[LLVMdev] How can I get rid of "OPFL_Chain" in myCPUGenInstrInfo.inc

[Tim Northover]

Hi Hilbert,

> i  had not understood the purpose of a TF node.
> my understanding was, the operands  were  not loaded together in one node. they were loaded separately.

The loads happen separately, but the TokenFactor node says that
whichever order they do happen in, they *both* have to be before
whatever comes next (the user of the TokenFactor). It's there to
constrain LLVM's scheduling.

> 4) replace any operands of the TF Node with ADDE did not make sense.

It does to me. Before we were saying that the load of "a+1" had to
happen before X (which might be, for example, a subsequent write to
the 16-bit variable "a"). If that load has been folded into an ADDE,
then that ADDE has to happen before X too.

> 3)the DAG after ADDC was seleced:

Now that's one thing I don't understand. The ADDC should be "above"
the ADDE in the DAG since the ADDE depends on the output of the ADDC.
How did it get selected first?

The DAGs you posted aren't really that useful I'm afraid: deciphering
the text layout is a massive pain in the neck; the machine nodes are
given purely by number (I have no idea what they are); your first dump
appears to be from half way through ISel (which *is* interesting), but
I'd mostly like before & after to begin with.

Cheers.

Tim.