[MLIR][OpenMP] Add private clause to omp.parallel (#81452)

Extends the `omp.parallel` op by adding a `private` clause to model
[first]private variables. This uses the `omp.private` op to map
privatized variables to their corresponding privatizers.

Example `omp.private` op with `private` variable:
```
omp.parallel private(@x.privatizer %arg0 -> %arg1 : !llvm.ptr) {
  ^bb0(%arg1: !llvm.ptr):
    // ... use %arg1 ...
    omp.terminator
}
```

Whether the variable is private or firstprivate is determined by the
attributes of the corresponding `omp.private` op.

flang/lib/Lower/OpenMP.cpp

@@ -2640,7 +2640,8 @@ genParallelOp(Fortran::lower::AbstractConverter &converter,
           ? nullptr
           : mlir::ArrayAttr::get(converter.getFirOpBuilder().getContext(),
                                  reductionDeclSymbols),
-      procBindKindAttr);
+      procBindKindAttr, /*private_vars=*/llvm::SmallVector<mlir::Value>{},
+      /*privatizers=*/nullptr);
 }
 
 static mlir::omp::SectionOp

mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td

@@ -276,7 +276,9 @@ def ParallelOp : OpenMP_Op<"parallel", [
              Variadic<AnyType>:$allocators_vars,
              Variadic<OpenMP_PointerLikeType>:$reduction_vars,
              OptionalAttr<SymbolRefArrayAttr>:$reductions,
-             OptionalAttr<ProcBindKindAttr>:$proc_bind_val);
+             OptionalAttr<ProcBindKindAttr>:$proc_bind_val,
+             Variadic<AnyType>:$private_vars,
+             OptionalAttr<SymbolRefArrayAttr>:$privatizers);
 
   let regions = (region AnyRegion:$region);
 
@@ -297,7 +299,9 @@ def ParallelOp : OpenMP_Op<"parallel", [
                 $allocators_vars, type($allocators_vars)
               ) `)`
           | `proc_bind` `(` custom<ClauseAttr>($proc_bind_val) `)`
-    ) custom<ParallelRegion>($region, $reduction_vars, type($reduction_vars), $reductions) attr-dict
+    ) custom<ParallelRegion>($region, $reduction_vars, type($reduction_vars),
+                             $reductions, $private_vars, type($private_vars),
+                             $privatizers) attr-dict
   }];
   let hasVerifier = 1;
 }

mlir/lib/Conversion/SCFToOpenMP/SCFToOpenMP.cpp

@@ -450,7 +450,9 @@ struct ParallelOpLowering : public OpRewritePattern<scf::ParallelOp> {
         /* allocators_vars = */ llvm::SmallVector<Value>{},
         /* reduction_vars = */ llvm::SmallVector<Value>{},
         /* reductions = */ ArrayAttr{},
-        /* proc_bind_val = */ omp::ClauseProcBindKindAttr{});
+        /* proc_bind_val = */ omp::ClauseProcBindKindAttr{},
+        /* private_vars = */ ValueRange(),
+        /* privatizers = */ nullptr);
     {
 
       OpBuilder::InsertionGuard guard(rewriter);

mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp

@@ -430,68 +430,102 @@ static void printScheduleClause(OpAsmPrinter &p, Operation *op,
 // Parser, printer and verifier for ReductionVarList
 //===----------------------------------------------------------------------===//
 
-ParseResult
-parseReductionClause(OpAsmParser &parser, Region &region,
-                     SmallVectorImpl<OpAsmParser::UnresolvedOperand> &operands,
-                     SmallVectorImpl<Type> &types, ArrayAttr &reductionSymbols,
-                     SmallVectorImpl<OpAsmParser::Argument> &privates) {
-  if (failed(parser.parseOptionalKeyword("reduction")))
-    return failure();
-
+ParseResult parseClauseWithRegionArgs(
+    OpAsmParser &parser, Region &region,
+    SmallVectorImpl<OpAsmParser::UnresolvedOperand> &operands,
+    SmallVectorImpl<Type> &types, ArrayAttr &symbols,
+    SmallVectorImpl<OpAsmParser::Argument> &regionPrivateArgs) {
   SmallVector<SymbolRefAttr> reductionVec;
+  unsigned regionArgOffset = regionPrivateArgs.size();
 
