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A general description is here.
‘R CMD INSTALL’ and ‘R CMD SHLIB’ make use of their flag ‘--use-LTO’ when the ‘LTO_OPT’ make macro is set in file ‘etc/${R_ARCH}/Makeconf’. (For details see ‘Writing R Extensions’ §4.5.)
This provides a valuable check on code consistency. It does work with GCC 8.3 as in Rtools40, but that does not detect everything the CRAN checks with GCC 10 do.
‘R CMD INSTALL’ and ‘R CMD SHLIB’ make use of the flag ‘--use-LTO’ when
the ‘LTO_OPT’ make macro is set in file ‘etc/${R_ARCH}/Makeconf’ - it
is not by default but a setting in ‘MkRules.local’ will be imported
when R is built.