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//===- FoldUtils.cpp ---- Fold Utilities ----------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines various operation fold utilities. These utilities are
// intended to be used by passes to unify and simply their logic.
#include "mlir/Transforms/FoldUtils.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/Matchers.h"
#include "mlir/IR/Operation.h"
using namespace mlir;
/// Given an operation, find the parent region that folded constants should be
/// inserted into.
static Region *
getInsertionRegion(DialectInterfaceCollection<DialectFoldInterface> &interfaces,
Block *insertionBlock) {
while (Region *region = insertionBlock->getParent()) {
// Insert in this region for any of the following scenarios:
// * The parent is unregistered, or is known to be isolated from above.
// * The parent is a top-level operation.
auto *parentOp = region->getParentOp();
if (parentOp->mightHaveTrait<OpTrait::IsIsolatedFromAbove>() ||
return region;
// Otherwise, check if this region is a desired insertion region.
auto *interface = interfaces.getInterfaceFor(parentOp);
if (LLVM_UNLIKELY(interface && interface->shouldMaterializeInto(region)))
return region;
// Traverse up the parent looking for an insertion region.
insertionBlock = parentOp->getBlock();
llvm_unreachable("expected valid insertion region");
/// A utility function used to materialize a constant for a given attribute and
/// type. On success, a valid constant value is returned. Otherwise, null is
/// returned
static Operation *materializeConstant(Dialect *dialect, OpBuilder &builder,
Attribute value, Type type,
Location loc) {
auto insertPt = builder.getInsertionPoint();
// Ask the dialect to materialize a constant operation for this value.
if (auto *constOp = dialect->materializeConstant(builder, value, type, loc)) {
assert(insertPt == builder.getInsertionPoint());
assert(matchPattern(constOp, m_Constant()));
return constOp;
return nullptr;
// OperationFolder
LogicalResult OperationFolder::tryToFold(
Operation *op, function_ref<void(Operation *)> processGeneratedConstants,
function_ref<void(Operation *)> preReplaceAction, bool *inPlaceUpdate) {
if (inPlaceUpdate)
*inPlaceUpdate = false;
// If this is a unique'd constant, return failure as we know that it has
// already been folded.
if (referencedDialects.count(op))
return failure();
// Try to fold the operation.
SmallVector<Value, 8> results;
OpBuilder builder(op);
if (failed(tryToFold(builder, op, results, processGeneratedConstants)))
return failure();
// Check to see if the operation was just updated in place.
if (results.empty()) {
if (inPlaceUpdate)
*inPlaceUpdate = true;
return success();
// Constant folding succeeded. We will start replacing this op's uses and
// erase this op. Invoke the callback provided by the caller to perform any
// pre-replacement action.
if (preReplaceAction)
// Replace all of the result values and erase the operation.
for (unsigned i = 0, e = results.size(); i != e; ++i)
return success();
/// Notifies that the given constant `op` should be remove from this
/// OperationFolder's internal bookkeeping.
void OperationFolder::notifyRemoval(Operation *op) {
// Check to see if this operation is uniqued within the folder.
auto it = referencedDialects.find(op);
if (it == referencedDialects.end())
// Get the constant value for this operation, this is the value that was used
// to unique the operation internally.
Attribute constValue;
matchPattern(op, m_Constant(&constValue));
// Get the constant map that this operation was uniqued in.
auto &uniquedConstants =
foldScopes[getInsertionRegion(interfaces, op->getBlock())];
// Erase all of the references to this operation.
auto type = op->getResult(0).getType();
for (auto *dialect : it->second)
uniquedConstants.erase(std::make_tuple(dialect, constValue, type));
/// Clear out any constants cached inside of the folder.
void OperationFolder::clear() {
/// Get or create a constant using the given builder. On success this returns
/// the constant operation, nullptr otherwise.
Value OperationFolder::getOrCreateConstant(OpBuilder &builder, Dialect *dialect,
Attribute value, Type type,
Location loc) {
OpBuilder::InsertionGuard foldGuard(builder);
// Use the builder insertion block to find an insertion point for the
// constant.
auto *insertRegion =
getInsertionRegion(interfaces, builder.getInsertionBlock());
auto &entry = insertRegion->front();
builder.setInsertionPoint(&entry, entry.begin());
// Get the constant map for the insertion region of this operation.
auto &uniquedConstants = foldScopes[insertRegion];
Operation *constOp = tryGetOrCreateConstant(uniquedConstants, dialect,
builder, value, type, loc);
return constOp ? constOp->getResult(0) : Value();
/// Tries to perform folding on the given `op`. If successful, populates
/// `results` with the results of the folding.