   if (failed(
           parser.parseCommaSeparatedList(OpAsmParser::Delimiter::Paren, [&]() {
             if (parser.parseAttribute(reductionVec.emplace_back()) ||
                 parser.parseOperand(operands.emplace_back()) ||
                 parser.parseArrow() ||
-                parser.parseArgument(privates.emplace_back()) ||
+                parser.parseArgument(regionPrivateArgs.emplace_back()) ||
                 parser.parseColonType(types.emplace_back()))
               return failure();
             return success();
           })))
     return failure();
 
-  for (auto [prv, type] : llvm::zip_equal(privates, types)) {
+  auto *argsBegin = regionPrivateArgs.begin();
+  MutableArrayRef argsSubrange(argsBegin + regionArgOffset,
+                               argsBegin + regionArgOffset + types.size());
+  for (auto [prv, type] : llvm::zip_equal(argsSubrange, types)) {
     prv.type = type;
   }
   SmallVector<Attribute> reductions(reductionVec.begin(), reductionVec.end());
-  reductionSymbols = ArrayAttr::get(parser.getContext(), reductions);
+  symbols = ArrayAttr::get(parser.getContext(), reductions);
   return success();
 }
 
-static void printReductionClause(OpAsmPrinter &p, Operation *op,
-                                 ValueRange reductionArgs, ValueRange operands,
-                                 TypeRange types, ArrayAttr reductionSymbols) {
-  p << "reduction(";
+static void printClauseWithRegionArgs(OpAsmPrinter &p, Operation *op,
+                                      ValueRange argsSubrange,
+                                      StringRef clauseName, ValueRange operands,
+                                      TypeRange types, ArrayAttr symbols) {
+  p << clauseName << "(";
   llvm::interleaveComma(
-      llvm::zip_equal(reductionSymbols, operands, reductionArgs, types), p,
-      [&p](auto t) {
+      llvm::zip_equal(symbols, operands, argsSubrange, types), p, [&p](auto t) {
         auto [sym, op, arg, type] = t;
         p << sym << " " << op << " -> " << arg << " : " << type;
       });
   p << ") ";
 }
 
-static ParseResult
-parseParallelRegion(OpAsmParser &parser, Region &region,
-                    SmallVectorImpl<OpAsmParser::UnresolvedOperand> &operands,
-                    SmallVectorImpl<Type> &types, ArrayAttr &reductionSymbols) {
+static ParseResult parseParallelRegion(
+    OpAsmParser &parser, Region &region,
+    SmallVectorImpl<OpAsmParser::UnresolvedOperand> &reductionVarOperands,
+    SmallVectorImpl<Type> &reductionVarTypes, ArrayAttr &reductionSymbols,
+    llvm::SmallVectorImpl<OpAsmParser::UnresolvedOperand> &privateVarOperands,
+    llvm::SmallVectorImpl<Type> &privateVarsTypes,
+    ArrayAttr &privatizerSymbols) {
+  llvm::SmallVector<OpAsmParser::Argument> regionPrivateArgs;
 
-  llvm::SmallVector<OpAsmParser::Argument> privates;
-  if (succeeded(parseReductionClause(parser, region, operands, types,
-                                     reductionSymbols, privates)))
-    return parser.parseRegion(region, privates);
+  if (succeeded(parser.parseOptionalKeyword("reduction"))) {
+    if (failed(parseClauseWithRegionArgs(parser, region, reductionVarOperands,
+                                         reductionVarTypes, reductionSymbols,
+                                         regionPrivateArgs)))
+      return failure();
+  }
 
