Introduce support for variadic function signatures for the LLVM dialect

LLVM function type has first-class support for variadic functions.  In the
current lowering pipeline, it is emulated using an attribute on functions of
standard function type.  In LLVMFuncOp that has LLVM function type, this can be
modeled directly.  Introduce parsing support for variadic arguments to the
function and use it to support variadic function declarations in LLVMFuncOp.
Function definitions are currently not supported as that would require modeling
va_start/va_end LLVM intrinsics in the dialect and we don't yet have a
consistent story for LLVM intrinsics.

PiperOrigin-RevId: 262372651

mlir/include/mlir/IR/FunctionSupport.h

@@ -55,23 +55,28 @@ inline ArrayRef<NamedAttribute> getArgAttrs(Operation *op, unsigned index) {
 
 /// Callback type for `parseFunctionLikeOp`, the callback should produce the
 /// type that will be associated with a function-like operation from lists of
-/// function arguments and results; in case of error, it may populate the last
+/// function arguments and results, the boolean operand is true if the function
+/// should have variadic arguments; in case of error, it may populate the last
 /// argument with a message.
-using FuncTypeBuilder = llvm::function_ref<Type(Builder &, ArrayRef<Type>,
-                                                ArrayRef<Type>, std::string &)>;
+using FuncTypeBuilder = llvm::function_ref<Type(
+    Builder &, ArrayRef<Type>, ArrayRef<Type>, bool, std::string &)>;
 
 /// Parser implementation for function-like operations.  Uses
 /// `funcTypeBuilder` to construct the custom function type given lists of
-/// input and output types.  If the builder returns a null type, `result` will
-/// not contain the `type` attribute.  The caller can then add a type, report
-/// the error or delegate the reporting to the op's verifier.
+/// input and output types.  If `allowVariadic` is set, the parser will accept
+/// trailing ellipsis in the function signature and indicate to the builder
+/// whether the function is variadic.  If the builder returns a null type,
+/// `result` will not contain the `type` attribute.  The caller can then add a
+/// type, report the error or delegate the reporting to the op's verifier.
 ParseResult parseFunctionLikeOp(OpAsmParser *parser, OperationState *result,
+                                bool allowVariadic,
                                 FuncTypeBuilder funcTypeBuilder);
 
 /// Printer implementation for function-like operations.  Accepts lists of
 /// argument and result types to use while printing.
 void printFunctionLikeOp(OpAsmPrinter *p, Operation *op,
-                         ArrayRef<Type> argTypes, ArrayRef<Type> results);
+                         ArrayRef<Type> argTypes, bool isVariadic,
+                         ArrayRef<Type> results);
 
 } // namespace impl
 

mlir/include/mlir/IR/OpImplementation.h

@@ -260,6 +260,9 @@ public:
   /// Parse a `]` token if present.
   virtual ParseResult parseOptionalRSquare() = 0;
 
+  /// Parse a `...` token if present;
+  virtual ParseResult parseOptionalEllipsis() = 0;
+
   //===--------------------------------------------------------------------===//
   // Attribute Parsing
   //===--------------------------------------------------------------------===//

mlir/include/mlir/LLVMIR/LLVMOps.td

@@ -344,7 +344,8 @@ def LLVM_LLVMFuncOp : LLVM_ZeroResultOp<"func",
   let verifier = [{ return ::verify(*this); }];
   let printer = [{ printLLVMFuncOp(p, *this); }];
   let parser = [{
-    return impl::parseFunctionLikeOp(parser, result, buildLLVMFunctionType);
+    return impl::parseFunctionLikeOp(parser, result, /*allowVariadic=*/true,
+                                     buildLLVMFunctionType);
   }];
 }
 

mlir/lib/IR/Function.cpp

@@ -76,15 +76,19 @@ void FuncOp::build(Builder *builder, OperationState *result, StringRef name,
 /// Parsing/Printing methods.
 
