[mlir] Support null interface to base conversion

[zero9178]

The current implicit conversion operator from an interface to a "base interface" of the interface unconditionally calls this->getImpl() which leads to accessing a null pointer if the interface instance is a null instance.

This PR changes the ODS generated interface instance to explicitly check and then return a null interface instance if the this instance is a null instance.

[llvmbot]

@llvm/pr-subscribers-mlir-core

Changes

The current implicit conversion operator from an interface to a "base interface" of the interface unconditionally calls this->getImpl() which leads to accessing a null pointer if the interface instance is a null instance.

This PR changes the ODS generated interface instance to explicitly check and then return a null interface instance if the this instance is a null instance.

Full diff: https://github.com/llvm/llvm-project/pull/65988.diff

2 Files Affected:

• (modified) mlir/tools/mlir-tblgen/OpInterfacesGen.cpp (+1)
• (modified) mlir/unittests/IR/InterfaceTest.cpp (+13)

diff --git a/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp b/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp
index 65c1e6392b1316e..9672a02cc08f68c 100644
--- a/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp
+++ b/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp
@@ -571,6 +571,7 @@ void InterfaceGenerator::emitInterfaceDecl(const Interface &interface) {
 
     // Allow implicit conversion to the base interface.
     os << "  operator " << baseQualName << " () const {\n"
+       << "    if (!*this) return nullptr;\n"
        << "    return " << baseQualName << "(*this, getImpl()->impl"
        << base.getName() << ");\n"
        << "  }\n\n";
diff --git a/mlir/unittests/IR/InterfaceTest.cpp b/mlir/unittests/IR/InterfaceTest.cpp
index 621a1c5fa18f3f8..5ab4d9a106231a1 100644
--- a/mlir/unittests/IR/InterfaceTest.cpp
+++ b/mlir/unittests/IR/InterfaceTest.cpp
@@ -70,3 +70,16 @@ TEST(InterfaceTest, TestCustomClassOf) {
   EXPECT_FALSE(isa(*op));
   op.erase();
 }
+
+TEST(InterfaceTest, TestImplicitConversion) {
+  MLIRContext context;
+  context.loadDialect();
+
+  TestBaseTypeInterfacePrintTypeB typeB;
+  TestBaseTypeInterfacePrintTypeA typeA = typeB;
+  EXPECT_EQ(typeA, nullptr);
+
+  typeB = TestType::get(&context);
+  typeA = typeB;
+  EXPECT_EQ(typeA, typeB);
+}

[llvmbot]

@llvm/pr-subscribers-mlir

Changes

The current implicit conversion operator from an interface to a "base interface" of the interface unconditionally calls this->getImpl() which leads to accessing a null pointer if the interface instance is a null instance.

This PR changes the ODS generated interface instance to explicitly check and then return a null interface instance if the this instance is a null instance.

Full diff: https://github.com/llvm/llvm-project/pull/65988.diff

2 Files Affected:

• (modified) mlir/tools/mlir-tblgen/OpInterfacesGen.cpp (+1)
• (modified) mlir/unittests/IR/InterfaceTest.cpp (+13)

diff --git a/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp b/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp
index 65c1e6392b1316e..9672a02cc08f68c 100644
--- a/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp
+++ b/mlir/tools/mlir-tblgen/OpInterfacesGen.cpp
@@ -571,6 +571,7 @@ void InterfaceGenerator::emitInterfaceDecl(const Interface &interface) {
 
     // Allow implicit conversion to the base interface.
     os << "  operator " << baseQualName << " () const {\n"
+       << "    if (!*this) return nullptr;\n"
        << "    return " << baseQualName << "(*this, getImpl()->impl"
        << base.getName() << ");\n"
        << "  }\n\n";
diff --git a/mlir/unittests/IR/InterfaceTest.cpp b/mlir/unittests/IR/InterfaceTest.cpp
index 621a1c5fa18f3f8..5ab4d9a106231a1 100644
--- a/mlir/unittests/IR/InterfaceTest.cpp
+++ b/mlir/unittests/IR/InterfaceTest.cpp
@@ -70,3 +70,16 @@ TEST(InterfaceTest, TestCustomClassOf) {
   EXPECT_FALSE(isa(*op));
   op.erase();
 }
+
+TEST(InterfaceTest, TestImplicitConversion) {
+  MLIRContext context;
+  context.loadDialect();
+
+  TestBaseTypeInterfacePrintTypeB typeB;
+  TestBaseTypeInterfacePrintTypeA typeA = typeB;
+  EXPECT_EQ(typeA, nullptr);
+
+  typeB = TestType::get(&context);
+  typeA = typeB;
+  EXPECT_EQ(typeA, typeB);
+}