[PATCH] D155929: [RISCV] Use the first element of source as the start value of reduction.

[Yeting Kuo via Phabricator via llvm-commits]

fakepaper56 added inline comments.


================
Comment at: llvm/lib/Target/RISCV/RISCVISelLowering.cpp:3438
+    MVT ExtractedVT = Scalar.getOperand(0).getSimpleValueType();
+    if (ExtractedVT.bitsLE(VT))
+      return DAG.getNode(ISD::INSERT_SUBVECTOR, DL, VT, Passthru,
----------------
> What happens it it's not converted to a scalable vector?
It just that fixed vectors are hard to compares with scalable vector type here.


================
Comment at: llvm/lib/Target/RISCV/RISCVISelLowering.cpp:7610-7611
+// Function to extract the first element of Vec. For fixed vector Vec, this
+// converts it to scalabe vector before extraction. It could let the following
+// optimizations not have to serve fixed vector.
+static SDValue getFirstElement(SDValue Vec, SelectionDAG &DAG,
----------------
luke wrote:
> What happens it it's not converted to a scalable vector?
Thank you for the feedback.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D155929/new/

https://reviews.llvm.org/D155929