lib/CodeGen/CGOpenMPRuntimeGPU.h

//===------ CGOpenMPRuntimeGPU.h - Interface to OpenMP GPU Runtimes ------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This provides a generalized class for OpenMP runtime code generation
// specialized by GPU targets NVPTX and AMDGCN.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_LIB_CODEGEN_CGOPENMPRUNTIMEGPU_H
#define LLVM_CLANG_LIB_CODEGEN_CGOPENMPRUNTIMEGPU_H

#include "CGOpenMPRuntime.h"
#include "CodeGenFunction.h"
#include "clang/AST/StmtOpenMP.h"

namespace clang {
namespace CodeGen {

class CGOpenMPRuntimeGPU : public CGOpenMPRuntime {
public:
  /// Defines the execution mode.
  enum ExecutionMode {
    /// SPMD execution mode (all threads are worker threads).
    EM_SPMD,
    /// Non-SPMD execution mode (1 master thread, others are workers).
    EM_NonSPMD,
    /// Unknown execution mode (orphaned directive).
    EM_Unknown,
  };

  /// Target codegen is specialized based on two data-sharing modes: CUDA, in
  /// which the local variables are actually global threadlocal, and Generic, in
  /// which the local variables are placed in global memory if they may escape
  /// their declaration context.
  enum DataSharingMode {
    /// CUDA data sharing mode.
    DS_CUDA,
    /// Generic data-sharing mode.
    DS_Generic,
  };

private:
  /// Parallel outlined function work for workers to execute.
  llvm::SmallVector<llvm::Function *, 16> Work;

  struct EntryFunctionState {
    SourceLocation Loc;
  };

  ExecutionMode getExecutionMode() const;

  DataSharingMode getDataSharingMode() const;

  /// Get barrier to synchronize all threads in a block.
  void syncCTAThreads(CodeGenFunction &CGF);

  /// Helper for target directive initialization.
  void emitKernelInit(const OMPExecutableDirective &D, CodeGenFunction &CGF,
                      EntryFunctionState &EST, bool IsSPMD);

  /// Helper for target directive finalization.
  void emitKernelDeinit(CodeGenFunction &CGF, EntryFunctionState &EST,
                        bool IsSPMD);

  /// Helper for generic variables globalization prolog.
  void emitGenericVarsProlog(CodeGenFunction &CGF, SourceLocation Loc);

  /// Helper for generic variables globalization epilog.
  void emitGenericVarsEpilog(CodeGenFunction &CGF);

  //
  // Base class overrides.
  //

  /// Emit outlined function specialized for the Fork-Join
  /// programming model for applicable target directives on the NVPTX device.
  /// \param D Directive to emit.
  /// \param ParentName Name of the function that encloses the target region.
  /// \param OutlinedFn Outlined function value to be defined by this call.
  /// \param OutlinedFnID Outlined function ID value to be defined by this call.
  /// \param IsOffloadEntry True if the outlined function is an offload entry.
  /// An outlined function may not be an entry if, e.g. the if clause always
  /// evaluates to false.
  void emitNonSPMDKernel(const OMPExecutableDirective &D, StringRef ParentName,
                         llvm::Function *&OutlinedFn,
                         llvm::Constant *&OutlinedFnID, bool IsOffloadEntry,
                         const RegionCodeGenTy &CodeGen);

  /// Emit outlined function specialized for the Single Program
  /// Multiple Data programming model for applicable target directives on the
  /// NVPTX device.
  /// \param D Directive to emit.
  /// \param ParentName Name of the function that encloses the target region.
  /// \param OutlinedFn Outlined function value to be defined by this call.
  /// \param OutlinedFnID Outlined function ID value to be defined by this call.
  /// \param IsOffloadEntry True if the outlined function is an offload entry.
  /// \param CodeGen Object containing the target statements.
  /// An outlined function may not be an entry if, e.g. the if clause always
  /// evaluates to false.
  void emitSPMDKernel(const OMPExecutableDirective &D, StringRef ParentName,
                      llvm::Function *&OutlinedFn,
                      llvm::Constant *&OutlinedFnID, bool IsOffloadEntry,
                      const RegionCodeGenTy &CodeGen);

