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May 8, 2025
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[mlir][OpenMP] cancel(lation point) taskgroup LLVMIR #137841

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0afaa2c
[mlir][OpenMP] cancel(lation point) taskgroup LLVMIR
tblah Apr 29, 2025
cbd71ce
Add todo for cancelling a taskloop
tblah May 6, 2025
4212948
Keep calls to checkImplementationStatus
tblah May 7, 2025
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4 changes: 2 additions & 2 deletions flang/docs/OpenMPSupport.md
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Expand Up @@ -51,8 +51,8 @@ Note : No distinction is made between the support in Parser/Semantics, MLIR, Low
| depend clause | P | depend clause with array sections are not supported |
| declare reduction construct | N | |
| atomic construct extensions | Y | |
| cancel construct | N | |
| cancellation point construct | N | |
| cancel construct | Y | |
| cancellation point construct | Y | |
| parallel do simd construct | P | linear clause is not supported |
| target teams construct | P | device and reduction clauses are not supported |
| teams distribute construct | P | reduction and dist_schedule clauses not supported |
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124 changes: 82 additions & 42 deletions mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
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Expand Up @@ -161,8 +161,18 @@ static LogicalResult checkImplementationStatus(Operation &op) {
auto checkCancelDirective = [&todo](auto op, LogicalResult &result) {
omp::ClauseCancellationConstructType cancelledDirective =
op.getCancelDirective();
if (cancelledDirective == omp::ClauseCancellationConstructType::Taskgroup)
result = todo("cancel directive construct type not yet supported");
// Cancelling a taskloop is not yet supported because we don't yet have LLVM
// IR conversion for taskloop
if (cancelledDirective == omp::ClauseCancellationConstructType::Taskgroup) {
Operation *parent = op->getParentOp();
while (parent) {
if (parent->getDialect() == op->getDialect())
break;
parent = parent->getParentOp();
}
if (isa_and_nonnull<omp::TaskloopOp>(parent))
result = todo("cancel directive inside of taskloop");
}
};
auto checkDepend = [&todo](auto op, LogicalResult &result) {
if (!op.getDependVars().empty() || op.getDependKinds())
Expand Down Expand Up @@ -1889,6 +1899,55 @@ buildDependData(std::optional<ArrayAttr> dependKinds, OperandRange dependVars,
}
}

/// Shared implementation of a callback which adds a termiator for the new block
/// created for the branch taken when an openmp construct is cancelled. The
/// terminator is saved in \p cancelTerminators. This callback is invoked only
/// if there is cancellation inside of the taskgroup body.
/// The terminator will need to be fixed to branch to the correct block to
/// cleanup the construct.
static void
pushCancelFinalizationCB(SmallVectorImpl<llvm::BranchInst *> &cancelTerminators,
llvm::IRBuilderBase &llvmBuilder,
llvm::OpenMPIRBuilder &ompBuilder, mlir::Operation *op,
llvm::omp::Directive cancelDirective) {
auto finiCB = [&](llvm::OpenMPIRBuilder::InsertPointTy ip) -> llvm::Error {
llvm::IRBuilderBase::InsertPointGuard guard(llvmBuilder);

// ip is currently in the block branched to if cancellation occured.
// We need to create a branch to terminate that block.
llvmBuilder.restoreIP(ip);

// We must still clean up the construct after cancelling it, so we need to
// branch to the block that finalizes the taskgroup.
// That block has not been created yet so use this block as a dummy for now
// and fix this after creating the operation.
cancelTerminators.push_back(llvmBuilder.CreateBr(ip.getBlock()));
return llvm::Error::success();
};
// We have to add the cleanup to the OpenMPIRBuilder before the body gets
// created in case the body contains omp.cancel (which will then expect to be
// able to find this cleanup callback).
ompBuilder.pushFinalizationCB(
{finiCB, cancelDirective, constructIsCancellable(op)});
}

