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Chapter 9 Optimizing with SIMD Instructions 209
Software Optimization Guide for AMD64 Processors
25112 Rev. 3.06 September 2005
9.9 Storing Floating-Point Data in MMX™ Registers
Optimization
Avoid storing floating-point data in MMX registers unless using 3DNow! instructions.
Application
This optimization applies to:
• 32-bit software
• 64-bit software
Rationale
Using MOVDQ2Q or MOVQ2DQ to shuffle integer data between MMX and XMM registers is useful
to relieve register pressure; however, doing so with floating-point data can impact performance. The
impact is greater if the floating-point data is denormalized.