diff --git a/flang/include/flang/Optimizer/Support/InitFIR.h b/flang/include/flang/Optimizer/Support/InitFIR.h
--- a/flang/include/flang/Optimizer/Support/InitFIR.h
+++ b/flang/include/flang/Optimizer/Support/InitFIR.h
@@ -18,6 +18,7 @@
 #include "mlir/Conversion/Passes.h"
 #include "mlir/Dialect/Affine/Passes.h"
 #include "mlir/Dialect/Complex/IR/Complex.h"
+#include "mlir/Dialect/Func/Extensions/InlinerExtension.h"
 #include "mlir/InitAllDialects.h"
 #include "mlir/Pass/Pass.h"
 #include "mlir/Pass/PassRegistry.h"
@@ -34,20 +35,28 @@
       mlir::vector::VectorDialect, mlir::math::MathDialect,                    \
       mlir::complex::ComplexDialect, mlir::DLTIDialect
 
+#define FLANG_CODEGEN_DIALECT_LIST FIRCodeGenDialect, mlir::LLVM::LLVMDialect
+
 // The definitive list of dialects used by flang.
 #define FLANG_DIALECT_LIST                                                     \
-  FLANG_NONCODEGEN_DIALECT_LIST, FIRCodeGenDialect, mlir::LLVM::LLVMDialect
+  FLANG_NONCODEGEN_DIALECT_LIST, FLANG_CODEGEN_DIALECT_LIST
 
 inline void registerNonCodegenDialects(mlir::DialectRegistry &registry) {
   registry.insert<FLANG_NONCODEGEN_DIALECT_LIST>();
+  mlir::func::registerInlinerExtension(registry);
 }
 
 /// Register all the dialects used by flang.
 inline void registerDialects(mlir::DialectRegistry &registry) {
-  registry.insert<FLANG_DIALECT_LIST>();
+  registerNonCodegenDialects(registry);
+  registry.insert<FLANG_CODEGEN_DIALECT_LIST>();
 }
 
 inline void loadNonCodegenDialects(mlir::MLIRContext &context) {
+  mlir::DialectRegistry registry;
+  registerNonCodegenDialects(registry);
+  context.appendDialectRegistry(registry);
+
   context.loadDialect<FLANG_NONCODEGEN_DIALECT_LIST>();
 }
 
@@ -55,6 +64,10 @@
 /// pass, but a producer of FIR and MLIR. It is therefore a requirement that the
 /// dialects be preloaded to be able to build the IR.
 inline void loadDialects(mlir::MLIRContext &context) {
+  mlir::DialectRegistry registry;
+  registerDialects(registry);
+  context.appendDialectRegistry(registry);
+
   context.loadDialect<FLANG_DIALECT_LIST>();
 }
 
diff --git a/flang/lib/Frontend/CMakeLists.txt b/flang/lib/Frontend/CMakeLists.txt
--- a/flang/lib/Frontend/CMakeLists.txt
+++ b/flang/lib/Frontend/CMakeLists.txt
@@ -1,4 +1,5 @@
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 
 add_flang_library(flangFrontend
   CompilerInstance.cpp
@@ -18,6 +19,7 @@
   HLFIRDialect
   MLIRIR
   ${dialect_libs}
+  ${extension_libs}
 
   LINK_LIBS
   FortranParser
@@ -39,6 +41,7 @@
   MLIRSCFToControlFlow
   MLIRTargetLLVMIRImport
   ${dialect_libs}
+  ${extension_libs}
 
   LINK_COMPONENTS
   Passes
diff --git a/flang/lib/Lower/CMakeLists.txt b/flang/lib/Lower/CMakeLists.txt
--- a/flang/lib/Lower/CMakeLists.txt
+++ b/flang/lib/Lower/CMakeLists.txt
@@ -1,4 +1,5 @@
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 
 add_flang_library(FortranLower
   Allocatable.cpp
@@ -33,6 +34,7 @@
   FIRTransforms
   HLFIRDialect
   ${dialect_libs}
+  ${extension_libs}
 
   LINK_LIBS
   FIRDialect
@@ -42,6 +44,7 @@
   FIRTransforms
   HLFIRDialect
   ${dialect_libs}
+  ${extension_libs}
   FortranCommon
   FortranParser
   FortranEvaluate
diff --git a/flang/lib/Optimizer/Builder/CMakeLists.txt b/flang/lib/Optimizer/Builder/CMakeLists.txt
--- a/flang/lib/Optimizer/Builder/CMakeLists.txt
+++ b/flang/lib/Optimizer/Builder/CMakeLists.txt
@@ -1,4 +1,5 @@
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 
 add_flang_library(FIRBuilder
   BoxValue.cpp
@@ -31,6 +32,7 @@
   FIRDialect
   HLFIRDialect
   ${dialect_libs}
+  ${extension_libs}
 
   LINK_LIBS
   FIRDialect
@@ -38,4 +40,5 @@
   FIRSupport
   HLFIRDialect
   ${dialect_libs}
+  ${extension_libs}
 )
diff --git a/flang/lib/Optimizer/Support/CMakeLists.txt b/flang/lib/Optimizer/Support/CMakeLists.txt
--- a/flang/lib/Optimizer/Support/CMakeLists.txt
+++ b/flang/lib/Optimizer/Support/CMakeLists.txt
@@ -1,4 +1,5 @@
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 
 add_flang_library(FIRSupport
   InitFIR.cpp
@@ -9,9 +10,11 @@
   HLFIROpsIncGen
   MLIRIR
   ${dialect_libs}
+  ${extension_libs}
 
