[mlir][OpenMP] Add copyprivate support to omp.single

[luporl]

This adds a new custom CopyPrivateVarList to the single operation.
Each list item is formed by a reference to the variable to be
updated, its type and the function to be used to perform the copy.

It will be translated to LLVM IR using OpenMP builder, that will
use the information in the copyprivate list to call
__kmpc_copyprivate.

This is patch 2 of 4, to add support for COPYPRIVATE in Flang.
Original PR: #73128

[llvmbot]

@llvm/pr-subscribers-flang-fir-hlfir
@llvm/pr-subscribers-flang-openmp
@llvm/pr-subscribers-mlir-openmp

@llvm/pr-subscribers-mlir

Author: Leandro Lupori (luporl)

Changes

This adds a new custom CopyPrivateVarList to the single operation.
Each list item is formed by a reference to the variable to be
updated, its type and the function to be used to perform the copy.

It will be translated to LLVM IR using OpenMP builder, that will
use the information in the copyprivate list to call
__kmpc_copyprivate.

This is patch 2 of 4, to add support for COPYPRIVATE in Flang.
Original PR: #73128

---

Full diff: https://github.com/llvm/llvm-project/pull/80477.diff

5 Files Affected:

• (modified) flang/lib/Lower/OpenMP.cpp (+3-1)
• (modified) mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td (+10)
• (modified) mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp (+103-1)
• (modified) mlir/test/Dialect/OpenMP/invalid.mlir (+47-1)
• (modified) mlir/test/Dialect/OpenMP/ops.mlir (+17)

diff --git a/flang/lib/Lower/OpenMP.cpp b/flang/lib/Lower/OpenMP.cpp
index 7dd25f75d9eb7..34ebf2e91b6d8 100644
--- a/flang/lib/Lower/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP.cpp
@@ -2481,6 +2481,7 @@ genSingleOp(Fortran::lower::AbstractConverter &converter,
             const Fortran::parser::OmpClauseList &beginClauseList,
             const Fortran::parser::OmpClauseList &endClauseList) {
   llvm::SmallVector<mlir::Value> allocateOperands, allocatorOperands;
+  llvm::SmallVector<mlir::Value> copyPrivateVars;
   mlir::UnitAttr nowaitAttr;
 
   ClauseProcessor cp(converter, beginClauseList);
@@ -2493,7 +2494,8 @@ genSingleOp(Fortran::lower::AbstractConverter &converter,
   return genOpWithBody<mlir::omp::SingleOp>(
       converter, eval, genNested, currentLocation,
       /*outerCombined=*/false, &beginClauseList, allocateOperands,
-      allocatorOperands, nowaitAttr);
+      allocatorOperands, copyPrivateVars, /*copyPrivateFuncs=*/nullptr,
+      nowaitAttr);
 }
 
 static mlir::omp::TaskOp
diff --git a/mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td b/mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td
index d614f2666a85a..088327c35b44f 100644
--- a/mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td
+++ b/mlir/include/mlir/Dialect/OpenMP/OpenMPOps.td
@@ -387,10 +387,16 @@ def SingleOp : OpenMP_Op<"single", [AttrSizedOperandSegments]> {
     master thread), in the context of its implicit task. The other threads
     in the team, which do not execute the block, wait at an implicit barrier
     at the end of the single construct unless a nowait clause is specified.
+
+    If copyprivate variables and functions are specified, then each thread
+    variable is updated with the variable value of the thread that executed
+    the single region, using the specified copy functions.
   }];
 
   let arguments = (ins Variadic<AnyType>:$allocate_vars,
                        Variadic<AnyType>:$allocators_vars,
+                       Variadic<OpenMP_PointerLikeType>:$copyprivate_vars,
+                       OptionalAttr<SymbolRefArrayAttr>:$copyprivate_funcs,
                        UnitAttr:$nowait);
 
   let regions = (region AnyRegion:$region);
@@ -402,6 +408,10 @@ def SingleOp : OpenMP_Op<"single", [AttrSizedOperandSegments]> {
                 $allocators_vars, type($allocators_vars)
               ) `)`
           |`nowait` $nowait
+          |`copyprivate` `(`
+              custom<CopyPrivateVarList>(
+                $copyprivate_vars, type($copyprivate_vars), $copyprivate_funcs
+              ) `)`
     ) $region attr-dict
   }];
   let hasVerifier = 1;
diff --git a/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp b/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp
index 2d3be76c65e81..b64391fb248ba 100644
--- a/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp
+++ b/mlir/lib/Dialect/OpenMP/IR/OpenMPDialect.cpp
@@ -505,6 +505,107 @@ static LogicalResult verifyReductionVarList(Operation *op,
   return success();
 }
 
