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This saves space in 'struct fpu'. It probably doesn't actually >make XSAVE/XRSTOR any faster because the init optimization is very >likely to be in place for these features. Thanks for the detailed explanation. You're absolutely right—this change aims to reduce the size of struct fpu. I see now that implying a perf improvement for XSAVE/XRSTOR was misleading, as the underlying optimization is likely handled by the init optimization. I'll revise the changelog to clarify this and incorporate your wording to avoid confusion. > >I'm not sure what point the changelog was trying to make about xstate_bv >and xcomp_bv. xstate_bv[12] would have been 0 if the feature was in its >init state.