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Problem with address reloading

I would appreciate any help in this reload problem
that I have been struggling with for some time:

I completed a gcc back end port to a processor that
supports both displaced and indexed addressing modes
for load, but only displaced for store. For example:

    ld.w Rd Rb imm    (load from Rb+imm)
    ld.w Rd Rb Ri     (load from Rb+4*Ri)
    st.w Rd Rb imm    (store to Rb+imm)
    st.w Rd Rb Ri     (indexed not allowed for store)
This compiler runs fine, but currently without
generating indexed load instructions.

In order to enable indexed loads, I extended
GO_IF_LEGITIMATE_ADDRESS to also match indexed
addresses, added a memory constraint 'R' to match
nonindexed addresses, and used R for stores in the
'mov' rule (see below). This rule now defines an
explicit case for all address modes, except indexed
stores. I understand that the reloader should convert
these by loading the store address into a register.

This appears not to happen: although indexed load
instructions are now indeed being generated, I get the
following error messages on such stores:

    (insn 25 14 15 0 (set (mem/s:SI (plus:SI (mult:SI
(reg:SI 11 a11 [ i ])
                        (const_int 4 [0x4]))
                    (reg/f:SI 9 a9 [26])) [3 n S4
            (reg:SI 15 a15)) 2 {movsi} (nil)
    x.c:6: internal compiler error: in
reload_cse_simplify_operands, at postreload.c:393

Tracing all this in find_reloads (reload.c), I see a
call to find_reloads_address, indeed with reload type
RELOAD_FOR_OUTPUT_ADDRESS, but this function
immediately discovers that the address is a
strict_memory_address, and decides to do nothing. This
leads me to believe that I made some error in the
STRICT case of GO_IF_LEGITIMATE_ADDRESS, but everyting
does look ok there.

Is there anything that I am doing obviously wrong?

 -- recognizes register, displaced, and indexed --
 (                                        \
  (C) == 'R' ? ( GET_CODE(X) == MEM       \
              && falcon_non_indexed_p(    \
                    XEXP(X,0), GET_MODE(X)\
               ))                       : \

(define_insn "mov<mode>"
    (match_operand:BWD 0 "nonimmediate_operand"
    (match_operand:BWD 1 "general_operand"      
     %L1<m> %0 %1;
     %S0<m> %0 %1;
     xor    %0 %0;
     mv     %0 %1;
     mv     %0 (%1);
     mv     %0 16@sext(%1);\;sethi %0 16@hi(%1);
     mv     %0 16@lo(%1);\;sethi %0 16@hi(%1);
     mv     %0 %1;
     mv     %0 %1;
     mv<m>  %0 %1;")

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