[mlir][EmitC] Add func, call and return operations and conversions (#79612)

This adds a `func`, `call` and `return` operation to the EmitC dialect,
closely related to the corresponding operations of the Func dialect. In
contrast to the operations of the Func dialect, the EmitC operations do
not support multiple results. The `emitc.func` op features a
`specifiers` argument that for example allows, with corresponding
support in the emitter, to emit `inline static` functions.

Furthermore, this adds patterns and a pass to convert the Func dialect
to EmitC. A `func.func` op that is `private` is converted to
`emitc.func` with a `"static"` specifier.

18 files changed, 815 insertions, 31 deletions

diff --git a/mlir/include/mlir/Conversion/FuncToEmitC/FuncToEmitC.h b/mlir/include/mlir/Conversion/FuncToEmitC/FuncToEmitC.h
new file mode 100644
index 000000000000..5c7f87e47030
--- /dev/null
+++ b/mlir/include/mlir/Conversion/FuncToEmitC/FuncToEmitC.h
@@ -0,0 +1,18 @@
+//===- FuncToEmitC.h - Func to EmitC Patterns -------------------*- 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_CONVERSION_FUNCTOEMITC_FUNCTOEMITC_H
+#define MLIR_CONVERSION_FUNCTOEMITC_FUNCTOEMITC_H
+
+namespace mlir {
+class RewritePatternSet;
+
+void populateFuncToEmitCPatterns(RewritePatternSet &patterns);
+} // namespace mlir
+
+#endif // MLIR_CONVERSION_FUNCTOEMITC_FUNCTOEMITC_H
diff --git a/mlir/include/mlir/Conversion/FuncToEmitC/FuncToEmitCPass.h b/mlir/include/mlir/Conversion/FuncToEmitC/FuncToEmitCPass.h
new file mode 100644
index 000000000000..65936703ee13
--- /dev/null
+++ b/mlir/include/mlir/Conversion/FuncToEmitC/FuncToEmitCPass.h
@@ -0,0 +1,21 @@
+//===- FuncToEmitCPass.h - Func to EmitC Pass -------------------*- 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_CONVERSION_FUNCTOEMITC_FUNCTOEMITCPASS_H
+#define MLIR_CONVERSION_FUNCTOEMITC_FUNCTOEMITCPASS_H
+
+#include <memory>
+
+namespace mlir {
+class Pass;
+
+#define GEN_PASS_DECL_CONVERTFUNCTOEMITC
+#include "mlir/Conversion/Passes.h.inc"
+} // namespace mlir
+
+#endif // MLIR_CONVERSION_FUNCTOEMITC_FUNCTOEMITCPASS_H
diff --git a/mlir/include/mlir/Conversion/Passes.h b/mlir/include/mlir/Conversion/Passes.h
index 0bfc5064c5dd..81f69210fade 100644
--- a/mlir/include/mlir/Conversion/Passes.h
+++ b/mlir/include/mlir/Conversion/Passes.h
@@ -29,6 +29,7 @@
 #include "mlir/Conversion/ControlFlowToSPIRV/ControlFlowToSPIRV.h"
 #include "mlir/Conversion/ControlFlowToSPIRV/ControlFlowToSPIRVPass.h"
 #include "mlir/Conversion/ConvertToLLVM/ToLLVMPass.h"
+#include "mlir/Conversion/FuncToEmitC/FuncToEmitCPass.h"
 #include "mlir/Conversion/FuncToLLVM/ConvertFuncToLLVMPass.h"
 #include "mlir/Conversion/FuncToSPIRV/FuncToSPIRVPass.h"
 #include "mlir/Conversion/GPUCommon/GPUCommonPass.h"
diff --git a/mlir/include/mlir/Conversion/Passes.td b/mlir/include/mlir/Conversion/Passes.td
index ec0a6284fe97..94fc7a7d2194 100644
--- a/mlir/include/mlir/Conversion/Passes.td
+++ b/mlir/include/mlir/Conversion/Passes.td
@@ -360,6 +360,15 @@ def ConvertControlFlowToSPIRV : Pass<"convert-cf-to-spirv"> {
 }
 
 //===----------------------------------------------------------------------===//
+// FuncToEmitC
+//===----------------------------------------------------------------------===//
+
+def ConvertFuncToEmitC : Pass<"convert-func-to-emitc", "ModuleOp"> {
+  let summary = "Convert Func dialect to EmitC dialect";
+  let dependentDialects = ["emitc::EmitCDialect"];
+}
+
+//===----------------------------------------------------------------------===//
 // FuncToLLVM
 //===----------------------------------------------------------------------===//
 
diff --git a/mlir/include/mlir/Dialect/EmitC/IR/EmitC.h b/mlir/include/mlir/Dialect/EmitC/IR/EmitC.h
index 4dff26e23c42..3d38744527d5 100644
--- a/mlir/include/mlir/Dialect/EmitC/IR/EmitC.h
+++ b/mlir/include/mlir/Dialect/EmitC/IR/EmitC.h
@@ -20,6 +20,7 @@
 #include "mlir/IR/Dialect.h"
 #include "mlir/Interfaces/CastInterfaces.h"
 #include "mlir/Interfaces/ControlFlowInterfaces.h"
+#include "mlir/Interfaces/FunctionInterfaces.h"
 #include "mlir/Interfaces/SideEffectInterfaces.h"
 
 #include "mlir/Dialect/EmitC/IR/EmitCDialect.h.inc"
diff --git a/mlir/include/mlir/Dialect/EmitC/IR/EmitC.td b/mlir/include/mlir/Dialect/EmitC/IR/EmitC.td
index ada64f10a167..5c8c3c9ce7bb 100644
--- a/mlir/include/mlir/Dialect/EmitC/IR/EmitC.td
+++ b/mlir/include/mlir/Dialect/EmitC/IR/EmitC.td
@@ -16,8 +16,10 @@
 include "mlir/Dialect/EmitC/IR/EmitCAttributes.td"
 include "mlir/Dialect/EmitC/IR/EmitCTypes.td"
 
