[llvm] r305468 - [DAG] Allow truncated and extend memory operations in Store Merge. NFCI.

[Ahmed Bougacha via llvm-commits]

Hi Nirav,

I reverted this in r305527 because it causes assertion failures (PR33475).

More generally, this change (and others) look pretty functional to me.
Is this all enabled by some future commit?  If so, the commit message
should probably mention that this really is a functional change
required for correctness;  it just happens to not be testable right
now (or even better, commit everything together to avoid adding dead
code).

Thanks!

-Ahmed

On Thu, Jun 15, 2017 at 7:04 AM, Nirav Dave via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: niravd
> Date: Thu Jun 15 09:04:07 2017
> New Revision: 305468
>
> URL: http://llvm.org/viewvc/llvm-project?rev=305468&view=rev
> Log:
> [DAG] Allow truncated and extend memory operations in Store Merge. NFCI.
>
> As all store merges checks are based on the memory operation
> performed, allow use of truncated stores and extended loads as valid
> input candidates for merging.
>
> Modified:
>     llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
>
> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=305468&r1=305467&r2=305468&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
> +++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Thu Jun 15 09:04:07 2017
> @@ -12874,9 +12874,6 @@ bool DAGCombiner::MergeConsecutiveStores
>        if (Ld->isVolatile() || Ld->isIndexed())
>          break;
>
> -      // We do not accept ext loads.
> -      if (Ld->getExtensionType() != ISD::NON_EXTLOAD)
> -        break;
>
>        // The stored memory type must be the same.
>        if (Ld->getMemoryVT() != MemVT)
> @@ -13014,17 +13011,31 @@ bool DAGCombiner::MergeConsecutiveStores
>
>      // The merged loads are required to have the same incoming chain, so
>      // using the first's chain is acceptable.
> -    SDValue NewLoad = DAG.getLoad(JointMemOpVT, LoadDL, FirstLoad->getChain(),
> -                                  FirstLoad->getBasePtr(),
> -                                  FirstLoad->getPointerInfo(), FirstLoadAlign);
>
>      SDValue NewStoreChain = getMergeStoreChains(StoreNodes, NumElem);
> -
>      AddToWorklist(NewStoreChain.getNode());
>
> -    SDValue NewStore = DAG.getStore(
> -        NewStoreChain, StoreDL, NewLoad, FirstInChain->getBasePtr(),
> -        FirstInChain->getPointerInfo(), FirstStoreAlign);
> +    SDValue NewLoad, NewStore;
> +    if (TLI.isTypeLegal(JointMemOpVT)) {
> +      NewLoad = DAG.getLoad(JointMemOpVT, LoadDL, FirstLoad->getChain(),
> +                            FirstLoad->getBasePtr(),
> +                            FirstLoad->getPointerInfo(), FirstLoadAlign);
> +      NewStore = DAG.getStore(NewStoreChain, StoreDL, NewLoad,
> +                              FirstInChain->getBasePtr(),
> +                              FirstInChain->getPointerInfo(), FirstStoreAlign);
> +    } else { // This must be the truncstore/extload case
> +      EVT ExtendedTy =
> +          TLI.getTypeToTransformTo(*DAG.getContext(), JointMemOpVT);
> +      NewLoad = DAG.getExtLoad(ISD::EXTLOAD, LoadDL, ExtendedTy,
> +                               FirstLoad->getChain(), FirstLoad->getBasePtr(),
> +                               FirstLoad->getPointerInfo(), JointMemOpVT,
> +                               FirstLoadAlign);
> +      NewStore = DAG.getTruncStore(NewStoreChain, StoreDL, NewLoad,
> +                                   FirstInChain->getBasePtr(),
> +                                   FirstInChain->getPointerInfo(), JointMemOpVT,
> +                                   FirstInChain->getAlignment(),
> +                                   FirstInChain->getMemOperand()->getFlags());
> +    }
>
>      // Transfer chain users from old loads to the new load.
>      for (unsigned i = 0; i < NumElem; ++i) {
>
>
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