 ParseResult FuncOp::parse(OpAsmParser *parser, OperationState *result) {
-  return impl::parseFunctionLikeOp(
-      parser, result,
-      [](Builder &builder, ArrayRef<Type> argTypes, ArrayRef<Type> results,
-         std::string &) { return builder.getFunctionType(argTypes, results); });
+  auto buildFuncType = [](Builder &builder, ArrayRef<Type> argTypes,
+                          ArrayRef<Type> results, bool, std::string &) {
+    return builder.getFunctionType(argTypes, results);
+  };
+
+  return impl::parseFunctionLikeOp(parser, result, /*allowVariadic=*/false,
+                                   buildFuncType);
 }
 
 void FuncOp::print(OpAsmPrinter *p) {
   FunctionType fnType = getType();
-  impl::printFunctionLikeOp(p, *this, fnType.getInputs(), fnType.getResults());
+  impl::printFunctionLikeOp(p, *this, fnType.getInputs(), /*isVariadic=*/false,
+                            fnType.getResults());
 }
 
 LogicalResult FuncOp::verify() {

mlir/lib/IR/FunctionSupport.cpp

@@ -22,9 +22,11 @@
 using namespace mlir;
 
 static ParseResult
-parseArgumentList(OpAsmParser *parser, SmallVectorImpl<Type> &argTypes,
+parseArgumentList(OpAsmParser *parser, bool allowVariadic,
+                  SmallVectorImpl<Type> &argTypes,
                   SmallVectorImpl<OpAsmParser::OperandType> &argNames,
-                  SmallVectorImpl<SmallVector<NamedAttribute, 2>> &argAttrs) {
+                  SmallVectorImpl<SmallVector<NamedAttribute, 2>> &argAttrs,
+                  bool &isVariadic) {
   if (parser->parseLParen())
     return failure();
 
@@ -47,6 +49,9 @@ parseArgumentList(OpAsmParser *parser, SmallVectorImpl<Type> &argTypes,
 
       if (parser->parseColonType(argumentType))
         return failure();
+    } else if (allowVariadic && succeeded(parser->parseOptionalEllipsis())) {
+      isVariadic = true;
+      return success();
     } else if (!argNames.empty()) {
       // Reject this if the preceding argument had a name.
       return parser->emitError(loc, "expected SSA identifier");
@@ -68,8 +73,15 @@ parseArgumentList(OpAsmParser *parser, SmallVectorImpl<Type> &argTypes,
   // Parse the function arguments.
   if (parser->parseOptionalRParen()) {
     do {
+      unsigned numTypedArguments = argTypes.size();
       if (parseArgument())
         return failure();
+
+      llvm::SMLoc loc = parser->getCurrentLocation();
+      if (argTypes.size() == numTypedArguments &&
+          succeeded(parser->parseOptionalComma()))
+        return parser->emitError(
+            loc, "variadic arguments must be in the end of the argument list");
     } while (succeeded(parser->parseOptionalComma()));
     parser->parseRParen();
   }
@@ -80,11 +92,13 @@ parseArgumentList(OpAsmParser *parser, SmallVectorImpl<Type> &argTypes,
 /// Parse a function signature, starting with a name and including the
 /// parameter list.
 static ParseResult parseFunctionSignature(
-    OpAsmParser *parser, SmallVectorImpl<OpAsmParser::OperandType> &argNames,
+    OpAsmParser *parser, bool allowVariadic,
+    SmallVectorImpl<OpAsmParser::OperandType> &argNames,
     SmallVectorImpl<Type> &argTypes,
-    SmallVectorImpl<SmallVector<NamedAttribute, 2>> &argAttrs,
+    SmallVectorImpl<SmallVector<NamedAttribute, 2>> &argAttrs, bool &isVariadic,
     SmallVectorImpl<Type> &results) {
-  if (parseArgumentList(parser, argTypes, argNames, argAttrs))
+  if (parseArgumentList(parser, allowVariadic, argTypes, argNames, argAttrs,
+                        isVariadic))
     return failure();
   // Parse the return types if present.
   return parser->parseOptionalArrowTypeList(results);
@@ -94,6 +108,7 @@ static ParseResult parseFunctionSignature(
 /// to construct the custom function type given lists of input and output types.
 ParseResult
 mlir::impl::parseFunctionLikeOp(OpAsmParser *parser, OperationState *result,
+                                bool allowVariadic,
                                 mlir::impl::FuncTypeBuilder funcTypeBuilder) {
   SmallVector<OpAsmParser::OperandType, 4> entryArgs;
   SmallVector<SmallVector<NamedAttribute, 2>, 4> argAttrs;
@@ -111,11 +126,14 @@ mlir::impl::parseFunctionLikeOp(OpAsmParser *parser, OperationState *result,
 
