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Chapter 6 Branch Optimizations 135
Software Optimization Guide for AMD64 Processors
25112 Rev. 3.06 September 2005
6.6 Nonzero Code-Segment Base Values
Optimization
In 32-bit threads, avoid using a nonzero code-segment (CS) base value. (In 64-bit mode, segmentation
is disabled and the segment base value is ignored and treated as zero.)
Application
This optimization applies to:
• 32-bit software
Rationale
A nonzero CS base value causes an additional two cycles of branch-misprediction penalty when
compared with a CS base value of zero:
CS base value
Minimum branch penalty (cycles)
Prediction sequential Prediction taken Misprediction
00 1 10
Not 0 0 1 12