[LLVMdev] Assignment instruction.

[Tobias Nurmiranta]

Thanks for the fast reply. I'll do as you suggested, and create my own
identity instructions with "add" for int's and "getelementptr" for
pointers.
,	Tobias

On Thu, 17 Jun 2004, Misha Brukman wrote:
> On Thu, Jun 17, 2004 at 05:09:30PM +0200, Tobias Nurmiranta wrote:
> > A small thing I miss in the intermediate representation is a simple
> > assignment instruction, like:
> >
> >   %x = uint 3
> > or:
> >   %x = uint %y
> >
> > It would simplify the implementation of frontends, I think.
>
> Neither of these is necessary, and adding new instructions means every
> transformation has to handle these (extra cases, extra complexity, etc.)
>
> In the first case, "x = 3", you can simply constant-propagate the 3 and
> use it everywhere you would use the x.  If you are programming an LLVM
> pass, create a Value* that is the "uint 3" and use it.  If you are
> writing LLVM assembly by hand, use "x = add uint 3, 0" and you have the
> same effect, without an extra special case for future transformations.
>
> As for "x = y", same as above: since we are using SSA, y cannot be
> assigned a new value, ever, so you can just use y anywhere below where
> you would otherwise use x, and the assignment isn't even necessary.
>
> Basically, the point is to have an orthogonal instruction set where
> little (or no) functionality is duplicated across the instructions,
> because that cuts down on the number of cases a transformation has to
> deal with.
>
> --
> Misha Brukman :: http://misha.brukman.net :: http://llvm.cs.uiuc.edu
>
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