[LLVMdev] Splitting a load with 2 consumers into 2 loads.

[Joseph Pusdesris]

I'll give that a shot, thanks!
-Joe


On Sun, Dec 2, 2012 at 12:06 PM, Triple Yang <triple.yang at gmail.com> wrote:

> OK, I get it.
>
> The essence of this problem is that a node can be covered exactly and
> just once but its result can be referred multiple times for a tree
> pattern matching isel. So to duplicate a load node (only if we can!)
> is convenient to conquer that case.
>
> The truth is, in pattern (add (load) (load)), source operands are
> memory addresses, and thus it can be treated         as (addmm
> address, address). Here is an alternative you can take into
> consideration: defining new node (like addmm, similiar with movmm) to
> specify matching patterns for isel.
>
> Regards.
>
> 2012/12/2 Joseph Pusdesris <joe at pusdesris.com>:
> > I am writing a target for an odd cisc-like architecture which has no
> support
> > for keeping most values in registers.  As such, memory-memory operations
> are
> > needed, but for isel to generate a memory-memory the pattern must be of
> the
> > form (store (op (load) (load))).
> >
> > Let's use a simple example to show how this can be problematic:
> >   %0 = load i32* %a.addr, align 4
> >   store i32 %0, i32* %other, align 4
> >   %1 = load i32* %b.addr, align 4
> >   %add = add i32 %0, %1
> > ----
> > In this example, the (store (load)) pair -- the first two lines -- will
> be
> > matched by isel as a MOVmm.  This will be problematic for the add though,
> > since the load SDNode will be gone, making that part of the DAG no
> longer of
> > the form (add (load) (load)).  To counteract this, I would create 2 load
> > SDNodes so that both of these patterns can be satisfied.  Does this make
> > sense?
> > -Joe
> >
> >
> >
> >
> > On Sat, Dec 1, 2012 at 11:44 PM, Triple Yang <triple.yang at gmail.com>
> wrote:
> >>
> >> Hi, Joe.
> >>
> >> I am sorry I did not catch your point. Can you provide more details?
> >>
> >> Since SDValue/SDNode can be used multiple times, why would you want to
> >> create two identical objects
> >> instead of reference to the same one?
> >>
> >> 2012/12/2 Joseph Pusdesris <joe at pusdesris.com>:
> >> > Yes, changing parameters will create a new Node, but is there some
> way I
> >> > can
> >> > force a new node with the same parameters?
> >> > -Joe
> >> >
> >> >
> >> > On Sat, Dec 1, 2012 at 10:57 PM, Triple Yang <triple.yang at gmail.com>
> >> > wrote:
> >> >>
> >> >> Hi, Joseph, I guess getLoad() will either search an existed SDValue
> >> >> *OR* create a new one for a non-existed one depending on real
> >> >> parameters.
> >> >>
> >> >> Since you use exactly the same attributes dupVal/dupNode have, no
> >> >> doubt getLoad() return the old one.
> >> >>
> >> >> I am not sure it's *volatile* that let you get a new result, you
> might
> >> >> want to try change some other parameters and check what it turns out.
> >> >>
> >> >> Regards.
> >> >>
> >> >> 2012/12/2 Joseph Pusdesris <joe at pusdesris.com>
> >> >> >
> >> >> > So I think I have made some progress.
> >> >> > SDValue dupVal  = consumer->getOperand(OpNo);
> >> >> > LoadSDNode *dupNode = (LoadSDNode*) dupVal.getNode();
> >> >> >
> >> >> > SDValue newLoad = CurDAG->getLoad(dupVal.getValueType(),
> >> >> > dupVal.getDebugLoc(),
> >> >> >                                dupVal.getOperand(0),
> >> >> > dupVal.getOperand(1),
> >> >> >                                dupNode->getPointerInfo(),
> >> >> >                                dupNode->isVolatile(),
> >> >> > dupNode->isNonTemporal(),
> >> >> >                                dupNode->isInvariant(),
> >> >> > dupNode->getAlignment(),
> >> >> >                                dupNode->getTBAAInfo(),
> >> >> > dupNode->getRanges());
> >> >> > However, my problem now is that it will re-use the same load still.
> >> >> > If
> >> >> > I change something, like setting volatile to true for example, it
> >> >> > will
> >> >> > create a new node, but otherwise it will not.  Any ideas?
> >> >> > -Joe
> >> >> >
> >> >> >
> >> >> > On Fri, Nov 30, 2012 at 9:55 PM, Joseph Pusdesris <
> joe at pusdesris.com>
> >> >> > wrote:
> >> >> >>
> >> >> >> Hi, I am writing an llvm target and I need both loads for isel
> >> >> >> reasons,
> >> >> >> but I am struggling to find the right way.  I have been trying to
> >> >> >> use
> >> >> >> DAG.getLoad() to make a copy, then just change the operand in the
> >> >> >> consumers,
> >> >> >> but I cannot seem to get all of the arguments needed for that
> >> >> >> function in
> >> >> >> order to make the copy.  Any help would be great, thanks!
> >> >> >> -Joe
> >> >> >
> >> >> >
> >> >> >
> >> >> > _______________________________________________
> >> >> > LLVM Developers mailing list
> >> >> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> >> >> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >> >> >
> >> >>
> >> >>
> >> >>
> >> >> --
> >> >> 杨勇勇 (Yang Yongyong)
> >> >
> >> >
> >>
> >>
> >>
> >> --
> >> 杨勇勇 (Yang Yongyong)
> >
> >
>
>
>
> --
> 杨勇勇 (Yang Yongyong)
>
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