[MLIR][OpenMP] Add TableGen pseudo-generator for OpenMP-specific verification

[skatrak]

The introduction of the clause-based approach to defining OpenMP operations can make it more difficult to detect and address certain programming errors derived from this change. Specifically, it's possible for an operation to inadvertently override otherwise automatically-populated properties and result in unexpected and difficult to debug errors or incomplete operation definitions.

This patch introduces a TableGen backend that doesn't produce any output, but rather only checks for these potential oversights in the definition of OpenMP dialect operations and flags them as warnings or errors. This provides descriptive and early feedback before any code is attempted to be generated for these problematic definitions.

[llvmbot]

@llvm/pr-subscribers-flang-openmp
@llvm/pr-subscribers-mlir-openmp
@llvm/pr-subscribers-mlir-core

@llvm/pr-subscribers-mlir

Author: Sergio Afonso (skatrak)

Changes

The introduction of the clause-based approach to defining OpenMP operations can make it more difficult to detect and address certain programming errors derived from this change. Specifically, it's possible for an operation to inadvertently override otherwise automatically-populated properties and result in unexpected and difficult to debug errors or incomplete operation definitions.

This patch introduces a TableGen backend that doesn't produce any output, but rather only checks for these potential oversights in the definition of OpenMP dialect operations and flags them as warnings or errors. This provides descriptive and early feedback before any code is attempted to be generated for these problematic definitions.

---

Full diff: https://github.com/llvm/llvm-project/pull/95552.diff

5 Files Affected:

• (modified) mlir/include/mlir/Dialect/OpenMP/CMakeLists.txt (+1)
• (modified) mlir/include/mlir/Dialect/OpenMP/OpenMPOpBase.td (+2)
• (added) mlir/test/mlir-tblgen/openmp-ops-verify.td (+143)
• (modified) mlir/tools/mlir-tblgen/CMakeLists.txt (+1)
• (added) mlir/tools/mlir-tblgen/OmpOpGen.cpp (+146)

diff --git a/mlir/include/mlir/Dialect/OpenMP/CMakeLists.txt b/mlir/include/mlir/Dialect/OpenMP/CMakeLists.txt
index 419e24a733536..fbde2def9e0b2 100644
--- a/mlir/include/mlir/Dialect/OpenMP/CMakeLists.txt
+++ b/mlir/include/mlir/Dialect/OpenMP/CMakeLists.txt
@@ -3,6 +3,7 @@ mlir_tablegen(OmpCommon.td --gen-directive-decl --directives-dialect=OpenMP)
 add_public_tablegen_target(omp_common_td)
 
