Re: Legitimize address, Please HELP!

[Jan Hubicka <jh at suse dot cz>]

> Jan, thanks for reply.
> I really do not know much about the process of the creation of 
> instructions - only that written in gcc info.
> 
> I will appreciate if you can tell me what's wrong with the expander like:
I don't see the bug directly in expanders you quoted, but few problems:
1) match_operand calls the predicate, so memory_operand call in movhi1
   condition is redundant.  Similary in movhi2, where you call
   nonimmediate_operand that is supperset of register_operand already
   tested.
2) the zero_shifted/indexed_location test probably should be hid
   in new operand writen in your md file used in patterns instead of
   general_operand to make thinks cleaner.
   Basically the condition should mention only tests that depdends
   on multiple
3) "m" is wrong constraint for general_operand. Eighter you need
   to use memory_operand, or allow some registers and constants
   in the constraint.
   The constraints and predicates should be in "harmony" one should
   not be considerably stronger/weaker than the other otherwise you
   are asking for problems in reload pass.
   In case the second pattern is expected to load address as integer
   value (i386 lea equivalent), it should use
   (match_operand "address_operand" "a"), not memory and should come last
   to avoid matches in dumb cases.
   
4) For speed you should probably move more probable movhi3 first.
5) All three patterns can be single pattern with multiple alternative
   output template.  This will result in faster compiler and better
   produced code if you do so.  Some late passes, as reload, do not
   take a look if different pattern match, only test if given pattern
   and usually also alternative, allow the suggested optimization.
6) Similary you can collapse multiple alternatives to single:
   "=m,r,r,m,r,m,m,r
     m,r,P,P,m,r,i,i"
   can be:
   "=m   ,r"
     mrPi,mrPi"
   Also it is good to prohibit mem->mem move in the conditional + add
   expander to split it into two instructions early like i386.md does.
   Otherwise the need for register in this case is discovered late in
   the register allocation progress often resulting in dumb spill.

In case you do have flags register (as cc attribute suggest), please
consider not using cc0, as it looks you do use.  We are tying to zap
that.  Look at i386.md/sparc.md about how new backends are usually
done.

Concerning your problem.  The problematic piece of code is not
contained in the mov expander, instead it is, most probably, some
other code generating the add/mov directly and getting thinks wrong.

one of ways to get it is to add test for current_insn_uid in emit-rtl.c
and break program in debugger when offending instruction is emit. Then
you will be probably able to figure out where it incarned.

See the gcc readings page.  I believe there are some links to other porting
docs, than the gcc manual itself.  it is good idea to read them (even when I
never did :), because it can save you some headaches later.

Hope this helps,
Honza
> 
> ========================
> (define_expand "movhi"
>  [(set (match_operand:HI 0 "nonimmediate_operand" "")
>        (match_operand:HI 1 "general_operand" ""))]
>  ""
>  "")
> 
> 
> (define_insn "*movhi1"
>  [(set (match_operand:HI 0 "memory_operand"      "=m")
>        (match_operand:HI 1 "general_operand"           "m"))]
>  "( memory_operand(operands[0], VOIDmode)
>        && !register_operand(operands[0], VOIDmode)
>        && zero_shifted(operands[1])       
>        && indexed_location(operands[1]))" 
> "mov\\t@%E1, %0"
>  [(set_attr "length" "3")
>   (set_attr "cc" "none")])
> 
> 
> (define_insn "*movhi2"
>  [(set (match_operand:HI 0 "register_operand" "=r")
>        (match_operand:HI 1 "general_operand"      "m"))]
>  "(nonimmediate_operand(operands[0], VOIDmode)
>                && zero_shifted(operands[1])  
>                && indexed_location(operands[1]) )"
>       "mov\\t@%E1, %A0"
>  [(set_attr "length" "2")
>   (set_attr "cc" "none")])
> 
> (define_insn "*movhi3"
>  [(set (match_operand:HI 0 "nonimmediate_operand"      "=m,r,r,m,r,m,m,r")
>        (match_operand:HI 1 "general_operand"           " 
> m,r,P,P,m,r,i,i"))]
>  "(nonimmediate_operand(operands[0], HImode)
>        && !zero_shifted(operands[1])
>        && !indexed_location(operands[1]) )"
>  "mov\\t%1, %0 "
>  [(set_attr "length" "1,3,1,2,2,2,3,2")
>   (set_attr "cc" "none")])
> ==============================