+include "mlir/Interfaces/CallInterfaces.td"
 include "mlir/Interfaces/CastInterfaces.td"
 include "mlir/Interfaces/ControlFlowInterfaces.td"
+include "mlir/Interfaces/FunctionInterfaces.td"
 include "mlir/Interfaces/SideEffectInterfaces.td"
 include "mlir/IR/RegionKindInterface.td"
 
@@ -386,6 +388,174 @@ def EmitC_ForOp : EmitC_Op<"for",
   let hasRegionVerifier = 1;
 }
 
+def EmitC_CallOp : EmitC_Op<"call",
+    [CallOpInterface,
+     DeclareOpInterfaceMethods<SymbolUserOpInterface>]> {
+  let summary = "call operation";
+  let description = [{
+    The `emitc.call` operation represents a direct call to an `emitc.func`
+    that is within the same symbol scope as the call. The operands and result type
+    of the call must match the specified function type. The callee is encoded as a
+    symbol reference attribute named "callee".
+
+    Example:
+
+    ```mlir
+    %2 = emitc.call @my_add(%0, %1) : (f32, f32) -> f32
+    ```
+  }];
+  let arguments = (ins FlatSymbolRefAttr:$callee, Variadic<AnyType>:$operands);
+  let results = (outs Variadic<AnyType>);
+
+  let builders = [
+    OpBuilder<(ins "FuncOp":$callee, CArg<"ValueRange", "{}">:$operands), [{
+      $_state.addOperands(operands);
+      $_state.addAttribute("callee", SymbolRefAttr::get(callee));
+      $_state.addTypes(callee.getFunctionType().getResults());
+    }]>,
+    OpBuilder<(ins "SymbolRefAttr":$callee, "TypeRange":$results,
+      CArg<"ValueRange", "{}">:$operands), [{
+      $_state.addOperands(operands);
+      $_state.addAttribute("callee", callee);
+      $_state.addTypes(results);
+    }]>,
+    OpBuilder<(ins "StringAttr":$callee, "TypeRange":$results,
+      CArg<"ValueRange", "{}">:$operands), [{
+      build($_builder, $_state, SymbolRefAttr::get(callee), results, operands);
+    }]>,
+    OpBuilder<(ins "StringRef":$callee, "TypeRange":$results,
+      CArg<"ValueRange", "{}">:$operands), [{
+      build($_builder, $_state, StringAttr::get($_builder.getContext(), callee),
+            results, operands);
+    }]>];
+
+  let extraClassDeclaration = [{
+    FunctionType getCalleeType();
+
+    /// Get the argument operands to the called function.
+    operand_range getArgOperands() {
+      return {arg_operand_begin(), arg_operand_end()};
+    }
+
+    MutableOperandRange getArgOperandsMutable() {
+      return getOperandsMutable();
+    }
+
+    operand_iterator arg_operand_begin() { return operand_begin(); }
+    operand_iterator arg_operand_end() { return operand_end(); }
+
+    /// Return the callee of this operation.
+    CallInterfaceCallable getCallableForCallee() {
+      return (*this)->getAttrOfType<SymbolRefAttr>("callee");
+    }
+
+    /// Set the callee for this operation.
+    void setCalleeFromCallable(CallInterfaceCallable callee) {
+      (*this)->setAttr("callee", callee.get<SymbolRefAttr>());
+    }
+  }];
+
+  let assemblyFormat = [{
+    $callee `(` $operands `)` attr-dict `:` functional-type($operands, results)
+  }];
+}
+
+def EmitC_FuncOp : EmitC_Op<"func", [
+  AutomaticAllocationScope,
+  FunctionOpInterface, IsolatedFromAbove
+]> {
+  let summary = "An operation with a name containing a single `SSACFG` region";
+  let description = [{
+    Operations within the function cannot implicitly capture values defined
+    outside of the function, i.e. Functions are `IsolatedFromAbove`. All
+    external references must use function arguments or attributes that establish
+    a symbolic connection (e.g. symbols referenced by name via a string
+    attribute like SymbolRefAttr). While the MLIR textual form provides a nice
+    inline syntax for function arguments, they are internally represented as
+    “block arguments” to the first block in the region.
+
+    Only dialect attribute names may be specified in the attribute dictionaries
+    for function arguments, results, or the function itself.
+
+    Example:
+
+    ```mlir
+    // A function with no results:
+    emitc.func @foo(%arg0 : i32) {
+      emitc.call_opaque "bar" (%arg0) : (i32) -> ()
+      emitc.return
+    }
+
+    // A function with its argument as single result:
+    emitc.func @foo(%arg0 : i32) -> i32 {
+      emitc.return %arg0 : i32
+    }
+
+    // A function with specifiers attribute:
+    emitc.func @example_specifiers_fn_attr() -> i32
+                attributes {specifiers = ["static","inline"]} {
+      %0 = emitc.call_opaque "foo" (): () -> i32
+      emitc.return %0 : i32
+    }
+
+    ```
+  }];
+  let arguments = (ins SymbolNameAttr:$sym_name,
+                       TypeAttrOf<FunctionType>:$function_type,
+                       OptionalAttr<StrArrayAttr>:$specifiers,
