[flang][OpenMP][NFC] Move reduction init and cleanup region gen to helper

[tblah]

This will allow code sharing between reduction and privatization after my (still WIP) changes to omp.private to use an alloc region similar to the one used for reduction declarations.

[llvmbot]

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

Author: Tom Eccles (tblah)

Changes

This will allow code sharing between reduction and privatization after my (still WIP) changes to omp.private to use an alloc region similar to the one used for reduction declarations.

---

Patch is 23.66 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/120761.diff

4 Files Affected:

• (modified) flang/lib/Lower/CMakeLists.txt (+1)
• (added) flang/lib/Lower/OpenMP/PrivateReductionUtils.cpp (+237)
• (added) flang/lib/Lower/OpenMP/PrivateReductionUtils.h (+51)
• (modified) flang/lib/Lower/OpenMP/ReductionProcessor.cpp (+16-218)

diff --git a/flang/lib/Lower/CMakeLists.txt b/flang/lib/Lower/CMakeLists.txt
index ba6622d8504a4f..f57f0e7a77a018 100644
--- a/flang/lib/Lower/CMakeLists.txt
+++ b/flang/lib/Lower/CMakeLists.txt
@@ -29,6 +29,7 @@ add_flang_library(FortranLower
   OpenMP/DataSharingProcessor.cpp
   OpenMP/Decomposer.cpp
   OpenMP/OpenMP.cpp
+  OpenMP/PrivateReductionUtils.cpp
   OpenMP/ReductionProcessor.cpp
   OpenMP/Utils.cpp
   PFTBuilder.cpp
diff --git a/flang/lib/Lower/OpenMP/PrivateReductionUtils.cpp b/flang/lib/Lower/OpenMP/PrivateReductionUtils.cpp
new file mode 100644
index 00000000000000..e6b5bde999f877
--- /dev/null
+++ b/flang/lib/Lower/OpenMP/PrivateReductionUtils.cpp
@@ -0,0 +1,237 @@
+//===-- PrivateReductionUtils.cpp -------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Coding style: https://mlir.llvm.org/getting_started/DeveloperGuide/
+//
+//===----------------------------------------------------------------------===//
+
+#include "PrivateReductionUtils.h"
+
+#include "flang/Optimizer/Builder/FIRBuilder.h"
+#include "flang/Optimizer/Builder/HLFIRTools.h"
+#include "flang/Optimizer/Builder/Todo.h"
+#include "flang/Optimizer/HLFIR/HLFIROps.h"
+#include "flang/Optimizer/Support/FatalError.h"
+#include "mlir/Dialect/OpenMP/OpenMPDialect.h"
+#include "mlir/IR/Location.h"
+#include <mlir/IR/Value.h>
+
+static void createCleanupRegion(fir::FirOpBuilder &builder, mlir::Location loc,
+                                mlir::Type argType,
+                                mlir::Region &cleanupRegion) {
+  assert(cleanupRegion.empty());
+  mlir::Block *block = builder.createBlock(&cleanupRegion, cleanupRegion.end(),
+                                           {argType}, {loc});
+  builder.setInsertionPointToEnd(block);
+
+  auto typeError = [loc]() {
+    fir::emitFatalError(loc,
+                        "Attempt to create an omp cleanup region "
+                        "for a type that wasn't allocated",
+                        /*genCrashDiag=*/true);
+  };
+
+  mlir::Type valTy = fir::unwrapRefType(argType);
+  if (auto boxTy = mlir::dyn_cast_or_null<fir::BaseBoxType>(valTy)) {
+    if (!mlir::isa<fir::HeapType, fir::PointerType>(boxTy.getEleTy())) {
+      mlir::Type innerTy = fir::extractSequenceType(boxTy);
+      if (!mlir::isa<fir::SequenceType>(innerTy))
+        typeError();
+    }
+
+    mlir::Value arg = builder.loadIfRef(loc, block->getArgument(0));
+    assert(mlir::isa<fir::BaseBoxType>(arg.getType()));