   LINK_LIBS
   ${dialect_libs}
+  ${extension_libs}
   MLIRBuiltinToLLVMIRTranslation
   MLIROpenACCToLLVMIRTranslation
   MLIROpenMPToLLVMIRTranslation
diff --git a/flang/tools/bbc/CMakeLists.txt b/flang/tools/bbc/CMakeLists.txt
--- a/flang/tools/bbc/CMakeLists.txt
+++ b/flang/tools/bbc/CMakeLists.txt
@@ -10,6 +10,7 @@
 
 llvm_update_compile_flags(bbc)
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 target_link_libraries(bbc PRIVATE
 FIRDialect
 FIRDialectSupport
@@ -19,6 +20,7 @@
 HLFIRDialect
 HLFIRTransforms
 ${dialect_libs}
+${extension_libs}
 MLIRAffineToStandard
 MLIRSCFToControlFlow
 FortranCommon
diff --git a/flang/tools/fir-opt/CMakeLists.txt b/flang/tools/fir-opt/CMakeLists.txt
--- a/flang/tools/fir-opt/CMakeLists.txt
+++ b/flang/tools/fir-opt/CMakeLists.txt
@@ -1,6 +1,7 @@
 add_flang_tool(fir-opt fir-opt.cpp)
 llvm_update_compile_flags(fir-opt)
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 
 if(FLANG_INCLUDE_TESTS)
   set(test_libs
@@ -18,6 +19,7 @@
   FIRAnalysis
   ${test_libs}
   ${dialect_libs}
+  ${extension_libs}
 
   # TODO: these should be transitive dependencies from a target providing
   # "registerFIRPasses()"
diff --git a/flang/tools/tco/CMakeLists.txt b/flang/tools/tco/CMakeLists.txt
--- a/flang/tools/tco/CMakeLists.txt
+++ b/flang/tools/tco/CMakeLists.txt
@@ -5,6 +5,7 @@
 add_flang_tool(tco tco.cpp)
 llvm_update_compile_flags(tco)
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 target_link_libraries(tco PRIVATE
   FIRCodeGen
   FIRDialect
@@ -15,13 +16,13 @@
   HLFIRDialect
   HLFIRTransforms
   ${dialect_libs}
+  ${extension_libs}
   MLIRIR
   MLIRLLVMDialect
   MLIRBuiltinToLLVMIRTranslation
   MLIRLLVMToLLVMIRTranslation
   MLIRTargetLLVMIRExport
   MLIRPass
-  MLIRFuncToLLVM
   MLIRTransforms
   MLIRAffineToStandard
   MLIRAnalysis
diff --git a/flang/unittests/Optimizer/CMakeLists.txt b/flang/unittests/Optimizer/CMakeLists.txt
--- a/flang/unittests/Optimizer/CMakeLists.txt
+++ b/flang/unittests/Optimizer/CMakeLists.txt
@@ -1,4 +1,5 @@
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 
 set(LIBS
   FIRBuilder
@@ -8,6 +9,7 @@
   FIRSupport
   HLFIRDialect
   ${dialect_libs}
+  ${extension_libs}
   LLVMTargetParser
 )
 
diff --git a/mlir/cmake/modules/AddMLIR.cmake b/mlir/cmake/modules/AddMLIR.cmake
--- a/mlir/cmake/modules/AddMLIR.cmake
+++ b/mlir/cmake/modules/AddMLIR.cmake
@@ -588,6 +588,12 @@
   add_mlir_library(${ARGV} DEPENDS mlir-headers)
 endfunction(add_mlir_conversion_library)
 
+# Declare the library associated with an extension.
+function(add_mlir_extension_library name)
+  set_property(GLOBAL APPEND PROPERTY MLIR_EXTENSION_LIBS ${name})
+  add_mlir_library(${ARGV} DEPENDS mlir-headers)
+endfunction(add_mlir_extension_library)
+
 # Declare the library associated with a translation.
 function(add_mlir_translation_library name)
   set_property(GLOBAL APPEND PROPERTY MLIR_TRANSLATION_LIBS ${name})
diff --git a/mlir/cmake/modules/CMakeLists.txt b/mlir/cmake/modules/CMakeLists.txt
--- a/mlir/cmake/modules/CMakeLists.txt
+++ b/mlir/cmake/modules/CMakeLists.txt
@@ -24,6 +24,7 @@
 get_property(MLIR_ALL_LIBS GLOBAL PROPERTY MLIR_ALL_LIBS)
 get_property(MLIR_DIALECT_LIBS GLOBAL PROPERTY MLIR_DIALECT_LIBS)
 get_property(MLIR_CONVERSION_LIBS GLOBAL PROPERTY MLIR_CONVERSION_LIBS)
+get_property(MLIR_EXTENSION_LIBS GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 get_property(MLIR_TRANSLATION_LIBS GLOBAL PROPERTY MLIR_TRANSLATION_LIBS)
 
 # Generate MlirConfig.cmake for the build tree.
diff --git a/mlir/cmake/modules/MLIRConfig.cmake.in b/mlir/cmake/modules/MLIRConfig.cmake.in
--- a/mlir/cmake/modules/MLIRConfig.cmake.in
+++ b/mlir/cmake/modules/MLIRConfig.cmake.in
@@ -21,6 +21,7 @@
 set_property(GLOBAL PROPERTY MLIR_ALL_LIBS "@MLIR_ALL_LIBS@")
 set_property(GLOBAL PROPERTY MLIR_DIALECT_LIBS "@MLIR_DIALECT_LIBS@")
 set_property(GLOBAL PROPERTY MLIR_CONVERSION_LIBS "@MLIR_CONVERSION_LIBS@")
+set_property(GLOBAL PROPERTY MLIR_EXTENSION_LIBS "@MLIR_EXTENSION_LIBS@")
 set_property(GLOBAL PROPERTY MLIR_TRANSLATION_LIBS "@MLIR_TRANSLATION_LIBS@")
 
