[tosa] Add more common utility functions (#525)

- Common code as TF repository, being moved to MLIR core.
- Will support further legalizations to be published.

Signed-off-by: Suraj Sudhir <suraj.sudhir@arm.com>

include/torch-mlir/Conversion/TorchToTosa/TosaLegalizeUtils.h

@@ -37,6 +37,14 @@ Value buildRescaleToInt32(PatternRewriter &rewriter, Operation *op,
 Value getTosaConstTensorSingleF32(PatternRewriter &rewriter, Operation *op,
                                   float val);
 
+// Templated function to create a constant op for given type and shape.
+// T: storage C type.
+// Default template creates a constant tensor in T.
+// To create INT48 TOSA constant, need to pass in llvm::APInt instead.
+template <typename T>
+llvm::Optional<Value> getConstTensor(PatternRewriter &rewriter, Operation *op,
+                                     ArrayRef<T> vec, ArrayRef<int64_t> shape);
+
 // Creates a TOSA operation and performs shape inference on the individual
 // op. This allows shape inference during the framework to TOSA lowering.
 template <typename TosaOp, typename... Args>

lib/Conversion/TorchToTosa/TosaLegalizeUtils.cpp

@@ -63,5 +63,83 @@ Value getTosaConstTensorSingleF32(PatternRewriter &rewriter, Operation *op,
   return const_op.getResult();
 }
 
+// Templated function to create a constant op for given type and shape.
+// T: storage C type.
+// Default template creates a constant tensor in T.
+template <typename T>
+llvm::Optional<Value> getConstTensor(PatternRewriter &rewriter, Operation *op,
+                                     ArrayRef<T> vec, ArrayRef<int64_t> shape) {
+  uint64_t num_total_elements = 1;
+  for (int64_t a : shape) {
+    num_total_elements *= a;
+  }
+
+  if (vec.size() != num_total_elements) {
+    op->emitOpError("getConstTensor(): number of elements mismatch.");
+    return llvm::None;
+  }
+
+  auto const_type =
+      RankedTensorType::get(shape, rewriter.getIntegerType(sizeof(T) * 8));
+  auto const_attr = DenseElementsAttr::get(const_type, vec);
+
+  auto const_op =
+      rewriter.create<tosa::ConstOp>(op->getLoc(), const_type, const_attr);
+  return const_op.getResult();
+}
+
+// Template specialization for APInt
+template <>
+llvm::Optional<Value> getConstTensor<APInt>(PatternRewriter &rewriter,
+                                            Operation *op, ArrayRef<APInt> vec,
+                                            ArrayRef<int64_t> shape) {
+  uint64_t num_total_elements = 1;
+  for (int64_t a : shape) {
+    num_total_elements *= a;
+  }
+
+  if (vec.size() != num_total_elements) {
+    op->emitOpError("getConstTensor(): number of elements mismatch.");
+    return llvm::None;
+  }
+
+  auto const_type = RankedTensorType::get(
+      shape, rewriter.getIntegerType(vec[0].getBitWidth()));
+  auto const_attr = DenseElementsAttr::get(const_type, vec);
+
+  auto const_op =
+      rewriter.create<tosa::ConstOp>(op->getLoc(), const_type, const_attr);
+  return const_op.getResult();
+}
+
+// Template specialization for float
+template <>
+llvm::Optional<Value> getConstTensor<float>(PatternRewriter &rewriter,
+                                            Operation *op, ArrayRef<float> vec,
+                                            ArrayRef<int64_t> shape) {
+  uint64_t num_total_elements = 1;
+  for (int64_t a : shape) {
+    num_total_elements *= a;
+  }
+
+  if (vec.size() != num_total_elements) {
+    op->emitOpError("getConstTensor(): number of elements mismatch.");
+    return llvm::None;
+  }
+
+  auto const_type = RankedTensorType::get(shape, rewriter.getF32Type());
+  auto const_attr = DenseElementsAttr::get(const_type, vec);
+
+  auto const_op =
+      rewriter.create<tosa::ConstOp>(op->getLoc(), const_type, const_attr);
+  return const_op.getResult();
+}
+
+// Template instantiation
+template llvm::Optional<Value> getConstTensor<int32_t>(PatternRewriter &,
+                                                       Operation *,
+                                                       ArrayRef<int32_t> vec,
+                                                       ArrayRef<int64_t> shape);
+
 } // namespace tosa
 } // namespace mlir