Create a minimal C API (#196)

* Enable cloning llvm submodule over HTTP

* Introduce C API

* Undo unrelated changes

* clang-format

* More format

* Add Header Comments

* Format

* Add basic test

* Add missing incantation

* Format

Co-authored-by: George <>

CMakeLists.txt

@@ -98,6 +98,17 @@ install(DIRECTORY include/circt
   PATTERN "LICENSE.TXT"
   )
 
+install(DIRECTORY include/circt-c
+  DESTINATION include
+  COMPONENT circt-headers
+  FILES_MATCHING
+  PATTERN "*.def"
+  PATTERN "*.h"
+  PATTERN "*.inc"
+  PATTERN "*.td"
+  PATTERN "LICENSE.TXT"
+  )
+
 install(DIRECTORY ${CIRCT_INCLUDE_DIR}/circt
   DESTINATION include
   COMPONENT circt-headers

include/circt-c/RTLDialect.h

@@ -0,0 +1,35 @@
+/*===-- circt-c/RTLDialect.h - C API for RTL dialect --------------*- C -*-===*\
+|*                                                                            *|
+|* This header declares the C interface for registering and accessing the     *|
+|* RTL dialect. A dialect should be registered with a context to make it      *|
+|* available to users of the context. These users must load the dialect       *|
+|* before using any of its attributes, operations or types. Parser and pass   *|
+|* manager can load registered dialects automatically.                        *|
+|*                                                                            *|
+\*===----------------------------------------------------------------------===*/
+
+#ifndef CIRCT_C_RTLDIALECT_H
+#define CIRCT_C_RTLDIALECT_H
+
+#include "mlir-c/IR.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** Registers the RTL dialect with the given context. This allows the
+ * dialect to be loaded dynamically if needed when parsing. */
+void mlirContextRegisterRTLDialect(MlirContext context);
+
+/** Loads the RTL dialect into the given context. The dialect does _not_
+ * have to be registered in advance. */
+MlirDialect mlirContextLoadRTLDialect(MlirContext context);
+
+/** Returns the namespace of the RTL dialect, suitable for loading it. */
+MlirStringRef mlirRTLDialectGetNamespace();
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // CIRCT_C_RTLDIALECT_H

lib/CAPI/CMakeLists.txt

@@ -0,0 +1 @@
+add_subdirectory(RTL)

lib/CAPI/RTL/CMakeLists.txt

@@ -0,0 +1,11 @@
+add_mlir_library(MLIRCAPIRTL
+
+  RTLDialect.cpp
+
+  ADDITIONAL_HEADER_DIRS
+  ${MLIR_MAIN_INCLUDE_DIR}/mlir-c
+
+  LINK_LIBS PUBLIC
+  MLIRCAPIIR
+  MLIRRTL
+  )

lib/CAPI/RTL/RTLDialect.cpp

@@ -0,0 +1,23 @@
+//===- RTLDialect.cpp - C Interface for the RTL Dialect -------------------===//
+//
+//  Implements a C Interface for the RTL Dialect
+//
+//===----------------------------------------------------------------------===//
+
+#include "circt-c/RTLDialect.h"
+#include "circt/Dialect/RTL/Ops.h"
+#include "mlir-c/IR.h"
+#include "mlir/CAPI/IR.h"
+#include "mlir/CAPI/Support.h"
+
+void mlirContextRegisterRTLDialect(MlirContext context) {
+  unwrap(context)->getDialectRegistry().insert<circt::rtl::RTLDialect>();
+}
+
+MlirDialect mlirContextLoadRTLDialect(MlirContext context) {
+  return wrap(unwrap(context)->getOrLoadDialect<circt::rtl::RTLDialect>());
+}
+
+MlirStringRef mlirRTLDialectGetNamespace() {
+  return wrap(circt::rtl::RTLDialect::getDialectNamespace());
+}