+
+    // Deallocate box
+    // The FIR type system doesn't nesecarrily know that this is a mutable box
+    // if we allocated the thread local array on the heap to avoid looped stack
+    // allocations.
+    mlir::Value addr =
+        hlfir::genVariableRawAddress(loc, builder, hlfir::Entity{arg});
+    mlir::Value isAllocated = builder.genIsNotNullAddr(loc, addr);
+    fir::IfOp ifOp =
+        builder.create<fir::IfOp>(loc, isAllocated, /*withElseRegion=*/false);
+    builder.setInsertionPointToStart(&ifOp.getThenRegion().front());
+
+    mlir::Value cast = builder.createConvert(
+        loc, fir::HeapType::get(fir::dyn_cast_ptrEleTy(addr.getType())), addr);
+    builder.create<fir::FreeMemOp>(loc, cast);
+
+    builder.setInsertionPointAfter(ifOp);
+    builder.create<mlir::omp::YieldOp>(loc);
+    return;
+  }
+
+  typeError();
+}
+
+fir::ShapeShiftOp Fortran::lower::omp::getShapeShift(fir::FirOpBuilder &builder,
+                                                     mlir::Location loc,
+                                                     mlir::Value box) {
+  fir::SequenceType sequenceType = mlir::cast<fir::SequenceType>(
+      hlfir::getFortranElementOrSequenceType(box.getType()));
+  const unsigned rank = sequenceType.getDimension();
+  llvm::SmallVector<mlir::Value> lbAndExtents;
+  lbAndExtents.reserve(rank * 2);
+
+  mlir::Type idxTy = builder.getIndexType();
+  for (unsigned i = 0; i < rank; ++i) {
+    // TODO: ideally we want to hoist box reads out of the critical section.
+    // We could do this by having box dimensions in block arguments like
+    // OpenACC does
+    mlir::Value dim = builder.createIntegerConstant(loc, idxTy, i);
+    auto dimInfo =
+        builder.create<fir::BoxDimsOp>(loc, idxTy, idxTy, idxTy, box, dim);
+    lbAndExtents.push_back(dimInfo.getLowerBound());
+    lbAndExtents.push_back(dimInfo.getExtent());
+  }
+
+  auto shapeShiftTy = fir::ShapeShiftType::get(builder.getContext(), rank);
+  auto shapeShift =
+      builder.create<fir::ShapeShiftOp>(loc, shapeShiftTy, lbAndExtents);
+  return shapeShift;
+}
+
+void Fortran::lower::omp::populateByRefInitAndCleanupRegions(
+    fir::FirOpBuilder &builder, mlir::Location loc, mlir::Type argType,
+    mlir::Value scalarInitValue, mlir::Block *initBlock,
+    mlir::Value allocatedPrivVarArg, mlir::Value moldArg,
+    mlir::Region &cleanupRegion) {
+  mlir::Type ty = fir::unwrapRefType(argType);
+  builder.setInsertionPointToEnd(initBlock);
+  auto yield = [&](mlir::Value ret) {
+    builder.create<mlir::omp::YieldOp>(loc, ret);
+  };
+
+  if (fir::isa_trivial(ty)) {
+    builder.setInsertionPointToEnd(initBlock);
+
+    if (scalarInitValue)
+      builder.createStoreWithConvert(loc, scalarInitValue, allocatedPrivVarArg);
+    yield(allocatedPrivVarArg);
+    return;
+  }
+
+  // check if an allocatable box is unallocated. If so, initialize the boxAlloca
+  // to be unallocated e.g.
+  // %box_alloca = fir.alloca !fir.box<!fir.heap<...>>
+  // %addr = fir.box_addr %box
+  // if (%addr == 0) {
+  //   %nullbox = fir.embox %addr
+  //   fir.store %nullbox to %box_alloca
+  // } else {
+  //   // ...
+  //   fir.store %something to %box_alloca
+  // }
+  // omp.yield %box_alloca
+  moldArg = builder.loadIfRef(loc, moldArg);
+  auto handleNullAllocatable = [&](mlir::Value boxAlloca) -> fir::IfOp {
