GPUOpsLowering.cpp

Go to the documentation of this file.

//===- GPUOpsLowering.cpp - GPU FuncOp / ReturnOp lowering ----------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
 
#include "GPUOpsLowering.h"
#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/BuiltinTypes.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/FormatVariadic.h"
 
using namespace mlir;
 
LogicalResult
GPUFuncOpLowering::matchAndRewrite(gpu::GPUFuncOp gpuFuncOp, OpAdaptor adaptor,
                                   ConversionPatternRewriter &rewriter) const {
  Location loc = gpuFuncOp.getLoc();
 
  SmallVector<LLVM::GlobalOp, 3> workgroupBuffers;
  workgroupBuffers.reserve(gpuFuncOp.getNumWorkgroupAttributions());
  for (const auto &en : llvm::enumerate(gpuFuncOp.getWorkgroupAttributions())) {
    Value attribution = en.value();
 
    auto type = attribution.getType().dyn_cast<MemRefType>();
    assert(type && type.hasStaticShape() && "unexpected type in attribution");
 
    uint64_t numElements = type.getNumElements();
 
    auto elementType =
        typeConverter->convertType(type.getElementType()).template cast<Type>();
    auto arrayType = LLVM::LLVMArrayType::get(elementType, numElements);
    std::string name = std::string(
        llvm::formatv("__wg_{0}_{1}", gpuFuncOp.getName(), en.index()));
    auto globalOp = rewriter.create<LLVM::GlobalOp>(
        gpuFuncOp.getLoc(), arrayType, /*isConstant=*/false,
        LLVM::Linkage::Internal, name, /*value=*/Attribute(),
        /*alignment=*/0, workgroupAddrSpace);
    workgroupBuffers.push_back(globalOp);
  }
 
  // Rewrite the original GPU function to an LLVM function.
  auto convertedType = typeConverter->convertType(gpuFuncOp.getFunctionType());
  if (!convertedType)
    return failure();
  auto funcType =
      convertedType.template cast<LLVM::LLVMPointerType>().getElementType();
 
  // Remap proper input types.
  TypeConverter::SignatureConversion signatureConversion(
      gpuFuncOp.front().getNumArguments());
  getTypeConverter()->convertFunctionSignature(
      gpuFuncOp.getFunctionType(), /*isVariadic=*/false, signatureConversion);
 
  // Create the new function operation. Only copy those attributes that are
  // not specific to function modeling.
  SmallVector<NamedAttribute, 4> attributes;
  for (const auto &attr : gpuFuncOp->getAttrs()) {
    if (attr.getName() == SymbolTable::getSymbolAttrName() ||
        attr.getName() == gpuFuncOp.getFunctionTypeAttrName() ||
        attr.getName() == gpu::GPUFuncOp::getNumWorkgroupAttributionsAttrName())
      continue;
    attributes.push_back(attr);
  }
  // Add a dialect specific kernel attribute in addition to GPU kernel
  // attribute. The former is necessary for further translation while the
  // latter is expected by gpu.launch_func.
  if (gpuFuncOp.isKernel())
    attributes.emplace_back(kernelAttributeName, rewriter.getUnitAttr());
  auto llvmFuncOp = rewriter.create<LLVM::LLVMFuncOp>(
      gpuFuncOp.getLoc(), gpuFuncOp.getName(), funcType,
      LLVM::Linkage::External, /*dsoLocal*/ false, /*cconv*/ LLVM::CConv::C,
      attributes);
 
  {
    // Insert operations that correspond to converted workgroup and private
    // memory attributions to the body of the function. This must operate on
    // the original function, before the body region is inlined in the new
    // function to maintain the relation between block arguments and the
    // parent operation that assigns their semantics.
    OpBuilder::InsertionGuard guard(rewriter);
 
