Quoting "Joseph S. Myers" <jos...@codesourcery.com>:
If something relates to an interface to a lower-level part of the compiler then BITS_PER_UNIT is probably right - but if somethis relates to whether a type is a variant of char, or to alignment of a non-bit-field object (you can't have smaller than char alignment), or things like that, then TYPE_PRECISION (char_type_node) may be better.
Yes, I see examples for both in the C++ front end. The tree optimizers seem mostly (or entirely?) concerned with the addressable unit size.
Note that BITS_PER_UNIT is used in code built for the target (libgcc2.c, dfp-bit.h, fixed-bit.h, fp-bit.h, libobjc/encoding.c, ...), and converting it to a hook requires eliminating those uses.
Full conversion does. For the moment I would be content with a partial conversion so that not every tree optimizer that currently uses
BITS_PER_UNIT has to include tm.h itself once the bogus tm.h includes from target.h / function.h / gimple.h are gone.