+                       OptionalAttr<DictArrayAttr>:$arg_attrs,
+                       OptionalAttr<DictArrayAttr>:$res_attrs);
+  let regions = (region AnyRegion:$body);
+
+  let builders = [OpBuilder<(ins
+    "StringRef":$name, "FunctionType":$type,
+    CArg<"ArrayRef<NamedAttribute>", "{}">:$attrs,
+    CArg<"ArrayRef<DictionaryAttr>", "{}">:$argAttrs)
+  >];
+  let extraClassDeclaration = [{
+    //===------------------------------------------------------------------===//
+    // FunctionOpInterface Methods
+    //===------------------------------------------------------------------===//
+
+    /// Returns the region on the current operation that is callable. This may
+    /// return null in the case of an external callable object, e.g. an external
+    /// function.
+    ::mlir::Region *getCallableRegion() { return isExternal() ? nullptr : &getBody(); }
+
+    /// Returns the argument types of this function.
+    ArrayRef<Type> getArgumentTypes() { return getFunctionType().getInputs(); }
+
+    /// Returns the result types of this function.
+    ArrayRef<Type> getResultTypes() { return getFunctionType().getResults(); }
+  }];
+  let hasCustomAssemblyFormat = 1;
+  let hasVerifier = 1;
+}
+
+def EmitC_ReturnOp : EmitC_Op<"return", [Pure, HasParent<"FuncOp">,
+                                ReturnLike, Terminator]> {
+  let summary = "Function return operation";
+  let description = [{
+    The `emitc.return` operation represents a return operation within a function.
+    The operation takes zero or exactly one operand and produces no results.
+    The operand number and type must match the signature of the function
+    that contains the operation.
+
+    Example:
+
+    ```mlir
+    emitc.func @foo() : (i32) {
+      ...
+      emitc.return %0 : i32
+    }
+    ```
+  }];
+  let arguments = (ins Optional<AnyType>:$operand);
+
+  let assemblyFormat = "attr-dict ($operand^ `:` type($operand))?";
+  let hasVerifier = 1;
+}
+
 def EmitC_IncludeOp
     : EmitC_Op<"include", [HasParent<"ModuleOp">]> {
   let summary = "Include operation";
diff --git a/mlir/lib/Conversion/CMakeLists.txt b/mlir/lib/Conversion/CMakeLists.txt
index 3a5dbc12c23f..9e421f7c49db 100644
--- a/mlir/lib/Conversion/CMakeLists.txt
+++ b/mlir/lib/Conversion/CMakeLists.txt
@@ -18,6 +18,7 @@ add_subdirectory(ControlFlowToLLVM)
 add_subdirectory(ControlFlowToSCF)
 add_subdirectory(ControlFlowToSPIRV)
 add_subdirectory(ConvertToLLVM)
+add_subdirectory(FuncToEmitC)
 add_subdirectory(FuncToLLVM)
 add_subdirectory(FuncToSPIRV)
 add_subdirectory(GPUCommon)
diff --git a/mlir/lib/Conversion/FuncToEmitC/CMakeLists.txt b/mlir/lib/Conversion/FuncToEmitC/CMakeLists.txt
new file mode 100644
index 000000000000..97752205bbcb
--- /dev/null
+++ b/mlir/lib/Conversion/FuncToEmitC/CMakeLists.txt
@@ -0,0 +1,16 @@
+add_mlir_conversion_library(MLIRFuncToEmitC
+  FuncToEmitC.cpp
+  FuncToEmitCPass.cpp
+
+  ADDITIONAL_HEADER_DIRS
+  ${MLIR_MAIN_INCLUDE_DIR}/mlir/Conversion/FuncToEmitC
+
+  DEPENDS
+  MLIRConversionPassIncGen
+
+  LINK_LIBS PUBLIC
+  MLIREmitCDialect
+  MLIRFuncDialect
+  MLIRPass
+  MLIRTransformUtils
+  )
diff --git a/mlir/lib/Conversion/FuncToEmitC/FuncToEmitC.cpp b/mlir/lib/Conversion/FuncToEmitC/FuncToEmitC.cpp
new file mode 100644
index 000000000000..ac3d8297953f
--- /dev/null
+++ b/mlir/lib/Conversion/FuncToEmitC/FuncToEmitC.cpp
@@ -0,0 +1,116 @@
+//===- FuncToEmitC.cpp - Func to EmitC Patterns -----------------*- 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 implements patterns to convert the Func dialect to the EmitC
+// dialect.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Conversion/FuncToEmitC/FuncToEmitC.h"
+
+#include "mlir/Dialect/EmitC/IR/EmitC.h"
+#include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/Transforms/DialectConversion.h"
+
+using namespace mlir;
+
+//===----------------------------------------------------------------------===//
+// Conversion Patterns
+//===----------------------------------------------------------------------===//
+
+namespace {
+class CallOpConversion final : public OpConversionPattern<func::CallOp> {
+public:
+  using OpConversionPattern<func::CallOp>::OpConversionPattern;
+
+  LogicalResult
+  matchAndRewrite(func::CallOp callOp, OpAdaptor adaptor,
+                  ConversionPatternRewriter &rewriter) const override {
+    // Multiple results func was not converted to `emitc.func`.
+    if (callOp.getNumResults() > 1)
+      return rewriter.notifyMatchFailure(
+          callOp, "only functions with zero or one result can be converted");
+
+    rewriter.replaceOpWithNewOp<emitc::CallOp>(