 set(LLVM_TARGET_DEFINITIONS OpenMPOps.td)
+mlir_tablegen(no-output -verify-openmp-ops)
 mlir_tablegen(OpenMPOpsDialect.h.inc -gen-dialect-decls -dialect=omp)
 mlir_tablegen(OpenMPOpsDialect.cpp.inc -gen-dialect-defs -dialect=omp)
 mlir_tablegen(OpenMPOps.h.inc -gen-op-decls)
diff --git a/mlir/include/mlir/Dialect/OpenMP/OpenMPOpBase.td b/mlir/include/mlir/Dialect/OpenMP/OpenMPOpBase.td
index d93abd63977ef..83e23599b37f6 100644
--- a/mlir/include/mlir/Dialect/OpenMP/OpenMPOpBase.td
+++ b/mlir/include/mlir/Dialect/OpenMP/OpenMPOpBase.td
@@ -135,6 +135,8 @@ class OpenMP_Op<string mnemonic, list<Trait> traits = [],
         traits
       )
     )> {
+  list<OpenMP_Clause> clauseList = clauses;
+
   // Aggregate `arguments` fields of all clauses into a single dag, to be used
   // by operations to populate their `arguments` field.
   defvar argsFilteredClauses =
diff --git a/mlir/test/mlir-tblgen/openmp-ops-verify.td b/mlir/test/mlir-tblgen/openmp-ops-verify.td
new file mode 100644
index 0000000000000..7fc962b4eaa4d
--- /dev/null
+++ b/mlir/test/mlir-tblgen/openmp-ops-verify.td
@@ -0,0 +1,143 @@
+// Tablegen tests for the verification of clause-based OpenMP dialect operation
+// definitions.
+
+// Run tablegen to generate OmpCommon.td in temp directory first.
+// RUN: mkdir -p %t/mlir/Dialect/OpenMP
+// RUN: mlir-tblgen --gen-directive-decl --directives-dialect=OpenMP \
+// RUN:   %S/../../../llvm/include/llvm/Frontend/OpenMP/OMP.td \
+// RUN:   -I %S/../../../llvm/include > %t/mlir/Dialect/OpenMP/OmpCommon.td
+
+// RUN: not mlir-tblgen -verify-openmp-ops -I %S/../../include -I %t %s 2>&1 | FileCheck %s
+
+include "mlir/Dialect/OpenMP/OpenMPOpBase.td"
+
+
+def OpenMP_SimpleClause : OpenMP_Clause<
+    /*isRequired=*/true, /*traits=*/false, /*arguments=*/false,
+    /*assemblyFormat=*/false, /*description=*/false,
+    /*extraClassDeclaration=*/false> {
+  let arguments = (ins I32:$val1);
+  let assemblyFormat = "`val1` `(` $val1 `)`";
+  let description = "Simple clause description.";
+  let extraClassDeclaration = "void simpleClauseExtraClassDecl();";
+}
+
+
+// -----------------------------------------------------------------------------
+// Verify errors / warnings for overriding each field.
+// -----------------------------------------------------------------------------
+
+def 1OverrideArgsOp : OpenMP_Op<"op", clauses=[OpenMP_SimpleClause]> {
+  let description = "Description of operation." # clausesDescription;
+  dag arguments = (ins I32:$myval);
+}
+// CHECK: warning: 'Simple' clause-defined argument 'I32:$val1' not present in operation.
+// CHECK-SAME: Consider `dag arguments = !con(clausesArgs, ...)` or explicitly skipping this field.
+// CHECK-NEXT: def 1OverrideArgsOp
+
+def 2OverrideAssemblyFormatOp : OpenMP_Op<"op", clauses=[OpenMP_SimpleClause]> {
+  let description = "Description of operation." # clausesDescription;
+  string assemblyFormat = "`alt_repr` `(` $val1 `)`";
+}
+// CHECK: warning: 'Simple' clause-defined `assemblyFormat` not present in operation.
+// CHECK-SAME: Consider concatenating `clausesAssemblyFormat` or explicitly skipping this field.
+// CHECK-NEXT: def 2OverrideAssemblyFormatOp
+
+def 3OverrideDescriptionOp : OpenMP_Op<"op", clauses=[OpenMP_SimpleClause]> {
+  let description = "Description of operation.";
+}
+// CHECK: error: 'Simple' clause-defined `description` not present in operation.
+// CHECK-SAME: Consider concatenating `clausesDescription` or explicitly skipping this field.
+// CHECK-NEXT: def 3OverrideDescriptionOp
+
+def 4OverrideExtraClassDeclarationOp : OpenMP_Op<"op", clauses=[OpenMP_SimpleClause]> {
+  let description = "Description of operation." # clausesDescription;
+  string extraClassDeclaration = "";
