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//===- TestConstantFold.cpp - Pass to test constant folding ---------------===//
//
// 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/AffineOps/AffineOps.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/Function.h"
#include "mlir/Pass/Pass.h"
#include "mlir/StandardOps/Ops.h"
#include "mlir/Transforms/ConstantFoldUtils.h"
#include "mlir/Transforms/Passes.h"
#include "mlir/Transforms/Utils.h"
using namespace mlir;
namespace {
/// Simple constant folding pass.
struct TestConstantFold : public FunctionPass<TestConstantFold> {
// All constants in the function post folding.
SmallVector<Operation *, 8> existingConstants;
// Operations that were folded and that need to be erased.
std::vector<Operation *> opsToErase;
void foldOperation(Operation *op, ConstantFoldHelper &helper);
void runOnFunction() override;
};
} // end anonymous namespace
void TestConstantFold::foldOperation(Operation *op,
ConstantFoldHelper &helper) {
// Attempt to fold the specified operation, including handling unused or
// duplicated constants.
if (helper.tryToConstantFold(op)) {
opsToErase.push_back(op);
}
// If this op is a constant that are used and cannot be de-duplicated,
// remember it for cleanup later.
else if (auto constant = op->dyn_cast<ConstantOp>()) {
existingConstants.push_back(op);
}
}
// For now, we do a simple top-down pass over a function folding constants. We
// don't handle conditional control flow, block arguments, folding conditional
// branches, or anything else fancy.
void TestConstantFold::runOnFunction() {
existingConstants.clear();
opsToErase.clear();
auto &f = getFunction();
ConstantFoldHelper helper(&f);
// Collect and fold the operations within the function.
SmallVector<Operation *, 8> ops;
f.walk([&](Operation *op) { ops.push_back(op); });
// Fold the constants in reverse so that the last generated constants from
// folding are at the beginning. This creates somewhat of a linear ordering to
// the newly generated constants that matches the operation order and improves
// the readability of test cases.
for (Operation *op : llvm::reverse(ops))
foldOperation(op, helper);
// At this point, these operations are dead, remove them.
for (auto *op : opsToErase) {
assert(op->hasNoSideEffect() && "Constant folded op with side effects?");
op->erase();
}
// By the time we are done, we may have simplified a bunch of code, leaving
// around dead constants. Check for them now and remove them.
for (auto *cst : existingConstants) {
if (cst->use_empty())
cst->erase();
}
}
/// Creates a constant folding pass.
FunctionPassBase *mlir::createTestConstantFoldPass() {
return new TestConstantFold();
}
static PassRegistration<TestConstantFold>
pass("test-constant-fold", "Test operation constant folding");
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