[mlir][vector] Add foldInsertUseChain folder function to insert op (#147045)

When the result of an insert op is used by an insert op, and the
subsequent insert op is inserted at the same location as the previous
insert op, replaces the dest of the subsequent insert op with the dest
of the previous insert op.This is because the previous insert op does
not affect subsequent insert ops.

---------

Co-authored-by: Mehdi Amini <joker.eph@gmail.com>
Co-authored-by: Andrzej Warzyński <andrzej.warzynski@gmail.com>

Author: 3 people

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

@@ -3334,7 +3334,6 @@ class InsertSplatToSplat final : public OpRewritePattern<InsertOp> {
     return success();
   }
 };
-
 } // namespace
 
 static Attribute
@@ -3387,12 +3386,26 @@ foldDenseElementsAttrDestInsertOp(InsertOp insertOp, Attribute srcAttr,
   return newAttr;
 }
 
+/// Folder to replace the `dest` operand of the insert op with the root dest of
+/// the insert op use chain.
+static Value foldInsertUseChain(InsertOp insertOp) {
+  auto destInsert = insertOp.getDest().getDefiningOp<InsertOp>();
+  if (!destInsert)
+    return {};
+
+  if (insertOp.getMixedPosition() != destInsert.getMixedPosition())
+    return {};
+
+  insertOp.setOperand(1, destInsert.getDest());
+  return insertOp.getResult();
+}
+
 void InsertOp::getCanonicalizationPatterns(RewritePatternSet &results,
                                            MLIRContext *context) {
   results.add<InsertToBroadcast, BroadcastFolder, InsertSplatToSplat>(context);
 }
 
-OpFoldResult vector::InsertOp::fold(FoldAdaptor adaptor) {
+OpFoldResult InsertOp::fold(FoldAdaptor adaptor) {
   // Do not create constants with more than `vectorSizeFoldThreashold` elements,
   // unless the source vector constant has a single use.
   constexpr int64_t vectorSizeFoldThreshold = 256;
@@ -3407,6 +3420,8 @@ OpFoldResult vector::InsertOp::fold(FoldAdaptor adaptor) {
   SmallVector<Value> operands = {getValueToStore(), getDest()};
   auto inplaceFolded = extractInsertFoldConstantOp(*this, adaptor, operands);
 
+  if (auto res = foldInsertUseChain(*this))
+    return res;
   if (auto res = foldPoisonIndexInsertExtractOp(
           getContext(), adaptor.getStaticPosition(), kPoisonIndex))
     return res;

mlir/test/Dialect/Vector/canonicalize.mlir

@@ -3470,3 +3470,32 @@ func.func @fold_insert_constant_indices(%arg : vector<4x1xi32>) -> vector<4x1xi3
   %res = vector.insert %1, %arg[%0, %0] : i32 into vector<4x1xi32>
   return %res : vector<4x1xi32>
 }
+
+// -----
+
+// CHECK-LABEL: @fold_insert_use_chain(
+//  CHECK-SAME:   %[[ARG:.*]]: vector<4x4xf32>,
+//  CHECK-SAME:   %[[VAL:.*]]: f32,
+//  CHECK-SAME:   %[[POS:.*]]: index) -> vector<4x4xf32> {
+//  CHECK-NEXT:   %[[RES:.*]] = vector.insert %[[VAL]], %[[ARG]] {{\[}}%[[POS]], 0] : f32 into vector<4x4xf32>
+//  CHECK-NEXT:   return %[[RES]] : vector<4x4xf32>
+func.func @fold_insert_use_chain(%arg : vector<4x4xf32>, %val : f32, %pos: index) -> vector<4x4xf32> {
+  %v_0 = vector.insert %val, %arg[%pos, 0] : f32 into vector<4x4xf32>
+  %v_1 = vector.insert %val, %v_0[%pos, 0] : f32 into vector<4x4xf32>
+  %v_2 = vector.insert %val, %v_1[%pos, 0] : f32 into vector<4x4xf32>
+  return %v_2 : vector<4x4xf32>  
+}
+
+// -----
+
+// CHECK-LABEL: @no_fold_insert_use_chain_mismatch_static_position(
+//  CHECK-SAME:   %[[ARG:.*]]: vector<4xf32>,
+//  CHECK-SAME:   %[[VAL:.*]]: f32) -> vector<4xf32> {
+//       CHECK:   %[[V_0:.*]] = vector.insert %[[VAL]], %[[ARG]] [0] : f32 into vector<4xf32>
+//       CHECK:   %[[V_1:.*]] = vector.insert %[[VAL]], %[[V_0]] [1] : f32 into vector<4xf32>
+//       CHECK:   return %[[V_1]] : vector<4xf32>
+func.func @no_fold_insert_use_chain_mismatch_static_position(%arg : vector<4xf32>, %val : f32) -> vector<4xf32> {
+  %v_0 = vector.insert %val, %arg[0] : f32 into vector<4xf32>
+  %v_1 = vector.insert %val, %v_0[1] : f32 into vector<4xf32>
+  return %v_1 : vector<4xf32>  
+}