[mlir][vector] Support multi-dimensional vectors in VectorFromElementsLowering

mlir/include/mlir/Conversion/LLVMCommon/VectorPattern.h

@@ -49,6 +49,13 @@ SmallVector<int64_t, 4> getCoordinates(ArrayRef<int64_t> basis,
 void nDVectorIterate(const NDVectorTypeInfo &info, OpBuilder &builder,
                      function_ref<void(ArrayRef<int64_t>)> fun);
 
+// Overload that accepts VectorType directly and extracts type info internally.
+// Returns failure if the vector type info extraction fails.
+LogicalResult nDVectorIterate(VectorType vectorType,
+                              const LLVMTypeConverter &converter,
+                              OpBuilder &builder,
+                              function_ref<void(ArrayRef<int64_t>)> fun);
+
 LogicalResult handleMultidimensionalVectors(
     Operation *op, ValueRange operands, const LLVMTypeConverter &typeConverter,
     std::function<Value(Type, ValueRange)> createOperand,

mlir/lib/Conversion/LLVMCommon/VectorPattern.cpp

@@ -77,6 +77,16 @@ void LLVM::detail::nDVectorIterate(const LLVM::detail::NDVectorTypeInfo &info,
   }
 }
 
+LogicalResult LLVM::detail::nDVectorIterate(
+    VectorType vectorType, const LLVMTypeConverter &converter,
+    OpBuilder &builder, function_ref<void(ArrayRef<int64_t>)> fun) {
+  auto vectorTypeInfo = extractNDVectorTypeInfo(vectorType, converter);
+  if (!vectorTypeInfo.llvmNDVectorTy)
+    return failure();
+  nDVectorIterate(vectorTypeInfo, builder, fun);
+  return success();
+}
+
 LogicalResult LLVM::detail::handleMultidimensionalVectors(
     Operation *op, ValueRange operands, const LLVMTypeConverter &typeConverter,
     std::function<Value(Type, ValueRange)> createOperand,

mlir/lib/Conversion/VectorToLLVM/ConvertVectorToLLVM.cpp

@@ -1890,15 +1890,68 @@ struct VectorFromElementsLowering
                   ConversionPatternRewriter &rewriter) const override {
     Location loc = fromElementsOp.getLoc();
     VectorType vectorType = fromElementsOp.getType();
-    // TODO: Multi-dimensional vectors lower to !llvm.array<... x vector<>>.
-    // Such ops should be handled in the same way as vector.insert.
-    if (vectorType.getRank() > 1)
-      return rewriter.notifyMatchFailure(fromElementsOp,
-                                         "rank > 1 vectors are not supported");
     Type llvmType = typeConverter->convertType(vectorType);
-    Value result = LLVM::PoisonOp::create(rewriter, loc, llvmType);
-    for (auto [idx, val] : llvm::enumerate(adaptor.getElements()))
-      result = vector::InsertOp::create(rewriter, loc, val, result, idx);
+    Type llvmIndexType = typeConverter->convertType(rewriter.getIndexType());
+
+    Value result;
+    // 0D vectors are converted to length-1 1D vectors by LLVMTypeConverter.
+    if (vectorType.getRank() == 0) {
+      result = LLVM::PoisonOp::create(rewriter, loc, llvmType);
+      auto index0 = LLVM::ConstantOp::create(rewriter, loc, llvmIndexType, 0);
+      result = LLVM::InsertElementOp::create(
+          rewriter, loc, result, adaptor.getElements().front(), index0);
+      rewriter.replaceOp(fromElementsOp, result);
+      return success();
+    }
+
+    // Build 1D vectors for the innermost dimension.
+    int64_t innerDimSize = vectorType.getShape().back();
+    assert(vectorType.getNumElements() % innerDimSize == 0 &&
+           "innerDimSize must divide vectorType.getNumElements()");
+    int64_t numInnerVectors = vectorType.getNumElements() / innerDimSize;
+
+    SmallVector<Value> innerVectors;
+    innerVectors.reserve(numInnerVectors);
+
+    auto innerVectorType =
+        VectorType::get(innerDimSize, vectorType.getElementType());
+    Type llvmInnerType = typeConverter->convertType(innerVectorType);
+
+    Value innerVector;
+    for (auto [elemIdx, val] : llvm::enumerate(adaptor.getElements())) {
+      int64_t elementInVectorIdx = elemIdx % innerDimSize;
+      if (elementInVectorIdx == 0)
+        innerVector = LLVM::PoisonOp::create(rewriter, loc, llvmInnerType);
+      auto position = LLVM::ConstantOp::create(rewriter, loc, llvmIndexType,
+                                               elementInVectorIdx);
+      innerVector = LLVM::InsertElementOp::create(rewriter, loc, llvmInnerType,
+                                                  innerVector, val, position);
+      if (elementInVectorIdx == innerDimSize - 1)
+        innerVectors.push_back(innerVector);
+    }
+
+    // For 1D vectors, we can just return the first innermost vector.
+    if (vectorType.getRank() == 1) {
+      assert(innerVectors.size() == 1 &&
+             "for 1D vectors, innerVectors should have exactly one element");
+      rewriter.replaceOp(fromElementsOp, innerVectors.front());
+      return success();
+    }
+
+    // Now build the nested aggregate structure from these 1D vectors.
+    result = LLVM::PoisonOp::create(rewriter, loc, llvmType);
+
+    // Iterate over each position of the first n-1 dimensions and insert the 1D
+    // vectors into the aggregate.
+    int64_t vectorIdx = 0;
+    if (failed(LLVM::detail::nDVectorIterate(
+            vectorType, *getTypeConverter(), rewriter,
+            [&](ArrayRef<int64_t> position) {
+              result = LLVM::InsertValueOp::create(
+                  rewriter, loc, result, innerVectors[vectorIdx++], position);
+            })))
+      return failure();
+
     rewriter.replaceOp(fromElementsOp, result);
     return success();
   }

