(truncdfsf2): Rewrite to allow FLOAT_REGS in constraints
   for better register preferences.
(movM): If REG_WAS_0, make sure the reg hasn't changed since then.
(cmpM expanders): Don't allow both operands to be MEM.
Use VOIDmode for the COMPARE rtx instead of CCmode.
(cmpM recognizers): Likewise.
Remove constraints for constants from operand 0.
(cmpdf,cmpsf recognizers): When using VOIDmode as mode of the COMPARE rtx,
   require that the mode be exactly VOIDmode.

From-SVN: r3716