    // Rewrite workgroup memory attributions to addresses of global buffers.
    rewriter.setInsertionPointToStart(&gpuFuncOp.front());
    unsigned numProperArguments = gpuFuncOp.getNumArguments();
 
    for (const auto &en : llvm::enumerate(workgroupBuffers)) {
      LLVM::GlobalOp global = en.value();
      Value address = rewriter.create<LLVM::AddressOfOp>(loc, global);
      auto elementType =
          global.getType().cast<LLVM::LLVMArrayType>().getElementType();
      Value memory = rewriter.create<LLVM::GEPOp>(
          loc, LLVM::LLVMPointerType::get(elementType, global.getAddrSpace()),
          address, ArrayRef<LLVM::GEPArg>{0, 0});
 
      // Build a memref descriptor pointing to the buffer to plug with the
      // existing memref infrastructure. This may use more registers than
      // otherwise necessary given that memref sizes are fixed, but we can try
      // and canonicalize that away later.
      Value attribution = gpuFuncOp.getWorkgroupAttributions()[en.index()];
      auto type = attribution.getType().cast<MemRefType>();
      auto descr = MemRefDescriptor::fromStaticShape(
          rewriter, loc, *getTypeConverter(), type, memory);
      signatureConversion.remapInput(numProperArguments + en.index(), descr);
    }
 
    // Rewrite private memory attributions to alloca'ed buffers.
    unsigned numWorkgroupAttributions = gpuFuncOp.getNumWorkgroupAttributions();
    auto int64Ty = IntegerType::get(rewriter.getContext(), 64);
    for (const auto &en : llvm::enumerate(gpuFuncOp.getPrivateAttributions())) {
      Value attribution = en.value();
      auto type = attribution.getType().cast<MemRefType>();
      assert(type && type.hasStaticShape() && "unexpected type in attribution");
 
      // Explicitly drop memory space when lowering private memory
      // attributions since NVVM models it as `alloca`s in the default
      // memory space and does not support `alloca`s with addrspace(5).
      auto ptrType = LLVM::LLVMPointerType::get(
          typeConverter->convertType(type.getElementType())
              .template cast<Type>(),
          allocaAddrSpace);
      Value numElements = rewriter.create<LLVM::ConstantOp>(
          gpuFuncOp.getLoc(), int64Ty, type.getNumElements());
      Value allocated = rewriter.create<LLVM::AllocaOp>(
          gpuFuncOp.getLoc(), ptrType, numElements, /*alignment=*/0);
      auto descr = MemRefDescriptor::fromStaticShape(
          rewriter, loc, *getTypeConverter(), type, allocated);
      signatureConversion.remapInput(
          numProperArguments + numWorkgroupAttributions + en.index(), descr);
    }
  }
 
  // Move the region to the new function, update the entry block signature.
  rewriter.inlineRegionBefore(gpuFuncOp.getBody(), llvmFuncOp.getBody(),
                              llvmFuncOp.end());
  if (failed(rewriter.convertRegionTypes(&llvmFuncOp.getBody(), *typeConverter,
                                         &signatureConversion)))
    return failure();
 
  // If bare memref pointers are being used, remap them back to memref
  // descriptors This must be done after signature conversion to get rid of the
  // unrealized casts.
  if (getTypeConverter()->getOptions().useBarePtrCallConv) {
    OpBuilder::InsertionGuard guard(rewriter);
    rewriter.setInsertionPointToStart(&llvmFuncOp.getBody().front());
    for (const auto &en : llvm::enumerate(gpuFuncOp.getArgumentTypes())) {
      auto memrefTy = en.value().dyn_cast<MemRefType>();
      if (!memrefTy)
        continue;
      assert(memrefTy.hasStaticShape() &&
             "Bare pointer convertion used with dynamically-shaped memrefs");
      // Use a placeholder when replacing uses of the memref argument to prevent
      // circular replacements.
      auto remapping = signatureConversion.getInputMapping(en.index());
      assert(remapping && remapping->size == 1 &&
             "Type converter should produce 1-to-1 mapping for bare memrefs");
      BlockArgument newArg =
          llvmFuncOp.getBody().getArgument(remapping->inputNo);
      auto placeholder = rewriter.create<LLVM::UndefOp>(
          loc, getTypeConverter()->convertType(memrefTy));
      rewriter.replaceUsesOfBlockArgument(newArg, placeholder);
      Value desc = MemRefDescriptor::fromStaticShape(
          rewriter, loc, *getTypeConverter(), memrefTy, newArg);
      rewriter.replaceOp(placeholder, {desc});
    }
  }
 