/// If we cancelled the construct, we should branch to the finalization block of
/// that construct. OMPIRBuilder structures the CFG such that the cleanup block
/// is immediately before the continuation block. Now this finalization has
/// been created we can fix the branch.
static void
popCancelFinalizationCB(const ArrayRef<llvm::BranchInst *> cancelTerminators,
llvm::OpenMPIRBuilder &ompBuilder,
const llvm::OpenMPIRBuilder::InsertPointTy &afterIP) {
ompBuilder.popFinalizationCB();
llvm::BasicBlock *constructFini = afterIP.getBlock()->getSinglePredecessor();
for (llvm::BranchInst *cancelBranch : cancelTerminators) {
assert(cancelBranch->getNumSuccessors() == 1 &&
"cancel branch should have one target");
cancelBranch->setSuccessor(0, constructFini);
}
}

namespace {
/// TaskContextStructManager takes care of creating and freeing a structure
/// containing information needed by the task body to execute.
Expand Down Expand Up @@ -2202,6 +2261,14 @@ convertOmpTaskOp(omp::TaskOp taskOp, llvm::IRBuilderBase &builder,
return llvm::Error::success();
};

llvm::OpenMPIRBuilder &ompBuilder = *moduleTranslation.getOpenMPBuilder();
SmallVector<llvm::BranchInst *> cancelTerminators;
// The directive to match here is OMPD_taskgroup because it is the taskgroup
// which is canceled. This is handled here because it is the task's cleanup
// block which should be branched to.
pushCancelFinalizationCB(cancelTerminators, builder, ompBuilder, taskOp,
llvm::omp::Directive::OMPD_taskgroup);

SmallVector<llvm::OpenMPIRBuilder::DependData> dds;
buildDependData(taskOp.getDependKinds(), taskOp.getDependVars(),
moduleTranslation, dds);
Expand All @@ -2219,6 +2286,9 @@ convertOmpTaskOp(omp::TaskOp taskOp, llvm::IRBuilderBase &builder,
if (failed(handleError(afterIP, *taskOp)))
return failure();

// Set the correct branch target for task cancellation
popCancelFinalizationCB(cancelTerminators, ompBuilder, afterIP.get());

builder.restoreIP(*afterIP);
return success();
}
Expand Down Expand Up @@ -2349,28 +2419,8 @@ convertOmpWsloop(Operation &opInst, llvm::IRBuilderBase &builder,
: llvm::omp::WorksharingLoopType::ForStaticLoop;

SmallVector<llvm::BranchInst *> cancelTerminators;
// This callback is invoked only if there is cancellation inside of the wsloop
// body.
auto finiCB = [&](llvm::OpenMPIRBuilder::InsertPointTy ip) -> llvm::Error {
llvm::IRBuilderBase &llvmBuilder = ompBuilder->Builder;
llvm::IRBuilderBase::InsertPointGuard guard(llvmBuilder);

// ip is currently in the block branched to if cancellation occured.
// We need to create a branch to terminate that block.
llvmBuilder.restoreIP(ip);

// We must still clean up the wsloop after cancelling it, so we need to
// branch to the block that finalizes the wsloop.
// That block has not been created yet so use this block as a dummy for now
// and fix this after creating the wsloop.
cancelTerminators.push_back(llvmBuilder.CreateBr(ip.getBlock()));
return llvm::Error::success();
};
// We have to add the cleanup to the OpenMPIRBuilder before the body gets
// created in case the body contains omp.cancel (which will then expect to be
// able to find this cleanup callback).
ompBuilder->pushFinalizationCB({finiCB, llvm::omp::Directive::OMPD_for,
constructIsCancellable(wsloopOp)});
pushCancelFinalizationCB(cancelTerminators, builder, *ompBuilder, wsloopOp,
llvm::omp::Directive::OMPD_for);

llvm::OpenMPIRBuilder::LocationDescription ompLoc(builder);
llvm::Expected<llvm::BasicBlock *> regionBlock = convertOmpOpRegions(
Expand All @@ -2393,18 +2443,8 @@ convertOmpWsloop(Operation &opInst, llvm::IRBuilderBase &builder,
if (failed(handleError(wsloopIP, opInst)))
return failure();

ompBuilder->popFinalizationCB();
if (!cancelTerminators.empty()) {
// If we cancelled the loop, we should branch to the finalization block of
// the wsloop (which is always immediately before the loop continuation
// block). Now the finalization has been created, we can fix the branch.
llvm::BasicBlock *wsloopFini = wsloopIP->getBlock()->getSinglePredecessor();
for (llvm::BranchInst *cancelBranch : cancelTerminators) {
assert(cancelBranch->getNumSuccessors() == 1 &&
"cancel branch should have one target");
cancelBranch->setSuccessor(0, wsloopFini);
}
}
// Set the correct branch target for task cancellation
popCancelFinalizationCB(cancelTerminators, *ompBuilder, wsloopIP.get());

