https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100830
Bug ID: 100830
Summary: Multilib directory picking logic handles default
arguments oddly
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: driver
Assignee: unassigned at gcc dot gnu.org
Reporter: mhjacobson at me dot com
Target Milestone: ---
`set_multilib_dir()` is responsible for selecting a multilib directory given
(a) `multilib_select` and (b) the state of the switches.
But (at least, IMO), it handles the following case very unintuitively:
Suppose `multilib_select` is (newlines added for clarity):
. !mmcu=avr4 !mmcu=avr5;
avr4 mmcu=avr4 !mmcu=avr5;
avr5 !mmcu=avr4 mmcu=avr5;
i.e., choose "avr4" if `-mmcu=avr4`; "avr5" if `-mmcu=avr5`, and "." if
neither.
Suppose also that the default value of `mmcu`, specified in
`multilib_defaults`, is `avr5`.
Then the logic described by this comment will unintuitively cause "." to be
picked even when `-mmcu=avr5` is explicitly passed as an argument to the
driver:
/* If this is a default argument, we can just ignore it.
This is true even if this_arg begins with '!'. Beginning
with '!' does not mean that this argument is necessarily
inappropriate for this library: it merely means that
there is a more specific library which uses this
argument. If this argument is a default, we need not
consider that more specific library. */
The code that actually implements this is the check of default_arg() after
we've already failed the used_arg() check.
Perhaps it's not a valid configuration to have a default value in
`multilib_defaults` that does not correspond to ".", but if so, I think that's
weird.
