[PATCH] D24683: [DAGCombine] Generalize build_vector -> vector_shuffle combine for more than 2 inputs

[Elena Demikhovsky via llvm-commits]

delena added inline comments.

================
Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:12883
@@ -12879,14 +12882,3 @@
 
-// If Vec holds a reference to a non-null node, return Vec.
-// Otherwise, return either a zero or an undef node of the appropriate type.
-static SDValue getRightHandValue(SelectionDAG &DAG, SDLoc DL, SDValue Vec,
-                                 EVT VT, bool Zero) {
-  if (Vec.getNode())
-    return Vec;
-
-  if (Zero)
-    return VT.isInteger() ? DAG.getConstant(0, DL, VT)
-                          : DAG.getConstantFP(0.0, DL, VT);
-
-  return DAG.getUNDEF(VT);
-}
+SDValue DAGCombiner::createBuildVecShuffle(
+    SDLoc DL, SDNode *N, const SmallVectorImpl<int> &VectorMask, SDValue VecIn1,
----------------
Please add a comment here.

================
Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:13030
@@ +13029,3 @@
+    // All inputs must have the same element type as the output.
+    if (VT.getVectorElementType() !=
+        ExtractedFromVec.getValueType().getVectorElementType())
----------------
I suppose you can put "assert" here.

================
Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:13079
@@ +13078,3 @@
+    else
+      return SDValue();
+  }
----------------
In what case it fails to create a shuffle?

================
Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:13084
@@ +13083,3 @@
+  // to the list of shuffles.
+  if (UsesZeroVector)
+    Shuffles.push_back(VT.isInteger() ? DAG.getConstant(0, dl, VT)
----------------
If you fail in shuffle creation, to you want to try zero-vector?


https://reviews.llvm.org/D24683