[Patch, mips] Fix compiler abort with -mips32r2 -mips16 -msynci

[Richard Sandiford]

"Steve Ellcey " <sellcey@mips.com> writes:
> While working on my favorite mips option (-msynci) I noticed an odd thing.
> If I compile with '-mips32 -mips16 -msynci' I got a warning about synci not
> being supported but if I compiled with '-mips32r2 -mips16 -msynci' I did not
> get a warning, even though -mips16 mode does not support synci.  Furthermore
> if I compiled a program that called __builtin___clear_cache with '-mips32r2
> -mips16 -msynci', the compiler would abort.

The abort sounds like the bug here.  It's deliberate that things like
-msynci, -mbranch-likely, etc., are OK with -mips16.  On the one hand,
you could compile with -mips16 but have an __attribute__((nomips16))
function that could benefit from using SYNCI.  On the other, you could
compile without -mips16 but have an __attribute__((mips16)) function
that needs to avoid SYNCI.

-mips16 really just sets the default ISA mode for functions that don't
specify one.  That's why override_options hides mips16ness so early on,
like you say.

Richard