  /// Emit outlined function for 'target' directive on the NVPTX
  /// device.
  /// \param D Directive to emit.
  /// \param ParentName Name of the function that encloses the target region.
  /// \param OutlinedFn Outlined function value to be defined by this call.
  /// \param OutlinedFnID Outlined function ID value to be defined by this call.
  /// \param IsOffloadEntry True if the outlined function is an offload entry.
  /// An outlined function may not be an entry if, e.g. the if clause always
  /// evaluates to false.
  void emitTargetOutlinedFunction(const OMPExecutableDirective &D,
                                  StringRef ParentName,
                                  llvm::Function *&OutlinedFn,
                                  llvm::Constant *&OutlinedFnID,
                                  bool IsOffloadEntry,
                                  const RegionCodeGenTy &CodeGen) override;

protected:
  /// Check if the default location must be constant.
  /// Constant for NVPTX for better optimization.
  bool isDefaultLocationConstant() const override { return true; }

public:
  explicit CGOpenMPRuntimeGPU(CodeGenModule &CGM);

  bool isGPU() const override { return true; };

  /// Declare generalized virtual functions which need to be defined
  /// by all specializations of OpenMPGPURuntime Targets like AMDGCN
  /// and NVPTX.

  /// Check if the variable length declaration is delayed:
  bool isDelayedVariableLengthDecl(CodeGenFunction &CGF,
                                   const VarDecl *VD) const override;

  /// Get call to __kmpc_alloc_shared
  std::pair<llvm::Value *, llvm::Value *>
  getKmpcAllocShared(CodeGenFunction &CGF, const VarDecl *VD) override;

  /// Get call to __kmpc_free_shared
  void getKmpcFreeShared(
      CodeGenFunction &CGF,
      const std::pair<llvm::Value *, llvm::Value *> &AddrSizePair) override;

  /// Get the GPU warp size.
  llvm::Value *getGPUWarpSize(CodeGenFunction &CGF);

  /// Get the id of the current thread on the GPU.
  llvm::Value *getGPUThreadID(CodeGenFunction &CGF);

  /// Get the maximum number of threads in a block of the GPU.
  llvm::Value *getGPUNumThreads(CodeGenFunction &CGF);

  /// Emit call to void __kmpc_push_proc_bind(ident_t *loc, kmp_int32
  /// global_tid, int proc_bind) to generate code for 'proc_bind' clause.
  void emitProcBindClause(CodeGenFunction &CGF,
                          llvm::omp::ProcBindKind ProcBind,
                          SourceLocation Loc) override;

  /// Emits call to void __kmpc_push_num_threads(ident_t *loc, kmp_int32
  /// global_tid, kmp_int32 num_threads) to generate code for 'num_threads'
  /// clause.
  /// \param NumThreads An integer value of threads.
  void emitNumThreadsClause(CodeGenFunction &CGF, llvm::Value *NumThreads,
                            SourceLocation Loc) override;

  /// This function ought to emit, in the general case, a call to
  // the openmp runtime kmpc_push_num_teams. In NVPTX backend it is not needed
  // as these numbers are obtained through the PTX grid and block configuration.
  /// \param NumTeams An integer expression of teams.
  /// \param ThreadLimit An integer expression of threads.
  void emitNumTeamsClause(CodeGenFunction &CGF, const Expr *NumTeams,
                          const Expr *ThreadLimit, SourceLocation Loc) override;

  /// Emits inlined function for the specified OpenMP parallel
  //  directive.
  /// \a D. This outlined function has type void(*)(kmp_int32 *ThreadID,
  /// kmp_int32 BoundID, struct context_vars*).
  /// \param CGF Reference to current CodeGenFunction.
  /// \param D OpenMP directive.
  /// \param ThreadIDVar Variable for thread id in the current OpenMP region.
  /// \param InnermostKind Kind of innermost directive (for simple directives it
  /// is a directive itself, for combined - its innermost directive).
  /// \param CodeGen Code generation sequence for the \a D directive.
  llvm::Function *emitParallelOutlinedFunction(
      CodeGenFunction &CGF, const OMPExecutableDirective &D,
      const VarDecl *ThreadIDVar, OpenMPDirectiveKind InnermostKind,
      const RegionCodeGenTy &CodeGen) override;

  /// Emits inlined function for the specified OpenMP teams
  //  directive.
  /// \a D. This outlined function has type void(*)(kmp_int32 *ThreadID,
  /// kmp_int32 BoundID, struct context_vars*).
  /// \param CGF Reference to current CodeGenFunction.
  /// \param D OpenMP directive.
  /// \param ThreadIDVar Variable for thread id in the current OpenMP region.
  /// \param InnermostKind Kind of innermost directive (for simple directives it
  /// is a directive itself, for combined - its innermost directive).
  /// \param CodeGen Code generation sequence for the \a D directive.
  llvm::Function *emitTeamsOutlinedFunction(
      CodeGenFunction &CGF, const OMPExecutableDirective &D,
      const VarDecl *ThreadIDVar, OpenMPDirectiveKind InnermostKind,
      const RegionCodeGenTy &CodeGen) override;

