DependenceAnalysis.cpp
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//===- DependenceAnalysis.cpp - Dependence analysis on SSA views ----------===//
//
// 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 view-based alias and dependence analyses.
//
//===----------------------------------------------------------------------===//
#include "mlir/Dialect/Linalg/Analysis/DependenceAnalysis.h"
#include "mlir/Dialect/Linalg/IR/LinalgOps.h"
#include "mlir/Dialect/StandardOps/IR/Ops.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#define DEBUG_TYPE "linalg-dependence-analysis"
using namespace mlir;
using namespace mlir::linalg;
using llvm::dbgs;
Value Aliases::find(Value v) {
if (v.isa<BlockArgument>())
return v;
auto it = aliases.find(v);
if (it != aliases.end()) {
assert(it->getSecond().getType().isa<BaseMemRefType>() &&
"Memref expected");
return it->getSecond();
}
while (true) {
if (v.isa<BlockArgument>())
return v;
Operation *defOp = v.getDefiningOp();
if (!defOp)
return v;
if (auto memEffect = dyn_cast<MemoryEffectOpInterface>(defOp)) {
// Collect all memory effects on `v`.
SmallVector<MemoryEffects::EffectInstance, 1> effects;
memEffect.getEffectsOnValue(v, effects);
// If we have the 'Allocate' memory effect on `v`, then `v` should be the
// original buffer.
if (llvm::any_of(
effects, [](const MemoryEffects::EffectInstance &instance) {
return isa<MemoryEffects::Allocate>(instance.getEffect());
}))
return v;
}
if (auto viewLikeOp = dyn_cast<ViewLikeOpInterface>(defOp)) {
auto it =
aliases.insert(std::make_pair(v, find(viewLikeOp.getViewSource())));
return it.first->second;
}
llvm::errs() << "View alias analysis reduces to: " << v << "\n";
llvm_unreachable("unsupported view alias case");
}
}
StringRef LinalgDependenceGraph::getDependenceTypeStr(DependenceType depType) {
switch (depType) {
case LinalgDependenceGraph::DependenceType::RAW:
return "RAW";
case LinalgDependenceGraph::DependenceType::RAR:
return "RAR";
case LinalgDependenceGraph::DependenceType::WAR:
return "WAR";
case LinalgDependenceGraph::DependenceType::WAW:
return "WAW";
default:
break;
}
llvm_unreachable("Unexpected DependenceType");
}
LinalgDependenceGraph
LinalgDependenceGraph::buildDependenceGraph(Aliases &aliases, FuncOp f) {
SmallVector<Operation *, 8> linalgOps;
f.walk([&](LinalgOp op) { linalgOps.push_back(op); });
return LinalgDependenceGraph(aliases, linalgOps);
}
LinalgDependenceGraph::LinalgDependenceGraph(Aliases &aliases,
ArrayRef<Operation *> ops)
: aliases(aliases), linalgOps(ops.begin(), ops.end()) {
for (auto en : llvm::enumerate(linalgOps)) {
assert(isa<LinalgOp>(en.value()) && "Expected value for LinalgOp");
linalgOpPositions.insert(std::make_pair(en.value(), en.index()));
}
for (unsigned i = 0, e = ops.size(); i < e; ++i) {
for (unsigned j = i + 1; j < e; ++j) {
addDependencesBetween(cast<LinalgOp>(ops[i]), cast<LinalgOp>(ops[j]));
}
}
}
void LinalgDependenceGraph::addDependenceElem(DependenceType dt,
LinalgOpView indexingOpView,
LinalgOpView dependentOpView) {
LLVM_DEBUG(dbgs() << "\nAdd dep type " << getDependenceTypeStr(dt) << ":\t"
<< *indexingOpView.op << " -> " << *dependentOpView.op);
dependencesFromGraphs[dt][indexingOpView.op].push_back(
LinalgDependenceGraphElem{dependentOpView, indexingOpView.view});
dependencesIntoGraphs[dt][dependentOpView.op].push_back(
LinalgDependenceGraphElem{indexingOpView, dependentOpView.view});
}
LinalgDependenceGraph::dependence_range
LinalgDependenceGraph::getDependencesFrom(
LinalgOp src, LinalgDependenceGraph::DependenceType dt) const {
return getDependencesFrom(src.getOperation(), dt);
}
LinalgDependenceGraph::dependence_range
LinalgDependenceGraph::getDependencesFrom(
Operation *src, LinalgDependenceGraph::DependenceType dt) const {
auto iter = dependencesFromGraphs[dt].find(src);
if (iter == dependencesFromGraphs[dt].end())
return llvm::make_range(nullptr, nullptr);
return llvm::make_range(iter->second.begin(), iter->second.end());
