[Bug target/78176] [MIPS] miscompiles ldxc1 with large pointers on 32-bits

["doug.gilmore at imgtec dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78176

--- Comment #17 from Doug Gilmore <doug.gilmore at imgtec dot com> ---
> This really throws off the costing of substituting different IVs on
> MIPS.
I forgot to mention that for MIPS the net of effect r216501 is to not
produce indexed memory OPs in simple examples where we should.  But
we also will produce problematic indexed memory OPs in situations
where address generation costing is a bit complicated (the original
issue associated with this bug report).

Applying the the two patches I just attached fixes the problem of
generating indexed memory OPs in simple examples, and also will cause
IVOPTS to select IVs that are similar to those that were made in the
past that avoids the problem executing indexed memory OPs in O32
binaries on 64-bit MIPS processors running current Linux kernels.

There is still the issue of recognizing that rewriting a "use" to use
a different IV can expose a problem with indexed memory OPs on 64-bit
MIPS processors, where an infinite cost should be associated in that
situation, that still needs to be addressed (thus the need for the
flag to turn off the generation of indexed memory OPs until this issue
is addressed).