 # Provide all our library targets to users.
diff --git a/mlir/examples/toy/Ch5/CMakeLists.txt b/mlir/examples/toy/Ch5/CMakeLists.txt
--- a/mlir/examples/toy/Ch5/CMakeLists.txt
+++ b/mlir/examples/toy/Ch5/CMakeLists.txt
@@ -28,9 +28,11 @@
 include_directories(${CMAKE_CURRENT_BINARY_DIR})
 include_directories(${CMAKE_CURRENT_BINARY_DIR}/include/)
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 target_link_libraries(toyc-ch5
   PRIVATE
     ${dialect_libs}
+    ${extension_libs}
     MLIRAnalysis
     MLIRCallInterfaces
     MLIRCastInterfaces
diff --git a/mlir/examples/toy/Ch5/toyc.cpp b/mlir/examples/toy/Ch5/toyc.cpp
--- a/mlir/examples/toy/Ch5/toyc.cpp
+++ b/mlir/examples/toy/Ch5/toyc.cpp
@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "mlir/Dialect/Func/Extensions/AllExtensions.h"
 #include "toy/Dialect.h"
 #include "toy/MLIRGen.h"
 #include "toy/Parser.h"
@@ -107,7 +108,10 @@
 }
 
 int dumpMLIR() {
-  mlir::MLIRContext context;
+  mlir::DialectRegistry registry;
+  mlir::func::registerAllExtensions(registry);
+
+  mlir::MLIRContext context(registry);
   // Load our Dialect in this MLIR Context.
   context.getOrLoadDialect<mlir::toy::ToyDialect>();
 
diff --git a/mlir/examples/toy/Ch6/CMakeLists.txt b/mlir/examples/toy/Ch6/CMakeLists.txt
--- a/mlir/examples/toy/Ch6/CMakeLists.txt
+++ b/mlir/examples/toy/Ch6/CMakeLists.txt
@@ -39,10 +39,12 @@
 include_directories(${CMAKE_CURRENT_BINARY_DIR}/include/)
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
 get_property(conversion_libs GLOBAL PROPERTY MLIR_CONVERSION_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 target_link_libraries(toyc-ch6
   PRIVATE
     ${dialect_libs}
     ${conversion_libs}
+    ${extension_libs}
     MLIRAnalysis
     MLIRBuiltinToLLVMIRTranslation
     MLIRCallInterfaces
diff --git a/mlir/examples/toy/Ch6/toyc.cpp b/mlir/examples/toy/Ch6/toyc.cpp
--- a/mlir/examples/toy/Ch6/toyc.cpp
+++ b/mlir/examples/toy/Ch6/toyc.cpp
@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "mlir/Dialect/Func/Extensions/AllExtensions.h"
 #include "toy/Dialect.h"
 #include "toy/MLIRGen.h"
 #include "toy/Parser.h"
@@ -289,8 +290,10 @@
     return dumpAST();
 
   // If we aren't dumping the AST, then we are compiling with/to MLIR.
+  mlir::DialectRegistry registry;
+  mlir::func::registerAllExtensions(registry);
 
-  mlir::MLIRContext context;
+  mlir::MLIRContext context(registry);
   // Load our Dialect in this MLIR Context.
   context.getOrLoadDialect<mlir::toy::ToyDialect>();
 
diff --git a/mlir/examples/toy/Ch7/CMakeLists.txt b/mlir/examples/toy/Ch7/CMakeLists.txt
--- a/mlir/examples/toy/Ch7/CMakeLists.txt
+++ b/mlir/examples/toy/Ch7/CMakeLists.txt
@@ -38,10 +38,12 @@
 include_directories(${CMAKE_CURRENT_BINARY_DIR}/include/)
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
 get_property(conversion_libs GLOBAL PROPERTY MLIR_CONVERSION_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 target_link_libraries(toyc-ch7
   PRIVATE
     ${dialect_libs}
     ${conversion_libs}
+    ${extension_libs}
     MLIRAnalysis
     MLIRBuiltinToLLVMIRTranslation
     MLIRCallInterfaces
diff --git a/mlir/examples/toy/Ch7/toyc.cpp b/mlir/examples/toy/Ch7/toyc.cpp
--- a/mlir/examples/toy/Ch7/toyc.cpp
+++ b/mlir/examples/toy/Ch7/toyc.cpp
@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "mlir/Dialect/Func/Extensions/AllExtensions.h"
 #include "toy/Dialect.h"
 #include "toy/MLIRGen.h"
 #include "toy/Parser.h"
@@ -290,8 +291,10 @@
     return dumpAST();
 
   // If we aren't dumping the AST, then we are compiling with/to MLIR.
+  mlir::DialectRegistry registry;
+  mlir::func::registerAllExtensions(registry);
 