+//===----------------------------------------------------------------------===//
+// Parser, printer and verifier for CopyPrivateVarList
+//===----------------------------------------------------------------------===//
+
+/// copyprivate-entry-list ::= copyprivate-entry
+///                          | copyprivate-entry-list `,` copyprivate-entry
+/// copyprivate-entry ::= ssa-id `->` symbol-ref `:` type
+static ParseResult parseCopyPrivateVarList(
+    OpAsmParser &parser,
+    SmallVectorImpl<OpAsmParser::UnresolvedOperand> &operands,
+    SmallVectorImpl<Type> &types, ArrayAttr &copyPrivateSymbols) {
+  SmallVector<SymbolRefAttr> copyPrivateFuncsVec;
+  if (failed(parser.parseCommaSeparatedList([&]() {
+        if (parser.parseOperand(operands.emplace_back()) ||
+            parser.parseArrow() ||
+            parser.parseAttribute(copyPrivateFuncsVec.emplace_back()) ||
+            parser.parseColonType(types.emplace_back()))
+          return failure();
+        return success();
+      })))
+    return failure();
+  SmallVector<Attribute> copyPrivateFuncs(copyPrivateFuncsVec.begin(),
+                                          copyPrivateFuncsVec.end());
+  copyPrivateSymbols = ArrayAttr::get(parser.getContext(), copyPrivateFuncs);
+  return success();
+}
+
+/// Print CopyPrivate clause
+static void printCopyPrivateVarList(OpAsmPrinter &p, Operation *op,
+                                    OperandRange copyPrivateVars,
+                                    TypeRange copyPrivateTypes,
+                                    std::optional<ArrayAttr> copyPrivateFuncs) {
+  assert(copyPrivateFuncs.has_value() || copyPrivateVars.empty());
+  for (unsigned i = 0, e = copyPrivateVars.size(); i < e; ++i) {
+    if (i != 0)
+      p << ", ";
+    p << copyPrivateVars[i] << " -> " << (*copyPrivateFuncs)[i] << " : "
+      << copyPrivateTypes[i];
+  }
+}
+
+/// Verifies CopyPrivate Clause
+static LogicalResult
+verifyCopyPrivateVarList(Operation *op, OperandRange copyPrivateVars,
+                         std::optional<ArrayAttr> copyPrivateFuncs) {
+  if (!copyPrivateVars.empty()) {
+    if (!copyPrivateFuncs || copyPrivateFuncs->size() != copyPrivateVars.size())
+      return op->emitOpError() << "expected as many copyPrivate functions as "
+                                  "copyPrivate variables";
+  } else {
+    if (copyPrivateFuncs)
+      return op->emitOpError() << "unexpected copyPrivate functions";
+    return success();
+  }
+
+  for (auto args : llvm::zip(copyPrivateVars, *copyPrivateFuncs)) {
+    auto symbolRef = llvm::cast<SymbolRefAttr>(std::get<1>(args));
+    std::optional<std::variant<mlir::func::FuncOp, mlir::LLVM::LLVMFuncOp>>
+        funcOp;
+    if (mlir::func::FuncOp mlirFuncOp =
+            SymbolTable::lookupNearestSymbolFrom<mlir::func::FuncOp>(op,
+                                                                     symbolRef))
+      funcOp = mlirFuncOp;
+    else if (mlir::LLVM::LLVMFuncOp llvmFuncOp =
+                 SymbolTable::lookupNearestSymbolFrom<mlir::LLVM::LLVMFuncOp>(
+                     op, symbolRef))
+      funcOp = llvmFuncOp;
+
+    auto getNumArguments = [&] {
+      return std::visit([](auto &f) { return f.getNumArguments(); }, *funcOp);
+    };
+
+    auto getArgumentType = [&](unsigned i) {
+      return std::visit([i](auto &f) { return f.getArgumentTypes()[i]; },
+                        *funcOp);
+    };
+
+    if (!funcOp)
+      return op->emitOpError() << "expected symbol reference " << symbolRef
+                               << " to point to a copy function";
+
+    if (getNumArguments() != 2)
+      return op->emitOpError()
+             << "expected copy function " << symbolRef << " to have 2 operands";
+
+    Type argTy = getArgumentType(0);
+    if (argTy != getArgumentType(1))
+      return op->emitOpError() << "expected copy function " << symbolRef
+                               << " arguments to have the same type";
+
+    Type varType = std::get<0>(args).getType();
+    if (argTy != varType)
+      return op->emitOpError()
+             << "expected copy function arguments' type (" << argTy
+             << ") to be the same as copyprivate variable's type (" << varType
+             << ")";
+  }
+
+  return success();
+}
+
 //===----------------------------------------------------------------------===//
 // Parser, printer and verifier for DependVarList
 //===----------------------------------------------------------------------===//
@@ -1072,7 +1173,8 @@ LogicalResult SingleOp::verify() {
     return emitError(
         "expected equal sizes for allocate and allocator variables");
 