+        callOp,
+        callOp.getNumResults() ? callOp.getResult(0).getType() : nullptr,
+        adaptor.getOperands(), callOp->getAttrs());
+
+    return success();
+  }
+};
+
+class FuncOpConversion final : public OpConversionPattern<func::FuncOp> {
+public:
+  using OpConversionPattern<func::FuncOp>::OpConversionPattern;
+
+  LogicalResult
+  matchAndRewrite(func::FuncOp funcOp, OpAdaptor adaptor,
+                  ConversionPatternRewriter &rewriter) const override {
+
+    if (funcOp.getFunctionType().getNumResults() > 1)
+      return rewriter.notifyMatchFailure(
+          funcOp, "only functions with zero or one result can be converted");
+
+    if (funcOp.isDeclaration())
+      return rewriter.notifyMatchFailure(funcOp,
+                                         "declarations cannot be converted");
+
+    // Create the converted `emitc.func` op.
+    emitc::FuncOp newFuncOp = rewriter.create<emitc::FuncOp>(
+        funcOp.getLoc(), funcOp.getName(), funcOp.getFunctionType());
+
+    // Copy over all attributes other than the function name and type.
+    for (const auto &namedAttr : funcOp->getAttrs()) {
+      if (namedAttr.getName() != funcOp.getFunctionTypeAttrName() &&
+          namedAttr.getName() != SymbolTable::getSymbolAttrName())
+        newFuncOp->setAttr(namedAttr.getName(), namedAttr.getValue());
+    }
+
+    // Add `static` to specifiers if `func.func` is private.
+    if (funcOp.isPrivate()) {
+      ArrayAttr specifiers = rewriter.getStrArrayAttr({"static"});
+      newFuncOp.setSpecifiersAttr(specifiers);
+    }
+
+    rewriter.inlineRegionBefore(funcOp.getBody(), newFuncOp.getBody(),
+                                newFuncOp.end());
+    rewriter.eraseOp(funcOp);
+
+    return success();
+  }
+};
+
+class ReturnOpConversion final : public OpConversionPattern<func::ReturnOp> {
+public:
+  using OpConversionPattern<func::ReturnOp>::OpConversionPattern;
+
+  LogicalResult
+  matchAndRewrite(func::ReturnOp returnOp, OpAdaptor adaptor,
+                  ConversionPatternRewriter &rewriter) const override {
+    if (returnOp.getNumOperands() > 1)
+      return rewriter.notifyMatchFailure(
+          returnOp, "only zero or one operand is supported");
+
+    rewriter.replaceOpWithNewOp<emitc::ReturnOp>(
+        returnOp,
+        returnOp.getNumOperands() ? adaptor.getOperands()[0] : nullptr);
+    return success();
+  }
+};
+} // namespace
+
+//===----------------------------------------------------------------------===//
+// Pattern population
+//===----------------------------------------------------------------------===//
+
+void mlir::populateFuncToEmitCPatterns(RewritePatternSet &patterns) {
+  MLIRContext *ctx = patterns.getContext();
+
+  patterns.add<CallOpConversion, FuncOpConversion, ReturnOpConversion>(ctx);
+}
diff --git a/mlir/lib/Conversion/FuncToEmitC/FuncToEmitCPass.cpp b/mlir/lib/Conversion/FuncToEmitC/FuncToEmitCPass.cpp
new file mode 100644
index 000000000000..26d32e29bef8
--- /dev/null
+++ b/mlir/lib/Conversion/FuncToEmitC/FuncToEmitCPass.cpp
@@ -0,0 +1,47 @@
+//===- FuncToEmitC.cpp - Func to EmitC Pass ---------------------*- 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 implements a pass to convert the Func dialect to the EmitC dialect.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/Conversion/FuncToEmitC/FuncToEmitCPass.h"
+
+#include "mlir/Conversion/FuncToEmitC/FuncToEmitC.h"
+#include "mlir/Dialect/EmitC/IR/EmitC.h"
+#include "mlir/Dialect/Func/IR/FuncOps.h"
+#include "mlir/Pass/Pass.h"
+#include "mlir/Transforms/DialectConversion.h"
+
+namespace mlir {
+#define GEN_PASS_DEF_CONVERTFUNCTOEMITC
+#include "mlir/Conversion/Passes.h.inc"
+} // namespace mlir
+
+using namespace mlir;
+
+namespace {
+struct ConvertFuncToEmitC
+    : public impl::ConvertFuncToEmitCBase<ConvertFuncToEmitC> {
+  void runOnOperation() override;
+};
+} // namespace
+
+void ConvertFuncToEmitC::runOnOperation() {
+  ConversionTarget target(getContext());
+
+  target.addLegalDialect<emitc::EmitCDialect>();
+  target.addIllegalOp<func::CallOp, func::FuncOp, func::ReturnOp>();
+
+  RewritePatternSet patterns(&getContext());
+  populateFuncToEmitCPatterns(patterns);
+
+  if (failed(
+          applyPartialConversion(getOperation(), target, std::move(patterns))))
+    signalPassFailure();
+}
diff --git a/mlir/lib/Dialect/EmitC/IR/CMakeLists.txt b/mlir/lib/Dialect/EmitC/IR/CMakeLists.txt
index 4665c41a62e8..4cc54201d274 100644
--- a/mlir/lib/Dialect/EmitC/IR/CMakeLists.txt
+++ b/mlir/lib/Dialect/EmitC/IR/CMakeLists.txt
@@ -9,8 +9,10 @@ add_mlir_dialect_library(MLIREmitCDialect
   MLIREmitCAttributesIncGen
 