  rewriter.eraseOp(gpuFuncOp);
  return success();
}
 
static SmallString<16> getUniqueFormatGlobalName(gpu::GPUModuleOp moduleOp) {
  const char formatStringPrefix[] = "printfFormat_";
  // Get a unique global name.
  unsigned stringNumber = 0;
  SmallString<16> stringConstName;
  do {
    stringConstName.clear();
    (formatStringPrefix + Twine(stringNumber++)).toStringRef(stringConstName);
  } while (moduleOp.lookupSymbol(stringConstName));
  return stringConstName;
}
 
template <typename T>
static LLVM::LLVMFuncOp getOrDefineFunction(T &moduleOp, const Location loc,
                                            ConversionPatternRewriter &rewriter,
                                            StringRef name,
                                            LLVM::LLVMFunctionType type) {
  LLVM::LLVMFuncOp ret;
  if (!(ret = moduleOp.template lookupSymbol<LLVM::LLVMFuncOp>(name))) {
    ConversionPatternRewriter::InsertionGuard guard(rewriter);
    rewriter.setInsertionPointToStart(moduleOp.getBody());
    ret = rewriter.create<LLVM::LLVMFuncOp>(loc, name, type,
                                            LLVM::Linkage::External);
  }
  return ret;
}
 
LogicalResult GPUPrintfOpToHIPLowering::matchAndRewrite(
    gpu::PrintfOp gpuPrintfOp, gpu::PrintfOpAdaptor adaptor,
    ConversionPatternRewriter &rewriter) const {
  Location loc = gpuPrintfOp->getLoc();
 
  mlir::Type llvmI8 = typeConverter->convertType(rewriter.getI8Type());
  mlir::Type i8Ptr = LLVM::LLVMPointerType::get(llvmI8);
  mlir::Type llvmI32 = typeConverter->convertType(rewriter.getI32Type());
  mlir::Type llvmI64 = typeConverter->convertType(rewriter.getI64Type());
  // Note: this is the GPUModule op, not the ModuleOp that surrounds it
  // This ensures that global constants and declarations are placed within
  // the device code, not the host code
  auto moduleOp = gpuPrintfOp->getParentOfType<gpu::GPUModuleOp>();
 
  auto ocklBegin =
      getOrDefineFunction(moduleOp, loc, rewriter, "__ockl_printf_begin",
                          LLVM::LLVMFunctionType::get(llvmI64, {llvmI64}));
  LLVM::LLVMFuncOp ocklAppendArgs;
  if (!adaptor.getArgs().empty()) {
    ocklAppendArgs = getOrDefineFunction(
        moduleOp, loc, rewriter, "__ockl_printf_append_args",
        LLVM::LLVMFunctionType::get(
            llvmI64, {llvmI64, /*numArgs*/ llvmI32, llvmI64, llvmI64, llvmI64,
                      llvmI64, llvmI64, llvmI64, llvmI64, /*isLast*/ llvmI32}));
  }
  auto ocklAppendStringN = getOrDefineFunction(
      moduleOp, loc, rewriter, "__ockl_printf_append_string_n",
      LLVM::LLVMFunctionType::get(
          llvmI64,
          {llvmI64, i8Ptr, /*length (bytes)*/ llvmI64, /*isLast*/ llvmI32}));
 
  /// Start the printf hostcall
  Value zeroI64 = rewriter.create<LLVM::ConstantOp>(loc, llvmI64, 0);
  auto printfBeginCall = rewriter.create<LLVM::CallOp>(loc, ocklBegin, zeroI64);
  Value printfDesc = printfBeginCall.getResult();
 