   // Parse the function signature.
   auto signatureLocation = parser->getCurrentLocation();
-  if (parseFunctionSignature(parser, entryArgs, argTypes, argAttrs, results))
+  bool isVariadic = false;
+  if (parseFunctionSignature(parser, allowVariadic, entryArgs, argTypes,
+                             argAttrs, isVariadic, results))
     return failure();
 
   std::string errorMessage;
-  if (auto type = funcTypeBuilder(builder, argTypes, results, errorMessage))
+  if (auto type =
+          funcTypeBuilder(builder, argTypes, results, isVariadic, errorMessage))
     result->addAttribute(getTypeAttrName(), builder.getTypeAttr(type));
   else
     return parser->emitError(signatureLocation)
@@ -147,7 +165,8 @@ mlir::impl::parseFunctionLikeOp(OpAsmParser *parser, OperationState *result,
 /// Print the signature of the function-like operation `op`.  Assumes `op` has
 /// the FunctionLike trait and passed the verification.
 static void printSignature(OpAsmPrinter *p, Operation *op,
-                           ArrayRef<Type> argTypes, ArrayRef<Type> results) {
+                           ArrayRef<Type> argTypes, bool isVariadic,
+                           ArrayRef<Type> results) {
   Region &body = op->getRegion(0);
   bool isExternal = body.empty();
 
@@ -165,6 +184,12 @@ static void printSignature(OpAsmPrinter *p, Operation *op,
     p->printOptionalAttrDict(::mlir::impl::getArgAttrs(op, i));
   }
 
+  if (isVariadic) {
+    if (!argTypes.empty())
+      *p << ", ";
+    *p << "...";
+  }
+
   *p << ')';
   p->printOptionalArrowTypeList(results);
 }
@@ -172,7 +197,7 @@ static void printSignature(OpAsmPrinter *p, Operation *op,
 /// Printer implementation for function-like operations.  Accepts lists of
 /// argument and result types to use while printing.
 void mlir::impl::printFunctionLikeOp(OpAsmPrinter *p, Operation *op,
-                                     ArrayRef<Type> argTypes,
+                                     ArrayRef<Type> argTypes, bool isVariadic,
                                      ArrayRef<Type> results) {
   // Print the operation and the function name.
   auto funcName =
@@ -181,7 +206,7 @@ void mlir::impl::printFunctionLikeOp(OpAsmPrinter *p, Operation *op,
   *p << op->getName() << " @" << funcName;
 
   // Print the signature.
-  printSignature(p, op, argTypes, results);
+  printSignature(p, op, argTypes, isVariadic, results);
 
   // Print out function attributes, if present.
   SmallVector<StringRef, 2> ignoredAttrs = {

mlir/lib/LLVMIR/IR/LLVMDialect.cpp

@@ -730,7 +730,7 @@ void LLVMFuncOp::build(Builder *builder, OperationState *result, StringRef name,
 // Returns a null type if any of the types provided are non-LLVM types, or if
 // there is more than one output type.
 static Type buildLLVMFunctionType(Builder &b, ArrayRef<Type> inputs,
-                                  ArrayRef<Type> outputs,
+                                  ArrayRef<Type> outputs, bool isVariadic,
                                   std::string &errorMessage) {
   if (outputs.size() > 1) {
     errorMessage = "expected zero or one function result";
@@ -761,8 +761,7 @@ static Type buildLLVMFunctionType(Builder &b, ArrayRef<Type> inputs,
     errorMessage = "expected LLVM type for function results";
     return {};
   }
-  return LLVMType::getFunctionTy(llvmOutput, llvmInputs,
-                                 /*isVarArg=*/false);
+  return LLVMType::getFunctionTy(llvmOutput, llvmInputs, isVariadic);
 }
 
 // Print the LLVMFuncOp.  Collects argument and result types and passes them
@@ -779,7 +778,7 @@ static void printLLVMFuncOp(OpAsmPrinter *p, LLVMFuncOp op) {
   if (!returnType.getUnderlyingType()->isVoidTy())
     resTypes.push_back(returnType);
 
-  impl::printFunctionLikeOp(p, op, argTypes, resTypes);
+  impl::printFunctionLikeOp(p, op, argTypes, op.isVarArg(), resTypes);
 }
 
 // Hook for OpTrait::FunctionLike, called after verifying that the 'type'
@@ -804,6 +803,9 @@ static LogicalResult verify(LLVMFuncOp op) {
   if (op.isExternal())
     return success();
 
