patch: alpha haifa abort

[Jeffrey A Law]

  In message < 9801042347.AA25082@rios1.watson.ibm.com >you write:
  > >>>>> Jeffrey A Law writes:
  > 
  > Jeff> The "trick" is to define an intermediate pattern so that combine
  > Jeff> will do a 2/3 -> 1 to create the intermediate pattern.  If that
  > Jeff> is successful combine will then try to combine the intermediate
  > Jeff> pattern with the 4th insn.
  > 
  > 	Doesn't the intermediate pattern need to be a valid instruction?
  > Mike and I went into this issue as well.
Absolutely.  I ran into this with the H8 mac stuff.  The questions you
have to ask are how expensive is it to handle a false positive, how many
false positives are typically encountered, and how many times you can
actually generate the real instruction.

  > 	I also remember some complexities due to other GCC optimizations
  > of the RTL generated for the shift-or way of writing the code.
Yea.  That would make this one a little trickier.  Maybe the place to
do this is in the simplify_blah routines.  Dunno.
jeff