+    mlir::Value addr = builder.create<fir::BoxAddrOp>(loc, moldArg);
+    mlir::Value isNotAllocated = builder.genIsNullAddr(loc, addr);
+    fir::IfOp ifOp = builder.create<fir::IfOp>(loc, isNotAllocated,
+                                               /*withElseRegion=*/true);
+    builder.setInsertionPointToStart(&ifOp.getThenRegion().front());
+    // just embox the null address and return
+    mlir::Value nullBox = builder.create<fir::EmboxOp>(loc, ty, addr);
+    builder.create<fir::StoreOp>(loc, nullBox, boxAlloca);
+    return ifOp;
+  };
+
+  // all arrays are boxed
+  if (auto boxTy = mlir::dyn_cast_or_null<fir::BaseBoxType>(ty)) {
+    bool isAllocatableOrPointer =
+        mlir::isa<fir::HeapType, fir::PointerType>(boxTy.getEleTy());
+
+    builder.setInsertionPointToEnd(initBlock);
+    mlir::Value boxAlloca = allocatedPrivVarArg;
+    mlir::Type innerTy = fir::unwrapRefType(boxTy.getEleTy());
+    if (fir::isa_trivial(innerTy)) {
+      // boxed non-sequence value e.g. !fir.box<!fir.heap<i32>>
+      if (!isAllocatableOrPointer)
+        TODO(loc,
+             "Reduction/Privatization of non-allocatable trivial typed box");
+
+      fir::IfOp ifUnallocated = handleNullAllocatable(boxAlloca);
+
+      builder.setInsertionPointToStart(&ifUnallocated.getElseRegion().front());
+      mlir::Value valAlloc = builder.create<fir::AllocMemOp>(loc, innerTy);
+      if (scalarInitValue)
+        builder.createStoreWithConvert(loc, scalarInitValue, valAlloc);
+      mlir::Value box = builder.create<fir::EmboxOp>(loc, ty, valAlloc);
+      builder.create<fir::StoreOp>(loc, box, boxAlloca);
+
+      createCleanupRegion(builder, loc, argType, cleanupRegion);
+      builder.setInsertionPointAfter(ifUnallocated);
+      yield(boxAlloca);
+      return;
+    }
+    innerTy = fir::extractSequenceType(boxTy);
+    if (!mlir::isa<fir::SequenceType>(innerTy))
+      TODO(loc, "Unsupported boxed type for reduction/privatization");
+
+    fir::IfOp ifUnallocated{nullptr};
+    if (isAllocatableOrPointer) {
+      ifUnallocated = handleNullAllocatable(boxAlloca);
+      builder.setInsertionPointToStart(&ifUnallocated.getElseRegion().front());
+    }
+
+    // Create the private copy from the initial fir.box:
+    mlir::Value loadedBox = builder.loadIfRef(loc, moldArg);
+    hlfir::Entity source = hlfir::Entity{loadedBox};
+
+    // Allocating on the heap in case the whole reduction is nested inside of a
+    // loop
+    // TODO: compare performance here to using allocas - this could be made to
+    // work by inserting stacksave/stackrestore around the reduction in
+    // openmpirbuilder
+    auto [temp, needsDealloc] = createTempFromMold(loc, builder, source);
+    // if needsDealloc isn't statically false, add cleanup region. Always
+    // do this for allocatable boxes because they might have been re-allocated
+    // in the body of the loop/parallel region
+
+    std::optional<int64_t> cstNeedsDealloc =
+        fir::getIntIfConstant(needsDealloc);
+    assert(cstNeedsDealloc.has_value() &&
+           "createTempFromMold decides this statically");
+    if (cstNeedsDealloc.has_value() && *cstNeedsDealloc != false) {
+      mlir::OpBuilder::InsertionGuard guard(builder);
+      createCleanupRegion(builder, loc, argType, cleanupRegion);
+    } else {
+      assert(!isAllocatableOrPointer &&