+  if (op.isVarArg())
+    return op.emitOpError("only external functions can be variadic");
+
   auto *funcType = cast<llvm::FunctionType>(op.getType().getUnderlyingType());
   unsigned numArguments = funcType->getNumParams();
   Block &entryBlock = op.front();

mlir/lib/Parser/Lexer.cpp

@@ -106,6 +106,8 @@ Token Lexer::lexToken() {
     return formToken(Token::colon, tokStart);
   case ',':
     return formToken(Token::comma, tokStart);
+  case '.':
+    return lexEllipsis(tokStart);
   case '(':
     return formToken(Token::l_paren, tokStart);
   case ')':
@@ -382,3 +384,17 @@ Token Lexer::lexString(const char *tokStart) {
     }
   }
 }
+
+/// Lex an ellipsis.
+///
+///   ellipsis ::= '...'
+///
+Token Lexer::lexEllipsis(const char *tokStart) {
+  assert(curPtr[-1] == '.');
+
+  if (curPtr == curBuffer.end() || *curPtr != '.' || *(curPtr + 1) != '.')
+    return emitError(curPtr, "expected three consecutive dots for an ellipsis");
+
+  curPtr += 2;
+  return formToken(Token::ellipsis, tokStart);
+}

mlir/lib/Parser/Lexer.h

@@ -60,6 +60,7 @@ private:
   Token lexPrefixedIdentifier(const char *tokStart);
   Token lexNumber(const char *tokStart);
   Token lexString(const char *tokStart);
+  Token lexEllipsis(const char *tokStart);
 
   const llvm::SourceMgr &sourceMgr;
   MLIRContext *context;

mlir/lib/Parser/Parser.cpp

@@ -3319,6 +3319,11 @@ public:
     return success(parser.consumeIf(Token::r_square));
   }
 
+  /// Parses a `...` if present.
+  ParseResult parseOptionalEllipsis() override {
+    return success(parser.consumeIf(Token::ellipsis));
+  }
+
   //===--------------------------------------------------------------------===//
   // Attribute Parsing
   //===--------------------------------------------------------------------===//

mlir/lib/Parser/TokenKinds.def

@@ -78,6 +78,7 @@ TOK_PUNCTUATION(r_square,         "]")
 TOK_PUNCTUATION(less,             "<")
 TOK_PUNCTUATION(greater,          ">")
 TOK_PUNCTUATION(equal,            "=")
+TOK_PUNCTUATION(ellipsis,         "...")
 // TODO: More punctuation.
 
 // Operators.

mlir/test/IR/invalid.mlir

@@ -443,6 +443,21 @@ func @return_inside_loop() {
 
 // -----
 
+// expected-error@+1 {{expected three consecutive dots for an ellipsis}}
+func @malformed_ellipsis_one(.)
+
+// -----
+
+// expected-error@+1 {{expected three consecutive dots for an ellipsis}}
+func @malformed_ellipsis_two(..)
+
+// -----
+
+// expected-error@+1 {{expected non-function type}}
+func @func_variadic(...)
+
+// -----
+
 func @redef()  // expected-note {{see existing symbol definition here}}
 func @redef()  // expected-error {{redefinition of symbol named 'redef'}}
 

mlir/test/LLVMIR/func.mlir

@@ -86,6 +86,12 @@ module {
   attributes {foo = 42 : i32} {
     llvm.return
   }
+
+  // CHECK: llvm.func @variadic(...)
+  llvm.func @variadic(...)
+
+  // CHECK: llvm.func @variadic_args(!llvm.i32, !llvm.i32, ...)
+  llvm.func @variadic_args(!llvm.i32, !llvm.i32, ...)
 }
 
 // -----
@@ -166,3 +172,19 @@ module {
   // expected-error@+1 {{failed to construct function type: expected zero or one function result}}
   llvm.func @foo() -> (!llvm.i64, !llvm.i64)
 }
+
+// -----
+
+module {
+  // expected-error@+1 {{only external functions can be variadic}}
+  llvm.func @variadic_def(...) {
+    llvm.return
+  }
+}
+
+// -----
+
+module {
+  // expected-error@+1 {{variadic arguments must be in the end of the argument list}}
+  llvm.func @variadic_inside(%arg0: !llvm.i32, ..., %arg1: !llvm.i32)
+}