[Bug target/50751] SH Target: Displacement addressing does not work for QImode and HImode

[oleg.endo@t-online.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50751

Oleg Endo <oleg.endo@t-online.de> changed:

           What    |Removed                     |Added
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  Attachment #25932|0                           |1
        is obsolete|                            |

--- Comment #18 from Oleg Endo <oleg.endo@t-online.de> 2011-12-11 00:24:17 UTC ---
Created attachment 26046
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26046
Proposed patch to add QImode displacement addressing

This version of the patch was tested against rev 182090 and did not introduce
new failures.

It allows the generation of QImode displacement addressing move insns, but only
if the addresses can be fixed before reload.  If reload needs to load/store
e.g. pseudos on the stack where displacement addressing would be required the
generated code is not as good unfortunately.  One good example for this kind of
scenario is the gcc.dg/compat/struct-by-value-11 test from the testsuite, which
shows that there is still some room for improvement.
Still, on the CSiBE I could observe a code size decrease of -1.2% avg, where
mpeg2dec goes down to -5.65% and libmpeg2/motion_comp down to -20% (-m4 -ml
taken as example).  Due to SH2A's 4 byte QImode displacement insn the benefit
on SH2A code is not that big (-0.2% avg).

There are probably smarter ways of doing what the patch does.  I have also
tried out implementing it with predicates and constraints, few load/store insns
and lots of alternatives in the insns.  However, reload would refuse to select
the displacement addressing due to pressure on R0 in many cases.

Would something like the attached patch be acceptable (after some cleanups)? 
If so, I'd also start adding HImode displacement addressing support.