+             "Pointer-like arrays must be heap allocated");
+    }
+
+    // Put the temporary inside of a box:
+    // hlfir::genVariableBox doesn't handle non-default lower bounds
+    mlir::Value box;
+    fir::ShapeShiftOp shapeShift = getShapeShift(builder, loc, loadedBox);
+    mlir::Type boxType = loadedBox.getType();
+    if (mlir::isa<fir::BaseBoxType>(temp.getType()))
+      // the box created by the declare form createTempFromMold is missing lower
+      // bounds info
+      box = builder.create<fir::ReboxOp>(loc, boxType, temp, shapeShift,
+                                         /*shift=*/mlir::Value{});
+    else
+      box = builder.create<fir::EmboxOp>(
+          loc, boxType, temp, shapeShift,
+          /*slice=*/mlir::Value{},
+          /*typeParams=*/llvm::ArrayRef<mlir::Value>{});
+
+    if (scalarInitValue)
+      builder.create<hlfir::AssignOp>(loc, scalarInitValue, box);
+    builder.create<fir::StoreOp>(loc, box, boxAlloca);
+    if (ifUnallocated)
+      builder.setInsertionPointAfter(ifUnallocated);
+    yield(boxAlloca);
+    return;
+  }
+
+  TODO(loc,
+       "creating reduction/privatization init region for unsupported type");
+  return;
+}
\ No newline at end of file
diff --git a/flang/lib/Lower/OpenMP/PrivateReductionUtils.h b/flang/lib/Lower/OpenMP/PrivateReductionUtils.h
new file mode 100644
index 00000000000000..b0d854584a700c
--- /dev/null
+++ b/flang/lib/Lower/OpenMP/PrivateReductionUtils.h
@@ -0,0 +1,51 @@
+//===-- Lower/OpenMP/PrivateReductionUtils.h --------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Coding style: https://mlir.llvm.org/getting_started/DeveloperGuide/
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FORTRAN_LOWER_OPENMP_PRIVATEREDUCTIONUTILS_H
+#define FORTRAN_LOWER_OPENMP_PRIVATEREDUCTIONUTILS_H
+
+#include "mlir/IR/Location.h"
+#include "mlir/IR/Value.h"
+
+namespace mlir {
+class Region;
+} // namespace mlir
+
+namespace fir {
+class FirOpBuilder;
+class ShapeShiftOp;
+} // namespace fir
+
+namespace Fortran {
+namespace lower {
+namespace omp {
+
+/// Generate init and cleanup regions suitable for reduction or privatizer
+/// declarations. `scalarInitValue` may be nullptr if there is no default
+/// initialization (for privatization).
+void populateByRefInitAndCleanupRegions(fir::FirOpBuilder &builder,
+                                        mlir::Location loc, mlir::Type argType,
+                                        mlir::Value scalarInitValue,
+                                        mlir::Block *initBlock,
+                                        mlir::Value allocatedPrivVarArg,
+                                        mlir::Value moldArg,
+                                        mlir::Region &cleanupRegion);
+
+/// Generate a fir::ShapeShift op describing the provided boxed array.
+fir::ShapeShiftOp getShapeShift(fir::FirOpBuilder &builder, mlir::Location loc,
+                                mlir::Value box);
+
+} // namespace omp
+} // namespace lower
+} // namespace Fortran
+
+#endif // FORTRAN_LOWER_OPENMP_PRIVATEREDUCTIONUTILS_H
\ No newline at end of file
diff --git a/flang/lib/Lower/OpenMP/ReductionProcessor.cpp b/flang/lib/Lower/OpenMP/ReductionProcessor.cpp
index 736de2ee511bef..2cd21107a916e4 100644
--- a/flang/lib/Lower/OpenMP/ReductionProcessor.cpp
+++ b/flang/lib/Lower/OpenMP/ReductionProcessor.cpp
@@ -12,6 +12,7 @@
 