}
LinalgDependenceGraph::dependence_range
LinalgDependenceGraph::getDependencesInto(
LinalgOp dst, LinalgDependenceGraph::DependenceType dt) const {
return getDependencesInto(dst.getOperation(), dt);
}
LinalgDependenceGraph::dependence_range
LinalgDependenceGraph::getDependencesInto(
Operation *dst, LinalgDependenceGraph::DependenceType dt) const {
auto iter = dependencesIntoGraphs[dt].find(dst);
if (iter == dependencesIntoGraphs[dt].end())
return llvm::make_range(nullptr, nullptr);
return llvm::make_range(iter->second.begin(), iter->second.end());
}
void LinalgDependenceGraph::addDependencesBetween(LinalgOp src, LinalgOp dst) {
assert(src.hasBufferSemantics() &&
"expected linalg op with buffer semantics");
assert(dst.hasBufferSemantics() &&
"expected linalg op with buffer semantics");
for (auto srcView : src.getOutputBuffers()) { // W
// RAW graph
for (auto dstView : dst.getInputs()) { // R
if (aliases.alias(srcView, dstView)) { // if alias, fill RAW
addDependenceElem(DependenceType::RAW,
LinalgOpView{src.getOperation(), srcView},
LinalgOpView{dst.getOperation(), dstView});
}
}
// WAW graph
for (auto dstView : dst.getOutputBuffers()) { // W
if (aliases.alias(srcView, dstView)) { // if alias, fill WAW
addDependenceElem(DependenceType::WAW,
LinalgOpView{src.getOperation(), srcView},
LinalgOpView{dst.getOperation(), dstView});
}
}
}
for (auto srcView : src.getInputs()) { // R
// RAR graph
for (auto dstView : dst.getInputs()) { // R
if (aliases.alias(srcView, dstView)) { // if alias, fill RAR
addDependenceElem(DependenceType::RAR,
LinalgOpView{src.getOperation(), srcView},
LinalgOpView{dst.getOperation(), dstView});
}
}
// WAR graph
for (auto dstView : dst.getOutputBuffers()) { // W
if (aliases.alias(srcView, dstView)) { // if alias, fill WAR
addDependenceElem(DependenceType::WAR,
LinalgOpView{src.getOperation(), srcView},
LinalgOpView{dst.getOperation(), dstView});
}
}
}
}
SmallVector<Operation *, 8>
LinalgDependenceGraph::findCoveringDependences(LinalgOp srcLinalgOp,
LinalgOp dstLinalgOp) const {
return findOperationsWithCoveringDependences(
srcLinalgOp, dstLinalgOp, nullptr,
{DependenceType::WAW, DependenceType::WAR, DependenceType::RAW});
}
SmallVector<Operation *, 8> LinalgDependenceGraph::findCoveringWrites(
LinalgOp srcLinalgOp, LinalgOp dstLinalgOp, Value view) const {
return findOperationsWithCoveringDependences(
srcLinalgOp, dstLinalgOp, view,
{DependenceType::WAW, DependenceType::WAR});
}
SmallVector<Operation *, 8> LinalgDependenceGraph::findCoveringReads(
LinalgOp srcLinalgOp, LinalgOp dstLinalgOp, Value view) const {
return findOperationsWithCoveringDependences(
srcLinalgOp, dstLinalgOp, view,
{DependenceType::RAR, DependenceType::RAW});
}
SmallVector<Operation *, 8>
LinalgDependenceGraph::findOperationsWithCoveringDependences(
LinalgOp srcLinalgOp, LinalgOp dstLinalgOp, Value view,
ArrayRef<DependenceType> types) const {
auto *src = srcLinalgOp.getOperation();
auto *dst = dstLinalgOp.getOperation();
auto srcPos = linalgOpPositions.lookup(src);
auto dstPos = linalgOpPositions.lookup(dst);
assert(srcPos < dstPos && "expected dst after src in IR traversal order");
SmallVector<Operation *, 8> res;
// Consider an intermediate interleaved `interim` op, look for any dependence
// to an aliasing view on a src -> op -> dst path.
// TODO: we are not considering paths yet, just interleaved positions.
for (auto dt : types) {
for (auto dependence : getDependencesFrom(src, dt)) {
auto interimPos = linalgOpPositions.lookup(dependence.dependentOpView.op);
// Skip if not interleaved.
if (interimPos >= dstPos || interimPos <= srcPos)
continue;
if (view && !aliases.alias(view, dependence.indexingView))
continue;
auto *op = dependence.dependentOpView.op;
LLVM_DEBUG(dbgs() << "\n***Found covering dependence of type "
<< getDependenceTypeStr(dt) << ": " << *src << " -> "
<< *op << " on " << dependence.indexingView);
res.push_back(op);
}
}
return res;
}