-  mlir::MLIRContext context;
+  mlir::MLIRContext context(registry);
   // Load our Dialect in this MLIR Context.
   context.getOrLoadDialect<mlir::toy::ToyDialect>();
 
diff --git a/mlir/include/mlir/Dialect/Func/Extensions/AllExtensions.h b/mlir/include/mlir/Dialect/Func/Extensions/AllExtensions.h
new file mode 100644
--- /dev/null
+++ b/mlir/include/mlir/Dialect/Func/Extensions/AllExtensions.h
@@ -0,0 +1,30 @@
+//===- AllExtensions.h - All Func Extensions --------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines a common entry point for registering all extensions to the
+// func dialect.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_DIALECT_FUNC_EXTENSIONS_ALLEXTENSIONS_H
+#define MLIR_DIALECT_FUNC_EXTENSIONS_ALLEXTENSIONS_H
+
+namespace mlir {
+class DialectRegistry;
+
+namespace func {
+/// Register all extensions of the func dialect. This should generally only be
+/// used by tools, or other use cases that really do want *all* extensions of
+/// the dialect. All other cases should prefer to instead register the specific
+/// extensions they intend to take advantage of.
+void registerAllExtensions(DialectRegistry &registry);
+} // namespace func
+
+} // namespace mlir
+
+#endif // MLIR_DIALECT_FUNC_EXTENSIONS_ALLEXTENSIONS_H
diff --git a/mlir/include/mlir/Dialect/Func/Extensions/InlinerExtension.h b/mlir/include/mlir/Dialect/Func/Extensions/InlinerExtension.h
new file mode 100644
--- /dev/null
+++ b/mlir/include/mlir/Dialect/Func/Extensions/InlinerExtension.h
@@ -0,0 +1,27 @@
+//===- InlinerExtension.h - Func Inliner Extension 0000----------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines an extension for the func dialect that implements the
+// interfaces necessary to support inlining.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_DIALECT_FUNC_EXTENSIONS_INLINEREXTENSION_H
+#define MLIR_DIALECT_FUNC_EXTENSIONS_INLINEREXTENSION_H
+
+namespace mlir {
+class DialectRegistry;
+
+namespace func {
+/// Register the extension used to support inlining the func dialect.
+void registerInlinerExtension(DialectRegistry &registry);
+} // namespace func
+
+} // namespace mlir
+
+#endif // MLIR_DIALECT_FUNC_EXTENSIONS_INLINEREXTENSION_H
diff --git a/mlir/include/mlir/Dialect/Func/IR/FuncOps.td b/mlir/include/mlir/Dialect/Func/IR/FuncOps.td
--- a/mlir/include/mlir/Dialect/Func/IR/FuncOps.td
+++ b/mlir/include/mlir/Dialect/Func/IR/FuncOps.td
@@ -21,7 +21,6 @@
 def Func_Dialect : Dialect {
   let name = "func";
   let cppNamespace = "::mlir::func";
-  let dependentDialects = ["cf::ControlFlowDialect"];
   let hasConstantMaterializer = 1;
   let usePropertiesForAttributes = 1;
 }
diff --git a/mlir/include/mlir/IR/Attributes.h b/mlir/include/mlir/IR/Attributes.h
--- a/mlir/include/mlir/IR/Attributes.h
+++ b/mlir/include/mlir/IR/Attributes.h
@@ -285,6 +285,14 @@
 private:
   /// Returns the impl interface instance for the given type.
   static typename InterfaceBase::Concept *getInterfaceFor(Attribute attr) {
+#ifndef NDEBUG
+    // Check that the current interface isn't an unresolved promise for the
+    // given attribute.
+    dialect_extension_detail::handleUseOfUndefinedPromisedInterface(
+        attr.getDialect(), ConcreteType::getInterfaceID(),
+        llvm::getTypeName<ConcreteType>());
+#endif
+
     return attr.getAbstractAttribute().getInterface<ConcreteType>();
   }
 
diff --git a/mlir/include/mlir/IR/Dialect.h b/mlir/include/mlir/IR/Dialect.h
--- a/mlir/include/mlir/IR/Dialect.h
+++ b/mlir/include/mlir/IR/Dialect.h
@@ -159,11 +159,20 @@
   /// Lookup an interface for the given ID if one is registered, otherwise
   /// nullptr.
   DialectInterface *getRegisteredInterface(TypeID interfaceID) {
+#ifndef NDEBUG
+    handleUseOfUndefinedPromisedInterface(interfaceID);
+#endif
+
     auto it = registeredInterfaces.find(interfaceID);
     return it != registeredInterfaces.end() ? it->getSecond().get() : nullptr;
   }
   template <typename InterfaceT>
   InterfaceT *getRegisteredInterface() {
+#ifndef NDEBUG
+    handleUseOfUndefinedPromisedInterface(InterfaceT::getInterfaceID(),
+                                          llvm::getTypeName<InterfaceT>());
+#endif
+
     return static_cast<InterfaceT *>(
         getRegisteredInterface(InterfaceT::getInterfaceID()));
   }
@@ -196,6 +205,37 @@
     return *interface;
   }
 
+  /// Declare that the given interface will be implemented, but has a delayed
+  /// registration. The promised interface type can be an interface of any type
+  /// not just a dialect interface, i.e. it may also be an
+  /// AttributeInterface/OpInterface/TypeInterface/etc.
+  template <typename InterfaceT>
+  void declarePromisedInterface() {
+    unresolvedPromisedInterfaces.insert(InterfaceT::getInterfaceID());
+  }
+
+  /// Checks if the given interface, which is attempting to be used, is a
+  /// promised interface of this dialect that has yet to be implemented. If so,
+  /// emits a fatal error. `interfaceName` is an optional string that contains a
+  /// more user readable name for the interface (such as the class name).
+  void handleUseOfUndefinedPromisedInterface(TypeID interfaceID,
+                                             StringRef interfaceName = "") {
+    if (unresolvedPromisedInterfaces.count(interfaceID)) {
+      llvm::report_fatal_error(
+          "checking for an interface (`" + interfaceName +
+          "`) that was promised by dialect '" + getNamespace() +
+          "' but never implemented. This is generally an indication "
+          "that the dialect extension implementing the interface was never "
+          "registered.");
+    }
+  }
+  /// Checks if the given interface, which is attempting to be attached to a
+  /// construct owned by this dialect, is a promised interface of this dialect
+  /// that has yet to be implemented. If so, it resolves the interface promise.
+  void handleAdditionOfUndefinedPromisedInterface(TypeID interfaceID) {
+    unresolvedPromisedInterfaces.erase(interfaceID);
+  }
+
 protected:
   /// The constructor takes a unique namespace for this dialect as well as the
   /// context to bind to.
@@ -289,6 +329,11 @@
   /// A collection of registered dialect interfaces.
   DenseMap<TypeID, std::unique_ptr<DialectInterface>> registeredInterfaces;
 