   LINK_LIBS PUBLIC
+  MLIRCallInterfaces
   MLIRCastInterfaces
   MLIRControlFlowInterfaces
+  MLIRFunctionInterfaces
   MLIRIR
   MLIRSideEffectInterfaces
   )
diff --git a/mlir/lib/Dialect/EmitC/IR/EmitC.cpp b/mlir/lib/Dialect/EmitC/IR/EmitC.cpp
index 5f502f1f7a17..df489c6d90fb 100644
--- a/mlir/lib/Dialect/EmitC/IR/EmitC.cpp
+++ b/mlir/lib/Dialect/EmitC/IR/EmitC.cpp
@@ -8,7 +8,10 @@
 
 #include "mlir/Dialect/EmitC/IR/EmitC.h"
 #include "mlir/IR/Builders.h"
+#include "mlir/IR/BuiltinAttributes.h"
 #include "mlir/IR/DialectImplementation.h"
+#include "mlir/IR/IRMapping.h"
+#include "mlir/Interfaces/FunctionImplementation.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/TypeSwitch.h"
 
@@ -348,6 +351,122 @@ LogicalResult ForOp::verifyRegions() {
 }
 
 //===----------------------------------------------------------------------===//
+// CallOp
+//===----------------------------------------------------------------------===//
+
+LogicalResult CallOp::verifySymbolUses(SymbolTableCollection &symbolTable) {
+  // Check that the callee attribute was specified.
+  auto fnAttr = (*this)->getAttrOfType<FlatSymbolRefAttr>("callee");
+  if (!fnAttr)
+    return emitOpError("requires a 'callee' symbol reference attribute");
+  FuncOp fn = symbolTable.lookupNearestSymbolFrom<FuncOp>(*this, fnAttr);
+  if (!fn)
+    return emitOpError() << "'" << fnAttr.getValue()
+                         << "' does not reference a valid function";
+
+  // Verify that the operand and result types match the callee.
+  auto fnType = fn.getFunctionType();
+  if (fnType.getNumInputs() != getNumOperands())
+    return emitOpError("incorrect number of operands for callee");
+
+  for (unsigned i = 0, e = fnType.getNumInputs(); i != e; ++i)
+    if (getOperand(i).getType() != fnType.getInput(i))
+      return emitOpError("operand type mismatch: expected operand type ")
+             << fnType.getInput(i) << ", but provided "
+             << getOperand(i).getType() << " for operand number " << i;
+
+  if (fnType.getNumResults() != getNumResults())
+    return emitOpError("incorrect number of results for callee");
+
+  for (unsigned i = 0, e = fnType.getNumResults(); i != e; ++i)
+    if (getResult(i).getType() != fnType.getResult(i)) {
+      auto diag = emitOpError("result type mismatch at index ") << i;
+      diag.attachNote() << "      op result types: " << getResultTypes();
+      diag.attachNote() << "function result types: " << fnType.getResults();
+      return diag;
+    }
+
+  return success();
+}
+
+FunctionType CallOp::getCalleeType() {
+  return FunctionType::get(getContext(), getOperandTypes(), getResultTypes());
+}
+
+//===----------------------------------------------------------------------===//
+// FuncOp
+//===----------------------------------------------------------------------===//
+
+void FuncOp::build(OpBuilder &builder, OperationState &state, StringRef name,
+                   FunctionType type, ArrayRef<NamedAttribute> attrs,
+                   ArrayRef<DictionaryAttr> argAttrs) {
+  state.addAttribute(SymbolTable::getSymbolAttrName(),
+                     builder.getStringAttr(name));
+  state.addAttribute(getFunctionTypeAttrName(state.name), TypeAttr::get(type));
+  state.attributes.append(attrs.begin(), attrs.end());
+  state.addRegion();
+
+  if (argAttrs.empty())
+    return;
+  assert(type.getNumInputs() == argAttrs.size());
+  function_interface_impl::addArgAndResultAttrs(
+      builder, state, argAttrs, /*resultAttrs=*/std::nullopt,
+      getArgAttrsAttrName(state.name), getResAttrsAttrName(state.name));
+}
+
+ParseResult FuncOp::parse(OpAsmParser &parser, OperationState &result) {
+  auto buildFuncType =
+      [](Builder &builder, ArrayRef<Type> argTypes, ArrayRef<Type> results,
+         function_interface_impl::VariadicFlag,
+         std::string &) { return builder.getFunctionType(argTypes, results); };
+
+  return function_interface_impl::parseFunctionOp(
+      parser, result, /*allowVariadic=*/false,
+      getFunctionTypeAttrName(result.name), buildFuncType,
+      getArgAttrsAttrName(result.name), getResAttrsAttrName(result.name));
+}
+
+void FuncOp::print(OpAsmPrinter &p) {
+  function_interface_impl::printFunctionOp(
+      p, *this, /*isVariadic=*/false, getFunctionTypeAttrName(),
+      getArgAttrsAttrName(), getResAttrsAttrName());
+}
+
+LogicalResult FuncOp::verify() {
+  if (getNumResults() > 1)
+    return emitOpError("requires zero or exactly one result, but has ")
+           << getNumResults();
+
+  if (isExternal())
+    return emitOpError("does not support empty function bodies");
+
+  return success();
+}
+
+//===----------------------------------------------------------------------===//
+// ReturnOp
+//===----------------------------------------------------------------------===//
+
+LogicalResult ReturnOp::verify() {
+  auto function = cast<FuncOp>((*this)->getParentOp());
+
+  // The operand number and types must match the function signature.
+  if (getNumOperands() != function.getNumResults())
+    return emitOpError("has ")
+           << getNumOperands() << " operands, but enclosing function (@"
+           << function.getName() << ") returns " << function.getNumResults();
+
+  if (function.getNumResults() == 1)
+    if (getOperand().getType() != function.getResultTypes()[0])
+      return emitError() << "type of the return operand ("
+                         << getOperand().getType()
+                         << ") doesn't match function result type ("
+                         << function.getResultTypes()[0] << ")"
+                         << " in function @" << function.getName();
+  return success();
+}
+
+//===----------------------------------------------------------------------===//
 // IfOp
 //===----------------------------------------------------------------------===//
 
diff --git a/mlir/lib/Target/Cpp/TranslateToCpp.cpp b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
index 72b382709925..c0c6105409f8 100644
--- a/mlir/lib/Target/Cpp/TranslateToCpp.cpp
+++ b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
@@ -504,18 +504,33 @@ static LogicalResult printOperation(CppEmitter &emitter,
   return success();
 }
 
-static LogicalResult printOperation(CppEmitter &emitter, func::CallOp callOp) {
-  if (failed(emitter.emitAssignPrefix(*callOp.getOperation())))
+static LogicalResult printCallOperation(CppEmitter &emitter, Operation *callOp,
+                                        StringRef callee) {
+  if (failed(emitter.emitAssignPrefix(*callOp)))
     return failure();
 
   raw_ostream &os = emitter.ostream();
-  os << callOp.getCallee() << "(";
-  if (failed(emitter.emitOperands(*callOp.getOperation())))
+  os << callee << "(";
+  if (failed(emitter.emitOperands(*callOp)))
     return failure();
   os << ")";
   return success();
 }
 
+static LogicalResult printOperation(CppEmitter &emitter, func::CallOp callOp) {
+  Operation *operation = callOp.getOperation();
+  StringRef callee = callOp.getCallee();
+
+  return printCallOperation(emitter, operation, callee);
+}
+
+static LogicalResult printOperation(CppEmitter &emitter, emitc::CallOp callOp) {
+  Operation *operation = callOp.getOperation();
+  StringRef callee = callOp.getCallee();
+
+  return printCallOperation(emitter, operation, callee);
+}
+
 static LogicalResult printOperation(CppEmitter &emitter,
                                     emitc::CallOpaqueOp callOpaqueOp) {
   raw_ostream &os = emitter.ostream();
@@ -733,6 +748,19 @@ static LogicalResult printOperation(CppEmitter &emitter,
   }
 }
 
