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Appendix E SSE and SSE2 Optimizations 359
Software Optimization Guide for AMD64 Processors
25112 Rev. 3.06 September 2005
E.3 Reuse of Dead Registers
Optimization
When it is necessary to save the contents of a register that is in FPS format to another unused (or
dead) register, where the previous contents of the dead register are unknown and could be a denormal,
then use movaps xmm1, xmm2 instead of movss xmm1, xmm2.
Application
This optimization applies to:
• 32-bit software
• 64-bit software
Rationale
The movss xmm1, xmm2 instruction takes additional time to execute if the previous contents of
XMM1 are a denormal.