[MLIR] Add IRDL dialect loading to C API (#91852)

Being able to add custom dialects is one of the big missing pieces of
the C API. This change should make it achievable via IRDL. Hopefully
this should open custom dialect definition to non-C++ users of MLIR.

mlir/include/mlir-c/Dialect/IRDL.h

@@ -0,0 +1,29 @@
+//===-- mlir-c/Dialect/IRDL.h - C API for IRDL --------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef MLIR_C_DIALECT_IRDL_H
+#define MLIR_C_DIALECT_IRDL_H
+
+#include "mlir-c/IR.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+MLIR_DECLARE_CAPI_DIALECT_REGISTRATION(IRDL, irdl);
+
+/// Loads all IRDL dialects in the provided module, registering the dialects in
+/// the module's associated context.
+MLIR_CAPI_EXPORTED MlirLogicalResult mlirLoadIRDLDialects(MlirModule module);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // MLIR_C_DIALECT_IRDL_H

mlir/lib/CAPI/Dialect/CMakeLists.txt

@@ -72,6 +72,15 @@ add_mlir_upstream_c_api_library(MLIRCAPIGPU
   MLIRPass
 )
 
+add_mlir_upstream_c_api_library(MLIRCAPIIRDL
+  IRDL.cpp
+
+  PARTIAL_SOURCES_INTENDED
+  LINK_LIBS PUBLIC
+  MLIRCAPIIR
+  MLIRIRDL
+)
+
 add_mlir_upstream_c_api_library(MLIRCAPILLVM
   LLVM.cpp
 

mlir/lib/CAPI/Dialect/IRDL.cpp

@@ -0,0 +1,18 @@
+//===- IRDL.cpp - C Interface for IRDL dialect ----------------------------===//
+//
+// 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-c/Dialect/IRDL.h"
+#include "mlir/CAPI/Registration.h"
+#include "mlir/Dialect/IRDL/IR/IRDL.h"
+#include "mlir/Dialect/IRDL/IRDLLoading.h"
+
+MLIR_DEFINE_CAPI_DIALECT_REGISTRATION(IRDL, irdl, mlir::irdl::IRDLDialect)
+
+MlirLogicalResult mlirLoadIRDLDialects(MlirModule module) {
+  return wrap(mlir::irdl::loadDialects(unwrap(module)));
+}

mlir/test/CAPI/CMakeLists.txt

@@ -38,6 +38,13 @@ _add_capi_test_executable(mlir-capi-ir-test
     MLIRCAPIRegisterEverything
 )
 
+_add_capi_test_executable(mlir-capi-irdl-test
+  irdl.c
+  LINK_LIBS PRIVATE
+    MLIRCAPIIR
+    MLIRCAPIIRDL
+)
+
 _add_capi_test_executable(mlir-capi-llvm-test
   llvm.c
   LINK_LIBS PRIVATE

mlir/test/CAPI/irdl.c

@@ -0,0 +1,58 @@
+//===- irdl.c - Test for the C bindings for IRDL registration -------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+/* RUN: mlir-capi-irdl-test 2>&1 | FileCheck %s
+ */
+
+#include "mlir-c/Dialect/IRDL.h"
+#include "mlir-c/IR.h"
+
+const char irdlDialect[] = "\
+  irdl.dialect @foo {\
+    irdl.operation @op {\
+      %i32 = irdl.is i32\
+      irdl.results(%i32)\
+    }\
+  }\
+  irdl.dialect @bar {\
+    irdl.operation @op {\
+      %i32 = irdl.is i32\
+      irdl.operands(%i32)\
+    }\
+  }";
+
+// CHECK:      module {
+// CHECK-NEXT:   %[[RES:.*]] = "foo.op"() : () -> i32
+// CHECK-NEXT:   "bar.op"(%[[RES]]) :  (i32) -> ()
+// CHECK-NEXT: }
+const char newDialectUsage[] = "\
+  module {\
+    %res = \"foo.op\"() : () -> i32\
+    \"bar.op\"(%res) : (i32) -> ()\
+  }";
+
+int main(void) {
+  MlirContext ctx = mlirContextCreate();
+  mlirDialectHandleLoadDialect(mlirGetDialectHandle__irdl__(), ctx);
+
+  MlirModule dialectDecl =
+      mlirModuleCreateParse(ctx, mlirStringRefCreateFromCString(irdlDialect));
+
+  mlirLoadIRDLDialects(dialectDecl);
+  mlirModuleDestroy(dialectDecl);
+
+  MlirModule usingModule = mlirModuleCreateParse(
+      ctx, mlirStringRefCreateFromCString(newDialectUsage));
+
+  mlirOperationDump(mlirModuleGetOperation(usingModule));
+
+  mlirModuleDestroy(usingModule);
+  mlirContextDestroy(ctx);
+  return 0;
+}

mlir/test/CMakeLists.txt

@@ -101,6 +101,7 @@ configure_lit_site_cfg(
 set(MLIR_TEST_DEPENDS
   FileCheck count not split-file
   mlir-capi-ir-test
+  mlir-capi-irdl-test
   mlir-capi-llvm-test
   mlir-capi-pass-test
   mlir-capi-quant-test

mlir/test/lit.cfg.py

@@ -100,6 +100,7 @@ tools = [
     "mlir-lsp-server",
     "mlir-capi-execution-engine-test",
     "mlir-capi-ir-test",
+    "mlir-capi-irdl-test",
     "mlir-capi-llvm-test",
     "mlir-capi-pass-test",
     "mlir-capi-pdl-test",