+}
+// CHECK: warning: 'Simple' clause-defined `extraClassDeclaration` not present in operation.
+// CHECK-SAME: Consider concatenating `clausesExtraClassDeclaration` or explicitly skipping this field.
+// CHECK-NEXT: def 4OverrideExtraClassDeclarationOp
+
+
+// -----------------------------------------------------------------------------
+// Verify that reporting is correct when OpenMP_Clause is inherited indirectly.
+// -----------------------------------------------------------------------------
+
+class OpenMP_IndirectClauseSkip<
+    bit traits = false, bit arguments = false, bit assemblyFormat = false,
+    bit description = false, bit extraClassDeclaration = false
+  > : OpenMP_Clause</*isRequired=*/true, traits, arguments, assemblyFormat,
+                    description, extraClassDeclaration> {
+  let arguments = (ins I32:$val2);
+  let assemblyFormat = "`val2` `(` $val2 `)`";
+  let description = "Indirectly-inherited clause description.";
+  let extraClassDeclaration = "void indirectClauseExtraClassDecl();";
+}
+
+def IndirectClause : OpenMP_IndirectClauseSkip<>;
+
+def 5IndirectClauseOp : OpenMP_Op<"op", clauses=[IndirectClause]> {
+  let description = "Description of operation." # clausesDescription;
+  dag arguments = (ins I32:$myval);
+}
+// CHECK: warning: 'Indirect' clause-defined argument 'I32:$val2' not present in operation.
+// CHECK-NEXT: def 5IndirectClauseOp
+
+
+// -----------------------------------------------------------------------------
+// Verify that multiple clauses are taken into account.
+// -----------------------------------------------------------------------------
+
+def 6MultiClauseOp : OpenMP_Op<"op", clauses=[OpenMP_SimpleClause, IndirectClause]> {
+  let description = "Description of operation." # clausesDescription;
+  let arguments = (ins I32:$val1);
+  let assemblyFormat = "`val2` `(` $val2 `)`";
+}
+// CHECK: warning: 'Simple' clause-defined `assemblyFormat` not present in operation.
+// CHECK-NEXT: def 6MultiClauseOp
+// CHECK: warning: 'Indirect' clause-defined argument 'I32:$val2' not present in operation.
+// CHECK-NEXT: def 6MultiClauseOp
+
+
+// -----------------------------------------------------------------------------
+// Verify that reporting is correct when clause definitions have other
+// superclasses in addition to OpenMP_Clause.
+// -----------------------------------------------------------------------------
+
+class Placeholder {}
+def MultiSuperClassClause : Placeholder, OpenMP_IndirectClauseSkip<>;
+
+def 7MultiSuperClassClauseOp : OpenMP_Op<"op", clauses=[IndirectClause]> {
+  let description = "Description of operation." # clausesDescription;
+  dag arguments = (ins I32:$myval);
+}
+// CHECK: warning: 'Indirect' clause-defined argument 'I32:$val2' not present in operation.
+// CHECK-NEXT: def 7MultiSuperClassClauseOp
+
+
+// -----------------------------------------------------------------------------
+// Verify that no errors are produced if the field being overriden is also
+// skipped for the clause.
+// -----------------------------------------------------------------------------
+
+def SkipArgsOp : OpenMP_Op<"op",
+    clauses=[OpenMP_IndirectClauseSkip<arguments=true>]> {
+  let description = "Description of operation." # clausesDescription;
+  dag arguments = (ins I32:$myval);
+}
+def SkipAssemblyFormatOp : OpenMP_Op<"op",
+    clauses=[OpenMP_IndirectClauseSkip<assemblyFormat=true>]> {
+  let description = "Description of operation." # clausesDescription;
+  string assemblyFormat = "`alt_repr` `(` $val1 `)`";
+}
+def SkipDescriptionOp : OpenMP_Op<"op",
+    clauses=[OpenMP_IndirectClauseSkip<description=true>]> {
+  let description = "Description of operation.";
+}
