ACCDeclareGPUModuleInsertion.cpp

Go to the documentation of this file.

//===- ACCDeclareGPUModuleInsertion.cpp
//------------------------------------===//
//
// 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 pass copies globals marked with the `acc.declare` attribute into the
// GPU module so that device code (e.g. acc routine, compute regions) can
// reference them.
//
// Overview:
// ---------
// Globals that have the `acc.declare` attribute (from the OpenACC declare
// directive or from the `ACCImplicitDeclare` pass) must be present in the
// GPU module for device code to use them. This pass inserts copies of those
// globals into the GPU module, creating the module if it does not yet exist.
// The host copy of each global remains in the parent module.
//
// Example:
// --------
//
// Before:
//   module {
//     memref.global @arr : memref<7xf32> = dense<0.0>
//         {acc.declare = #acc.declare<dataClause = acc_create>}
//   }
//
// After:
//   module attributes {gpu.container_module} {
//     memref.global @arr : memref<7xf32> = dense<0.0>
//         {acc.declare = #acc.declare<dataClause = acc_create>}
//     gpu.module @acc_gpu_module {
//       memref.global @arr : memref<7xf32> = dense<0.0>
//           {acc.declare = #acc.declare<dataClause = acc_create>}
//     }
//   }
//
// Requirements:
// -------------
// The pass uses the `acc::OpenACCSupport` for:
// - getOrCreateGPUModule: to obtain or create the GPU module.
// - emitNYI: to report failure when GPU module creation is not supported.
// If no custom implementation is registered, the default implementation is
// used (see OpenACCSupport).
//
//===----------------------------------------------------------------------===//
 
#include "mlir/Dialect/GPU/IR/GPUDialect.h"
#include "mlir/Dialect/OpenACC/Analysis/OpenACCSupport.h"
#include "mlir/Dialect/OpenACC/OpenACC.h"
#include "mlir/Dialect/OpenACC/Transforms/Passes.h"
#include "mlir/IR/BuiltinOps.h"
#include "mlir/IR/Operation.h"
#include "mlir/IR/OperationSupport.h"
#include "mlir/IR/SymbolTable.h"
 
namespace mlir {
namespace acc {
#define GEN_PASS_DEF_ACCDECLAREGPUMODULEINSERTION
#include "mlir/Dialect/OpenACC/Transforms/Passes.h.inc"
} // namespace acc
} // namespace mlir
 
#define DEBUG_TYPE "acc-declare-gpu-module-insertion"
 
using namespace mlir;
 
namespace {
 
static bool hasAccDeclareGlobals(ModuleOp mod) {
  for (Operation &op : mod.getBody()->getOperations())
    if (op.getAttr(acc::getDeclareAttrName()))
      return true;
  return false;
}
 
static void makeDeviceGlobalDeclaration(Operation &globalOp) {
  globalOp.removeAttr("initVal");
  globalOp.removeAttr("linkName");
  for (Region &region : globalOp.getRegions()) {
    region.dropAllReferences();
    region.getBlocks().clear();
  }
}
 
class ACCDeclareGPUModuleInsertion
    : public acc::impl::ACCDeclareGPUModuleInsertionBase<
          ACCDeclareGPUModuleInsertion> {
public:
  using acc::impl::ACCDeclareGPUModuleInsertionBase<
      ACCDeclareGPUModuleInsertion>::ACCDeclareGPUModuleInsertionBase;
 
  LogicalResult copyGlobalsToGPUModule(gpu::GPUModuleOp gpuMod, ModuleOp mod,
                                       acc::OpenACCSupport &accSupport) const {
    SymbolTable gpuSymTable(gpuMod);
 
    for (Operation &globalOp : mod.getBody()->getOperations()) {
      if (!globalOp.getAttr(acc::getDeclareAttrName()))
        continue;
 
      auto symOp = dyn_cast<SymbolOpInterface>(&globalOp);
      if (!symOp)
        continue;
 
      StringAttr name = symOp.getNameAttr();
      Operation *deviceGlobal = globalOp.clone();
      auto declareAttr =
          globalOp.getAttrOfType<acc::DeclareAttr>(acc::getDeclareAttrName());
      auto globalVar = dyn_cast<acc::GlobalVariableOpInterface>(&globalOp);
      bool makeUnifiedDeclaration =
          cudaUnified &&
          declareAttr.getDataClause().getValue() !=
              acc::DataClause::acc_declare_device_resident &&
          (!globalVar || !globalVar.isConstant());
      if (makeUnifiedDeclaration)
        makeDeviceGlobalDeclaration(*deviceGlobal);
 
      if (Operation *existing = gpuSymTable.lookup(name.getValue())) {
        // Reuse when structurally equivalent ignoring locations and discardable
        // attrs such as `acc.declare` attributes. Only a different op type or a
        // true definition mismatch is a conflict.
        auto isEquivalent = [](Operation *lhs, Operation *rhs) {
          return lhs->getName() == rhs->getName() &&
                 OperationEquivalence::isEquivalentTo(
                     lhs, rhs, OperationEquivalence::ignoreValueEquivalence,
                     /*markEquivalent=*/nullptr,
                     OperationEquivalence::IgnoreLocations |
                         OperationEquivalence::IgnoreDiscardableAttrs);
        };
        if (!isEquivalent(existing, deviceGlobal)) {
          // Earlier GPU lowering can create a global in the GPU module before
          // this pass. In unified memory, convert an equivalent pre-existing
          // global to the declaration form expected for an OpenACC global.
          if (makeUnifiedDeclaration) {
            Operation *normalizedExisting = existing->clone();
            makeDeviceGlobalDeclaration(*normalizedExisting);
            bool canReuse = isEquivalent(normalizedExisting, deviceGlobal);
            normalizedExisting->destroy();
            if (canReuse)
              makeDeviceGlobalDeclaration(*existing);
          }
        }
        if (!isEquivalent(existing, deviceGlobal)) {
          deviceGlobal->destroy();
          accSupport.emitNYI(globalOp.getLoc(),
                             llvm::Twine("duplicate global symbol '") +
                                 name.getValue() + "' in gpu module");
          return failure();
        }
        // Propagate acc.declare onto the GPU copy if it was cloned before the
        // host global was marked.
        if (!existing->getAttr(acc::getDeclareAttrName()))
          if (Attribute declareAttr =
                  globalOp.getAttr(acc::getDeclareAttrName()))
            existing->setAttr(acc::getDeclareAttrName(), declareAttr);
        deviceGlobal->destroy();
        continue;
      }
 
      gpuSymTable.insert(deviceGlobal);
    }
    return success();
  }
 
  void runOnOperation() override {
    ModuleOp mod = getOperation();
 
    // Check for any candidates first - do this to avoid creating the GPU module
    // if there are no candidates.
    if (!hasAccDeclareGlobals(mod))
      return;
 
    acc::OpenACCSupport &accSupport = getAnalysis<acc::OpenACCSupport>();
    std::optional<gpu::GPUModuleOp> gpuMod =
        accSupport.getOrCreateGPUModule(mod);
    if (!gpuMod) {
      accSupport.emitNYI(mod.getLoc(), "Failed to create GPU module");
      return;
    }
 
    if (failed(copyGlobalsToGPUModule(*gpuMod, mod, accSupport)))
      return;
  }
};
 
} // namespace