jdoerfert created this revision.
jdoerfert added reviewers: kiranchandramohan, ABataev, RaviNarayanaswamy,
gtbercea, grokos, sdmitriev, JonChesterfield, hfinkel, fghanim.
Herald added subscribers: cfe-commits, guansong, bollu, hiraditya.
Herald added projects: clang, LLVM.
As a permanent and generic solution to the problem of variable
finalization (destructors, lastprivate, ...), this patch introduces the
finalization stack. The objects on the stack describe (1) the
(structured) regions the OpenMP-IR-Builder is currently constructing,
(2) if these are cancellable, and (3) the callback that will perform the
finalization (=cleanup) when necessary.
As the finalization can be necessary multiple times, at different source
locations, the callback takes the position at which code is currently
generated. This position will also encode the destination of the "region
exit" block *iff* the finalization call was issues for a region
generated by the OpenMPIRBuilder. For regions generated through the old
Clang OpenMP code geneneration, the "region exit" is determined by Clang
inside the finalization call instead (see getOMPCancelDestination).
As a first user, the parallel + cancel barrier interaction is changed.
In contrast to the temporary solution before, the barrier generation in
Clang does not need to be aware of the "CancelDestination" block.
Instead, the finalization callback is and, as described above, later
even that one does not need to be.
D70109 <https://reviews.llvm.org/D70109> will be updated to use this scheme.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D70258
Files:
clang/lib/CodeGen/CGOpenMPRuntime.cpp
llvm/include/llvm/Frontend/OpenMPIRBuilder.h
llvm/lib/Frontend/OpenMPIRBuilder.cpp
Index: llvm/lib/Frontend/OpenMPIRBuilder.cpp
===================================================================
--- llvm/lib/Frontend/OpenMPIRBuilder.cpp
+++ llvm/lib/Frontend/OpenMPIRBuilder.cpp
@@ -228,7 +228,8 @@
// If we are in a cancellable parallel region, barriers are cancellation
// points.
// TODO: Check why we would force simple calls or to ignore the cancel flag.
- bool UseCancelBarrier = !ForceSimpleCall && CancellationBlock;
+ bool UseCancelBarrier =
+ !ForceSimpleCall && isLastFinalizationInfoCancellable(OMPD_parallel);
Value *Result = Builder.CreateCall(
getOrCreateRuntimeFunction(UseCancelBarrier ? OMPRTL___kmpc_cancel_barrier
@@ -248,13 +249,14 @@
Builder.CreateCondBr(Cmp, NonCancellationBlock, CancellationBlock,
/* TODO weight */ nullptr, nullptr);
- Builder.SetInsertPoint(NonCancellationBlock);
- assert(CancellationBlock->getParent() == BB->getParent() &&
- "Unexpected cancellation block parent!");
+ // From the cancellation block we finalize all variables and go to the
+ // post finalization block that is known to the FiniCB callback.
+ Builder.SetInsertPoint(CancellationBlock);
+ auto &FI = FinalizationStack.back();
+ FI.FiniCB(Builder.saveIP());
- // TODO: This is a workaround for now, we always reset the cancellation
- // block until we manage it ourselves here.
- CancellationBlock = nullptr;
+ // The continuation block is where code generation continues.
+ Builder.SetInsertPoint(NonCancellationBlock);
}
return Builder.saveIP();
Index: llvm/include/llvm/Frontend/OpenMPIRBuilder.h
===================================================================
--- llvm/include/llvm/Frontend/OpenMPIRBuilder.h
+++ llvm/include/llvm/Frontend/OpenMPIRBuilder.h
@@ -37,12 +37,44 @@
/// Add attributes known for \p FnID to \p Fn.
void addAttributes(omp::RuntimeFunction FnID, Function &Fn);
- /// Set the cancellation block to \p CBB.
- void setCancellationBlock(BasicBlock *CBB) { CancellationBlock = CBB; }
-
/// Type used throughout for insertion points.
using InsertPointTy = IRBuilder<>::InsertPoint;
+ /// Callback type for variable finalization (think destructors).
+ ///
+ /// \param CodeGenIP is the insertion point at which the finalization code
+ /// should be placed.
+ ///
+ /// A finalize callback knows about all objects that need finalization, e.g.
+ /// destruction, when the scope of the currently generated construct is left
+ /// at the time, and location, the callback is invoked.
+ using FinalizeCallbackTy = function_ref<void(InsertPointTy /* CodeGenIP */)>;
+
+ struct FinalizationInfo {
+ /// The finalization callback provided by the last in-flight invocation of
+ /// CreateXXXX for the directive of kind DK.
+ FinalizeCallbackTy FiniCB;
+
+ /// The directive kind of the innermost directive that has an associated
+ /// region which might require finalization when it is left.
+ omp::Directive DK;
+
+ /// Flag to indicate if the directive is cancellable.
+ bool IsCancellable;
+ };
+
+ /// Push a finalization callback on the finalization stack.
+ ///
+ /// NOTE: Temporary solution until Clang CG is gone.
+ void pushFinalizationCB(FinalizationInfo &&FI) {
+ FinalizationStack.emplace_back(std::move(FI));
+ }
+
+ /// Pop the last finalization callback from the finalization stack.
+ ///
+ /// NOTE: Temporary solution until Clang CG is gone.
+ void popFinalizationCB() { FinalizationStack.pop_back(); }
+
/// Description of a LLVM-IR insertion point (IP) and a debug/source location
/// (filename, line, column, ...).
struct LocationDescription {
@@ -112,6 +144,19 @@
omp::Directive DK, bool ForceSimpleCall,
bool CheckCancelFlag);
+ /// The finalization stack made up of finalize callbacks currently in-flight,
+ /// wrapped into FinalizationInfo objects that reference also the finalization
+ /// target block and the kind of cancellable directive.
