Re: DImode operations

[Dave Korn <dave.korn.cygwin@googlemail.com>]

daniel tian wrote:
> Hi:
> 
>     Do I have to write the DImode operations on my *.md target description file?

  Yes.  movMM must be implemented for all types that you want the compiler to
be able to handle at all; it's the only way it knows to move them around.
(Technically, it's supposed to be able to treat DImode as BLKmode and break it
down by pieces, but this code hasn't always been reliable and is definitely
less efficient than implementing a proper movdi pattern in your backend.)

> My target is a RISC32 chip. There is no 64bit operations. And now I
> don't wanna any 64bit operations in my C programs.
> So do I have to finish the DImode operations?

  I think you really should.  Take a look at how other ports handle it;
generally they use a define_expand for movdi, which emits the move as two
separate SI-mode move insns.  (Note in particular how they have to take care
what order to emit the two word moves in, as it's possible for the register
pairs used in input and output operations to overlap.)

  If you insisted, you could probably just hack the *di* routines out of the
libgcc makefile and get through to the end of the build, but I really wouldn't
recommend it, since "long long" is a standard C99 type.  It's not a great deal
of work to add the expander pattern and code that you'll need.

    cheers,
      DaveK