241 lines
10 KiB
C++
241 lines
10 KiB
C++
//====- LowerToLLVM.cpp - Lowering from Toy+Affine+Std to LLVM ------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements full lowering of Toy operations to LLVM MLIR dialect.
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// 'toy.print' is lowered to a loop nest that calls `printf` on each element of
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// the input array. The file also sets up the ToyToLLVMLoweringPass. This pass
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// lowers the combination of Arithmetic + Affine + SCF + Func dialects to the
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// LLVM one:
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//
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// Affine --
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// |
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// v
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// Arithmetic + Func --> LLVM (Dialect)
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// ^
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// |
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// 'toy.print' --> Loop (SCF) --
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/Dialect/LLVMIR/LLVMAttrs.h"
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#include "mlir/Dialect/LLVMIR/LLVMTypes.h"
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#include "mlir/IR/BuiltinAttributes.h"
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#include "mlir/IR/BuiltinOps.h"
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#include "mlir/IR/BuiltinTypes.h"
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#include "mlir/Support/LLVM.h"
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#include "mlir/Support/TypeID.h"
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#include "toy/Dialect.h"
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#include "toy/Passes.h"
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#include "mlir/Conversion/AffineToStandard/AffineToStandard.h"
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#include "mlir/Conversion/ArithToLLVM/ArithToLLVM.h"
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#include "mlir/Conversion/ControlFlowToLLVM/ControlFlowToLLVM.h"
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#include "mlir/Conversion/FuncToLLVM/ConvertFuncToLLVM.h"
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#include "mlir/Conversion/FuncToLLVM/ConvertFuncToLLVMPass.h"
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#include "mlir/Conversion/LLVMCommon/ConversionTarget.h"
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#include "mlir/Conversion/LLVMCommon/TypeConverter.h"
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#include "mlir/Conversion/MemRefToLLVM/MemRefToLLVM.h"
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#include "mlir/Conversion/SCFToControlFlow/SCFToControlFlow.h"
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#include "mlir/Dialect/Arith/IR/Arith.h"
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#include "mlir/Dialect/Func/IR/FuncOps.h"
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#include "mlir/Dialect/LLVMIR/LLVMDialect.h"
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#include "mlir/Dialect/MemRef/IR/MemRef.h"
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#include "mlir/Dialect/SCF/IR/SCF.h"
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#include "mlir/Pass/Pass.h"
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#include "mlir/Transforms/DialectConversion.h"
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#include "llvm/Support/Casting.h"
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#include <memory>
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#include <utility>
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using namespace mlir;
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//===----------------------------------------------------------------------===//
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// ToyToLLVM RewritePatterns
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//===----------------------------------------------------------------------===//
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namespace {
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/// Lowers `toy.print` to a loop nest calling `printf` on each of the individual
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/// elements of the array.
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class PrintOpLowering : public ConversionPattern {
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public:
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explicit PrintOpLowering(MLIRContext *context)
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: ConversionPattern(toy::PrintOp::getOperationName(), 1, context) {}
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LogicalResult
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matchAndRewrite(Operation *op, ArrayRef<Value> operands,
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ConversionPatternRewriter &rewriter) const override {
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auto *context = rewriter.getContext();
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auto memRefType = llvm::cast<MemRefType>((*op->operand_type_begin()));
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auto memRefShape = memRefType.getShape();
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auto loc = op->getLoc();
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ModuleOp parentModule = op->getParentOfType<ModuleOp>();
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// Get a symbol reference to the printf function, inserting it if necessary.
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auto printfRef = getOrInsertPrintf(rewriter, parentModule);
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Value formatSpecifierCst = getOrCreateGlobalString(
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loc, rewriter, "frmt_spec", StringRef("%f \0", 4), parentModule);
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Value newLineCst = getOrCreateGlobalString(
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loc, rewriter, "nl", StringRef("\n\0", 2), parentModule);
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// Create a loop for each of the dimensions within the shape.
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SmallVector<Value, 4> loopIvs;
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for (unsigned i = 0, e = memRefShape.size(); i != e; ++i) {
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auto lowerBound = rewriter.create<arith::ConstantIndexOp>(loc, 0);
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auto upperBound =
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rewriter.create<arith::ConstantIndexOp>(loc, memRefShape[i]);
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auto step = rewriter.create<arith::ConstantIndexOp>(loc, 1);
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auto loop =
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rewriter.create<scf::ForOp>(loc, lowerBound, upperBound, step);
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for (Operation &nested : *loop.getBody())
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rewriter.eraseOp(&nested);
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loopIvs.push_back(loop.getInductionVar());
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// Terminate the loop body.
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rewriter.setInsertionPointToEnd(loop.getBody());
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// Insert a newline after each of the inner dimensions of the shape.
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if (i != e - 1)
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rewriter.create<LLVM::CallOp>(loc, getPrintfType(context), printfRef,
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newLineCst);
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rewriter.create<scf::YieldOp>(loc);
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rewriter.setInsertionPointToStart(loop.getBody());
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}
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// Generate a call to printf for the current element of the loop.
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auto printOp = cast<toy::PrintOp>(op);
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auto elementLoad =
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rewriter.create<memref::LoadOp>(loc, printOp.getInput(), loopIvs);
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rewriter.create<LLVM::CallOp>(
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loc, getPrintfType(context), printfRef,
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ArrayRef<Value>({formatSpecifierCst, elementLoad}));
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// Notify the rewriter that this operation has been removed.
