[flang][Lower][OpenMP] Don't read moldarg for static sized array (llvm#125901)

This should further reduce the number of spurious barriers

Author: tblah

flang/lib/Lower/OpenMP/DataSharingProcessor.cpp

@@ -508,6 +508,8 @@ void DataSharingProcessor::doPrivatize(const semantics::Symbol *sym,
 
  lower::SymbolBox hsb = converter.lookupOneLevelUpSymbol(*sym);
  assert(hsb && "Host symbol box not found");
+ hlfir::Entity entity{hsb.getAddr()};
+ bool cannotHaveNonDefaultLowerBounds = !entity.mayHaveNonDefaultLowerBounds();
 
  mlir::Location symLoc = hsb.getAddr().getLoc();
  std::string privatizerName = sym->name().ToString() + ".privatizer";
@@ -528,7 +530,6 @@ void DataSharingProcessor::doPrivatize(const semantics::Symbol *sym,
  // an alloca for a fir.array type there. Get around this by boxing all
  // arrays.
  if (mlir::isa<fir::SequenceType>(allocType)) {
- hlfir::Entity entity{hsb.getAddr()};
  entity = genVariableBox(symLoc, firOpBuilder, entity);
  privVal = entity.getBase();
  allocType = privVal.getType();
@@ -590,7 +591,7 @@ void DataSharingProcessor::doPrivatize(const semantics::Symbol *sym,
  result.getDeallocRegion(),
  isFirstPrivate ? DeclOperationKind::FirstPrivate
  : DeclOperationKind::Private,
- sym);
+ sym, cannotHaveNonDefaultLowerBounds);
  // TODO: currently there are false positives from dead uses of the mold
  // arg
  if (!result.getInitMoldArg().getUses().empty())

flang/lib/Lower/OpenMP/PrivateReductionUtils.cpp

@@ -122,25 +122,40 @@ static void createCleanupRegion(Fortran::lower::AbstractConverter &converter,
  typeError();
 }
 
-fir::ShapeShiftOp Fortran::lower::omp::getShapeShift(fir::FirOpBuilder &builder,
- mlir::Location loc,
- mlir::Value box) {
+fir::ShapeShiftOp
+Fortran::lower::omp::getShapeShift(fir::FirOpBuilder &builder,
+ mlir::Location loc, mlir::Value box,
+ bool cannotHaveNonDefaultLowerBounds) {
  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());
+
+ if (cannotHaveNonDefaultLowerBounds && !sequenceType.hasDynamicExtents()) {
+ // We don't need fir::BoxDimsOp if all of the extents are statically known
+ // and we can assume default lower bounds. This helps avoids reads from the
+ // mold arg.
+ mlir::Value one = builder.createIntegerConstant(loc, idxTy, 1);
+ for (int64_t extent : sequenceType.getShape()) {
+ assert(extent != sequenceType.getUnknownExtent());
+ mlir::Value extentVal = builder.createIntegerConstant(loc, idxTy, extent);
+ lbAndExtents.push_back(one);
+ lbAndExtents.push_back(extentVal);
+ }
+ } else {
+ 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);
@@ -248,12 +263,13 @@ class PopulateInitAndCleanupRegionsHelper {
  mlir::Type argType, mlir::Value scalarInitValue,
  mlir::Value allocatedPrivVarArg, mlir::Value moldArg,
  mlir::Block *initBlock, mlir::Region &cleanupRegion,
- DeclOperationKind kind, const Fortran::semantics::Symbol *sym)
+ DeclOperationKind kind, const Fortran::semantics::Symbol *sym,
+ bool cannotHaveLowerBounds)
  : converter{converter}, builder{converter.getFirOpBuilder()}, loc{loc},
  argType{argType}, scalarInitValue{scalarInitValue},
  allocatedPrivVarArg{allocatedPrivVarArg}, moldArg{moldArg},
  initBlock{initBlock}, cleanupRegion{cleanupRegion}, kind{kind},
- sym{sym} {
+ sym{sym}, cannotHaveNonDefaultLowerBounds{cannotHaveLowerBounds} {
  valType = fir::unwrapRefType(argType);
  }
 
@@ -295,6 +311,10 @@ class PopulateInitAndCleanupRegionsHelper {
  /// Any length parameters which have been fetched for the type
  mlir::SmallVector<mlir::Value> lenParams;
 