LogicalResult OperationFolder::tryToFold(
OpBuilder &builder, Operation *op, SmallVectorImpl<Value> &results,
function_ref<void(Operation *)> processGeneratedConstants) {
SmallVector<Attribute, 8> operandConstants;
SmallVector<OpFoldResult, 8> foldResults;
// If this is a commutative operation, move constants to be trailing operands.
if (op->getNumOperands() >= 2 && op->hasTrait<OpTrait::IsCommutative>()) {
op->getOpOperands().begin(), op->getOpOperands().end(),
[&](OpOperand &O) { return !matchPattern(O.get(), m_Constant()); });
// Check to see if any operands to the operation is constant and whether
// the operation knows how to constant fold itself.
operandConstants.assign(op->getNumOperands(), Attribute());
for (unsigned i = 0, e = op->getNumOperands(); i != e; ++i)
matchPattern(op->getOperand(i), m_Constant(&operandConstants[i]));
// Attempt to constant fold the operation.
if (failed(op->fold(operandConstants, foldResults)))
return failure();
// Check to see if the operation was just updated in place.
if (foldResults.empty())
return success();
assert(foldResults.size() == op->getNumResults());
// Create a builder to insert new operations into the entry block of the
// insertion region.
auto *insertRegion =
getInsertionRegion(interfaces, builder.getInsertionBlock());
auto &entry = insertRegion->front();
OpBuilder::InsertionGuard foldGuard(builder);
builder.setInsertionPoint(&entry, entry.begin());
// Get the constant map for the insertion region of this operation.
auto &uniquedConstants = foldScopes[insertRegion];
// Create the result constants and replace the results.
auto *dialect = op->getDialect();
for (unsigned i = 0, e = op->getNumResults(); i != e; ++i) {
assert(!foldResults[i].isNull() && "expected valid OpFoldResult");
// Check if the result was an SSA value.
if (auto repl = foldResults[i].dyn_cast<Value>()) {
if (repl.getType() != op->getResult(i).getType())
return failure();
// Check to see if there is a canonicalized version of this constant.
auto res = op->getResult(i);
Attribute attrRepl = foldResults[i].get<Attribute>();
if (auto *constOp =
tryGetOrCreateConstant(uniquedConstants, dialect, builder, attrRepl,
res.getType(), op->getLoc())) {
// Ensure that this constant dominates the operation we are replacing it
// with. This may not automatically happen if the operation being folded
// was inserted before the constant within the insertion block.
Block *opBlock = op->getBlock();
if (opBlock == constOp->getBlock() && &opBlock->front() != constOp)
// If materialization fails, cleanup any operations generated for the
// previous results and return failure.
for (Operation &op : llvm::make_early_inc_range(
llvm::make_range(entry.begin(), builder.getInsertionPoint()))) {
return failure();
// Process any newly generated operations.
if (processGeneratedConstants) {
for (auto i = entry.begin(), e = builder.getInsertionPoint(); i != e; ++i)
return success();
/// Try to get or create a new constant entry. On success this returns the
/// constant operation value, nullptr otherwise.
Operation *OperationFolder::tryGetOrCreateConstant(
ConstantMap &uniquedConstants, Dialect *dialect, OpBuilder &builder,
Attribute value, Type type, Location loc) {
// Check if an existing mapping already exists.
auto constKey = std::make_tuple(dialect, value, type);
Operation *&constOp = uniquedConstants[constKey];
if (constOp)
return constOp;
// If one doesn't exist, try to materialize one.
if (!(constOp = materializeConstant(dialect, builder, value, type, loc)))
return nullptr;
// Check to see if the generated constant is in the expected dialect.
auto *newDialect = constOp->getDialect();
if (newDialect == dialect) {
return constOp;
// If it isn't, then we also need to make sure that the mapping for the new
// dialect is valid.
auto newKey = std::make_tuple(newDialect, value, type);
// If an existing operation in the new dialect already exists, delete the
// materialized operation in favor of the existing one.
if (auto *existingOp = uniquedConstants.lookup(newKey)) {
return constOp = existingOp;
// Otherwise, update the new dialect to the materialized operation.
referencedDialects[constOp].assign({dialect, newDialect});
auto newIt = uniquedConstants.insert({newKey, constOp});
return newIt.first->second;