regclass.c: scan_one_insn special casing

[Eric Christopher <echristo at redhat dot com>]

There's this code in scan_one_insn:

 /* Improve handling of two-address insns such as
     (set X (ashift CONST Y)) where CONST must be made to
     match X. Change it into two insns: (set X CONST)
     (set X (ashift X Y)).  If we left this for reloading, it
     would probably get three insns because X and Y might go
     in the same place. This prevents X and Y from receiving
     the same hard reg.
                                                                                
     We can only do this if the modes of operands 0 and 1
     (which might not be the same) are tieable and we only need
     do this during our first pass.  */
                                                                                
  if (pass == 0 && optimize
      && recog_data.n_operands >= 3
      && recog_data.constraints[1][0] == '0'
      && recog_data.constraints[1][1] == 0
      && CONSTANT_P (recog_data.operand[1])
      && ! rtx_equal_p (recog_data.operand[0], recog_data.operand[1])
      && ! rtx_equal_p (recog_data.operand[0], recog_data.operand[2])
      && GET_CODE (recog_data.operand[0]) == REG
      && MODES_TIEABLE_P (GET_MODE (recog_data.operand[0]),
                          recog_data.operand_mode[1]))
    {

....


That appears to do something a port specific splitter would do. Now,
I've also looked and mips has a splitter that does something similar,
I'm not sure about other ports. I'm also really curious what port this
was added in for and perhaps the testcase...

I added an abort () right after the if statement above, and bootstrapped
and tested on x86-linux, mips-elf, sh-elf, arm-elf and couldn't trip it.

Any thoughts? I also have a patch to just remove it.

-eric

-- 
Eric Christopher <echristo@redhat.com>