+ SmallVector<FinalizationInfo, 8> FinalizationStack;
+
+ /// Return true if the last entry in the finalization stack is of kind \p DK
+ /// and cancellable.
+ bool isLastFinalizationInfoCancellable(omp::Directive DK) {
+ return !FinalizationStack.empty() &&
+ FinalizationStack.back().IsCancellable &&
+ FinalizationStack.back().DK == DK;
+ }
+
/// Return the current thread ID.
///
/// \param Ident The ident (ident_t*) describing the query origin.
@@ -123,9 +168,6 @@
/// The LLVM-IR Builder used to create IR.
IRBuilder<> Builder;
- /// TODO: Stub for a cancellation block stack.
- BasicBlock *CancellationBlock = nullptr;
-
/// Map to remember the thread in a function.
DenseMap<Function *, Value *> ThreadIDMap;
Index: clang/lib/CodeGen/CGOpenMPRuntime.cpp
===================================================================
--- clang/lib/CodeGen/CGOpenMPRuntime.cpp
+++ clang/lib/CodeGen/CGOpenMPRuntime.cpp
@@ -1462,10 +1462,53 @@
else if (const auto *OPFD =
dyn_cast<OMPTargetTeamsDistributeParallelForDirective>(&D))
HasCancel = OPFD->hasCancel();
+
+ // TODO: Temporarily inform the OpenMPIRBuilder, if any, about the new
+ // parallel region to make cancellation barriers work properly.
+ llvm::OpenMPIRBuilder *OMPBuilder = CGM.getOpenMPIRBuilder();
+ if (OMPBuilder) {
+
+ // The following callback is the crucial part of clangs cleanup process.
+ //
+ // NOTE:
+ // Once the OpenMPIRBuilder is used to create parallel regions (and
+ // similar), the cancellation destination (Dest below) is determined via
+ // IP. That means if we have variables to finalize we split the block at IP,
+ // use the new block (=BB) as destination to build a JumpDest (via
+ // getJumpDestInCurrentScope(BB)) which then is fed to
+ // EmitBranchThroughCleanup. Furhtermore, there will not be the need
+ // to push & pop an FinalizationInfo object.
+ // The FiniCB will still be needed otherwise but at the point where the
+ // OpenMPIRBuilder is asked to construct a parallel (or similar) construct.
+ auto FiniCB = [&](llvm::OpenMPIRBuilder::InsertPointTy IP) {
+ assert(IP.getBlock()->end() == IP.getPoint() &&
+ "Clang CG should cause non-terminated block!");
+ auto OldIP = CGF.Builder.saveIP();
+ CGF.Builder.restoreIP(IP);
+ CodeGenFunction::JumpDest Dest =
+ CGF.getOMPCancelDestination(OMPD_parallel);
+ assert(Dest.getBlock());
+ CGF.EmitBranchThroughCleanup(Dest);
+ CGF.Builder.restoreIP(OldIP);
+ };
+
+ // TODO: Remove this once we emit parallel regions through the
+ // OpenMPIRBuilder as it can do this setup internally.
+ llvm::OpenMPIRBuilder::FinalizationInfo FI(
+ {FiniCB, OMPD_parallel, HasCancel});
+ OMPBuilder->pushFinalizationCB(std::move(FI));
+ }
+
CGOpenMPOutlinedRegionInfo CGInfo(*CS, ThreadIDVar, CodeGen, InnermostKind,
HasCancel, OutlinedHelperName);
CodeGenFunction::CGCapturedStmtRAII CapInfoRAII(CGF, &CGInfo);
- return CGF.GenerateOpenMPCapturedStmtFunction(*CS);
+ llvm::Function *Fn = CGF.GenerateOpenMPCapturedStmtFunction(*CS);
+
+ // TODO: See the TODOs above.
+ if (OMPBuilder)
+ OMPBuilder->popFinalizationCB();
+
+ return Fn;
}
llvm::Function *CGOpenMPRuntime::emitParallelOutlinedFunction(
@@ -3483,22 +3526,8 @@
dyn_cast_or_null<CGOpenMPRegionInfo>(CGF.CapturedStmtInfo);
llvm::OpenMPIRBuilder *OMPBuilder = CGF.CGM.getOpenMPIRBuilder();
if (OMPBuilder) {
- // TODO: Move cancelation point handling into the IRBuilder.
- if (EmitChecks && !ForceSimpleCall && OMPRegionInfo &&
- OMPRegionInfo->hasCancel()) {
- auto IP = CGF.Builder.saveIP();
- llvm::BasicBlock *ExitBB =
- CGF.createBasicBlock(".cancel.exit", IP.getBlock()->getParent());
- OMPBuilder->setCancellationBlock(ExitBB);
- CGF.Builder.SetInsertPoint(ExitBB);
- CodeGenFunction::JumpDest CancelDestination =
- CGF.getOMPCancelDestination(OMPRegionInfo->getDirectiveKind());
- CGF.EmitBranchThroughCleanup(CancelDestination);
- CGF.Builder.restoreIP(IP);
- }
- auto IP = OMPBuilder->CreateBarrier(CGF.Builder, Kind, ForceSimpleCall,
- EmitChecks);
- CGF.Builder.restoreIP(IP);
+ CGF.Builder.restoreIP(OMPBuilder->CreateBarrier(
+ CGF.Builder, Kind, ForceSimpleCall, EmitChecks));
return;
}
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