lib/CMakeLists.txt

@@ -1,3 +1,4 @@
+add_subdirectory(CAPI)
 add_subdirectory(Conversion)
 add_subdirectory(Dialect)
 add_subdirectory(FIRParser)

test/CAPI/CMakeLists.txt

@@ -0,0 +1,17 @@
+set(LLVM_LINK_COMPONENTS
+  Core
+  Support
+  )
+
+add_llvm_executable(circt-capi-ir-test
+  ir.c
+  )
+llvm_update_compile_flags(circt-capi-ir-test)
+
+get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+target_link_libraries(circt-capi-ir-test
+  PRIVATE
+  MLIRCAPIIR
+  MLIRCAPIRegistration
+  MLIRCAPIRTL
+  ${dialect_libs})

test/CAPI/ir.c

@@ -0,0 +1,72 @@
+/*===- ir.c - Simple test of C APIs ---------------------------------------===*\
+|*                                                                            *|
+|* 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: circt-capi-ir-test 2>&1 | FileCheck %s
+ */
+
+#include "mlir-c/IR.h"
+#include "circt-c/RTLDialect.h"
+#include "mlir-c/AffineExpr.h"
+#include "mlir-c/AffineMap.h"
+#include "mlir-c/Diagnostics.h"
+#include "mlir-c/Registration.h"
+
+#include <assert.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int registerOnlyRTL() {
+  MlirContext ctx = mlirContextCreate();
+  // The built-in dialect is always loaded.
+  if (mlirContextGetNumLoadedDialects(ctx) != 1)
+    return 1;
+
+  MlirDialect std =
+      mlirContextGetOrLoadDialect(ctx, mlirRTLDialectGetNamespace());
+  if (!mlirDialectIsNull(std))
+    return 2;
+
+  mlirContextRegisterRTLDialect(ctx);
+  if (mlirContextGetNumRegisteredDialects(ctx) != 1)
+    return 3;
+  if (mlirContextGetNumLoadedDialects(ctx) != 1)
+    return 4;
+
+  std = mlirContextGetOrLoadDialect(ctx, mlirRTLDialectGetNamespace());
+  if (mlirDialectIsNull(std))
+    return 5;
+  if (mlirContextGetNumLoadedDialects(ctx) != 2)
+    return 6;
+
+  MlirDialect alsoStd = mlirContextLoadRTLDialect(ctx);
+  if (!mlirDialectEqual(std, alsoStd))
+    return 7;
+
+  MlirStringRef stdNs = mlirDialectGetNamespace(std);
+  MlirStringRef alsoStdNs = mlirRTLDialectGetNamespace();
+  if (stdNs.length != alsoStdNs.length ||
+      strncmp(stdNs.data, alsoStdNs.data, stdNs.length))
+    return 8;
+
+  return 0;
+}
+
+int main() {
+  fprintf(stderr, "@registration\n");
+  int errcode = registerOnlyRTL();
+  fprintf(stderr, "%d\n", errcode);
+  // clang-format off
+  // CHECK-LABEL: @registration
+  // CHECK: 0
+  // clang-format on
+
+  return 0;
+}

test/CAPI/lit.local.cfg

@@ -0,0 +1 @@
+config.suffixes.add('.c')

test/CMakeLists.txt

@@ -1,3 +1,5 @@
+add_subdirectory(CAPI)
+
 configure_lit_site_cfg(
   ${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.py.in
   ${CMAKE_CURRENT_BINARY_DIR}/lit.site.cfg.py
@@ -7,6 +9,7 @@ configure_lit_site_cfg(
 
 set(CIRCT_TEST_DEPENDS
   FileCheck count not
+  circt-capi-ir-test
   circt-opt
   circt-translate
   handshake-runner

test/lit.cfg.py

@@ -59,6 +59,7 @@ tools = [
     'handshake-runner',
     'circt-opt',
     'circt-translate',
+    'circt-capi-ir-test',
     'llhd-sim'
 ]