+static LogicalResult printOperation(CppEmitter &emitter,
+                                    emitc::ReturnOp returnOp) {
+  raw_ostream &os = emitter.ostream();
+  os << "return";
+  if (returnOp.getNumOperands() == 0)
+    return success();
+
+  os << " ";
+  if (failed(emitter.emitOperand(returnOp.getOperand())))
+    return failure();
+  return success();
+}
+
 static LogicalResult printOperation(CppEmitter &emitter, ModuleOp moduleOp) {
   CppEmitter::Scope scope(emitter);
 
@@ -743,39 +771,34 @@ static LogicalResult printOperation(CppEmitter &emitter, ModuleOp moduleOp) {
   return success();
 }
 
-static LogicalResult printOperation(CppEmitter &emitter,
-                                    func::FuncOp functionOp) {
-  // We need to declare variables at top if the function has multiple blocks.
-  if (!emitter.shouldDeclareVariablesAtTop() &&
-      functionOp.getBlocks().size() > 1) {
-    return functionOp.emitOpError(
-        "with multiple blocks needs variables declared at top");
-  }
-
-  CppEmitter::Scope scope(emitter);
+static LogicalResult printFunctionArgs(CppEmitter &emitter,
+                                       Operation *functionOp,
+                                       Region::BlockArgListType arguments) {
   raw_indented_ostream &os = emitter.ostream();
-  if (failed(emitter.emitTypes(functionOp.getLoc(),
-                               functionOp.getFunctionType().getResults())))
-    return failure();
-  os << " " << functionOp.getName();
 
-  os << "(";
   if (failed(interleaveCommaWithError(
-          functionOp.getArguments(), os,
-          [&](BlockArgument arg) -> LogicalResult {
-            if (failed(emitter.emitType(functionOp.getLoc(), arg.getType())))
+          arguments, os, [&](BlockArgument arg) -> LogicalResult {
+            if (failed(emitter.emitType(functionOp->getLoc(), arg.getType())))
               return failure();
             os << " " << emitter.getOrCreateName(arg);
             return success();
           })))
     return failure();
-  os << ") {\n";
+
+  return success();
+}
+
+static LogicalResult printFunctionBody(CppEmitter &emitter,
+                                       Operation *functionOp,
+                                       Region::BlockListType &blocks) {
+  raw_indented_ostream &os = emitter.ostream();
   os.indent();
+
   if (emitter.shouldDeclareVariablesAtTop()) {
     // Declare all variables that hold op results including those from nested
     // regions.
     WalkResult result =
-        functionOp.walk<WalkOrder::PreOrder>([&](Operation *op) -> WalkResult {
+        functionOp->walk<WalkOrder::PreOrder>([&](Operation *op) -> WalkResult {
           if (isa<emitc::LiteralOp>(op) ||
               isa<emitc::ExpressionOp>(op->getParentOp()) ||
               (isa<emitc::ExpressionOp>(op) &&
@@ -794,7 +817,6 @@ static LogicalResult printOperation(CppEmitter &emitter,
       return failure();
   }
 
-  Region::BlockListType &blocks = functionOp.getBlocks();
   // Create label names for basic blocks.
   for (Block &block : blocks) {
     emitter.getOrCreateName(block);
@@ -804,7 +826,7 @@ static LogicalResult printOperation(CppEmitter &emitter,
   for (Block &block : llvm::drop_begin(blocks)) {
     for (BlockArgument &arg : block.getArguments()) {
       if (emitter.hasValueInScope(arg))
-        return functionOp.emitOpError(" block argument #")
+        return functionOp->emitOpError(" block argument #")
                << arg.getArgNumber() << " is out of scope";
       if (failed(
               emitter.emitType(block.getParentOp()->getLoc(), arg.getType()))) {
@@ -833,7 +855,71 @@ static LogicalResult printOperation(CppEmitter &emitter,
         return failure();
     }
   }
-  os.unindent() << "}\n";
+
+  os.unindent();
+
+  return success();
+}
+
+static LogicalResult printOperation(CppEmitter &emitter,
+                                    func::FuncOp functionOp) {
+  // We need to declare variables at top if the function has multiple blocks.
+  if (!emitter.shouldDeclareVariablesAtTop() &&
+      functionOp.getBlocks().size() > 1) {
+    return functionOp.emitOpError(
+        "with multiple blocks needs variables declared at top");
+  }
+
+  CppEmitter::Scope scope(emitter);
+  raw_indented_ostream &os = emitter.ostream();
+  if (failed(emitter.emitTypes(functionOp.getLoc(),
+                               functionOp.getFunctionType().getResults())))
+    return failure();
+  os << " " << functionOp.getName();
+
+  os << "(";
+  Operation *operation = functionOp.getOperation();
+  if (failed(printFunctionArgs(emitter, operation, functionOp.getArguments())))
+    return failure();
+  os << ") {\n";
+  if (failed(printFunctionBody(emitter, operation, functionOp.getBlocks())))
+    return failure();
+  os << "}\n";
+
+  return success();
+}
+
+static LogicalResult printOperation(CppEmitter &emitter,
+                                    emitc::FuncOp functionOp) {
+  // We need to declare variables at top if the function has multiple blocks.
+  if (!emitter.shouldDeclareVariablesAtTop() &&
+      functionOp.getBlocks().size() > 1) {
+    return functionOp.emitOpError(
+        "with multiple blocks needs variables declared at top");
+  }
+
+  CppEmitter::Scope scope(emitter);
+  raw_indented_ostream &os = emitter.ostream();
+  if (functionOp.getSpecifiers()) {
+    for (Attribute specifier : functionOp.getSpecifiersAttr()) {
+      os << cast<StringAttr>(specifier).str() << " ";
+    }
+  }
+
+  if (failed(emitter.emitTypes(functionOp.getLoc(),
+                               functionOp.getFunctionType().getResults())))
+    return failure();
+  os << " " << functionOp.getName();
+
+  os << "(";
+  Operation *operation = functionOp.getOperation();
+  if (failed(printFunctionArgs(emitter, operation, functionOp.getArguments())))
+    return failure();
+  os << ") {\n";
+  if (failed(printFunctionBody(emitter, operation, functionOp.getBlocks())))
+    return failure();
+  os << "}\n";
+
   return success();
 }
 