 #include "ReductionProcessor.h"
 
+#include "PrivateReductionUtils.h"
 #include "flang/Lower/AbstractConverter.h"
 #include "flang/Lower/ConvertType.h"
 #include "flang/Lower/SymbolMap.h"
@@ -294,33 +295,6 @@ mlir::Value ReductionProcessor::createScalarCombiner(
   return reductionOp;
 }
 
-/// Generate a fir::ShapeShift op describing the provided boxed array.
-static fir::ShapeShiftOp getShapeShift(fir::FirOpBuilder &builder,
-                                       mlir::Location loc, mlir::Value box) {
-  fir::SequenceType sequenceType = mlir::cast<fir::SequenceType>(
-      hlfir::getFortranElementOrSequenceType(box.getType()));
-  const unsigned rank = sequenceType.getDimension();
-  llvm::SmallVector<mlir::Value> lbAndExtents;
-  lbAndExtents.reserve(rank * 2);
-
-  mlir::Type idxTy = builder.getIndexType();
-  for (unsigned i = 0; i < rank; ++i) {
-    // TODO: ideally we want to hoist box reads out of the critical section.
-    // We could do this by having box dimensions in block arguments like
-    // OpenACC does
-    mlir::Value dim = builder.createIntegerConstant(loc, idxTy, i);
-    auto dimInfo =
-        builder.create<fir::BoxDimsOp>(loc, idxTy, idxTy, idxTy, box, dim);
-    lbAndExtents.push_back(dimInfo.getLowerBound());
-    lbAndExtents.push_back(dimInfo.getExtent());
-  }
-
-  auto shapeShiftTy = fir::ShapeShiftType::get(builder.getContext(), rank);
-  auto shapeShift =
-      builder.create<fir::ShapeShiftOp>(loc, shapeShiftTy, lbAndExtents);
-  return shapeShift;
-}
-
 /// Create reduction combiner region for reduction variables which are boxed
 /// arrays
 static void genBoxCombiner(fir::FirOpBuilder &builder, mlir::Location loc,
@@ -422,59 +396,6 @@ static void genCombiner(fir::FirOpBuilder &builder, mlir::Location loc,
   TODO(loc, "OpenMP genCombiner for unsupported reduction variable type");
 }
 
-static void
-createReductionCleanupRegion(fir::FirOpBuilder &builder, mlir::Location loc,
-                             mlir::omp::DeclareReductionOp &reductionDecl) {
-  mlir::Type redTy = reductionDecl.getType();
-
-  mlir::Region &cleanupRegion = reductionDecl.getCleanupRegion();
-  assert(cleanupRegion.empty());
-  mlir::Block *block =
-      builder.createBlock(&cleanupRegion, cleanupRegion.end(), {redTy}, {loc});
-  builder.setInsertionPointToEnd(block);
-
-  auto typeError = [loc]() {
-    fir::emitFatalError(loc,
-                        "Attempt to create an omp reduction cleanup region "
-                        "for a type that wasn't allocated",
-                        /*genCrashDiag=*/true);
-  };
-
-  mlir::Type valTy = fir::unwrapRefType(redTy);
-  if (auto boxTy = mlir::dyn_cast_or_null<fir::BaseBoxType>(valTy)) {
-    if (!mlir::isa<fir::HeapType, fir::PointerType>(boxTy.getEleTy())) {
-      mlir::Type innerTy = fir::extractSequenceType(boxTy);
-      if (!mlir::isa<fir::SequenceType>(innerTy))
-        typeError();
-    }
-
-    mlir::Value arg = block->getArgument(0);
-    arg = builder.loadIfRef(loc, arg);
-    assert(mlir::isa<fir::BaseBoxType>(arg.getType()));
-
-    // Deallocate box
-    // The FIR type system doesn't nesecarrily know that this is a mutable box
-    // if we allocated the thread local array on the heap to avoid looped stack
-    // allocations.
-    mlir::Value addr =
-        hlfir::genVariableRawAddress(loc, builder, hlfir::Entity{arg});
-    mlir::Value isAllocated = builder.genIsNotNullAddr(loc, addr);
-    fir::IfOp ifOp =
-        builder.create<fir::IfOp>(loc, isAllocated, /*withElseRegion=*/false);
-    builder.setInsertionPointToStart(&ifOp.getThenRegion().front());
-
-    mlir::Value cast = builder.createConvert(
-        loc, fir::HeapType::get(fir::dyn_cast_ptrEleTy(addr.getType())), addr);
-    builder.create<fir::FreeMemOp>(loc, cast);
-
-    builder.setInsertionPointAfter(ifOp);
-    builder.create<mlir::omp::YieldOp>(loc);
-    return;
-  }
-
-  typeError();
-}
-
 // like fir::unwrapSeqOrBoxedSeqType except it also works for non-sequence boxes
 static mlir::Type unwrapSeqOrBoxedType(mlir::Type ty) {
   if (auto seqTy = mlir::dyn_cast<fir::SequenceType>(ty))
@@ -517,154 +438,31 @@ static void createReductionAllocAndInitRegions(
   mlir::Value initValue = ReductionProcessor::getReductionInitValue(
       loc, unwrapSeqOrBoxedType(ty), redId, builder);
 
