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A general description is here.
(Not Windows.) ‘R CMD INSTALL’ and ‘R CMD SHLIB’ have a new flag ‘--use-LTO’ to use Link-Time Optimization when compiling code, for use with R configured with ‘--enable-lto=R’. For R configured with ‘--enable-lto’, they have the new flag ‘--no-use-LTO’.
Packages can opt in or out of LTO compilation _via_ a ‘UseLTO’ field in the ‘DESCRIPTION’ file. (As usual this can be overridden by the command-line flags.)
Configuring with flag ‘--enable-lto=R’ now also uses LTO when installing the recommended packages.
There is now support for parallelized Link-Time Optimization _via_ setting the ‘LTO’ macro.