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//===- UseDefAnalysis.cpp - Analysis for Transitive UseDef chains ---------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements Analysis functions specific to slicing in Function.
//
//===----------------------------------------------------------------------===//
#include "mlir/Analysis/SliceAnalysis.h"
#include "mlir/Dialect/Affine/IR/AffineOps.h"
#include "mlir/Dialect/Linalg/IR/LinalgOps.h"
#include "mlir/Dialect/SCF/SCF.h"
#include "mlir/IR/BuiltinOps.h"
#include "mlir/IR/Operation.h"
#include "mlir/Support/LLVM.h"
#include "llvm/ADT/SetVector.h"
///
/// Implements Analysis functions specific to slicing in Function.
///
using namespace mlir;
using llvm::SetVector;
static void getForwardSliceImpl(Operation *op,
SetVector<Operation *> *forwardSlice,
TransitiveFilter filter) {
if (!op) {
return;
}
// Evaluate whether we should keep this use.
// This is useful in particular to implement scoping; i.e. return the
// transitive forwardSlice in the current scope.
if (!filter(op)) {
return;
}
if (auto forOp = dyn_cast<AffineForOp>(op)) {
for (Operation *userOp : forOp.getInductionVar().getUsers())
if (forwardSlice->count(userOp) == 0)
getForwardSliceImpl(userOp, forwardSlice, filter);
} else if (auto forOp = dyn_cast<scf::ForOp>(op)) {
for (Operation *userOp : forOp.getInductionVar().getUsers())
if (forwardSlice->count(userOp) == 0)
getForwardSliceImpl(userOp, forwardSlice, filter);
for (Value result : forOp.getResults())
for (Operation *userOp : result.getUsers())
if (forwardSlice->count(userOp) == 0)
getForwardSliceImpl(userOp, forwardSlice, filter);
} else {
assert(op->getNumRegions() == 0 && "unexpected generic op with regions");
for (Value result : op->getResults()) {
for (Operation *userOp : result.getUsers())
if (forwardSlice->count(userOp) == 0)
getForwardSliceImpl(userOp, forwardSlice, filter);
}
}
forwardSlice->insert(op);
}
void mlir::getForwardSlice(Operation *op, SetVector<Operation *> *forwardSlice,
TransitiveFilter filter) {
getForwardSliceImpl(op, forwardSlice, filter);
// Don't insert the top level operation, we just queried on it and don't
// want it in the results.
forwardSlice->remove(op);
// Reverse to get back the actual topological order.
// std::reverse does not work out of the box on SetVector and I want an
// in-place swap based thing (the real std::reverse, not the LLVM adapter).
std::vector<Operation *> v(forwardSlice->takeVector());
forwardSlice->insert(v.rbegin(), v.rend());
}
static void getBackwardSliceImpl(Operation *op,
SetVector<Operation *> *backwardSlice,
TransitiveFilter filter) {
if (!op)
return;
assert((op->getNumRegions() == 0 ||
isa<AffineForOp, scf::ForOp, linalg::LinalgOp>(op)) &&
"unexpected generic op with regions");
// Evaluate whether we should keep this def.
// This is useful in particular to implement scoping; i.e. return the
// transitive forwardSlice in the current scope.
if (!filter(op)) {
return;
}
for (auto en : llvm::enumerate(op->getOperands())) {
auto operand = en.value();
if (auto blockArg = operand.dyn_cast<BlockArgument>()) {
if (auto affIv = getForInductionVarOwner(operand)) {
auto *affOp = affIv.getOperation();
if (backwardSlice->count(affOp) == 0)
getBackwardSliceImpl(affOp, backwardSlice, filter);
} else if (auto loopIv = scf::getForInductionVarOwner(operand)) {
auto *loopOp = loopIv.getOperation();
if (backwardSlice->count(loopOp) == 0)
getBackwardSliceImpl(loopOp, backwardSlice, filter);
} else if (blockArg.getOwner() !=
&op->getParentOfType<FuncOp>().getBody().front()) {
op->emitError("unsupported CF for operand ") << en.index();
llvm_unreachable("Unsupported control flow");
}
continue;
}
auto *op = operand.getDefiningOp();
if (backwardSlice->count(op) == 0) {
getBackwardSliceImpl(op, backwardSlice, filter);
}
}
backwardSlice->insert(op);
}
void mlir::getBackwardSlice(Operation *op,
SetVector<Operation *> *backwardSlice,
TransitiveFilter filter) {
getBackwardSliceImpl(op, backwardSlice, filter);
// Don't insert the top level operation, we just queried on it and don't
// want it in the results.
backwardSlice->remove(op);
}
SetVector<Operation *> mlir::getSlice(Operation *op,
TransitiveFilter backwardFilter,
TransitiveFilter forwardFilter) {
SetVector<Operation *> slice;
slice.insert(op);
unsigned currentIndex = 0;
SetVector<Operation *> backwardSlice;
SetVector<Operation *> forwardSlice;
while (currentIndex != slice.size()) {
auto *currentOp = (slice)[currentIndex];
// Compute and insert the backwardSlice starting from currentOp.
backwardSlice.clear();
getBackwardSlice(currentOp, &backwardSlice, backwardFilter);
slice.insert(backwardSlice.begin(), backwardSlice.end());
// Compute and insert the forwardSlice starting from currentOp.
forwardSlice.clear();
getForwardSlice(currentOp, &forwardSlice, forwardFilter);
slice.insert(forwardSlice.begin(), forwardSlice.end());
++currentIndex;
}
return topologicalSort(slice);
}
namespace {
/// DFS post-order implementation that maintains a global count to work across
/// multiple invocations, to help implement topological sort on multi-root DAGs.
/// We traverse all operations but only record the ones that appear in
/// `toSort` for the final result.
struct DFSState {
DFSState(const SetVector<Operation *> &set)
: toSort(set), topologicalCounts(), seen() {}
const SetVector<Operation *> &toSort;
SmallVector<Operation *, 16> topologicalCounts;
DenseSet<Operation *> seen;
};
} // namespace
static void DFSPostorder(Operation *current, DFSState *state) {
for (Value result : current->getResults()) {
for (Operation *op : result.getUsers())
DFSPostorder(op, state);
}
bool inserted;
using IterTy = decltype(state->seen.begin());
IterTy iter;
std::tie(iter, inserted) = state->seen.insert(current);
if (inserted) {
if (state->toSort.count(current) > 0) {
state->topologicalCounts.push_back(current);
}
}
}
SetVector<Operation *>
mlir::topologicalSort(const SetVector<Operation *> &toSort) {
if (toSort.empty()) {
return toSort;
}
// Run from each root with global count and `seen` set.
DFSState state(toSort);
for (auto *s : toSort) {
assert(toSort.count(s) == 1 && "NYI: multi-sets not supported");
DFSPostorder(s, &state);
}
// Reorder and return.
SetVector<Operation *> res;
for (auto it = state.topologicalCounts.rbegin(),
eit = state.topologicalCounts.rend();
it != eit; ++it) {
res.insert(*it);
}
return res;
}
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