[PATCH] D122563: [RISCV] Add DAGCombine to fold base operation and reduction.

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


================
Comment at: llvm/lib/Target/RISCV/RISCVISelLowering.cpp:7254
+  if (Opc == ISD::FADD && !N->getFlags().hasAllowReassociation() &&
+      ReduceIdx == 0)
+    return SDValue();
----------------
fakepaper56 wrote:
> craig.topper wrote:
> > The ReduceIdx is relevant here. The order of the fadd operands doesn't matter. The reduce operation is before the fadd, we need to know if the fadd can be moved before the reduce.
> VECREDUCE_FADD_VL always has reassociation, so I think I only need to check `N->getFlags().hasAllowReassociation()` to make sure fadd can be moved before the reduce.
I meant to say “ReduceIdx ISN’T relevant”


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  https://reviews.llvm.org/D122563/new/

https://reviews.llvm.org/D122563