[OpenMP][FIX] Allocate per launch memory for GPU team reductions

We used to perform team reduction on global memory allocated in the
runtime and by clang. This was racy as multiple instances of a kernel,
or different kernels with team reductions, would use the same locations.
Since we now have the kernel launch environment, we can allocate dynamic
memory per-launch, allowing us to move all the state into a non-racy
place.

Fixes: #70249

Author: jdoerfert

clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp

@@ -803,8 +803,30 @@ void CGOpenMPRuntimeGPU::emitKernelDeinit(CodeGenFunction &CGF,
   if (!IsSPMD)
     emitGenericVarsEpilog(CGF);
 
+  // This is temporary until we remove the fixed sized buffer.
+  ASTContext &C = CGM.getContext();
+  RecordDecl *StaticRD = C.buildImplicitRecord(
+      "_openmp_teams_reduction_type_$_", RecordDecl::TagKind::TTK_Union);
+  StaticRD->startDefinition();
+  for (const RecordDecl *TeamReductionRec : TeamsReductions) {
+    QualType RecTy = C.getRecordType(TeamReductionRec);
+    auto *Field = FieldDecl::Create(
+        C, StaticRD, SourceLocation(), SourceLocation(), nullptr, RecTy,
+        C.getTrivialTypeSourceInfo(RecTy, SourceLocation()),
+        /*BW=*/nullptr, /*Mutable=*/false,
+        /*InitStyle=*/ICIS_NoInit);
+    Field->setAccess(AS_public);
+    StaticRD->addDecl(Field);
+  }
+  StaticRD->completeDefinition();
+  QualType StaticTy = C.getRecordType(StaticRD);
+  llvm::Type *LLVMReductionsBufferTy =
+      CGM.getTypes().ConvertTypeForMem(StaticTy);
+  const auto &DL = CGM.getModule().getDataLayout();
+  uint64_t BufferSize =
+      DL.getTypeAllocSize(LLVMReductionsBufferTy).getFixedValue();
   CGBuilderTy &Bld = CGF.Builder;
-  OMPBuilder.createTargetDeinit(Bld);
+  OMPBuilder.createTargetDeinit(Bld, BufferSize);
 }
 
 void CGOpenMPRuntimeGPU::emitSPMDKernel(const OMPExecutableDirective &D,
@@ -2998,15 +3020,10 @@ void CGOpenMPRuntimeGPU::emitReduction(
         CGM.getContext(), PrivatesReductions, std::nullopt, VarFieldMap,
         C.getLangOpts().OpenMPCUDAReductionBufNum);
     TeamsReductions.push_back(TeamReductionRec);
-    if (!KernelTeamsReductionPtr) {
-      KernelTeamsReductionPtr = new llvm::GlobalVariable(
-          CGM.getModule(), CGM.VoidPtrTy, /*isConstant=*/true,
-          llvm::GlobalValue::InternalLinkage, nullptr,
-          "_openmp_teams_reductions_buffer_$_$ptr");
-    }
-    llvm::Value *GlobalBufferPtr = CGF.EmitLoadOfScalar(
-        Address(KernelTeamsReductionPtr, CGF.VoidPtrTy, CGM.getPointerAlign()),
-        /*Volatile=*/false, C.getPointerType(C.VoidPtrTy), Loc);
+    auto *KernelTeamsReductionPtr = CGF.EmitRuntimeCall(
+        OMPBuilder.getOrCreateRuntimeFunction(
+            CGM.getModule(), OMPRTL___kmpc_reduction_get_fixed_buffer),
+        {}, "_openmp_teams_reductions_buffer_$_$ptr");
     llvm::Value *GlobalToBufferCpyFn = ::emitListToGlobalCopyFunction(
         CGM, Privates, ReductionArrayTy, Loc, TeamReductionRec, VarFieldMap);
     llvm::Value *GlobalToBufferRedFn = ::emitListToGlobalReduceFunction(
@@ -3021,7 +3038,7 @@ void CGOpenMPRuntimeGPU::emitReduction(
     llvm::Value *Args[] = {
         RTLoc,
         ThreadId,
-        GlobalBufferPtr,
+        KernelTeamsReductionPtr,
         CGF.Builder.getInt32(C.getLangOpts().OpenMPCUDAReductionBufNum),
         RL,
         ShuffleAndReduceFn,
@@ -3654,42 +3671,6 @@ void CGOpenMPRuntimeGPU::processRequiresDirective(
   CGOpenMPRuntime::processRequiresDirective(D);
 }
 
-void CGOpenMPRuntimeGPU::clear() {
-
-  if (!TeamsReductions.empty()) {
-    ASTContext &C = CGM.getContext();
-    RecordDecl *StaticRD = C.buildImplicitRecord(
-        "_openmp_teams_reduction_type_$_", RecordDecl::TagKind::TTK_Union);
-    StaticRD->startDefinition();
-    for (const RecordDecl *TeamReductionRec : TeamsReductions) {
-      QualType RecTy = C.getRecordType(TeamReductionRec);
-      auto *Field = FieldDecl::Create(
-          C, StaticRD, SourceLocation(), SourceLocation(), nullptr, RecTy,
-          C.getTrivialTypeSourceInfo(RecTy, SourceLocation()),
-          /*BW=*/nullptr, /*Mutable=*/false,
-          /*InitStyle=*/ICIS_NoInit);
-      Field->setAccess(AS_public);
-      StaticRD->addDecl(Field);
-    }
-    StaticRD->completeDefinition();
-    QualType StaticTy = C.getRecordType(StaticRD);
-    llvm::Type *LLVMReductionsBufferTy =
-        CGM.getTypes().ConvertTypeForMem(StaticTy);
-    // FIXME: nvlink does not handle weak linkage correctly (object with the
-    // different size are reported as erroneous).
-    // Restore CommonLinkage as soon as nvlink is fixed.
-    auto *GV = new llvm::GlobalVariable(
-        CGM.getModule(), LLVMReductionsBufferTy,
-        /*isConstant=*/false, llvm::GlobalValue::InternalLinkage,
-        llvm::Constant::getNullValue(LLVMReductionsBufferTy),
-        "_openmp_teams_reductions_buffer_$_");
-    KernelTeamsReductionPtr->setInitializer(
-        llvm::ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV,
-                                                             CGM.VoidPtrTy));
-  }
-  CGOpenMPRuntime::clear();
-}
-
 llvm::Value *CGOpenMPRuntimeGPU::getGPUNumThreads(CodeGenFunction &CGF) {
   CGBuilderTy &Bld = CGF.Builder;
   llvm::Module *M = &CGF.CGM.getModule();

clang/lib/CodeGen/CGOpenMPRuntimeGPU.h

@@ -130,7 +130,6 @@ class CGOpenMPRuntimeGPU : public CGOpenMPRuntime {
 
 public:
   explicit CGOpenMPRuntimeGPU(CodeGenModule &CGM);
-  void clear() override;
 
   bool isGPU() const override { return true; };
 
@@ -386,7 +385,6 @@ class CGOpenMPRuntimeGPU : public CGOpenMPRuntime {
   /// Maps the function to the list of the globalized variables with their
   /// addresses.
   llvm::SmallDenseMap<llvm::Function *, FunctionData> FunctionGlobalizedDecls;
-  llvm::GlobalVariable *KernelTeamsReductionPtr = nullptr;
   /// List of the records with the list of fields for the reductions across the
   /// teams. Used to build the intermediate buffer for the fast teams
   /// reductions.