-  return success();
+  return verifyCopyPrivateVarList(*this, getCopyprivateVars(),
+                                  getCopyprivateFuncs());
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/Dialect/OpenMP/invalid.mlir b/mlir/test/Dialect/OpenMP/invalid.mlir
index 2b0e86ddd22bb..2089cbccc9c2d 100644
--- a/mlir/test/Dialect/OpenMP/invalid.mlir
+++ b/mlir/test/Dialect/OpenMP/invalid.mlir
@@ -1284,7 +1284,53 @@ func.func @omp_single(%data_var : memref<i32>) -> () {
   // expected-error @below {{expected equal sizes for allocate and allocator variables}}
   "omp.single" (%data_var) ({
     omp.barrier
-  }) {operandSegmentSizes = array<i32: 1,0>} : (memref<i32>) -> ()
+  }) {operandSegmentSizes = array<i32: 1,0,0>} : (memref<i32>) -> ()
+  return
+}
+
+// -----
+
+func.func @omp_single_copyprivate(%data_var : memref<i32>) -> () {
+  // expected-error @below {{expected symbol reference @copy_func to point to a copy function}}
+  omp.single copyprivate(%data_var -> @copy_func : memref<i32>) {
+    omp.barrier
+  }
+  return
+}
+
+// -----
+
+func.func private @copy_func(memref<i32>)
+
+func.func @omp_single_copyprivate(%data_var : memref<i32>) -> () {
+  // expected-error @below {{expected copy function @copy_func to have 2 operands}}
+  omp.single copyprivate(%data_var -> @copy_func : memref<i32>) {
+    omp.barrier
+  }
+  return
+}
+
+// -----
+
+func.func private @copy_func(memref<i32>, memref<f32>)
+
+func.func @omp_single_copyprivate(%data_var : memref<i32>) -> () {
+  // expected-error @below {{expected copy function @copy_func arguments to have the same type}}
+  omp.single copyprivate(%data_var -> @copy_func : memref<i32>) {
+    omp.barrier
+  }
+  return
+}
+
+// -----
+
+func.func private @copy_func(memref<f32>, memref<f32>)
+
+func.func @omp_single_copyprivate(%data_var : memref<i32>) -> () {
+  // expected-error @below {{expected copy function arguments' type ('memref<f32>') to be the same as copyprivate variable's type ('memref<i32>')}}
+  omp.single copyprivate(%data_var -> @copy_func : memref<i32>) {
+    omp.barrier
+  }
   return
 }
 
diff --git a/mlir/test/Dialect/OpenMP/ops.mlir b/mlir/test/Dialect/OpenMP/ops.mlir
index 3d4f6435572f7..af7879652a1a9 100644
--- a/mlir/test/Dialect/OpenMP/ops.mlir
+++ b/mlir/test/Dialect/OpenMP/ops.mlir
@@ -1577,6 +1577,23 @@ func.func @omp_single_multiple_blocks() {
   return
 }
 
+func.func private @copy_i32(memref<i32>, memref<i32>)
+
+// CHECK-LABEL: func @omp_single_copyprivate
+func.func @omp_single_copyprivate(%data_var: memref<i32>) {
+  omp.parallel {
+    // CHECK: omp.single copyprivate(%{{.*}} -> @copy_i32 : memref<i32>) {
+    omp.single copyprivate(%data_var -> @copy_i32 : memref<i32>) {
+      "test.payload"() : () -> ()
+      // CHECK: omp.terminator
+      omp.terminator
+    }
+    // CHECK: omp.terminator
+    omp.terminator
+  }
+  return
+}
+
 // CHECK-LABEL: @omp_task
 // CHECK-SAME: (%[[bool_var:.*]]: i1, %[[i64_var:.*]]: i64, %[[i32_var:.*]]: i32, %[[data_var:.*]]: memref<i32>)
 func.func @omp_task(%bool_var: i1, %i64_var: i64, %i32_var: i32, %data_var: memref<i32>) {

[kiranchandramohan]

Looks OK. Have a few comments inline.

[kiranchandramohan]

LG.

[luporl]

Thanks for the reviews @kiranchandramohan and @ergawy !