[PATCH] D129666: [SDAG] Remove single-result restriction on commutative CSE

[Sergei Barannikov via Phabricator via llvm-commits]

barannikov88 added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1872
-  if (!RV.getNode() && TLI.isCommutativeBinOp(N->getOpcode()) &&
-      N->getNumValues() == 1) {
     SDValue N0 = N->getOperand(0);
----------------
craig.topper wrote:
> craig.topper wrote:
> > craig.topper wrote:
> > > RKSimon wrote:
> > > > Do we know why this limit was here in the first place?
> > > At the time that was added, the commutable binops with 2 values were SMUL_LOHI/UMUL_LOHI/ADDC/ADDE.
> > > 
> > > Am I unsure if its safe to do this for ADDC/ADDE which use Glue results. CSEing would increase the use count of the Glue. Maybe that's what it was protecting?
> > Oops "Am I unsure" -> "I am unsure".
> So it's probably safer as
> 
> ```
>   if (!RV.getNode() && TLI.isCommutativeBinOp(N->getOpcode()) &&
>       N->getValueType(N->getNumValues()-1) != MVT::Glue) {
> ```
> Am I unsure if its safe to do this for ADDC/ADDE which use Glue results. CSEing would increase the use count of the Glue.

AFAIK nodes with Glue result are never CSEd. See [[ https://github.com/s-barannikov/llvm-neuromatrix/blob/ede600377cb6df1bef71f070130d8cfe734cc5b7/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp#L8984 | getNode ]] [[ https://github.com/s-barannikov/llvm-neuromatrix/blob/ede600377cb6df1bef71f070130d8cfe734cc5b7/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp#L9722 | getNodeIfExists ]].


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  https://reviews.llvm.org/D129666/new/

https://reviews.llvm.org/D129666