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rewriter.eraseOp(op);
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return success();
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}
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private:
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/// Create a function declaration for printf, the signature is:
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/// * `i32 (i8*, ...)`
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static LLVM::LLVMFunctionType getPrintfType(MLIRContext *context) {
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auto llvmI32Ty = IntegerType::get(context, 32);
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auto llvmPtrTy = LLVM::LLVMPointerType::get(context);
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auto llvmFnType = LLVM::LLVMFunctionType::get(llvmI32Ty, llvmPtrTy,
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/*isVarArg=*/true);
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return llvmFnType;
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}
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/// Return a symbol reference to the printf function, inserting it into the
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/// module if necessary.
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static FlatSymbolRefAttr getOrInsertPrintf(PatternRewriter &rewriter,
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ModuleOp module) {
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auto *context = module.getContext();
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if (module.lookupSymbol<LLVM::LLVMFuncOp>("printf"))
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return SymbolRefAttr::get(context, "printf");
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// Insert the printf function into the body of the parent module.
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PatternRewriter::InsertionGuard insertGuard(rewriter);
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rewriter.setInsertionPointToStart(module.getBody());
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rewriter.create<LLVM::LLVMFuncOp>(module.getLoc(), "printf",
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getPrintfType(context));
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return SymbolRefAttr::get(context, "printf");
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}
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/// Return a value representing an access into a global string with the given
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/// name, creating the string if necessary.
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static Value getOrCreateGlobalString(Location loc, OpBuilder &builder,
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StringRef name, StringRef value,
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ModuleOp module) {
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// Create the global at the entry of the module.
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LLVM::GlobalOp global;
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if (!(global = module.lookupSymbol<LLVM::GlobalOp>(name))) {
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OpBuilder::InsertionGuard insertGuard(builder);
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builder.setInsertionPointToStart(module.getBody());
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auto type = LLVM::LLVMArrayType::get(
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IntegerType::get(builder.getContext(), 8), value.size());
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global = builder.create<LLVM::GlobalOp>(loc, type, /*isConstant=*/true,
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LLVM::Linkage::Internal, name,
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builder.getStringAttr(value),
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/*alignment=*/0);
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}
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// Get the pointer to the first character in the global string.
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Value globalPtr = builder.create<LLVM::AddressOfOp>(loc, global);
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Value cst0 = builder.create<LLVM::ConstantOp>(loc, builder.getI64Type(),
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builder.getIndexAttr(0));
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return builder.create<LLVM::GEPOp>(
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loc, LLVM::LLVMPointerType::get(builder.getContext()), global.getType(),
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globalPtr, ArrayRef<Value>({cst0, cst0}));
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}
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};
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} // namespace
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//===----------------------------------------------------------------------===//
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// ToyToLLVMLoweringPass
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//===----------------------------------------------------------------------===//
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namespace {
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struct ToyToLLVMLoweringPass
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: public PassWrapper<ToyToLLVMLoweringPass, OperationPass<ModuleOp>> {
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MLIR_DEFINE_EXPLICIT_INTERNAL_INLINE_TYPE_ID(ToyToLLVMLoweringPass)
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void getDependentDialects(DialectRegistry ®istry) const override {
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registry.insert<LLVM::LLVMDialect, scf::SCFDialect>();
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}
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void runOnOperation() final;
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};
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} // namespace
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void ToyToLLVMLoweringPass::runOnOperation() {
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// The first thing to define is the conversion target. This will define the
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// final target for this lowering. For this lowering, we are only targeting
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// the LLVM dialect.
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LLVMConversionTarget target(getContext());
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target.addLegalOp<ModuleOp>();
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// During this lowering, we will also be lowering the MemRef types, that are
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// currently being operated on, to a representation in LLVM. To perform this
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// conversion we use a TypeConverter as part of the lowering. This converter
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// details how one type maps to another. This is necessary now that we will be
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// doing more complicated lowerings, involving loop region arguments.
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LLVMTypeConverter typeConverter(&getContext());
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// Now that the conversion target has been defined, we need to provide the
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// patterns used for lowering. At this point of the compilation process, we
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// have a combination of `toy`, `affine`, and `std` operations. Luckily, there
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// are already exists a set of patterns to transform `affine` and `std`
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// dialects. These patterns lowering in multiple stages, relying on transitive
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// lowerings. Transitive lowering, or A->B->C lowering, is when multiple
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// patterns must be applied to fully transform an illegal operation into a
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// set of legal ones.
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RewritePatternSet patterns(&getContext());
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populateAffineToStdConversionPatterns(patterns);
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populateSCFToControlFlowConversionPatterns(patterns);
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mlir::arith::populateArithToLLVMConversionPatterns(typeConverter, patterns);
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populateFinalizeMemRefToLLVMConversionPatterns(typeConverter, patterns);
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cf::populateControlFlowToLLVMConversionPatterns(typeConverter, patterns);
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populateFuncToLLVMConversionPatterns(typeConverter, patterns);
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// The only remaining operation to lower from the `toy` dialect, is the
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// PrintOp.
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patterns.add<PrintOpLowering>(&getContext());
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// We want to completely lower to LLVM, so we use a `FullConversion`. This
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// ensures that only legal operations will remain after the conversion.
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auto module = getOperation();
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if (failed(applyFullConversion(module, target, std::move(patterns))))
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signalPassFailure();
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}
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/// Create a pass for lowering operations the remaining `Toy` operations, as
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/// well as `Affine` and `Std`, to the LLVM dialect for codegen.
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std::unique_ptr<mlir::Pass> mlir::toy::createLowerToLLVMPass() {
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return std::make_unique<ToyToLLVMLoweringPass>();
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}
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