+  /// A set of interfaces that the dialect (or its constructs, i.e.
+  /// Attributes/Operations/Types/etc.) has promised to implement, but has yet
+  /// to provide an implementation for.
+  DenseSet<TypeID> unresolvedPromisedInterfaces;
+
   friend class DialectRegistry;
   friend void registerDialect();
   friend class MLIRContext;
diff --git a/mlir/include/mlir/IR/DialectRegistry.h b/mlir/include/mlir/IR/DialectRegistry.h
--- a/mlir/include/mlir/IR/DialectRegistry.h
+++ b/mlir/include/mlir/IR/DialectRegistry.h
@@ -97,6 +97,22 @@
   }
 };
 
+namespace dialect_extension_detail {
+
+/// Checks if the given interface, which is attempting to be used, is a
+/// promised interface of this dialect that has yet to be implemented. If so,
+/// emits a fatal error.
+void handleUseOfUndefinedPromisedInterface(Dialect &dialect, TypeID interfaceID,
+                                           StringRef interfaceName);
+
+/// Checks if the given interface, which is attempting to be attached, is a
+/// promised interface of this dialect that has yet to be implemented. If so,
+/// the promised interface is marked as resolved.
+void handleAdditionOfUndefinedPromisedInterface(Dialect &dialect,
+                                                TypeID interfaceID);
+
+} // namespace dialect_extension_detail
+
 //===----------------------------------------------------------------------===//
 // DialectRegistry
 //===----------------------------------------------------------------------===//
diff --git a/mlir/include/mlir/IR/OpDefinition.h b/mlir/include/mlir/IR/OpDefinition.h
--- a/mlir/include/mlir/IR/OpDefinition.h
+++ b/mlir/include/mlir/IR/OpDefinition.h
@@ -2083,6 +2083,16 @@
   static typename InterfaceBase::Concept *getInterfaceFor(Operation *op) {
     OperationName name = op->getName();
 
+#ifndef NDEBUG
+    // Check that the current interface isn't an unresolved promise for the
+    // given operation.
+    if (Dialect *dialect = name.getDialect()) {
+      dialect_extension_detail::handleUseOfUndefinedPromisedInterface(
+          *dialect, ConcreteType::getInterfaceID(),
+          llvm::getTypeName<ConcreteType>());
+    }
+#endif
+
     // Access the raw interface from the operation info.
     if (std::optional<RegisteredOperationName> rInfo =
             name.getRegisteredInfo()) {
diff --git a/mlir/include/mlir/IR/OperationSupport.h b/mlir/include/mlir/IR/OperationSupport.h
--- a/mlir/include/mlir/IR/OperationSupport.h
+++ b/mlir/include/mlir/IR/OperationSupport.h
@@ -18,6 +18,7 @@
 #include "mlir/IR/BlockSupport.h"
 #include "mlir/IR/BuiltinAttributes.h"
 #include "mlir/IR/Diagnostics.h"
+#include "mlir/IR/DialectRegistry.h"
 #include "mlir/IR/Location.h"
 #include "mlir/IR/TypeRange.h"
 #include "mlir/IR/Types.h"
@@ -348,6 +349,11 @@
   /// interfaces for the concrete operation.
   template <typename... Models>
   void attachInterface() {
+    // Handle the case where the models resolve a promised interface.
+    (dialect_extension_detail::handleAdditionOfUndefinedPromisedInterface(
+         *getDialect(), Models::Interface::getInterfaceID()),
+     ...);
+
     getImpl()->getInterfaceMap().insertModels<Models...>();
   }
 
diff --git a/mlir/include/mlir/IR/StorageUniquerSupport.h b/mlir/include/mlir/IR/StorageUniquerSupport.h
--- a/mlir/include/mlir/IR/StorageUniquerSupport.h
+++ b/mlir/include/mlir/IR/StorageUniquerSupport.h
@@ -14,6 +14,7 @@
 #define MLIR_IR_STORAGEUNIQUERSUPPORT_H
 
 #include "mlir/IR/AttrTypeSubElements.h"
+#include "mlir/IR/DialectRegistry.h"
 #include "mlir/Support/InterfaceSupport.h"
 #include "mlir/Support/LogicalResult.h"
 #include "mlir/Support/StorageUniquer.h"
@@ -160,6 +161,11 @@
       llvm::report_fatal_error("Registering an interface for an attribute/type "
                                "that is not itself registered.");
 