+  if (isByRef) {
+    populateByRefInitAndCleanupRegions(builder, loc, type, initValue, initBlock,
+                                       reductionDecl.getInitializerAllocArg(),
+                                       reductionDecl.getInitializerMoldArg(),
+                                       reductionDecl.getCleanupRegion());
+  }
+
   if (fir::isa_trivial(ty)) {
     if (isByRef) {
       // alloc region
-      {
-        builder.setInsertionPointToEnd(allocBlock);
-        mlir::Value alloca = builder.create<fir::AllocaOp>(loc, ty);
-        yield(alloca);
-      }
-
-      // init region
-      {
-        builder.setInsertionPointToEnd(initBlock);
-        // block arg is mapped to the alloca yielded from the alloc region
-        mlir::Value alloc = reductionDecl.getInitializerAllocArg();
-        builder.createStoreWithConvert(loc, initValue, alloc);
-        yield(alloc);
-      }
+      builder.setInsertionPointToEnd(allocBlock);
+      mlir::Value alloca = builder.create<fir::AllocaOp>(loc, ty);
+      yield(alloca);
       return;
     }
     // by val
     yield(initValue);
     return;
   }
+  assert(isByRef && "passing non-trivial types by val is unsupported");
 
-  // check if an allocatable box is unallocated. If so, initialize the boxAlloca
-  // to be unallocated e.g.
-  // %box_alloca = fir.alloca !fir.box<!fir.heap<...>>
-  // %addr = fir.box_addr %box
-  // if (%addr == 0) {
-  //   %nullbox = fir.embox %addr
-  //   fir.store %nullbox to %box_alloca
-  // } else {
-  //   // ...
-  //   fir.store %something to %box_alloca
-  // }
-  // omp.yield %box_alloca
-  mlir::Value moldArg =
-      builder.loadIfRef(loc, reductionDecl.getInitializerMoldArg());
-  auto handleNullAllocatable = [&](mlir::Value boxAlloca) -> fir::IfOp {
-    mlir::Value addr = builder.create<fir::BoxAddrOp>(loc, moldArg);
-    mlir::Value isNotAllocated = builder.genIsNullAddr(loc, addr);
-    fir::IfOp ifOp = builder.create<fir::IfOp>(loc, isNotAllocated,
-                                               /*withElseRegion=*/true);
-    builder.setInsertionPointToStart(&ifOp.getThenRegion().front());
-    // just embox the null address and return
-    mlir::Value nullBox = builder.create<fir::EmboxOp>(loc, ty, addr);
-    builder.create<fir::StoreOp>(loc, nullBox, boxAlloca);
-    return ifOp;
-  };
-
-  // all arrays are boxed
-  if (auto boxTy = mlir::dyn_cast_or_null<fir::BaseBoxType>(ty)) {
-    assert(isByRef && "passing boxes by value is unsupported");
-    bool isAllocatableOrPointer =
-        mlir::isa<fir::HeapType, fir::PointerType>(boxTy.getEleTy());
-
-    // alloc region
-    {
-      builder.setInsertionPointToEnd(allocBlock);
-      mlir::Value boxAlloca = builder.create<fir::AllocaOp>(loc, ty);
-      yield(boxAlloca);
-    }
-
-    // init region
-    builder.setInsertionPointToEnd(initBlock);
-    mlir::Value boxAlloca = reductionDecl.getInitializerAllocArg();
-    mlir::Type innerTy = fir::unwrapRefType(boxTy.getEleTy());
-    if (fir::isa_trivial(innerTy)) {
-      // ...
[truncated]

[ergawy]

LGTM. Just a small question to make sure no behavior changed due to refactoring.

[ergawy]

I think this store is unconditional in the deleted version of the code, right?

[tblah]

Thanks for taking a look.

This is a modification to make the initialization optional for privatization because the standard does not require scalar private variables to be initialized. For reduction, scalarInitValue will never be null and so the store will still always happen.