+ /// If the source variable being privatized definitely can't have non-default
+ /// lower bounds then we don't need to generate code to read them.
+ bool cannotHaveNonDefaultLowerBounds;
+
  void createYield(mlir::Value ret) {
  builder.create<mlir::omp::YieldOp>(loc, ret);
  }
@@ -432,7 +452,8 @@ void PopulateInitAndCleanupRegionsHelper::initAndCleanupBoxedArray(
  // Special case for (possibly allocatable) arrays of polymorphic types
  // e.g. !fir.class<!fir.heap<!fir.array<?x!fir.type<>>>>
  if (source.isPolymorphic()) {
- fir::ShapeShiftOp shape = getShapeShift(builder, loc, source);
+ fir::ShapeShiftOp shape =
+ getShapeShift(builder, loc, source, cannotHaveNonDefaultLowerBounds);
  mlir::Type arrayType = source.getElementOrSequenceType();
  mlir::Value allocatedArray = builder.create<fir::AllocMemOp>(
  loc, arrayType, /*typeparams=*/mlir::ValueRange{}, shape.getExtents());
@@ -471,8 +492,8 @@ void PopulateInitAndCleanupRegionsHelper::initAndCleanupBoxedArray(
  // 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, getLoadedMoldArg());
+ fir::ShapeShiftOp shapeShift = getShapeShift(builder, loc, getLoadedMoldArg(),
+  cannotHaveNonDefaultLowerBounds);
  mlir::Type boxType = getLoadedMoldArg().getType();
  if (mlir::isa<fir::BaseBoxType>(temp.getType()))
  // the box created by the declare form createTempFromMold is missing
@@ -607,10 +628,10 @@ void Fortran::lower::omp::populateByRefInitAndCleanupRegions(
  mlir::Type argType, mlir::Value scalarInitValue, mlir::Block *initBlock,
  mlir::Value allocatedPrivVarArg, mlir::Value moldArg,
  mlir::Region &cleanupRegion, DeclOperationKind kind,
- const Fortran::semantics::Symbol *sym) {
+ const Fortran::semantics::Symbol *sym, bool cannotHaveLowerBounds) {
  PopulateInitAndCleanupRegionsHelper helper(
  converter, loc, argType, scalarInitValue, allocatedPrivVarArg, moldArg,
- initBlock, cleanupRegion, kind, sym);
+ initBlock, cleanupRegion, kind, sym, cannotHaveLowerBounds);
  helper.populateByRefInitAndCleanupRegions();
 
  // Often we load moldArg to check something (e.g. length parameters, shape)

flang/lib/Lower/OpenMP/PrivateReductionUtils.h

@@ -55,11 +55,13 @@ void populateByRefInitAndCleanupRegions(
  mlir::Value scalarInitValue, mlir::Block *initBlock,
  mlir::Value allocatedPrivVarArg, mlir::Value moldArg,
  mlir::Region &cleanupRegion, DeclOperationKind kind,
- const Fortran::semantics::Symbol *sym = nullptr);
+ const Fortran::semantics::Symbol *sym = nullptr,
+ bool cannotHaveNonDefaultLowerBounds = false);
 
 /// Generate a fir::ShapeShift op describing the provided boxed array.
 fir::ShapeShiftOp getShapeShift(fir::FirOpBuilder &builder, mlir::Location loc,
- mlir::Value box);
+ mlir::Value box,
+ bool cannotHaveNonDefaultLowerBounds = false);
 
 } // namespace omp
 } // namespace lower

flang/test/Lower/OpenMP/delayed-privatization-array.f90

@@ -108,15 +108,14 @@ program main
 ! ONE_DIM_DEFAULT_LB-SAME: @[[PRIVATIZER_SYM:.*]] : [[BOX_TYPE:!fir.box<!fir.array<10xi32>>]] init {
 
 ! ONE_DIM_DEFAULT_LB-NEXT: ^bb0(%[[PRIV_ARG:.*]]: [[TYPE:!fir.ref<!fir.box<!fir.array<10xi32>>>]], %[[PRIV_BOX_ALLOC:.*]]: [[TYPE]]):
-! ONE_DIM_DEFAULT_LB-NEXT: %[[PRIV_ARG_VAL:.*]] = fir.load %[[PRIV_ARG]]
 ! ONE_DIM_DEFAULT_LB-NEXT: %[[C10:.*]] = arith.constant 10 : index
 ! ONE_DIM_DEFAULT_LB-NEXT: %[[SHAPE:.*]] = fir.shape %[[C10]]
 ! ONE_DIM_DEFAULT_LB-NEXT: %[[ARRAY_ALLOC:.*]] = fir.allocmem !fir.array<10xi32>
 ! ONE_DIM_DEFAULT_LB-NEXT: %[[TRUE:.*]] = arith.constant true
 ! ONE_DIM_DEFAULT_LB-NEXT: %[[DECL:.*]]:2 = hlfir.declare %[[ARRAY_ALLOC]](%[[SHAPE]])
-! ONE_DIM_DEFAULT_LB-NEXT: %[[C0_0:.*]] = arith.constant 0
-! ONE_DIM_DEFAULT_LB-NEXT: %[[DIMS2:.*]]:3 = fir.box_dims %[[PRIV_ARG_VAL]], %[[C0_0]]
-! ONE_DIM_DEFAULT_LB-NEXT: %[[SHAPE_SHIFT:.*]] = fir.shape_shift %[[DIMS2]]#0, %[[DIMS2]]#1
+! ONE_DIM_DEFAULT_LB-NEXT: %[[ONE:.*]] = arith.constant 1 : index
+! ONE_DIM_DEFAULT_LB-NEXT: %[[TEN:.*]] = arith.constant 10 : index
+! ONE_DIM_DEFAULT_LB-NEXT: %[[SHAPE_SHIFT:.*]] = fir.shape_shift %[[ONE]], %[[TEN]]
 ! ONE_DIM_DEFAULT_LB-NEXT: %[[EMBOX:.*]] = fir.embox %[[DECL]]#0(%[[SHAPE_SHIFT]])
 ! ONE_DIM_DEFAULT_LB-NEXT: fir.store %[[EMBOX]] to %[[PRIV_BOX_ALLOC]]
 ! ONE_DIM_DEFAULT_LB-NEXT: omp.yield(%[[PRIV_BOX_ALLOC]] : [[TYPE]])