  /// Emits code for teams call of the \a OutlinedFn with
  /// variables captured in a record which address is stored in \a
  /// CapturedStruct.
  /// \param OutlinedFn Outlined function to be run by team masters. Type of
  /// this function is void(*)(kmp_int32 *, kmp_int32, struct context_vars*).
  /// \param CapturedVars A pointer to the record with the references to
  /// variables used in \a OutlinedFn function.
  ///
  void emitTeamsCall(CodeGenFunction &CGF, const OMPExecutableDirective &D,
                     SourceLocation Loc, llvm::Function *OutlinedFn,
                     ArrayRef<llvm::Value *> CapturedVars) override;

  /// Emits code for parallel or serial call of the \a OutlinedFn with
  /// variables captured in a record which address is stored in \a
  /// CapturedStruct.
  /// \param OutlinedFn Outlined function to be run in parallel threads. Type of
  /// this function is void(*)(kmp_int32 *, kmp_int32, struct context_vars*).
  /// \param CapturedVars A pointer to the record with the references to
  /// variables used in \a OutlinedFn function.
  /// \param IfCond Condition in the associated 'if' clause, if it was
  /// specified, nullptr otherwise.
  /// \param NumThreads The value corresponding to the num_threads clause, if
  /// any,
  ///                   or nullptr.
  void emitParallelCall(CodeGenFunction &CGF, SourceLocation Loc,
                        llvm::Function *OutlinedFn,
                        ArrayRef<llvm::Value *> CapturedVars,
                        const Expr *IfCond, llvm::Value *NumThreads) override;

  /// Emit an implicit/explicit barrier for OpenMP threads.
  /// \param Kind Directive for which this implicit barrier call must be
  /// generated. Must be OMPD_barrier for explicit barrier generation.
  /// \param EmitChecks true if need to emit checks for cancellation barriers.
  /// \param ForceSimpleCall true simple barrier call must be emitted, false if
  /// runtime class decides which one to emit (simple or with cancellation
  /// checks).
  ///
  void emitBarrierCall(CodeGenFunction &CGF, SourceLocation Loc,
                       OpenMPDirectiveKind Kind, bool EmitChecks = true,
                       bool ForceSimpleCall = false) override;

  /// Emits a critical region.
  /// \param CriticalName Name of the critical region.
  /// \param CriticalOpGen Generator for the statement associated with the given
  /// critical region.
  /// \param Hint Value of the 'hint' clause (optional).
  void emitCriticalRegion(CodeGenFunction &CGF, StringRef CriticalName,
                          const RegionCodeGenTy &CriticalOpGen,
                          SourceLocation Loc,
                          const Expr *Hint = nullptr) override;

  /// Emit a code for reduction clause.
  ///
  /// \param Privates List of private copies for original reduction arguments.
  /// \param LHSExprs List of LHS in \a ReductionOps reduction operations.
  /// \param RHSExprs List of RHS in \a ReductionOps reduction operations.
  /// \param ReductionOps List of reduction operations in form 'LHS binop RHS'
  /// or 'operator binop(LHS, RHS)'.
  /// \param Options List of options for reduction codegen:
  ///     WithNowait true if parent directive has also nowait clause, false
  ///     otherwise.
  ///     SimpleReduction Emit reduction operation only. Used for omp simd
  ///     directive on the host.
  ///     ReductionKind The kind of reduction to perform.
  void emitReduction(CodeGenFunction &CGF, SourceLocation Loc,
                     ArrayRef<const Expr *> Privates,
                     ArrayRef<const Expr *> LHSExprs,
                     ArrayRef<const Expr *> RHSExprs,
                     ArrayRef<const Expr *> ReductionOps,
                     ReductionOptionsTy Options) override;

  /// Translates the native parameter of outlined function if this is required
  /// for target.
  /// \param FD Field decl from captured record for the parameter.
  /// \param NativeParam Parameter itself.
  const VarDecl *translateParameter(const FieldDecl *FD,
                                    const VarDecl *NativeParam) const override;

  /// Gets the address of the native argument basing on the address of the
  /// target-specific parameter.
  /// \param NativeParam Parameter itself.
  /// \param TargetParam Corresponding target-specific parameter.
  Address getParameterAddress(CodeGenFunction &CGF, const VarDecl *NativeParam,
                              const VarDecl *TargetParam) const override;

  /// Emits call of the outlined function with the provided arguments,
  /// translating these arguments to correct target-specific arguments.
  void emitOutlinedFunctionCall(
      CodeGenFunction &CGF, SourceLocation Loc, llvm::FunctionCallee OutlinedFn,
      ArrayRef<llvm::Value *> Args = std::nullopt) const override;

