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//===- MemRefDependenceCheck.cpp - MemRef DependenceCheck Class -*- C++ -*-===//
//
// 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.
// =============================================================================
//
// This file implements a pass to run pair-wise memref access dependence checks.
//
//===----------------------------------------------------------------------===//
#include "mlir/Analysis/AffineAnalysis.h"
#include "mlir/Analysis/AffineStructures.h"
#include "mlir/Analysis/Passes.h"
#include "mlir/Analysis/Utils.h"
#include "mlir/IR/Builders.h"
#include "mlir/IR/BuiltinOps.h"
#include "mlir/IR/StmtVisitor.h"
#include "mlir/Pass.h"
#include "mlir/StandardOps/StandardOps.h"
#include "llvm/Support/Debug.h"
#define DEBUG_TYPE "memref-dependence-check"
using namespace mlir;
namespace {
// TODO(andydavis) Add common surrounding loop depth-wise dependence checks.
/// Checks dependences between all pairs of memref accesses in an MLFunction.
struct MemRefDependenceCheck : public FunctionPass,
StmtWalker<MemRefDependenceCheck> {
SmallVector<OperationStmt *, 4> loadsAndStores;
explicit MemRefDependenceCheck()
: FunctionPass(&MemRefDependenceCheck::passID) {}
PassResult runOnMLFunction(MLFunction *f) override;
// Not applicable to CFG functions.
PassResult runOnCFGFunction(CFGFunction *f) override { return success(); }
void visitOperationStmt(OperationStmt *opStmt) {
if (opStmt->isa<LoadOp>() || opStmt->isa<StoreOp>()) {
loadsAndStores.push_back(opStmt);
}
}
static char passID;
};
} // end anonymous namespace
char MemRefDependenceCheck::passID = 0;
FunctionPass *mlir::createMemRefDependenceCheckPass() {
return new MemRefDependenceCheck();
}
// Adds memref access indices 'opIndices' from 'memrefType' to 'access'.
static void addMemRefAccessIndices(
llvm::iterator_range<Operation::const_operand_iterator> opIndices,
MemRefType memrefType, MemRefAccess *access) {
access->indices.reserve(memrefType.getRank());
for (auto *index : opIndices) {
access->indices.push_back(const_cast<mlir::Value *>(index));
}
}
// Populates 'access' with memref, indices and opstmt from 'loadOrStoreOpStmt'.
static void getMemRefAccess(const OperationStmt *loadOrStoreOpStmt,
MemRefAccess *access) {
access->opStmt = loadOrStoreOpStmt;
if (auto loadOp = loadOrStoreOpStmt->dyn_cast<LoadOp>()) {
access->memref = loadOp->getMemRef();
addMemRefAccessIndices(loadOp->getIndices(), loadOp->getMemRefType(),
access);
} else {
assert(loadOrStoreOpStmt->isa<StoreOp>());
auto storeOp = loadOrStoreOpStmt->dyn_cast<StoreOp>();
access->memref = storeOp->getMemRef();
addMemRefAccessIndices(storeOp->getIndices(), storeOp->getMemRefType(),
access);
}
}
// Returns the number of surrounding loops common to 'loopsA' and 'loopsB',
// where each lists loops from outer-most to inner-most in loop nest.
static unsigned getNumCommonSurroundingLoops(ArrayRef<const ForStmt *> loopsA,
ArrayRef<const ForStmt *> loopsB) {
unsigned minNumLoops = std::min(loopsA.size(), loopsB.size());
unsigned numCommonLoops = 0;
for (unsigned i = 0; i < minNumLoops; ++i) {
if (loopsA[i] != loopsB[i])
break;
++numCommonLoops;
}
return numCommonLoops;
}
// Returns a result string which represents the direction vector (if there was
// a dependence), returns the string "false" otherwise.
static string
getDirectionVectorStr(bool ret, unsigned numCommonLoops, unsigned loopNestDepth,
ArrayRef<DependenceComponent> dependenceComponents) {
if (!ret)
return "false";
if (dependenceComponents.empty() || loopNestDepth > numCommonLoops)
return "true";
string result;
for (unsigned i = 0, e = dependenceComponents.size(); i < e; ++i) {
string lbStr = dependenceComponents[i].lb.hasValue()
? std::to_string(dependenceComponents[i].lb.getValue())
: "-inf";
string ubStr = dependenceComponents[i].ub.hasValue()
? std::to_string(dependenceComponents[i].ub.getValue())
: "+inf";
result += "[" + lbStr + ", " + ubStr + "]";
}
return result;
}
// For each access in 'loadsAndStores', runs a depence check between this
// "source" access and all subsequent "destination" accesses in
// 'loadsAndStores'. Emits the result of the dependence check as a note with
// the source access.
static void checkDependences(ArrayRef<OperationStmt *> loadsAndStores) {
for (unsigned i = 0, e = loadsAndStores.size(); i < e; ++i) {
auto *srcOpStmt = loadsAndStores[i];
MemRefAccess srcAccess;
getMemRefAccess(srcOpStmt, &srcAccess);
SmallVector<ForStmt *, 4> srcLoops;
getLoopIVs(*srcOpStmt, &srcLoops);
for (unsigned j = 0; j < e; ++j) {
auto *dstOpStmt = loadsAndStores[j];
MemRefAccess dstAccess;
getMemRefAccess(dstOpStmt, &dstAccess);
SmallVector<ForStmt *, 4> dstLoops;
getLoopIVs(*dstOpStmt, &dstLoops);
unsigned numCommonLoops =
getNumCommonSurroundingLoops(srcLoops, dstLoops);
for (unsigned d = 1; d <= numCommonLoops + 1; ++d) {
FlatAffineConstraints dependenceConstraints;
llvm::SmallVector<DependenceComponent, 2> dependenceComponents;
bool ret = checkMemrefAccessDependence(srcAccess, dstAccess, d,
&dependenceConstraints,
&dependenceComponents);
// TODO(andydavis) Print dependence type (i.e. RAW, etc) and print
// distance vectors as: ([2, 3], [0, 10]). Also, shorten distance
// vectors from ([1, 1], [3, 3]) to (1, 3).
srcOpStmt->emitNote(
"dependence from " + Twine(i) + " to " + Twine(j) + " at depth " +
Twine(d) + " = " +
getDirectionVectorStr(ret, numCommonLoops, d, dependenceComponents)
.c_str());
}
}
}
}
// Walks the MLFunction 'f' adding load and store ops to 'loadsAndStores'.
// Runs pair-wise dependence checks.
PassResult MemRefDependenceCheck::runOnMLFunction(MLFunction *f) {
loadsAndStores.clear();
walk(f);
checkDependences(loadsAndStores);
return success();
}
static PassRegistration<MemRefDependenceCheck>
pass("memref-dependence-check",
"Checks dependences between all pairs of memref accesses.");
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