[LLVMdev] Proposal for new Legalization framework

[Chris Lattner]

On Apr 25, 2013, at 5:16 AM, reed kotler <rkotler at mips.com> wrote:
> On 04/24/2013 07:39 PM, Chris Lattner wrote:
>> On Apr 24, 2013, at 6:27 PM, Reed Kotler <rkotler at mips.com> wrote:
>>> I would really push towards doing this in LLVM IR as the next step.
>> What makes you say that?
>> 
> Partly for the reasons Dan stated. For me, the IR is definitely way more friendly too and not tangled
> up in lots of undocumented obscurity as selection DAG is with tablegen and many other idiosyncrasies of the backend design.

See my response to David.  Making LLVM IR less friendly to solve backend problems isn't acceptable to me.

> Solving problems with selection DAG, to me, is like playing dungeons and dragons. I feel like I need to ask the wizard for a magic spell to capture a gnome. I don't feel like I'm doing science. It's too much like a game with thousands of rules to know.

Also, don't conflate dislike of SelectionDAG (which many people share) with a forgone conclusion that the only way to fix it is in LLVM IR.  If there is a specific problem with MachineInstrs that make them difficult to work with, we should fix that.  Few people will argue that SelectionDAG is worth saving. :-)

-Chris