  /// Emits OpenMP-specific function prolog.
  /// Required for device constructs.
  void emitFunctionProlog(CodeGenFunction &CGF, const Decl *D) override;

  /// Gets the OpenMP-specific address of the local variable.
  Address getAddressOfLocalVariable(CodeGenFunction &CGF,
                                    const VarDecl *VD) override;

  /// Cleans up references to the objects in finished function.
  ///
  void functionFinished(CodeGenFunction &CGF) override;

  /// Choose a default value for the dist_schedule clause.
  void getDefaultDistScheduleAndChunk(CodeGenFunction &CGF,
      const OMPLoopDirective &S, OpenMPDistScheduleClauseKind &ScheduleKind,
      llvm::Value *&Chunk) const override;

  /// Choose a default value for the schedule clause.
  void getDefaultScheduleAndChunk(CodeGenFunction &CGF,
      const OMPLoopDirective &S, OpenMPScheduleClauseKind &ScheduleKind,
      const Expr *&ChunkExpr) const override;

  /// Adjust some parameters for the target-based directives, like addresses of
  /// the variables captured by reference in lambdas.
  void adjustTargetSpecificDataForLambdas(
      CodeGenFunction &CGF, const OMPExecutableDirective &D) const override;

  /// Perform check on requires decl to ensure that target architecture
  /// supports unified addressing
  void processRequiresDirective(const OMPRequiresDecl *D) override;

  /// Checks if the variable has associated OMPAllocateDeclAttr attribute with
  /// the predefined allocator and translates it into the corresponding address
  /// space.
  bool hasAllocateAttributeForGlobalVar(const VarDecl *VD, LangAS &AS) override;

private:
  /// Track the execution mode when codegening directives within a target
  /// region. The appropriate mode (SPMD/NON-SPMD) is set on entry to the
  /// target region and used by containing directives such as 'parallel'
  /// to emit optimized code.
  ExecutionMode CurrentExecutionMode = EM_Unknown;

  /// Track the data sharing mode when codegening directives within a target
  /// region.
  DataSharingMode CurrentDataSharingMode = DataSharingMode::DS_Generic;

  /// true if currently emitting code for target/teams/distribute region, false
  /// - otherwise.
  bool IsInTTDRegion = false;

  /// Map between an outlined function and its wrapper.
  llvm::DenseMap<llvm::Function *, llvm::Function *> WrapperFunctionsMap;

  /// Emit function which wraps the outline parallel region
  /// and controls the parameters which are passed to this function.
  /// The wrapper ensures that the outlined function is called
  /// with the correct arguments when data is shared.
  llvm::Function *createParallelDataSharingWrapper(
      llvm::Function *OutlinedParallelFn, const OMPExecutableDirective &D);

  /// The data for the single globalized variable.
  struct MappedVarData {
    /// Corresponding field in the global record.
    llvm::Value *GlobalizedVal = nullptr;
    /// Corresponding address.
    Address PrivateAddr = Address::invalid();
  };
  /// The map of local variables to their addresses in the global memory.
  using DeclToAddrMapTy = llvm::MapVector<const Decl *, MappedVarData>;
  /// Set of the parameters passed by value escaping OpenMP context.
  using EscapedParamsTy = llvm::SmallPtrSet<const Decl *, 4>;
  struct FunctionData {
    DeclToAddrMapTy LocalVarData;
    EscapedParamsTy EscapedParameters;
    llvm::SmallVector<const ValueDecl*, 4> EscapedVariableLengthDecls;
    llvm::SmallVector<const ValueDecl *, 4> DelayedVariableLengthDecls;
    llvm::SmallVector<std::pair<llvm::Value *, llvm::Value *>, 4>
        EscapedVariableLengthDeclsAddrs;
    std::unique_ptr<CodeGenFunction::OMPMapVars> MappedParams;
  };
  /// Maps the function to the list of the globalized variables with their
  /// addresses.
  llvm::SmallDenseMap<llvm::Function *, FunctionData> FunctionGlobalizedDecls;
  /// 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.
  /// All the records are gathered into a union `union.type` is created.
  llvm::SmallVector<const RecordDecl *, 4> TeamsReductions;
  /// Pair of the Non-SPMD team and all reductions variables in this team
  /// region.
  std::pair<const Decl *, llvm::SmallVector<const ValueDecl *, 4>>
      TeamAndReductions;
};

} // CodeGen namespace.
} // clang namespace.

#endif // LLVM_CLANG_LIB_CODEGEN_CGOPENMPRUNTIMEGPU_H