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//===- PatternMatch.cpp - Base classes for pattern match ------------------===//
//
// Copyright 2019 The MLIR Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// =============================================================================
#include "mlir/IR/SSAValue.h"
#include "mlir/IR/Statements.h"
#include "mlir/StandardOps/StandardOps.h"
#include "mlir/Transforms/PatternMatch.h"
using namespace mlir;
PatternBenefit::PatternBenefit(unsigned benefit) : representation(benefit) {
assert(representation == benefit && benefit != ImpossibleToMatchSentinel &&
"This pattern match benefit is too large to represent");
}
unsigned short PatternBenefit::getBenefit() const {
assert(representation != ImpossibleToMatchSentinel &&
"Pattern doesn't match");
return representation;
}
bool PatternBenefit::operator==(const PatternBenefit& other) {
if (isImpossibleToMatch())
return other.isImpossibleToMatch();
if (other.isImpossibleToMatch())
return false;
return getBenefit() == other.getBenefit();
}
bool PatternBenefit::operator!=(const PatternBenefit& other) {
return !(*this == other);
}
//===----------------------------------------------------------------------===//
// Pattern implementation
//===----------------------------------------------------------------------===//
Pattern::Pattern(StringRef rootName, MLIRContext *context,
Optional<PatternBenefit> staticBenefit)
: rootKind(OperationName(rootName, context)), staticBenefit(staticBenefit) {
}
Pattern::Pattern(StringRef rootName, MLIRContext *context,
unsigned staticBenefit)
: rootKind(rootName, context), staticBenefit(staticBenefit) {}
Optional<PatternBenefit> Pattern::getStaticBenefit() const {
return staticBenefit;
}
OperationName Pattern::getRootKind() const { return rootKind; }
void Pattern::rewrite(Operation *op, std::unique_ptr<PatternState> state,
PatternRewriter &rewriter) const {
rewrite(op, rewriter);
}
void Pattern::rewrite(Operation *op, PatternRewriter &rewriter) const {
llvm_unreachable("need to implement one of the rewrite functions!");
}
/// This method indicates that no match was found.
PatternMatchResult Pattern::matchFailure() {
return {PatternBenefit::impossibleToMatch(), std::unique_ptr<PatternState>()};
}
/// This method indicates that a match was found and has the specified cost.
PatternMatchResult
Pattern::matchSuccess(PatternBenefit benefit,
std::unique_ptr<PatternState> state) const {
assert((!getStaticBenefit().hasValue() ||
getStaticBenefit().getValue() == benefit) &&
"This version of matchSuccess must be called with a benefit that "
"matches the static benefit if set!");
return {benefit, std::move(state)};
}
/// This method indicates that a match was found for patterns that have a
/// known static benefit.
PatternMatchResult
Pattern::matchSuccess(std::unique_ptr<PatternState> state) const {
auto benefit = getStaticBenefit();
assert(benefit.hasValue() && "Pattern doesn't have a static benefit");
return matchSuccess(benefit.getValue(), std::move(state));
}
//===----------------------------------------------------------------------===//
// PatternRewriter implementation
//===----------------------------------------------------------------------===//
PatternRewriter::~PatternRewriter() {
// Out of line to provide a vtable anchor for the class.
}
/// This method is used as the final replacement hook for patterns that match
/// a single result value. In addition to replacing and removing the
/// specified operation, clients can specify a list of other nodes that this
/// replacement may make (perhaps transitively) dead. If any of those ops are
/// dead, this will remove them as well.
void PatternRewriter::replaceSingleResultOp(
Operation *op, SSAValue *newValue, ArrayRef<SSAValue *> opsToRemoveIfDead) {
// Notify the rewriter subclass that we're about to replace this root.
notifyRootReplaced(op);
assert(op->getNumResults() == 1 && "op isn't a SingleResultOp!");
op->getResult(0)->replaceAllUsesWith(newValue);
notifyOperationRemoved(op);
op->erase();
// TODO: Process the opsToRemoveIfDead list, removing things and calling the
// notifyOperationRemoved hook in the process.
}
/// This method is used as the final notification hook for patterns that end
/// up modifying the pattern root in place, by changing its operands. This is
/// a minor efficiency win (it avoids creating a new instruction and removing
/// the old one) but also often allows simpler code in the client.
///
/// The opsToRemoveIfDead list is an optional list of nodes that the rewriter
/// should remove if they are dead at this point.
///
void PatternRewriter::updatedRootInPlace(
Operation *op, ArrayRef<SSAValue *> opsToRemoveIfDead) {
// Notify the rewriter subclass that we're about to replace this root.
notifyRootUpdated(op);
// TODO: Process the opsToRemoveIfDead list, removing things and calling the
// notifyOperationRemoved hook in the process.
}
//===----------------------------------------------------------------------===//
// PatternMatcher implementation
//===----------------------------------------------------------------------===//
/// Find the highest benefit pattern available in the pattern set for the DAG
/// rooted at the specified node. This returns the pattern if found, or null
/// if there are no matches.
auto PatternMatcher::findMatch(Operation *op) -> MatchResult {
// TODO: This is a completely trivial implementation, expand this in the
// future.
// Keep track of the best match, the benefit of it, and any matcher specific
// state it is maintaining.
MatchResult bestMatch = {nullptr, nullptr};
Optional<PatternBenefit> bestBenefit;
for (auto &pattern : patterns) {
// Ignore patterns that are for the wrong root.
if (pattern->getRootKind() != op->getName())
continue;
// If we know the static cost of the pattern is worse than what we've
// already found then don't run it.
auto staticBenefit = pattern->getStaticBenefit();
if (staticBenefit.hasValue() && bestBenefit.hasValue() &&
staticBenefit.getValue().getBenefit() <
bestBenefit.getValue().getBenefit())
continue;
// Check to see if this pattern matches this node.
auto result = pattern->match(op);
auto benefit = result.first;
// If this pattern failed to match, ignore it.
if (benefit.isImpossibleToMatch())
continue;
// If it matched but had lower benefit than our best match so far, then
// ignore it.
if (bestBenefit.hasValue() &&
benefit.getBenefit() < bestBenefit.getValue().getBenefit())
continue;
// Okay we found a match that is better than our previous one, remember it.
bestBenefit = benefit;
bestMatch = {pattern.get(), std::move(result.second)};
}
// If we found any match, return it.
return bestMatch;
}
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