[mlir][vector] Fold vector.extractelement(vector.broadcast)

[ftynse]

Thanks, I was missing this in one of the flows!

mlir/lib/Dialect/Vector/IR/VectorOps.cpp

OpFoldResult vector::ExtractElementOp::fold(ArrayRef<Attribute> operands) {
 
   Attribute src = operands[0];
   Attribute pos = operands[1];
 
   // Fold extractelement (splat X) -> X.
   if (auto splat = getVector().getDefiningOp<vector::SplatOp>())
     return splat.getInput();
 
+  // Fold extractelement(broadcast(X)) -> X.
+  if (auto broadcast = getVector().getDefiningOp<vector::BroadcastOp>())
+    if (!broadcast.getSource().getType().isa<VectorType>())
+      return broadcast.getSource();
+
   if (!pos || !src)
     return {};
 
   auto srcElements = src.cast<DenseElementsAttr>().getValues<Attribute>();
 
   auto attr = pos.dyn_cast<IntegerAttr>();
   uint64_t posIdx = attr.getInt();
 

mlir/test/Dialect/Vector/canonicalize.mlir

func.func @extract_strided_slice_of_constant_mask() -> vector<5x7xi1>{
   //  CHECK-NEXT:   %[[RES:.*]] = vector.constant_mask [5, 4] : vector<5x7xi1>
   //  CHECK-NEXT:   return %[[RES]] : vector<5x7xi1>
   %c4 = arith.constant 4 : index
   %c10 = arith.constant 10 : index
   %mask = vector.create_mask %c10, %c4 : vector<12x7xi1>
   %res = vector.extract_strided_slice %mask {offsets = [3], sizes = [5], strides = [1]} : vector<12x7xi1> to vector<5x7xi1>
   return %res : vector<5x7xi1>
 }
+
+// -----
+
+// CHECK-LABEL: func.func @fold_extractelement_of_broadcast(
+//  CHECK-SAME:     %[[f:.*]]: f32
+//       CHECK:   return %[[f]]
+func.func @fold_extractelement_of_broadcast(%f: f32) -> f32 {
+  %0 = vector.broadcast %f : f32 to vector<15xf32>
+  %c5 = arith.constant 5 : index
+  %1 = vector.extractelement %0 [%c5 : index] : vector<15xf32>
+  return %1 : f32
+}