+def SkipExtraClassDeclarationOp : OpenMP_Op<"op",
+    clauses=[OpenMP_IndirectClauseSkip<extraClassDeclaration=true>]> {
+  let description = "Description of operation." # clausesDescription;
+  string extraClassDeclaration = "";
+}
+// CHECK-NOT: error:
+// CHECK-NOT: warning:
diff --git a/mlir/tools/mlir-tblgen/CMakeLists.txt b/mlir/tools/mlir-tblgen/CMakeLists.txt
index 20a200bc35408..fb507dc7f8c3c 100644
--- a/mlir/tools/mlir-tblgen/CMakeLists.txt
+++ b/mlir/tools/mlir-tblgen/CMakeLists.txt
@@ -19,6 +19,7 @@ add_tablegen(mlir-tblgen MLIR
   LLVMIRConversionGen.cpp
   LLVMIRIntrinsicGen.cpp
   mlir-tblgen.cpp
+  OmpOpGen.cpp
   OpClass.cpp
   OpDefinitionsGen.cpp
   OpDocGen.cpp
diff --git a/mlir/tools/mlir-tblgen/OmpOpGen.cpp b/mlir/tools/mlir-tblgen/OmpOpGen.cpp
new file mode 100644
index 0000000000000..a9ba86a777d8e
--- /dev/null
+++ b/mlir/tools/mlir-tblgen/OmpOpGen.cpp
@@ -0,0 +1,146 @@
+//===- OmpOpGen.cpp - OpenMP dialect op specific generators ---------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// OmpOpGen defines OpenMP dialect operation specific generators.
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/TableGen/GenInfo.h"
+
+#include "llvm/TableGen/Error.h"
+#include "llvm/TableGen/Record.h"
+
+using namespace llvm;
+
+static StringRef extractOmpClauseName(Record *clause) {
+  Record *ompClause = clause->getRecords().getClass("OpenMP_Clause");
+  assert(ompClause && "base OpenMP records expected to be defined");
+
+  StringRef clauseClassName;
+  SmallVector<Record *, 1> clauseSuperClasses;
+  clause->getDirectSuperClasses(clauseSuperClasses);
+
+  // Check if OpenMP_Clause is a direct superclass.
+  for (Record *superClass : clauseSuperClasses) {
+    if (superClass == ompClause) {
+      clauseClassName = clause->getName();
+      break;
+    }
+  }
+
+  // Support indirectly-inherited OpenMP_Clauses.
+  if (clauseClassName.empty()) {
+    for (auto [superClass, _] : clause->getSuperClasses()) {
+      if (superClass->isSubClassOf(ompClause)) {
+        clauseClassName = superClass->getName();
+        break;
+      }
+    }
+  }
+
+  assert(!clauseClassName.empty() && "clause name must be found");
+
+  // Keep only the OpenMP clause name itself for reporting purposes.
+  StringRef prefix = "OpenMP_";
+  StringRef suffixes[] = {"Skip", "Clause"};
+
+  if (clauseClassName.starts_with(prefix))
+    clauseClassName = clauseClassName.substr(prefix.size());
+
+  for (StringRef suffix : suffixes) {
+    if (clauseClassName.ends_with(suffix))
+      clauseClassName =
+          clauseClassName.substr(0, clauseClassName.size() - suffix.size());
+  }
+
+  return clauseClassName;
+}
+
+static bool verifyArgument(DagInit *arguments, StringRef argName,
+                           Init *argInit) {
+  auto range = zip_equal(arguments->getArgNames(), arguments->getArgs());
+  return std::find_if(
+             range.begin(), range.end(),
+             [&](std::tuple<llvm::StringInit *const &, llvm::Init *const &> v) {
+               return std::get<0>(v)->getAsUnquotedString() == argName &&
+                      std::get<1>(v) == argInit;
+             }) != range.end();
+}
+
+static bool verifyStringValue(StringRef value, Record *op, Record *clause) {
+  auto opValue = op->getValueAsOptionalString(value);
+  auto clauseValue = clause->getValueAsOptionalString(value);
+  if (!opValue)
+    return !clauseValue || clauseValue->empty();
+
+  return !clauseValue || opValue->contains(clauseValue->trim());
+}
+
+// Verify that all fields of the given clause not explicitly ignored are present
+// in the corresponding operation field.
+static void verifyClause(Record *op, Record *clause) {
+  StringRef clauseClassName = extractOmpClauseName(clause);
+
