[PATCH] D157976: [RISCV] Use materialization cost when lowering constant build_vector

[Luke Lau via Phabricator via llvm-commits]

luke added inline comments.


================
Comment at: llvm/lib/Target/RISCV/RISCVISelLowering.cpp:3361
 
-    SDValue Vec = DAG.getNode(ISD::INSERT_VECTOR_ELT, DL, ViaVecVT,
-                              DAG.getUNDEF(ViaVecVT),
-                              DAG.getConstant(SplatValue, DL, XLenVT),
-                              DAG.getConstant(0, DL, XLenVT));
-    if (ViaVecLen != 1)
-      Vec = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL,
-                        MVT::getVectorVT(ViaIntVT, 1), Vec,
-                        DAG.getConstant(0, DL, XLenVT));
-    return DAG.getBitcast(VT, Vec);
+    // Base cost of 1 for vmv.s.x.
+    unsigned Cost = 1;
----------------
reames wrote:
> This is off when we can use a vmv.v.i to perform the insert.  
I think I'm missing something, I can't find anywhere where the insert_vector_elt below would get lowered or combined to a vmv.v.i. There doesn't seem to be any vmv.v.i's introduced in the test diff in https://reviews.llvm.org/D157299 either?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D157976/new/

https://reviews.llvm.org/D157976