Which supports more cmdline options in the meantime than what we have
been supporting manually, and should be future-proof, similar to
InitTargetOptionsFromCodeGenFlags().
Attributes are only set if explicitly specified in the cmdline (and not
already present in the function's existing attributes).
This started out as a workaround for not being able to determine whether
the user has explicitly set -frame-pointer in the cmdline with LLVM 11,
and ended with having to touch more than I wanted. An *enabled*
-ffast-math flag (from us, not LLVM) overriding LLVM's
-enable-unsafe-fp-math, but e.g. -ffast-math=false NOT overriding was/is
one of the quirks.
I.e., llvm/CodeGen/CommandFlags.h which in turn includes
llvm/MC/MCTargetOptionsCommandFlags.h.
This gets rid of a few duplicates on our side and includes about 35
(depending on LLVM version) new command-line options. LLVM provides a
helper function to set up the TargetOptions according to (most of) these
options.
Newer LLVM versions may add new options and we'll automatically inherit
them, including setting up the TargetOptions accordingly.
I did my best (TM) to remove a few unused/undesirable options and hide all
remaining new ones except for `-fp-contract`. The lists will need to be
tweaked from time to time.