+    // Handle the case where the models resolve a promised interface.
+    (dialect_extension_detail::handleAdditionOfUndefinedPromisedInterface(
+         abstract->getDialect(), IfaceModels::Interface::getInterfaceID()),
+     ...);
+
     (checkInterfaceTarget<IfaceModels>(), ...);
     abstract->interfaceMap.template insertModels<IfaceModels...>();
   }
diff --git a/mlir/include/mlir/IR/Types.h b/mlir/include/mlir/IR/Types.h
--- a/mlir/include/mlir/IR/Types.h
+++ b/mlir/include/mlir/IR/Types.h
@@ -269,6 +269,14 @@
 private:
   /// Returns the impl interface instance for the given type.
   static typename InterfaceBase::Concept *getInterfaceFor(Type type) {
+#ifndef NDEBUG
+    // Check that the current interface isn't an unresolved promise for the
+    // given type.
+    dialect_extension_detail::handleUseOfUndefinedPromisedInterface(
+        type.getDialect(), ConcreteType::getInterfaceID(),
+        llvm::getTypeName<ConcreteType>());
+#endif
+
     return type.getAbstractType().getInterface<ConcreteType>();
   }
 
diff --git a/mlir/include/mlir/InitAllExtensions.h b/mlir/include/mlir/InitAllExtensions.h
new file mode 100644
--- /dev/null
+++ b/mlir/include/mlir/InitAllExtensions.h
@@ -0,0 +1,34 @@
+//===- InitAllExtensions.h - MLIR Extension Registration --------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines a helper to trigger the registration of all dialect
+// extensions to the system.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_INITALLEXTENSIONS_H_
+#define MLIR_INITALLEXTENSIONS_H_
+
+#include "mlir/Dialect/Func/Extensions/AllExtensions.h"
+
+#include <cstdlib>
+
+namespace mlir {
+
+/// This function may be called to register all MLIR dialect extensions with the
+/// provided registry.
+/// If you're building a compiler, you generally shouldn't use this: you would
+/// individually register the specific extensions that are useful for the
+/// pipelines and transformations you are using.
+inline void registerAllExtensions(DialectRegistry &registry) {
+  func::registerAllExtensions(registry);
+}
+
+} // namespace mlir
+
+#endif // MLIR_INITALLEXTENSIONS_H_
diff --git a/mlir/lib/Dialect/Func/CMakeLists.txt b/mlir/lib/Dialect/Func/CMakeLists.txt
--- a/mlir/lib/Dialect/Func/CMakeLists.txt
+++ b/mlir/lib/Dialect/Func/CMakeLists.txt
@@ -1,2 +1,3 @@
+add_subdirectory(Extensions)
 add_subdirectory(IR)
 add_subdirectory(Transforms)
diff --git a/mlir/lib/Dialect/Func/Extensions/AllExtensions.cpp b/mlir/lib/Dialect/Func/Extensions/AllExtensions.cpp
new file mode 100644
--- /dev/null
+++ b/mlir/lib/Dialect/Func/Extensions/AllExtensions.cpp
@@ -0,0 +1,16 @@
+//===- AllExtensions.cpp - All Func Dialect Extensions --------------------===//
+//
+// 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 "mlir/Dialect/Func/Extensions/AllExtensions.h"
+#include "mlir/Dialect/Func/Extensions/InlinerExtension.h"
+
+using namespace mlir;
+
+void mlir::func::registerAllExtensions(DialectRegistry &registry) {
+  registerInlinerExtension(registry);
+}
diff --git a/mlir/lib/Dialect/Func/Extensions/CMakeLists.txt b/mlir/lib/Dialect/Func/Extensions/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/mlir/lib/Dialect/Func/Extensions/CMakeLists.txt
@@ -0,0 +1,27 @@
+set(LLVM_OPTIONAL_SOURCES
+  AllExtensions.cpp
+  InlinerExtension.cpp
+  )
+
+add_mlir_extension_library(MLIRFuncInlinerExtension
+  InlinerExtension.cpp
+
+  ADDITIONAL_HEADER_DIRS
+  ${MLIR_MAIN_INCLUDE_DIR}/mlir/Dialect/Func/Extensions
+
+  LINK_LIBS PUBLIC
+  MLIRControlFlowDialect
+  MLIRInferTypeOpInterface
+  MLIRIR
+  MLIRFuncDialect
+  )
+
+add_mlir_extension_library(MLIRFuncAllExtensions
+  AllExtensions.cpp
+
+  ADDITIONAL_HEADER_DIRS
+  ${MLIR_MAIN_INCLUDE_DIR}/mlir/Dialect/Func/Extensions
+
+  LINK_LIBS PUBLIC
+  MLIRFuncInlinerExtension
+  )
diff --git a/mlir/lib/Dialect/Func/Extensions/InlinerExtension.cpp b/mlir/lib/Dialect/Func/Extensions/InlinerExtension.cpp
new file mode 100644
--- /dev/null
+++ b/mlir/lib/Dialect/Func/Extensions/InlinerExtension.cpp
@@ -0,0 +1,90 @@
+//===- InlinerExtension.cpp - Func Inliner Extension ----------------------===//
+//
+// 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 "mlir/Dialect/Func/Extensions/InlinerExtension.h"
+#include "mlir/Dialect/ControlFlow/IR/ControlFlowOps.h"
+#include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/IR/DialectInterface.h"
+#include "mlir/Transforms/InliningUtils.h"
+
+using namespace mlir;
+using namespace mlir::func;
+
+//===----------------------------------------------------------------------===//
+// FuncDialect Interfaces
+//===----------------------------------------------------------------------===//
+namespace {
+/// This class defines the interface for handling inlining with func operations.
+struct FuncInlinerInterface : public DialectInlinerInterface {
+  using DialectInlinerInterface::DialectInlinerInterface;
+
+  //===--------------------------------------------------------------------===//
+  // Analysis Hooks
+  //===--------------------------------------------------------------------===//
+
+  /// All call operations can be inlined.
+  bool isLegalToInline(Operation *call, Operation *callable,
+                       bool wouldBeCloned) const final {
+    return true;
+  }
+
+  /// All operations can be inlined.
+  bool isLegalToInline(Operation *, Region *, bool, IRMapping &) const final {
+    return true;
+  }
+
+  /// All functions can be inlined.
+  bool isLegalToInline(Region *, Region *, bool, IRMapping &) const final {
+    return true;
+  }
+
+  //===--------------------------------------------------------------------===//
+  // Transformation Hooks
+  //===--------------------------------------------------------------------===//
+
+  /// Handle the given inlined terminator by replacing it with a new operation
+  /// as necessary.
+  void handleTerminator(Operation *op, Block *newDest) const final {
+    // Only return needs to be handled here.
+    auto returnOp = dyn_cast<ReturnOp>(op);
+    if (!returnOp)
+      return;
+
+    // Replace the return with a branch to the dest.
+    OpBuilder builder(op);
+    builder.create<cf::BranchOp>(op->getLoc(), newDest, returnOp.getOperands());
+    op->erase();
+  }
+
+  /// Handle the given inlined terminator by replacing it with a new operation
+  /// as necessary.
+  void handleTerminator(Operation *op,
+                        ArrayRef<Value> valuesToRepl) const final {
+    // Only return needs to be handled here.
+    auto returnOp = cast<ReturnOp>(op);
+
+    // Replace the values directly with the return operands.
+    assert(returnOp.getNumOperands() == valuesToRepl.size());
+    for (const auto &it : llvm::enumerate(returnOp.getOperands()))
+      valuesToRepl[it.index()].replaceAllUsesWith(it.value());
+  }
+};
+} // namespace
+
+//===----------------------------------------------------------------------===//
+// Registration
+//===----------------------------------------------------------------------===//
+
+void mlir::func::registerInlinerExtension(DialectRegistry &registry) {
+  registry.addExtension(+[](MLIRContext *ctx, func::FuncDialect *dialect) {
+    dialect->addInterfaces<FuncInlinerInterface>();
+
+    // The inliner extension relies on the ControlFlow dialect.
+    ctx->getOrLoadDialect<cf::ControlFlowDialect>();
+  });
+}
diff --git a/mlir/lib/Dialect/Func/IR/CMakeLists.txt b/mlir/lib/Dialect/Func/IR/CMakeLists.txt
--- a/mlir/lib/Dialect/Func/IR/CMakeLists.txt
+++ b/mlir/lib/Dialect/Func/IR/CMakeLists.txt
@@ -9,7 +9,6 @@
 
