SPIRVLowerOCLBlocks.cpp

//===- SPIRVLowerOCLBlocks.cpp - OCL Utilities ----------------------------===//
//
//                     The LLVM/SPIRV Translator
//
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//===----------------------------------------------------------------------===//
//
// SPIR-V specification doesn't allow function pointers, so SPIR-V translator
// is designed to fail if a value with function type (except calls) occurs.
// Currently there is only two cases, when function pointers are generating in
// LLVM IR in OpenCL - block calls and device side enqueue built-in calls.
//
// In both cases values with function type used as intermediate representation
// for block literal structure.
//
// In LLVM IR produced by clang, blocks are represented with the following
// structure:
// %struct.__opencl_block_literal_generic = type { i32, i32, i8 addrspace(4)* }
// Pointers to block invoke functions are stored in the third field. Clang
// replaces indirect function calls in all cases except if block is passed as a
// function argument. Note that it is somewhat unclear if the OpenCL C spec
// should allow passing blocks as function arguments. This pass is not supposed
// to work correctly with such functions.
// Clang though has to store function pointers to this structure. Purpose of
// this pass is to replace store of function pointers(not allowed in SPIR-V)
// with null pointers.
//
//===----------------------------------------------------------------------===//

#include "SPIRVLowerOCLBlocks.h"
#include "SPIRVInternal.h"

#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Pass.h"
#include "llvm/Support/Regex.h"

#define DEBUG_TYPE "spv-lower-ocl-blocks"

using namespace llvm;

namespace {

static bool isBlockInvoke(Function &F) {
  static Regex BlockInvokeRegex("_block_invoke_?[0-9]*$");
  return BlockInvokeRegex.match(F.getName());
}

} // namespace

namespace SPIRV {

bool SPIRVLowerOCLBlocksBase::runLowerOCLBlocks(Module &M) {
  bool Changed = false;
  for (Function &F : M) {
    if (!isBlockInvoke(F))
      continue;
    for (User *U : F.users()) {
      if (!isa<Constant>(U))
        continue;
      Constant *Null = Constant::getNullValue(U->getType());
      if (U != Null) {
        U->replaceAllUsesWith(Null);
        Changed = true;
      }
    }
  }
  return Changed;
}

llvm::PreservedAnalyses
SPIRVLowerOCLBlocksPass::run(llvm::Module &M,
                             llvm::ModuleAnalysisManager &MAM) {
  return runLowerOCLBlocks(M) ? llvm::PreservedAnalyses::none()
                              : llvm::PreservedAnalyses::all();
}

char SPIRVLowerOCLBlocksLegacy::ID = 0;

} // namespace SPIRV

INITIALIZE_PASS(SPIRVLowerOCLBlocksLegacy, "spv-lower-ocl-blocks",
                "Remove function pointers originating from OpenCL blocks",
                false, false)

llvm::ModulePass *llvm::createSPIRVLowerOCLBlocksLegacy() {
  return new SPIRVLowerOCLBlocksLegacy();
}