[mlir] Allow accessing DialectResourceBlobManager::blobMap (cherry-pick) (#142)

Add a new API to access all blobs that are stored in the blob manager.
The main purpose (as of now) is to allow users of dialect resources to
iterate over all blobs, especially when the blobs are no longer used in
IR (e.g. the operation that uses the blob is deleted) and thus cannot be
easily accessed without manual tracking of keys.

Author: andrey-golubev

mlir/include/mlir/IR/DialectResourceBlobManager.h

@@ -93,9 +93,14 @@ class DialectResourceBlobManager {
     return HandleT(&entry, dialect);
   }
 
+  /// Provide access to all the registered blobs via a callable. During access
+  /// the blob map is guaranteed to remain unchanged.
+  void getBlobMap(llvm::function_ref<void(const llvm::StringMap<BlobEntry> &)>
+                      accessor) const;
+
 private:
   /// A mutex to protect access to the blob map.
-  llvm::sys::SmartRWMutex<true> blobMapLock;
+  mutable llvm::sys::SmartRWMutex<true> blobMapLock;
 
   /// The internal map of tracked blobs. StringMap stores entries in distinct
   /// allocations, so we can freely take references to the data without fear of

mlir/lib/IR/DialectResourceBlobManager.cpp

@@ -63,3 +63,11 @@ auto DialectResourceBlobManager::insert(StringRef name,
     nameStorage.resize(name.size() + 1);
   } while (true);
 }
+
+void DialectResourceBlobManager::getBlobMap(
+    llvm::function_ref<void(const llvm::StringMap<BlobEntry> &)> accessor)
+    const {
+  llvm::sys::SmartScopedReader<true> reader(blobMapLock);
+
+  accessor(blobMap);
+}

mlir/unittests/IR/BlobManagerTest.cpp

@@ -0,0 +1,74 @@
+//===- mlir/unittest/IR/BlobManagerTest.cpp - Blob management unit tests --===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "../../test/lib/Dialect/Test/TestDialect.h"
+#include "mlir/IR/DialectResourceBlobManager.h"
+#include "mlir/Parser/Parser.h"
+
+#include "gtest/gtest.h"
+
+using namespace mlir;
+
+namespace {
+
+StringLiteral moduleStr = R"mlir(
+"test.use1"() {attr = dense_resource<blob1> : tensor<1xi64> } : () -> ()
+
+{-#
+    dialect_resources: {
+    builtin: {
+        blob1: "0x08000000ABCDABCDABCDABCE"
+    }
+    }
+#-}
+)mlir";
+
+TEST(DialectResourceBlobManagerTest, Lookup) {
+  MLIRContext context;
+  context.loadDialect<test::TestDialect>();
+
+  OwningOpRef<ModuleOp> m = parseSourceString<ModuleOp>(moduleStr, &context);
+  ASSERT_TRUE(m);
+
+  const auto &dialectManager =
+      mlir::DenseResourceElementsHandle::getManagerInterface(&context);
+  ASSERT_NE(dialectManager.getBlobManager().lookup("blob1"), nullptr);
+}
+
+TEST(DialectResourceBlobManagerTest, GetBlobMap) {
+  MLIRContext context;
+  context.loadDialect<test::TestDialect>();
+
+  OwningOpRef<ModuleOp> m = parseSourceString<ModuleOp>(moduleStr, &context);
+  ASSERT_TRUE(m);
+
+  Block *block = m->getBody();
+  auto &op = block->getOperations().front();
+  auto resourceAttr = op.getAttrOfType<DenseResourceElementsAttr>("attr");
+  ASSERT_NE(resourceAttr, nullptr);
+
+  const auto &dialectManager =
+      resourceAttr.getRawHandle().getManagerInterface(&context);
+
+  bool blobsArePresent = false;
+  dialectManager.getBlobManager().getBlobMap(
+      [&](const llvm::StringMap<DialectResourceBlobManager::BlobEntry>
+              &blobMap) { blobsArePresent = blobMap.contains("blob1"); });
+  ASSERT_TRUE(blobsArePresent);
+
+  // remove operations that use resources - resources must still be accessible
+  block->clear();
+
+  blobsArePresent = false;
+  dialectManager.getBlobManager().getBlobMap(
+      [&](const llvm::StringMap<DialectResourceBlobManager::BlobEntry>
+              &blobMap) { blobsArePresent = blobMap.contains("blob1"); });
+  ASSERT_TRUE(blobsArePresent);
+}
+
+} // end anonymous namespace

mlir/unittests/IR/CMakeLists.txt

@@ -15,6 +15,7 @@ add_mlir_unittest(MLIRIRTests
   TypeTest.cpp
   TypeAttrNamesTest.cpp
   OpPropertiesTest.cpp
+  BlobManagerTest.cpp
 
   DEPENDS
   MLIRTestInterfaceIncGen