   LINK_LIBS PUBLIC
   MLIRCallInterfaces
-  MLIRControlFlowDialect
   MLIRControlFlowInterfaces
   MLIRInferTypeOpInterface
   MLIRIR
diff --git a/mlir/lib/Dialect/Func/IR/FuncOps.cpp b/mlir/lib/Dialect/Func/IR/FuncOps.cpp
--- a/mlir/lib/Dialect/Func/IR/FuncOps.cpp
+++ b/mlir/lib/Dialect/Func/IR/FuncOps.cpp
@@ -8,8 +8,6 @@
 
 #include "mlir/Dialect/Func/IR/FuncOps.h"
 
-#include "mlir/Dialect/ControlFlow/IR/ControlFlowOps.h"
-#include "mlir/IR/Builders.h"
 #include "mlir/IR/BuiltinOps.h"
 #include "mlir/IR/BuiltinTypes.h"
 #include "mlir/IR/FunctionImplementation.h"
@@ -33,67 +31,6 @@
 using namespace mlir;
 using namespace mlir::func;
 
-//===----------------------------------------------------------------------===//
-// FuncDialect Interfaces
-//===----------------------------------------------------------------------===//
-namespace {
-/// This class defines the interface for handling inlining with func operations.
-struct FuncInlinerInterface : public DialectInlinerInterface {
-  using DialectInlinerInterface::DialectInlinerInterface;
-
-  //===--------------------------------------------------------------------===//
-  // Analysis Hooks
-  //===--------------------------------------------------------------------===//
-
-  /// All call operations can be inlined.
-  bool isLegalToInline(Operation *call, Operation *callable,
-                       bool wouldBeCloned) const final {
-    return true;
-  }
-
-  /// All operations can be inlined.
-  bool isLegalToInline(Operation *, Region *, bool, IRMapping &) const final {
-    return true;
-  }
-
-  /// All functions can be inlined.
-  bool isLegalToInline(Region *, Region *, bool, IRMapping &) const final {
-    return true;
-  }
-
-  //===--------------------------------------------------------------------===//
-  // Transformation Hooks
-  //===--------------------------------------------------------------------===//
-
-  /// Handle the given inlined terminator by replacing it with a new operation
-  /// as necessary.
-  void handleTerminator(Operation *op, Block *newDest) const final {
-    // Only return needs to be handled here.
-    auto returnOp = dyn_cast<ReturnOp>(op);
-    if (!returnOp)
-      return;
-
-    // Replace the return with a branch to the dest.
-    OpBuilder builder(op);
-    builder.create<cf::BranchOp>(op->getLoc(), newDest, returnOp.getOperands());
-    op->erase();
-  }
-
-  /// Handle the given inlined terminator by replacing it with a new operation
-  /// as necessary.
-  void handleTerminator(Operation *op,
-                        ArrayRef<Value> valuesToRepl) const final {
-    // Only return needs to be handled here.
-    auto returnOp = cast<ReturnOp>(op);
-
-    // Replace the values directly with the return operands.
-    assert(returnOp.getNumOperands() == valuesToRepl.size());
-    for (const auto &it : llvm::enumerate(returnOp.getOperands()))
-      valuesToRepl[it.index()].replaceAllUsesWith(it.value());
-  }
-};
-} // namespace
-
 //===----------------------------------------------------------------------===//
 // FuncDialect
 //===----------------------------------------------------------------------===//
@@ -103,7 +40,7 @@
 #define GET_OP_LIST
 #include "mlir/Dialect/Func/IR/FuncOps.cpp.inc"
       >();
-  addInterfaces<FuncInlinerInterface>();
+  declarePromisedInterface<DialectInlinerInterface>();
 }
 