-  return parser.parseRegion(region);
+  if (succeeded(parser.parseOptionalKeyword("private"))) {
+    if (failed(parseClauseWithRegionArgs(parser, region, privateVarOperands,
+                                         privateVarsTypes, privatizerSymbols,
+                                         regionPrivateArgs)))
+      return failure();
+  }
+
+  return parser.parseRegion(region, regionPrivateArgs);
 }
 
 static void printParallelRegion(OpAsmPrinter &p, Operation *op, Region &region,
-                                ValueRange operands, TypeRange types,
-                                ArrayAttr reductionSymbols) {
-  if (reductionSymbols)
-    printReductionClause(p, op, region.front().getArguments(), operands, types,
-                         reductionSymbols);
+                                ValueRange reductionVarOperands,
+                                TypeRange reductionVarTypes,
+                                ArrayAttr reductionSymbols,
+                                ValueRange privateVarOperands,
+                                TypeRange privateVarTypes,
+                                ArrayAttr privatizerSymbols) {
+  if (reductionSymbols) {
+    auto *argsBegin = region.front().getArguments().begin();
+    MutableArrayRef argsSubrange(argsBegin,
+                                 argsBegin + reductionVarTypes.size());
+    printClauseWithRegionArgs(p, op, argsSubrange, "reduction",
+                              reductionVarOperands, reductionVarTypes,
+                              reductionSymbols);
+  }
+
+  if (privatizerSymbols) {
+    auto *argsBegin = region.front().getArguments().begin();
+    MutableArrayRef argsSubrange(argsBegin + reductionVarOperands.size(),
+                                 argsBegin + reductionVarOperands.size() +
+                                     privateVarTypes.size());
+    printClauseWithRegionArgs(p, op, argsSubrange, "private",
+                              privateVarOperands, privateVarTypes,
+                              privatizerSymbols);
+  }
+
   p.printRegion(region, /*printEntryBlockArgs=*/false);
 }
 
@@ -1174,14 +1208,64 @@ void ParallelOp::build(OpBuilder &builder, OperationState &state,
       builder, state, /*if_expr_var=*/nullptr, /*num_threads_var=*/nullptr,
       /*allocate_vars=*/ValueRange(), /*allocators_vars=*/ValueRange(),
       /*reduction_vars=*/ValueRange(), /*reductions=*/nullptr,
-      /*proc_bind_val=*/nullptr);
+      /*proc_bind_val=*/nullptr, /*private_vars=*/ValueRange(),
+      /*privatizers=*/nullptr);
   state.addAttributes(attributes);
 }
 
+template <typename OpType>
+static LogicalResult verifyPrivateVarList(OpType &op) {
+  auto privateVars = op.getPrivateVars();
+  auto privatizers = op.getPrivatizersAttr();
+
+  if (privateVars.empty() && (privatizers == nullptr || privatizers.empty()))
+    return success();
+
+  auto numPrivateVars = privateVars.size();
+  auto numPrivatizers = (privatizers == nullptr) ? 0 : privatizers.size();
+
+  if (numPrivateVars != numPrivatizers)
+    return op.emitError() << "inconsistent number of private variables and "
+                             "privatizer op symbols, private vars: "
+                          << numPrivateVars
+                          << " vs. privatizer op symbols: " << numPrivatizers;
+
+  for (auto privateVarInfo : llvm::zip_equal(privateVars, privatizers)) {
+    Type varType = std::get<0>(privateVarInfo).getType();
+    SymbolRefAttr privatizerSym =
+        std::get<1>(privateVarInfo).template cast<SymbolRefAttr>();
+    PrivateClauseOp privatizerOp =
+        SymbolTable::lookupNearestSymbolFrom<PrivateClauseOp>(op,
+                                                              privatizerSym);
+
+    if (privatizerOp == nullptr)
+      return op.emitError() << "failed to lookup privatizer op with symbol: '"
+                            << privatizerSym << "'";
+
+    Type privatizerType = privatizerOp.getType();
+
+    if (varType != privatizerType)
+      return op.emitError()
+             << "type mismatch between a "
+             << (privatizerOp.getDataSharingType() ==
+                         DataSharingClauseType::Private
+                     ? "private"
+                     : "firstprivate")
+             << " variable and its privatizer op, var type: " << varType
+             << " vs. privatizer op type: " << privatizerType;
+  }
+
+  return success();
+}
+
 LogicalResult ParallelOp::verify() {
   if (getAllocateVars().size() != getAllocatorsVars().size())
     return emitError(
         "expected equal sizes for allocate and allocator variables");
+
+  if (failed(verifyPrivateVarList(*this)))
+    return failure();
+
   return verifyReductionVarList(*this, getReductions(), getReductionVars());
 }
 