  // Get a unique global name for the format.
  SmallString<16> stringConstName = getUniqueFormatGlobalName(moduleOp);
 
  llvm::SmallString<20> formatString(adaptor.getFormat());
  formatString.push_back('\0'); // Null terminate for C
  size_t formatStringSize = formatString.size_in_bytes();
 
  auto globalType = LLVM::LLVMArrayType::get(llvmI8, formatStringSize);
  LLVM::GlobalOp global;
  {
    ConversionPatternRewriter::InsertionGuard guard(rewriter);
    rewriter.setInsertionPointToStart(moduleOp.getBody());
    global = rewriter.create<LLVM::GlobalOp>(
        loc, globalType,
        /*isConstant=*/true, LLVM::Linkage::Internal, stringConstName,
        rewriter.getStringAttr(formatString));
  }
 
  // Get a pointer to the format string's first element and pass it to printf()
  Value globalPtr = rewriter.create<LLVM::AddressOfOp>(loc, global);
  Value stringStart = rewriter.create<LLVM::GEPOp>(
      loc, i8Ptr, globalPtr, ArrayRef<LLVM::GEPArg>{0, 0});
  Value stringLen =
      rewriter.create<LLVM::ConstantOp>(loc, llvmI64, formatStringSize);
 
  Value oneI32 = rewriter.create<LLVM::ConstantOp>(loc, llvmI32, 1);
  Value zeroI32 = rewriter.create<LLVM::ConstantOp>(loc, llvmI32, 0);
 
  auto appendFormatCall = rewriter.create<LLVM::CallOp>(
      loc, ocklAppendStringN,
      ValueRange{printfDesc, stringStart, stringLen,
                 adaptor.getArgs().empty() ? oneI32 : zeroI32});
  printfDesc = appendFormatCall.getResult();
 
  // __ockl_printf_append_args takes 7 values per append call
  constexpr size_t argsPerAppend = 7;
  size_t nArgs = adaptor.getArgs().size();
  for (size_t group = 0; group < nArgs; group += argsPerAppend) {
    size_t bound = std::min(group + argsPerAppend, nArgs);
    size_t numArgsThisCall = bound - group;
 
    SmallVector<mlir::Value, 2 + argsPerAppend + 1> arguments;
    arguments.push_back(printfDesc);
    arguments.push_back(
        rewriter.create<LLVM::ConstantOp>(loc, llvmI32, numArgsThisCall));
    for (size_t i = group; i < bound; ++i) {
      Value arg = adaptor.getArgs()[i];
      if (auto floatType = arg.getType().dyn_cast<FloatType>()) {
        if (!floatType.isF64())
          arg = rewriter.create<LLVM::FPExtOp>(
              loc, typeConverter->convertType(rewriter.getF64Type()), arg);
        arg = rewriter.create<LLVM::BitcastOp>(loc, llvmI64, arg);
      }
      if (arg.getType().getIntOrFloatBitWidth() != 64)
        arg = rewriter.create<LLVM::ZExtOp>(loc, llvmI64, arg);
 
      arguments.push_back(arg);
    }
    // Pad out to 7 arguments since the hostcall always needs 7
    for (size_t extra = numArgsThisCall; extra < argsPerAppend; ++extra) {
      arguments.push_back(zeroI64);
    }
 
    auto isLast = (bound == nArgs) ? oneI32 : zeroI32;
    arguments.push_back(isLast);
    auto call = rewriter.create<LLVM::CallOp>(loc, ocklAppendArgs, arguments);
    printfDesc = call.getResult();
  }
  rewriter.eraseOp(gpuPrintfOp);
  return success();
}
 
LogicalResult GPUPrintfOpToLLVMCallLowering::matchAndRewrite(
    gpu::PrintfOp gpuPrintfOp, gpu::PrintfOpAdaptor adaptor,
    ConversionPatternRewriter &rewriter) const {
  Location loc = gpuPrintfOp->getLoc();
 
  mlir::Type llvmI8 = typeConverter->convertType(rewriter.getIntegerType(8));
  mlir::Type i8Ptr = LLVM::LLVMPointerType::get(llvmI8, addressSpace);
 