 /// Materialize a single constant operation from a given attribute value with
diff --git a/mlir/lib/IR/Dialect.cpp b/mlir/lib/IR/Dialect.cpp
--- a/mlir/lib/IR/Dialect.cpp
+++ b/mlir/lib/IR/Dialect.cpp
@@ -96,6 +96,9 @@
 
 /// Register a set of dialect interfaces with this dialect instance.
 void Dialect::addInterface(std::unique_ptr<DialectInterface> interface) {
+  // Handle the case where the models resolve a promised interface.
+  handleAdditionOfUndefinedPromisedInterface(interface->getID());
+
   auto it = registeredInterfaces.try_emplace(interface->getID(),
                                              std::move(interface));
   (void)it;
@@ -143,6 +146,16 @@
 
 DialectExtensionBase::~DialectExtensionBase() = default;
 
+void dialect_extension_detail::handleUseOfUndefinedPromisedInterface(
+    Dialect &dialect, TypeID interfaceID, StringRef interfaceName) {
+  dialect.handleUseOfUndefinedPromisedInterface(interfaceID, interfaceName);
+}
+
+void dialect_extension_detail::handleAdditionOfUndefinedPromisedInterface(
+    Dialect &dialect, TypeID interfaceID) {
+  dialect.handleAdditionOfUndefinedPromisedInterface(interfaceID);
+}
+
 //===----------------------------------------------------------------------===//
 // DialectRegistry
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/CAPI/ir.c b/mlir/test/CAPI/ir.c
--- a/mlir/test/CAPI/ir.c
+++ b/mlir/test/CAPI/ir.c
@@ -1725,10 +1725,10 @@
   fprintf(stderr, "@registration\n");
   // CHECK-LABEL: @registration
 
-  // CHECK: cf.cond_br is_registered: 1
-  fprintf(stderr, "cf.cond_br is_registered: %d\n",
+  // CHECK: func.call is_registered: 1
+  fprintf(stderr, "func.call is_registered: %d\n",
           mlirContextIsRegisteredOperation(
-              ctx, mlirStringRefCreateFromCString("cf.cond_br")));
+              ctx, mlirStringRefCreateFromCString("func.call")));
 
   // CHECK: func.not_existing_op is_registered: 0
   fprintf(stderr, "func.not_existing_op is_registered: %d\n",
@@ -1942,6 +1942,7 @@
   registerAllUpstreamDialects(ctx);
 
   mlirContextGetOrLoadDialect(ctx, mlirStringRefCreateFromCString("func"));
+  mlirContextGetOrLoadDialect(ctx, mlirStringRefCreateFromCString("arith"));
   MlirLocation loc = mlirLocationUnknownGet(ctx);
   MlirType indexType = mlirIndexTypeGet(ctx);
   MlirStringRef valueStringRef = mlirStringRefCreateFromCString("value");
diff --git a/mlir/tools/mlir-opt/CMakeLists.txt b/mlir/tools/mlir-opt/CMakeLists.txt
--- a/mlir/tools/mlir-opt/CMakeLists.txt
+++ b/mlir/tools/mlir-opt/CMakeLists.txt
@@ -4,6 +4,7 @@
 
 get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
 get_property(conversion_libs GLOBAL PROPERTY MLIR_CONVERSION_LIBS)
+get_property(extension_libs GLOBAL PROPERTY MLIR_EXTENSION_LIBS)
 set(LLVM_LINK_COMPONENTS
   Core
   Support
@@ -50,7 +51,9 @@
 set(LIBS
   ${dialect_libs}
   ${conversion_libs}
+  ${extension_libs}
   ${test_libs}
+
   MLIRAffineAnalysis
   MLIRAnalysis
   MLIRCastInterfaces
diff --git a/mlir/tools/mlir-opt/mlir-opt.cpp b/mlir/tools/mlir-opt/mlir-opt.cpp
--- a/mlir/tools/mlir-opt/mlir-opt.cpp
+++ b/mlir/tools/mlir-opt/mlir-opt.cpp
@@ -14,6 +14,7 @@
 #include "mlir/IR/Dialect.h"
 #include "mlir/IR/MLIRContext.h"
 #include "mlir/InitAllDialects.h"
+#include "mlir/InitAllExtensions.h"
 #include "mlir/InitAllPasses.h"
 #include "mlir/Pass/Pass.h"
 #include "mlir/Pass/PassManager.h"
@@ -259,6 +260,8 @@
 #endif
   DialectRegistry registry;
   registerAllDialects(registry);
+  registerAllExtensions(registry);
+
 #ifdef MLIR_INCLUDE_TESTS
   ::test::registerTestDialect(registry);
   ::test::registerTestTransformDialectExtension(registry);
diff --git a/mlir/unittests/Interfaces/CMakeLists.txt b/mlir/unittests/Interfaces/CMakeLists.txt
--- a/mlir/unittests/Interfaces/CMakeLists.txt
+++ b/mlir/unittests/Interfaces/CMakeLists.txt
@@ -7,6 +7,7 @@
 
 target_link_libraries(MLIRInterfacesTests
   PRIVATE
+  MLIRArithDialect
   MLIRControlFlowInterfaces
   MLIRDataLayoutInterfaces
   MLIRDLTIDialect