@@ -1148,12 +1234,12 @@ LogicalResult CppEmitter::emitOperation(Operation &op, bool trailingSemicolon) {
           .Case<cf::BranchOp, cf::CondBranchOp>(
               [&](auto op) { return printOperation(*this, op); })
           // EmitC ops.
-          .Case<emitc::AddOp, emitc::ApplyOp, emitc::AssignOp,
+          .Case<emitc::AddOp, emitc::ApplyOp, emitc::AssignOp, emitc::CallOp,
                 emitc::CallOpaqueOp, emitc::CastOp, emitc::CmpOp,
                 emitc::ConstantOp, emitc::DivOp, emitc::ExpressionOp,
-                emitc::ForOp, emitc::IfOp, emitc::IncludeOp, emitc::MulOp,
-                emitc::RemOp, emitc::SubOp, emitc::VariableOp,
-                emitc::VerbatimOp>(
+                emitc::ForOp, emitc::FuncOp, emitc::IfOp, emitc::IncludeOp,
+                emitc::MulOp, emitc::RemOp, emitc::ReturnOp, emitc::SubOp,
+                emitc::VariableOp, emitc::VerbatimOp>(
               [&](auto op) { return printOperation(*this, op); })
           // Func ops.
           .Case<func::CallOp, func::ConstantOp, func::FuncOp, func::ReturnOp>(
diff --git a/mlir/test/Conversion/FuncToEmitC/func-to-emitc.mlir b/mlir/test/Conversion/FuncToEmitC/func-to-emitc.mlir
new file mode 100644
index 000000000000..a1c8af2587aa
--- /dev/null
+++ b/mlir/test/Conversion/FuncToEmitC/func-to-emitc.mlir
@@ -0,0 +1,55 @@
+// RUN: mlir-opt -split-input-file -convert-func-to-emitc %s | FileCheck %s
+
+// CHECK-LABEL: emitc.func @foo()
+// CHECK-NEXT: emitc.return
+func.func @foo() {
+  return
+}
+
+// -----
+
+// CHECK-LABEL: emitc.func private @foo() attributes {specifiers = ["static"]}
+// CHECK-NEXT: emitc.return
+func.func private @foo() {
+  return
+}
+
+// -----
+
+// CHECK-LABEL: emitc.func @foo(%arg0: i32)
+func.func @foo(%arg0: i32) {
+  emitc.call_opaque "bar"(%arg0) : (i32) -> ()
+  return
+}
+
+// -----
+
+// CHECK-LABEL: emitc.func @foo(%arg0: i32) -> i32
+// CHECK-NEXT: emitc.return %arg0 : i32
+func.func @foo(%arg0: i32) -> i32 {
+  return %arg0 : i32
+}
+
+// -----
+
+// CHECK-LABEL: emitc.func @foo(%arg0: i32, %arg1: i32) -> i32
+func.func @foo(%arg0: i32, %arg1: i32) -> i32 {
+  %0 = "emitc.add" (%arg0, %arg1) : (i32, i32) -> i32
+  return %0 : i32
+}
+
+// -----
+
+// CHECK-LABEL: emitc.func private @return_i32(%arg0: i32) -> i32 attributes {specifiers = ["static"]}
+// CHECK-NEXT: emitc.return %arg0 : i32
+func.func private @return_i32(%arg0: i32) -> i32 {
+  return %arg0 : i32
+}
+
+// CHECK-LABEL: emitc.func @call(%arg0: i32) -> i32
+// CHECK-NEXT: %0 = emitc.call @return_i32(%arg0) : (i32) -> i32
+// CHECK-NEXT: emitc.return %0 : i32
+func.func @call(%arg0: i32) -> i32 {
+  %0 = call @return_i32(%arg0) : (i32) -> (i32)
+  return %0 : i32
+}
diff --git a/mlir/test/Dialect/EmitC/invalid_ops.mlir b/mlir/test/Dialect/EmitC/invalid_ops.mlir
index 46eccb1c24ee..707f9a5b23b0 100644
--- a/mlir/test/Dialect/EmitC/invalid_ops.mlir
+++ b/mlir/test/Dialect/EmitC/invalid_ops.mlir
@@ -289,3 +289,40 @@ func.func @test_expression_multiple_results(%arg0: i32) -> i32 {
   }
   return %r : i32
 }
+
+// -----
+
+// expected-error @+1 {{'emitc.func' op requires zero or exactly one result, but has 2}}
+emitc.func @multiple_results(%0: i32) -> (i32, i32) {
+  emitc.return %0 : i32
+}
+
+// -----
+
+emitc.func @resulterror() -> i32 {
+^bb42:
+  emitc.return    // expected-error {{'emitc.return' op has 0 operands, but enclosing function (@resulterror) returns 1}}
+}
+
+// -----
+
+emitc.func @return_type_mismatch() -> i32 {
+  %0 = emitc.call_opaque "foo()"(): () -> f32
+  emitc.return %0 : f32  // expected-error {{type of the return operand ('f32') doesn't match function result type ('i32') in function @return_type_mismatch}}
+}
+
+// -----
+
+func.func @return_inside_func.func(%0: i32) -> (i32) {
+  // expected-error@+1 {{'emitc.return' op expects parent op 'emitc.func'}}
+  emitc.return %0 : i32
+}
+// -----
+
+// expected-error@+1 {{expected non-function type}}
+emitc.func @func_variadic(...)
+
+// -----
+
+// expected-error@+1 {{'emitc.func' op does not support empty function bodies}}
+emitc.func private @empty()
diff --git a/mlir/test/Dialect/EmitC/ops.mlir b/mlir/test/Dialect/EmitC/ops.mlir
index 7ad3787558b7..b41333faa4d4 100644
--- a/mlir/test/Dialect/EmitC/ops.mlir
+++ b/mlir/test/Dialect/EmitC/ops.mlir
@@ -15,6 +15,21 @@ func.func @f(%arg0: i32, %f: !emitc.opaque<"int32_t">) {
   return
 }
 
