[Mlir-commits] [mlir] [mlir][tosa] Require signless types in validation and add corresponding conversion pass (PR #144367)

[Peng Sun]

================
@@ -0,0 +1,138 @@
+//===- TosaConvertIntegerTypeToSignless.cpp
+//-------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===-------------------------------------------------------------------------------===//
+
+// -----------
+// Motivation:
+// -----------
+
+// The TOSA specification uses a signless type system, which means that
+// information about signedness must be encapsulated by the operations
+// themselves. For example, tosa.rescale provides the attrbutes `input_unsigned`
+// and `output_unsigned` to indicate whether the input/output should be
+// interpreted as unsigned or signed.
+
+// The TOSA dialect, on the other hand, allows the use of signed or unsigned
+// types in addition to signless. As such, when converting from TOSA dialect to
+// other formats, we need to ensure that we conform to the TOSA specification.
+
+// ---------
+// Overview:
+// ---------
+
+// This pass converts signed or unsigned integer types to signless. It currently
+// does this greedily for all operators and can also change the signature of the
+// function. Should the signature of the entrypoint function change, it will be
+// the responsibility of the user to carry signedness information of the inputs
+// and outputs independently.
+
+#include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/Dialect/Func/Transforms/FuncConversions.h"
+#include "mlir/Dialect/Tosa/IR/TosaOps.h"
+#include "mlir/Dialect/Tosa/Transforms/Passes.h"
+#include "mlir/Transforms/DialectConversion.h"
+
+namespace mlir {
+namespace tosa {
+
+#define GEN_PASS_DEF_TOSACONVERTINTEGERTYPETOSIGNLESS
+#include "mlir/Dialect/Tosa/Transforms/Passes.h.inc"
+
+namespace {
+class ToSignlessTensorTypeConverter : public TypeConverter {
+  static Type convertType(Type type) {
+    const auto tensorType = dyn_cast<TensorType>(type);
+    if (!tensorType)
+      return type;
+
+    const auto intType = dyn_cast<IntegerType>(tensorType.getElementType());
+    if (!intType ||
+        intType.getSignedness() == IntegerType::SignednessSemantics::Signless)
+      return type;
+
+    const auto signlessType = IntegerType::get(
+        intType.getContext(), intType.getWidth(), IntegerType::Signless);
+    return tensorType.cloneWith(std::nullopt, signlessType);
+  }
+
+public:
+  explicit ToSignlessTensorTypeConverter() { addConversion(convertType); }
+};
+
+class ConvertGenericOpWithIntegerTensorType : public ConversionPattern {
+public:
+  ConvertGenericOpWithIntegerTensorType(TypeConverter &typeConverter,
+                                        MLIRContext *context)
+      : ConversionPattern(typeConverter, MatchAnyOpTypeTag{}, 0, context) {}
+
+  LogicalResult
+  matchAndRewrite(Operation *op, ArrayRef<Value> operands,
+                  ConversionPatternRewriter &rewriter) const final {
+    // Typically TOSA operators have a single result, but some have an
+    // arbitrary number. 4 seems like a good balance.
----------------
psunn wrote:

Nit: Could we add a comment noting that 4 is just an optimization hint for SmallVector — not a functional limit?
I was initially concerned about what happens when the result count exceeds 4, but realized it handles it safely via dynamic allocation.

https://github.com/llvm/llvm-project/pull/144367