  // Note: this is the GPUModule op, not the ModuleOp that surrounds it
  // This ensures that global constants and declarations are placed within
  // the device code, not the host code
  auto moduleOp = gpuPrintfOp->getParentOfType<gpu::GPUModuleOp>();
 
  auto printfType = LLVM::LLVMFunctionType::get(rewriter.getI32Type(), {i8Ptr},
                                                /*isVarArg=*/true);
  LLVM::LLVMFuncOp printfDecl =
      getOrDefineFunction(moduleOp, loc, rewriter, "printf", printfType);
 
  // Get a unique global name for the format.
  SmallString<16> stringConstName = getUniqueFormatGlobalName(moduleOp);
 
  llvm::SmallString<20> formatString(adaptor.getFormat());
  formatString.push_back('\0'); // Null terminate for C
  auto globalType =
      LLVM::LLVMArrayType::get(llvmI8, formatString.size_in_bytes());
  LLVM::GlobalOp global;
  {
    ConversionPatternRewriter::InsertionGuard guard(rewriter);
    rewriter.setInsertionPointToStart(moduleOp.getBody());
    global = rewriter.create<LLVM::GlobalOp>(
        loc, globalType,
        /*isConstant=*/true, LLVM::Linkage::Internal, stringConstName,
        rewriter.getStringAttr(formatString), /*allignment=*/0, addressSpace);
  }
 
  // Get a pointer to the format string's first element
  Value globalPtr = rewriter.create<LLVM::AddressOfOp>(loc, global);
  Value stringStart = rewriter.create<LLVM::GEPOp>(
      loc, i8Ptr, globalPtr, ArrayRef<LLVM::GEPArg>{0, 0});
 
  // Construct arguments and function call
  auto argsRange = adaptor.getArgs();
  SmallVector<Value, 4> printfArgs;
  printfArgs.reserve(argsRange.size() + 1);
  printfArgs.push_back(stringStart);
  printfArgs.append(argsRange.begin(), argsRange.end());
 
  rewriter.create<LLVM::CallOp>(loc, printfDecl, printfArgs);
  rewriter.eraseOp(gpuPrintfOp);
  return success();
}
 
LogicalResult GPUPrintfOpToVPrintfLowering::matchAndRewrite(
    gpu::PrintfOp gpuPrintfOp, gpu::PrintfOpAdaptor adaptor,
    ConversionPatternRewriter &rewriter) const {
  Location loc = gpuPrintfOp->getLoc();
 
  mlir::Type llvmI8 = typeConverter->convertType(rewriter.getIntegerType(8));
  mlir::Type i8Ptr = LLVM::LLVMPointerType::get(llvmI8);
 
  // Note: this is the GPUModule op, not the ModuleOp that surrounds it
  // This ensures that global constants and declarations are placed within
  // the device code, not the host code
  auto moduleOp = gpuPrintfOp->getParentOfType<gpu::GPUModuleOp>();
 
  auto vprintfType =
      LLVM::LLVMFunctionType::get(rewriter.getI32Type(), {i8Ptr, i8Ptr});
  LLVM::LLVMFuncOp vprintfDecl =
      getOrDefineFunction(moduleOp, loc, rewriter, "vprintf", vprintfType);
 
  // Get a unique global name for the format.
  SmallString<16> stringConstName = getUniqueFormatGlobalName(moduleOp);
 
  llvm::SmallString<20> formatString(adaptor.getFormat());
  formatString.push_back('\0'); // Null terminate for C
  auto globalType =
      LLVM::LLVMArrayType::get(llvmI8, formatString.size_in_bytes());
  LLVM::GlobalOp global;
  {
    ConversionPatternRewriter::InsertionGuard guard(rewriter);
    rewriter.setInsertionPointToStart(moduleOp.getBody());
    global = rewriter.create<LLVM::GlobalOp>(
        loc, globalType,
        /*isConstant=*/true, LLVM::Linkage::Internal, stringConstName,
        rewriter.getStringAttr(formatString), /*allignment=*/0);
  }
 
