RFA: Fix PR21767 (Was: Re: RFD: what to do about stale REG_EQUAL notes in dead_or_predictable)

[Joern RENNECKE]

I've tried removing REG_EQUAL notes altogether unless we
know that the source of the move is function invariant, and got
identical assembler for all the EEMBC tests as without the patch.
Likewise for an entire sh4-elf multilibbed libgcc, libstdc++-v3
and newlib build.   I think it is therefore reasonable to assume
that removing the notes doesn't cause any relevant performance
loss.  For a 3.4 based compiler, that was just a small ifcvt.c
patch; for 4.x, I also had to reinstate function_invariant_p  as
a global function.

I can't do an i686-pc-linux-gnu bootstrap at the moment because
the bootstrap fails building libjava, both with unpatched sources
from 12:00 and 16:00 UTC.  I'll do a bootstrap / regression test
of the patch when we are back in bootstrap land.

FWIW, this is the failure:
./../.././gcc/gcjh -classpath '' -bootclasspath . 
java/lang/AbstractMethodError
make[2]: *** [java/lang/AbstractMethodError.h] Segmentation fault
make[2]: *** Deleting file `java/lang/AbstractMethodError.h'
make[2]: Leaving directory 
`/mnt/scratch/nightly/2005-05-31/i686/i686-pc-linux-gnu/libjava'

AFAICS, jcf-io.c:format_uint is miscompiled, base is not handed as
second parameter to umoddi, it uses the saved values of esi/edi
instead.
   
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