131 lines
4.5 KiB
C++
131 lines
4.5 KiB
C++
//===- Unroll.cpp - Code to perform loop unrolling ------------------------===//
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//
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// Copyright 2019 The MLIR Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// =============================================================================
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//
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// This file implements loop unrolling.
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//
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//===----------------------------------------------------------------------===//
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#include "mlir/IR/Builders.h"
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#include "mlir/IR/CFGFunction.h"
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#include "mlir/IR/MLFunction.h"
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#include "mlir/IR/Module.h"
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#include "mlir/IR/OperationSet.h"
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#include "mlir/IR/Pass.h"
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#include "mlir/IR/Statements.h"
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#include "mlir/IR/StmtVisitor.h"
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#include "mlir/Transforms/Passes.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace mlir;
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namespace {
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struct LoopUnroll : public MLFunctionPass {
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void runOnMLFunction(MLFunction *f) override;
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void runOnForStmt(ForStmt *forStmt);
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};
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} // end anonymous namespace
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MLFunctionPass *mlir::createLoopUnrollPass() { return new LoopUnroll(); }
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/// Unrolls all the innermost loops of this MLFunction.
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void LoopUnroll::runOnMLFunction(MLFunction *f) {
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// Gathers all innermost loops through a post order pruned walk.
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// TODO: figure out the right reusable template here to better refactor code.
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class InnermostLoopGatherer : public StmtWalker<InnermostLoopGatherer, bool> {
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public:
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// Store innermost loops as we walk.
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std::vector<ForStmt *> loops;
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// This method specialized to encode custom return logic.
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typedef llvm::iplist<Statement> StmtListType;
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bool walkPostOrder(StmtListType::iterator Start,
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StmtListType::iterator End) {
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while (Start != End)
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if (walkPostOrder(&(*Start++)))
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return true;
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return false;
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}
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// FIXME: can't use base class method for this because that in turn would
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// need to use the derived class method above. CRTP doesn't allow it, and
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// the compiler error resulting from it is also very misleading!
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void walkPostOrder(MLFunction *f) { walkPostOrder(f->begin(), f->end()); }
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bool walkForStmtPostOrder(ForStmt *forStmt) {
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bool hasInnerLoops = walkPostOrder(forStmt->begin(), forStmt->end());
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if (!hasInnerLoops)
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loops.push_back(forStmt);
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return true;
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}
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bool walkIfStmtPostOrder(IfStmt *ifStmt) {
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if (walkPostOrder(ifStmt->getThenClause()->begin(),
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ifStmt->getThenClause()->end()) ||
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walkPostOrder(ifStmt->getElseClause()->begin(),
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ifStmt->getElseClause()->end()))
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return true;
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return false;
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}
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bool walkOpStmt(OperationStmt *opStmt) { return false; }
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using StmtWalker<InnermostLoopGatherer, bool>::walkPostOrder;
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};
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InnermostLoopGatherer ilg;
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ilg.walkPostOrder(f);
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auto &loops = ilg.loops;
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for (auto *forStmt : loops)
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runOnForStmt(forStmt);
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}
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/// Unrolls this loop completely. Returns true if the unrolling happens.
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void LoopUnroll::runOnForStmt(ForStmt *forStmt) {
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auto lb = forStmt->getLowerBound()->getValue();
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auto ub = forStmt->getUpperBound()->getValue();
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auto step = forStmt->getStep()->getValue();
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auto trip_count = (ub - lb + 1) / step;
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auto *block = forStmt->getBlock();
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MLFuncBuilder builder(forStmt->Statement::getFunction());
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builder.setInsertionPoint(block);
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for (int i = 0; i < trip_count; i++) {
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for (auto &stmt : forStmt->getStatements()) {
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switch (stmt.getKind()) {
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case Statement::Kind::For:
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llvm_unreachable("unrolling loops that have only operations");
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break;
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case Statement::Kind::If:
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llvm_unreachable("unrolling loops that have only operations");
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break;
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case Statement::Kind::Operation:
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auto *op = cast<OperationStmt>(&stmt);
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// TODO: clone operands and result types.
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builder.createOperation(op->getName(), /*operands*/ {},
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/*resultTypes*/ {}, op->getAttrs());
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// TODO: loop iterator parsing not yet implemented; replace loop
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// iterator uses in unrolled body appropriately.
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break;
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}
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}
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}
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forStmt->eraseFromBlock();
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}
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