// Process the reductions if required.
if (failed(createReductionsAndCleanup(
Expand Down Expand Up @@ -3060,12 +3100,12 @@ static llvm::omp::Directive convertCancellationConstructType(
static LogicalResult
convertOmpCancel(omp::CancelOp op, llvm::IRBuilderBase &builder,
LLVM::ModuleTranslation &moduleTranslation) {
llvm::OpenMPIRBuilder::LocationDescription ompLoc(builder);
llvm::OpenMPIRBuilder *ompBuilder = moduleTranslation.getOpenMPBuilder();

if (failed(checkImplementationStatus(*op.getOperation())))
return failure();

llvm::OpenMPIRBuilder::LocationDescription ompLoc(builder);
llvm::OpenMPIRBuilder *ompBuilder = moduleTranslation.getOpenMPBuilder();

llvm::Value *ifCond = nullptr;
if (Value ifVar = op.getIfExpr())
ifCond = moduleTranslation.lookupValue(ifVar);
Expand All @@ -3088,12 +3128,12 @@ static LogicalResult
convertOmpCancellationPoint(omp::CancellationPointOp op,
llvm::IRBuilderBase &builder,
LLVM::ModuleTranslation &moduleTranslation) {
llvm::OpenMPIRBuilder::LocationDescription ompLoc(builder);
llvm::OpenMPIRBuilder *ompBuilder = moduleTranslation.getOpenMPBuilder();

if (failed(checkImplementationStatus(*op.getOperation())))
return failure();

llvm::OpenMPIRBuilder::LocationDescription ompLoc(builder);
llvm::OpenMPIRBuilder *ompBuilder = moduleTranslation.getOpenMPBuilder();

llvm::omp::Directive cancelledDirective =
convertCancellationConstructType(op.getCancelDirective());

Expand Down
48 changes: 48 additions & 0 deletions mlir/test/Target/LLVMIR/openmp-cancel.mlir
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Expand Up @@ -243,3 +243,51 @@ llvm.func @cancel_wsloop_if(%lb : i32, %ub : i32, %step : i32, %cond : i1) {
// CHECK: ret void
// CHECK: .cncl: ; preds = %[[VAL_44]]
// CHECK: br label %[[VAL_38]]

omp.private {type = firstprivate} @i32_priv : i32 copy {
^bb0(%arg0: !llvm.ptr, %arg1: !llvm.ptr):
%0 = llvm.load %arg0 : !llvm.ptr -> i32
llvm.store %0, %arg1 : i32, !llvm.ptr
omp.yield(%arg1 : !llvm.ptr)
}

llvm.func @do_something(!llvm.ptr)

llvm.func @cancel_taskgroup(%arg0: !llvm.ptr) {
omp.taskgroup {
// Using firstprivate clause so we have some end of task cleanup to branch to
// after the cancellation.
omp.task private(@i32_priv %arg0 -> %arg1 : !llvm.ptr) {
omp.cancel cancellation_construct_type(taskgroup)
llvm.call @do_something(%arg1) : (!llvm.ptr) -> ()
omp.terminator
}
omp.terminator
}
llvm.return
}
// CHECK-LABEL: define internal void @cancel_taskgroup..omp_par(
// CHECK: task.alloca:
// CHECK: %[[VAL_21:.*]] = load ptr, ptr %[[VAL_22:.*]], align 8
// CHECK: %[[VAL_23:.*]] = getelementptr { ptr }, ptr %[[VAL_21]], i32 0, i32 0
// CHECK: %[[VAL_24:.*]] = load ptr, ptr %[[VAL_23]], align 8, !align !1
// CHECK: br label %[[VAL_25:.*]]
// CHECK: task.body: ; preds = %[[VAL_26:.*]]
// CHECK: %[[VAL_27:.*]] = getelementptr { i32 }, ptr %[[VAL_24]], i32 0, i32 0
// CHECK: br label %[[VAL_28:.*]]
// CHECK: omp.task.region: ; preds = %[[VAL_25]]
// CHECK: %[[VAL_29:.*]] = call i32 @__kmpc_global_thread_num(ptr @1)
// CHECK: %[[VAL_30:.*]] = call i32 @__kmpc_cancel(ptr @1, i32 %[[VAL_29]], i32 4)
// CHECK: %[[VAL_31:.*]] = icmp eq i32 %[[VAL_30]], 0
// CHECK: br i1 %[[VAL_31]], label %omp.task.region.split, label %omp.task.region.cncl
// CHECK: omp.task.region.cncl:
// CHECK: br label %omp.region.cont2
// CHECK: omp.region.cont2:
// Both cancellation and normal paths reach the end-of-task cleanup:
// CHECK: tail call void @free(ptr %[[VAL_24]])
// CHECK: br label %task.exit.exitStub
// CHECK: omp.task.region.split:
// CHECK: call void @do_something(ptr %[[VAL_27]])
// CHECK: br label %omp.region.cont2
// CHECK: task.exit.exitStub:
// CHECK: ret void
30 changes: 30 additions & 0 deletions mlir/test/Target/LLVMIR/openmp-cancellation-point.mlir
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Expand Up @@ -186,3 +186,33 @@ llvm.func @cancellation_point_wsloop(%lb : i32, %ub : i32, %step : i32) {
// CHECK: ret void
// CHECK: omp.loop_nest.region.cncl: ; preds = %[[VAL_100]]
// CHECK: br label %[[VAL_96]]


