two dfa problems

[Richard Henderson <rth at redhat dot com>]

Both of these issues show up with -mcpu=ev5, with the patch attached,
on the fortran test case also attached.

(1) Exponential behaviour in max_issue.

    While compiling (iirc) iqtest_, we have 18 instructions ready at
    the beginning of the block, which as far as I can see causes us
    to try 2**18 alternatives.  Certainly the compiler hangs for 
    longer than I cared to wait.

    I think the algorithm here is wrong, but I don't know how to fix
    it exactly.  The hack attached prevents the exponential runaway,
    but I think we should not be trying alternatives with instructions
    of the same type.  That is, once we've tried an instruction of 
    type TYPE_IADD at position 0, we should not try a different insn
    of type TYPE_IADD there, since it won't help produce a better
    sloting.

(2) Too many instructions issued per cycle.

    The .28.sched2 dump contains for MAIN__

         16--> 1144 $29=unspec[$29,0x3e] 10            :ev5_e01
         16--> 34   $16=$9                             :ev5_e01
         16--> 38   $18=0x18                           :ev5_e01
         16--> 40   $19=0x18                           :ev5_e01

    which has overcommitted both E0 and E1.  The issue rate is
    set to 4 because we can issue to E0,E1,FA,FM in one cycle,
    but that is not the case here.  I'm not sure what is going on.


r~

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