  // Get a pointer to the format string's first element
  Value globalPtr = rewriter.create<LLVM::AddressOfOp>(loc, global);
  Value stringStart = rewriter.create<LLVM::GEPOp>(
      loc, i8Ptr, globalPtr, ArrayRef<LLVM::GEPArg>{0, 0});
  SmallVector<Type> types;
  SmallVector<Value> args;
  // Promote and pack the arguments into a stack allocation.
  for (Value arg : adaptor.getArgs()) {
    Type type = arg.getType();
    Value promotedArg = arg;
    assert(type.isIntOrFloat());
    if (type.isa<FloatType>()) {
      type = rewriter.getF64Type();
      promotedArg = rewriter.create<LLVM::FPExtOp>(loc, type, arg);
    }
    types.push_back(type);
    args.push_back(promotedArg);
  }
  Type structType =
      LLVM::LLVMStructType::getLiteral(gpuPrintfOp.getContext(), types);
  Type structPtrType = LLVM::LLVMPointerType::get(structType);
  Value one = rewriter.create<LLVM::ConstantOp>(loc, rewriter.getI64Type(),
                                                rewriter.getIndexAttr(1));
  Value tempAlloc = rewriter.create<LLVM::AllocaOp>(loc, structPtrType, one,
                                                    /*alignment=*/0);
  for (auto [index, arg] : llvm::enumerate(args)) {
    Value ptr = rewriter.create<LLVM::GEPOp>(
        loc, LLVM::LLVMPointerType::get(arg.getType()), tempAlloc,
        ArrayRef<LLVM::GEPArg>{0, index});
    rewriter.create<LLVM::StoreOp>(loc, arg, ptr);
  }
  tempAlloc = rewriter.create<LLVM::BitcastOp>(loc, i8Ptr, tempAlloc);
  std::array<Value, 2> printfArgs = {stringStart, tempAlloc};
 
  rewriter.create<LLVM::CallOp>(loc, vprintfDecl, printfArgs);
  rewriter.eraseOp(gpuPrintfOp);
  return success();
}
 
/// Unrolls op if it's operating on vectors.
LogicalResult impl::scalarizeVectorOp(Operation *op, ValueRange operands,
                                      ConversionPatternRewriter &rewriter,
                                      LLVMTypeConverter &converter) {
  TypeRange operandTypes(operands);
  if (llvm::none_of(operandTypes,
                    [](Type type) { return type.isa<VectorType>(); })) {
    return rewriter.notifyMatchFailure(op, "expected vector operand");
  }
  if (op->getNumRegions() != 0 || op->getNumSuccessors() != 0)
    return rewriter.notifyMatchFailure(op, "expected no region/successor");
  if (op->getNumResults() != 1)
    return rewriter.notifyMatchFailure(op, "expected single result");
  VectorType vectorType = op->getResult(0).getType().dyn_cast<VectorType>();
  if (!vectorType)
    return rewriter.notifyMatchFailure(op, "expected vector result");
 
  Location loc = op->getLoc();
  Value result = rewriter.create<LLVM::UndefOp>(loc, vectorType);
  Type indexType = converter.convertType(rewriter.getIndexType());
  StringAttr name = op->getName().getIdentifier();
  Type elementType = vectorType.getElementType();
 
  for (int64_t i = 0; i < vectorType.getNumElements(); ++i) {
    Value index = rewriter.create<LLVM::ConstantOp>(loc, indexType, i);
    auto extractElement = [&](Value operand) -> Value {
      if (!operand.getType().isa<VectorType>())
        return operand;
      return rewriter.create<LLVM::ExtractElementOp>(loc, operand, index);
    };
    auto scalarOperands =
        llvm::to_vector(llvm::map_range(operands, extractElement));
    Operation *scalarOp =
        rewriter.create(loc, name, scalarOperands, elementType, op->getAttrs());
    rewriter.create<LLVM::InsertElementOp>(loc, result, scalarOp->getResult(0),
                                           index);
  }
 
  rewriter.replaceOp(op, result);
  return success();
}