+  if (!clause->getValueAsBit("ignoreArgs")) {
+    DagInit *opArguments = op->getValueAsDag("arguments");
+    DagInit *arguments = clause->getValueAsDag("arguments");
+
+    for (auto [name, arg] :
+         zip(arguments->getArgNames(), arguments->getArgs())) {
+      if (!verifyArgument(opArguments, name->getAsUnquotedString(), arg))
+        PrintWarning(
+            op->getLoc(),
+            "'" + clauseClassName + "' clause-defined argument '" +
+                arg->getAsUnquotedString() + ":$" +
+                name->getAsUnquotedString() +
+                "' not present in operation. Consider `dag arguments = "
+                "!con(clausesArgs, ...)` or explicitly skipping this field.");
+    }
+  }
+
+  if (!clause->getValueAsBit("ignoreAsmFormat") &&
+      !verifyStringValue("assemblyFormat", op, clause))
+    PrintWarning(
+        op->getLoc(),
+        "'" + clauseClassName +
+            "' clause-defined `assemblyFormat` not present in operation. "
+            "Consider concatenating `clausesAssemblyFormat` or explicitly "
+            "skipping this field.");
+
+  if (!clause->getValueAsBit("ignoreDesc") &&
+      !verifyStringValue("description", op, clause))
+    PrintError(op->getLoc(),
+               "'" + clauseClassName +
+                   "' clause-defined `description` not present in operation. "
+                   "Consider concatenating `clausesDescription` or explicitly "
+                   "skipping this field.");
+
+  if (!clause->getValueAsBit("ignoreExtraDecl") &&
+      !verifyStringValue("extraClassDeclaration", op, clause))
+    PrintWarning(
+        op->getLoc(),
+        "'" + clauseClassName +
+            "' clause-defined `extraClassDeclaration` not present in "
+            "operation. Consider concatenating `clausesExtraClassDeclaration` "
+            "or explicitly skipping this field.");
+}
+
+static bool verifyDecls(const RecordKeeper &recordKeeper, raw_ostream &) {
+  for (Record *op : recordKeeper.getAllDerivedDefinitions("OpenMP_Op")) {
+    for (Record *clause : op->getValueAsListOfDefs("clauseList"))
+      verifyClause(op, clause);
+  }
+
+  return false;
+}
+
+// Registers the generator to mlir-tblgen.
+static mlir::GenRegistration
+    verifyOpenmpOps("verify-openmp-ops",
+                    "Verify OpenMP operations (produce no output file)",
+                    verifyDecls);

[ftynse]

Hmm, will this generate a file called no-output, which will further me included into the MlirOpenMPOpsIncGen target below?

[skatrak]

Thank you for the quick review! I suppose it might do, though if that's the case it will always be empty. I'm not very familiar with how this infrastructure works, so I don't know if that could cause an issue. After a quick search I can't find a definition for add_public_tablegen_target to check this either 🤔.

Edit: Found it now, will check and get back if I can think of a better solution.

[skatrak]

I made some changes here that basically remove the empty "no-output" files from the build directory and also prevent it from being added as a dependency. It's admittedly a bit of a hack, but I don't know if it's worth the effort to refactor the mlir_tablegen and tablegen CMake functions to allow non-generators like this one, since it seems like something that won't be useful that often.

[ftynse]

Thanks for investigating! It's not a big issue if the file is still present, but better avoid it in dependencies. In case you get complains about windows builds where paths are different, feel free to drop the file removal and only keep the variable manipulation.

[skatrak]

Ping @ftynse, let me know if I addressed your concerns with my latest changes to the PR. Thank you for your time!