c8457eb532
This patch adds a topological sort utility and pass. A topological sort reorders the operations in a block without SSA dominance such that, as much as possible, users of values come after their producers. The utility function sorts topologically the operation range in a given block with an optional user-provided callback that can be used to virtually break cycles. The toposort pass itself recursively sorts graph regions under the target op. Reviewed By: mehdi_amini Differential Revision: https://reviews.llvm.org/D125063
99 lines
3.5 KiB
C++
99 lines
3.5 KiB
C++
//===- TopologicalSortUtils.h - Topological sort utilities ------*- C++ -*-===//
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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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#include "mlir/Transforms/TopologicalSortUtils.h"
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#include "mlir/IR/OpDefinition.h"
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using namespace mlir;
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bool mlir::sortTopologically(
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Block *block, llvm::iterator_range<Block::iterator> ops,
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function_ref<bool(Value, Operation *)> isOperandReady) {
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if (ops.empty())
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return true;
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// The set of operations that have not yet been scheduled.
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DenseSet<Operation *> unscheduledOps;
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// Mark all operations as unscheduled.
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for (Operation &op : ops)
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unscheduledOps.insert(&op);
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Block::iterator nextScheduledOp = ops.begin();
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Block::iterator end = ops.end();
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// An operation is ready to be scheduled if all its operands are ready. An
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// operation is ready if:
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const auto isReady = [&](Value value, Operation *top) {
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// - the user-provided callback marks it as ready,
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if (isOperandReady && isOperandReady(value, top))
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return true;
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Operation *parent = value.getDefiningOp();
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// - it is a block argument,
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if (!parent)
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return true;
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Operation *ancestor = block->findAncestorOpInBlock(*parent);
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// - it is an implicit capture,
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if (!ancestor)
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return true;
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// - it is defined in a nested region, or
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if (ancestor == top)
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return true;
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// - its ancestor in the block is scheduled.
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return !unscheduledOps.contains(ancestor);
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};
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bool allOpsScheduled = true;
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while (!unscheduledOps.empty()) {
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bool scheduledAtLeastOnce = false;
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// Loop over the ops that are not sorted yet, try to find the ones "ready",
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// i.e. the ones for which there aren't any operand produced by an op in the
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// set, and "schedule" it (move it before the `nextScheduledOp`).
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for (Operation &op :
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llvm::make_early_inc_range(llvm::make_range(nextScheduledOp, end))) {
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// An operation is recursively ready to be scheduled of it and its nested
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// operations are ready.
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WalkResult readyToSchedule = op.walk([&](Operation *nestedOp) {
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return llvm::all_of(
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nestedOp->getOperands(),
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[&](Value operand) { return isReady(operand, &op); })
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? WalkResult::advance()
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: WalkResult::interrupt();
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});
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if (readyToSchedule.wasInterrupted())
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continue;
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// Schedule the operation by moving it to the start.
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unscheduledOps.erase(&op);
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op.moveBefore(block, nextScheduledOp);
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scheduledAtLeastOnce = true;
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// Move the iterator forward if we schedule the operation at the front.
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if (&op == &*nextScheduledOp)
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++nextScheduledOp;
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}
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// If no operations were scheduled, give up and advance the iterator.
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if (!scheduledAtLeastOnce) {
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allOpsScheduled = false;
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unscheduledOps.erase(&*nextScheduledOp);
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++nextScheduledOp;
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}
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}
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return allOpsScheduled;
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}
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bool mlir::sortTopologically(
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Block *block, function_ref<bool(Value, Operation *)> isOperandReady) {
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if (block->empty())
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return true;
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if (block->back().hasTrait<OpTrait::IsTerminator>())
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return sortTopologically(block, block->without_terminator(),
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isOperandReady);
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return sortTopologically(block, *block, isOperandReady);
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}
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