+emitc.func @func(%arg0 : i32) {
+  emitc.call_opaque "foo"(%arg0) : (i32) -> ()
+  emitc.return
+}
+
+emitc.func @return_i32() -> i32 attributes {specifiers = ["static","inline"]} {
+  %0 = emitc.call_opaque "foo"(): () -> i32
+  emitc.return %0 : i32
+}
+
+emitc.func @call() -> i32 {
+  %0 = emitc.call @return_i32() : () -> (i32)
+  emitc.return %0 : i32
+}
+
 func.func @cast(%arg0: i32) {
   %1 = emitc.cast %arg0: i32 to f32
   return
diff --git a/mlir/test/Target/Cpp/func.mlir b/mlir/test/Target/Cpp/func.mlir
new file mode 100644
index 000000000000..d2e14a9e5a7a
--- /dev/null
+++ b/mlir/test/Target/Cpp/func.mlir
@@ -0,0 +1,39 @@
+// RUN: mlir-translate -mlir-to-cpp %s | FileCheck %s -check-prefix=CPP-DEFAULT
+// RUN: mlir-translate -mlir-to-cpp -declare-variables-at-top %s | FileCheck %s -check-prefix=CPP-DECLTOP
+
+
+emitc.func @emitc_func(%arg0 : i32) {
+  emitc.call_opaque "foo" (%arg0) : (i32) -> ()
+  emitc.return
+}
+// CPP-DEFAULT: void emitc_func(int32_t [[V0:[^ ]*]]) {
+// CPP-DEFAULT-NEXT: foo([[V0:[^ ]*]]);
+// CPP-DEFAULT-NEXT: return;
+
+
+emitc.func @return_i32() -> i32 attributes {specifiers = ["static","inline"]} {
+  %0 = emitc.call_opaque "foo" (): () -> i32
+  emitc.return %0 : i32
+}
+// CPP-DEFAULT: static inline int32_t return_i32() {
+// CPP-DEFAULT-NEXT: [[V0:[^ ]*]] = foo();
+// CPP-DEFAULT-NEXT: return [[V0:[^ ]*]];
+
+// CPP-DECLTOP: static inline int32_t return_i32() {
+// CPP-DECLTOP-NEXT: int32_t [[V0:[^ ]*]];
+// CPP-DECLTOP-NEXT: [[V0:]] = foo();
+// CPP-DECLTOP-NEXT: return [[V0:[^ ]*]];
+
+
+emitc.func @emitc_call() -> i32 {
+  %0 = emitc.call @return_i32() : () -> (i32)
+  emitc.return %0 : i32
+}
+// CPP-DEFAULT: int32_t emitc_call() {
+// CPP-DEFAULT-NEXT: int32_t [[V0:[^ ]*]] = return_i32();
+// CPP-DEFAULT-NEXT: return [[V0:[^ ]*]];
+
+// CPP-DECLTOP: int32_t emitc_call() {
+// CPP-DECLTOP-NEXT: int32_t [[V0:[^ ]*]];
+// CPP-DECLTOP-NEXT: [[V0:[^ ]*]] = return_i32();
+// CPP-DECLTOP-NEXT: return [[V0:[^ ]*]];
diff --git a/utils/bazel/llvm-project-overlay/mlir/BUILD.bazel b/utils/bazel/llvm-project-overlay/mlir/BUILD.bazel
index bc7f48a563b0..7dd52ffff258 100644
--- a/utils/bazel/llvm-project-overlay/mlir/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/mlir/BUILD.bazel
@@ -1583,8 +1583,10 @@ td_library(
     includes = ["include"],
     deps = [
         ":BuiltinDialectTdFiles",
+        ":CallInterfacesTdFiles",
         ":CastInterfacesTdFiles",
         ":ControlFlowInterfacesTdFiles",
+        ":FunctionInterfacesTdFiles",
         ":OpBaseTdFiles",
         ":SideEffectInterfacesTdFiles",
     ],
@@ -3687,10 +3689,12 @@ cc_library(
     ]),
     includes = ["include"],
     deps = [
+        ":CallOpInterfaces",
         ":CastInterfaces",
         ":ControlFlowInterfaces",
         ":EmitCAttributesIncGen",
         ":EmitCOpsIncGen",
+        ":FunctionInterfaces",
         ":IR",
         ":SideEffectInterfaces",
         "//llvm:Support",
@@ -3927,6 +3931,7 @@ cc_library(
         ":ControlFlowToSPIRV",
         ":ConversionPassIncGen",
         ":ConvertToLLVM",
+        ":FuncToEmitC",
         ":FuncToLLVM",
         ":FuncToSPIRV",
         ":GPUToGPURuntimeTransforms",
@@ -6866,6 +6871,32 @@ cc_library(
 )
 
 cc_library(
+    name = "FuncToEmitC",
+    srcs = glob([
+        "lib/Conversion/FuncToEmitC*.cpp",
+        "lib/Conversion/FuncToEmitC/*.h",
+    ]),
+    hdrs = glob([
+        "include/mlir/Conversion/FuncToEmitC/*.h",
+    ]),
+    includes = [
+        "include",
+        "lib/Conversion/FuncToEmitC",
+    ],
+    deps = [
+        ":ConversionPassIncGen",
+        ":FuncDialect",
+        ":EmitCDialect",
+        ":IR",
+        ":Pass",
+        ":Support",
+        ":TransformUtils",
+        ":Transforms",
+        "//llvm:Support",
+    ],
+)
+
+cc_library(
     name = "FuncToSPIRV",
     srcs = glob([
         "lib/Conversion/FuncToSPIRV/*.cpp",