llvm.func @cancellation_point_taskgroup() {
omp.taskgroup {
omp.task {
omp.cancellation_point cancellation_construct_type(taskgroup)
omp.terminator
}
omp.terminator
}
llvm.return
}
// CHECK-LABEL: define internal void @cancellation_point_taskgroup..omp_par(
// CHECK: task.alloca:
// CHECK: br label %[[VAL_50:.*]]
// CHECK: task.body: ; preds = %[[VAL_51:.*]]
// CHECK: br label %[[VAL_52:.*]]
// CHECK: omp.task.region: ; preds = %[[VAL_50]]
// CHECK: %[[VAL_53:.*]] = call i32 @__kmpc_global_thread_num(ptr @1)
// CHECK: %[[VAL_54:.*]] = call i32 @__kmpc_cancellationpoint(ptr @1, i32 %[[VAL_53]], i32 4)
// CHECK: %[[VAL_55:.*]] = icmp eq i32 %[[VAL_54]], 0
// CHECK: br i1 %[[VAL_55]], label %omp.task.region.split, label %omp.task.region.cncl
// CHECK: omp.task.region.cncl:
// CHECK: br label %omp.region.cont1
// CHECK: omp.region.cont1:
// CHECK: br label %task.exit.exitStub
// CHECK: omp.task.region.split:
// CHECK: br label %omp.region.cont1
// CHECK: task.exit.exitStub:
// CHECK: ret void
34 changes: 0 additions & 34 deletions mlir/test/Target/LLVMIR/openmp-todo.mlir
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Expand Up @@ -26,40 +26,6 @@ llvm.func @atomic_hint(%v : !llvm.ptr, %x : !llvm.ptr, %expr : i32) {

// -----

llvm.func @cancel_taskgroup() {
// expected-error@below {{LLVM Translation failed for operation: omp.taskgroup}}
omp.taskgroup {
// expected-error@below {{LLVM Translation failed for operation: omp.task}}
omp.task {
// expected-error@below {{not yet implemented: Unhandled clause cancel directive construct type not yet supported in omp.cancel operation}}
// expected-error@below {{LLVM Translation failed for operation: omp.cancel}}
omp.cancel cancellation_construct_type(taskgroup)
omp.terminator
}
omp.terminator
}
llvm.return
}

// -----

llvm.func @cancellation_point_taskgroup() {
// expected-error@below {{LLVM Translation failed for operation: omp.taskgroup}}
omp.taskgroup {
// expected-error@below {{LLVM Translation failed for operation: omp.task}}
omp.task {
// expected-error@below {{not yet implemented: Unhandled clause cancel directive construct type not yet supported in omp.cancellation_point operation}}
// expected-error@below {{LLVM Translation failed for operation: omp.cancellation_point}}
omp.cancellation_point cancellation_construct_type(taskgroup)
omp.terminator
}
omp.terminator
}
llvm.return
}

// -----

llvm.func @do_simd(%lb : i32, %ub : i32, %step : i32) {
omp.wsloop {
// expected-warning@below {{simd information on composite construct discarded}}
Expand Down
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