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

[Joseph Pusdesris]

This worked perfectly.  Thankyou.
-Joe


On Sun, Dec 2, 2012 at 12:34 PM, Joseph Pusdesris <joe at pusdesris.com> wrote:

> 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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