mlir/test/Conversion/VectorToLLVM/vector-to-llvm-interface.mlir

@@ -2286,6 +2286,30 @@ func.func @from_elements_0d(%arg0: f32) -> vector<f32> {
 
 // -----
 
+// CHECK-LABEL: func.func @from_elements_3d(
+//  CHECK-SAME:     %[[ARG_0:.*]]: f32, %[[ARG_1:.*]]: f32, %[[ARG_2:.*]]: f32, %[[ARG_3:.*]]: f32)
+//       CHECK:   %[[UNDEF_VEC0:.*]] = llvm.mlir.poison : vector<2xf32>
+//       CHECK:   %[[C0_0:.*]] = llvm.mlir.constant(0 : i64) : i64
+//       CHECK:   %[[VEC0_0:.*]] = llvm.insertelement %[[ARG_0]], %[[UNDEF_VEC0]][%[[C0_0]] : i64] : vector<2xf32>
+//       CHECK:   %[[C1_0:.*]] = llvm.mlir.constant(1 : i64) : i64
+//       CHECK:   %[[VEC0_1:.*]] = llvm.insertelement %[[ARG_1]], %[[VEC0_0]][%[[C1_0]] : i64] : vector<2xf32>
+//       CHECK:   %[[UNDEF_VEC1:.*]] = llvm.mlir.poison : vector<2xf32>
+//       CHECK:   %[[C0_1:.*]] = llvm.mlir.constant(0 : i64) : i64
+//       CHECK:   %[[VEC1_0:.*]] = llvm.insertelement %[[ARG_2]], %[[UNDEF_VEC1]][%[[C0_1]] : i64] : vector<2xf32>
+//       CHECK:   %[[C1_1:.*]] = llvm.mlir.constant(1 : i64) : i64
+//       CHECK:   %[[VEC1_1:.*]] = llvm.insertelement %[[ARG_3]], %[[VEC1_0]][%[[C1_1]] : i64] : vector<2xf32>
+//       CHECK:   %[[UNDEF_RES:.*]] = llvm.mlir.poison : !llvm.array<2 x array<1 x vector<2xf32>>>
+//       CHECK:   %[[RES_0:.*]] = llvm.insertvalue %[[VEC0_1]], %[[UNDEF_RES]][0, 0] : !llvm.array<2 x array<1 x vector<2xf32>>>
+//       CHECK:   %[[RES_1:.*]] = llvm.insertvalue %[[VEC1_1]], %[[RES_0]][1, 0] : !llvm.array<2 x array<1 x vector<2xf32>>>
+//       CHECK:   %[[CAST:.*]] = builtin.unrealized_conversion_cast %[[RES_1]] : !llvm.array<2 x array<1 x vector<2xf32>>> to vector<2x1x2xf32>
+//       CHECK:   return %[[CAST]]
+func.func @from_elements_3d(%arg0: f32, %arg1: f32, %arg2: f32, %arg3: f32) -> vector<2x1x2xf32> {
+  %0 = vector.from_elements %arg0, %arg1, %arg2, %arg3 : vector<2x1x2xf32>
+  return %0 : vector<2x1x2xf32>
+}
+
+// -----
+
 //===----------------------------------------------------------------------===//
 // vector.to_elements
 //===----------------------------------------------------------------------===//