@@ -1279,9 +1363,10 @@ parseWsLoop(OpAsmParser &parser, Region &region,
 
   // Parse an optional reduction clause
   llvm::SmallVector<OpAsmParser::Argument> privates;
-  bool hasReduction = succeeded(
-      parseReductionClause(parser, region, reductionOperands, reductionTypes,
-                           reductionSymbols, privates));
+  bool hasReduction = succeeded(parser.parseOptionalKeyword("reduction")) &&
+                      succeeded(parseClauseWithRegionArgs(
+                          parser, region, reductionOperands, reductionTypes,
+                          reductionSymbols, privates));
 
   if (parser.parseKeyword("for"))
     return failure();
@@ -1328,8 +1413,9 @@ void printWsLoop(OpAsmPrinter &p, Operation *op, Region &region,
   if (reductionSymbols) {
     auto reductionArgs =
         region.front().getArguments().drop_front(loopVarTypes.size());
-    printReductionClause(p, op, reductionArgs, reductionOperands,
-                         reductionTypes, reductionSymbols);
+    printClauseWithRegionArgs(p, op, reductionArgs, "reduction",
+                              reductionOperands, reductionTypes,
+                              reductionSymbols);
   }
 
   p << " for ";

mlir/test/Dialect/OpenMP/invalid.mlir

@@ -1865,3 +1865,59 @@ omp.private {type = firstprivate} @x.privatizer : f32 alloc {
 ^bb0(%arg0: f32):
   omp.yield(%arg0 : f32)
 }
+
+// -----
+
+func.func @private_type_mismatch(%arg0: index) {
+// expected-error @below {{type mismatch between a private variable and its privatizer op, var type: 'index' vs. privatizer op type: '!llvm.ptr'}}
+  omp.parallel private(@var1.privatizer %arg0 -> %arg2 : index) {
+    omp.terminator
+  }
+
+  return
+}
+
+omp.private {type = private} @var1.privatizer : !llvm.ptr alloc {
+^bb0(%arg0: !llvm.ptr):
+  omp.yield(%arg0 : !llvm.ptr)
+}
+
+// -----
+
+func.func @firstprivate_type_mismatch(%arg0: index) {
+  // expected-error @below {{type mismatch between a firstprivate variable and its privatizer op, var type: 'index' vs. privatizer op type: '!llvm.ptr'}}
+  omp.parallel private(@var1.privatizer %arg0 -> %arg2 : index) {
+    omp.terminator
+  }
+
+  return
+}
+
+omp.private {type = firstprivate} @var1.privatizer : !llvm.ptr alloc {
+^bb0(%arg0: !llvm.ptr):
+  omp.yield(%arg0 : !llvm.ptr)
+} copy {
+^bb0(%arg0: !llvm.ptr, %arg1: !llvm.ptr):
+  omp.yield(%arg0 : !llvm.ptr)
+}
+
+// -----
+
+func.func @undefined_privatizer(%arg0: index) {
+  // expected-error @below {{failed to lookup privatizer op with symbol: '@var1.privatizer'}}
+  omp.parallel private(@var1.privatizer %arg0 -> %arg2 : index) {
+    omp.terminator
+  }
+
+  return
+}
+
+// -----
+func.func @undefined_privatizer(%arg0: !llvm.ptr) {
+  // expected-error @below {{inconsistent number of private variables and privatizer op symbols, private vars: 1 vs. privatizer op symbols: 2}}
+  "omp.parallel"(%arg0) <{operandSegmentSizes = array<i32: 0, 0, 0, 0, 0, 1>, privatizers = [@x.privatizer, @y.privatizer]}> ({
+    ^bb0(%arg2: !llvm.ptr):
+      omp.terminator
+    }) : (!llvm.ptr) -> ()
+  return
+}