for 128 bits and MOVQ for 64 bits) when restoring registers of unknown
format from the stack.
format from the stack.
Application
This optimization applies to:
•
32-bit software
•
64-bit software
Rationale
All stores of 64-bits or more from an XMM register to memory may be performed without concern
for the type of the data in the XMM register. This allows called procedures to save registers on the
stack without knowing what their format was. Conversely, all INT loads (MOVDQA for 128 bits and
MOVQ for 64 bits) leave the register in a format that is acceptable to all SSE and SSE2 instructions
and is recommended when restoring registers of unknown format from the stack.
for the type of the data in the XMM register. This allows called procedures to save registers on the
stack without knowing what their format was. Conversely, all INT loads (MOVDQA for 128 bits and
MOVQ for 64 bits) leave the register in a format that is acceptable to all SSE and SSE2 instructions
and is recommended when restoring registers of unknown format from the stack.