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

Wed Jul 13 10:59:57 PDT 2022

craig.topper 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);
----------------
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?

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D129666/new/

https://reviews.llvm.org/D129666