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//===- MemRefBoundCheck.cpp - MLIR Affine Structures 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 check memref accessses for out of bound
// accesses.
//
//===----------------------------------------------------------------------===//
#include "mlir/Analysis/AffineAnalysis.h"
#include "mlir/Analysis/AffineStructures.h"
#include "mlir/Analysis/Passes.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-bound-check"
using namespace mlir;
namespace {
/// Checks for out of bound memef access subscripts..
struct MemRefBoundCheck : public FunctionPass, StmtWalker<MemRefBoundCheck> {
explicit MemRefBoundCheck() {}
PassResult runOnMLFunction(MLFunction *f) override;
// Not applicable to CFG functions.
PassResult runOnCFGFunction(CFGFunction *f) override { return success(); }
void visitOperationStmt(OperationStmt *opStmt);
};
} // end anonymous namespace
FunctionPass *mlir::createMemRefBoundCheckPass() {
return new MemRefBoundCheck();
}
// Forward substitutes into 'valueMap' all AffineApplyOps reachable from the
// operands of 'valueMap'.
static void forwardSubstituteReachableOps(AffineValueMap *valueMap) {
// Gather AffineApplyOps reachable from 'indices'.
SmallVector<OperationStmt *, 4> affineApplyOps;
getReachableAffineApplyOps(valueMap->getOperands(), affineApplyOps);
// Compose AffineApplyOps in 'affineApplyOps'.
for (auto *opStmt : affineApplyOps) {
assert(opStmt->isa<AffineApplyOp>());
auto affineApplyOp = opStmt->dyn_cast<AffineApplyOp>();
// Forward substitute 'affineApplyOp' into 'valueMap'.
valueMap->forwardSubstitute(*affineApplyOp);
}
}
/// Returns the memory region accessed by this memref.
// TODO(bondhugula): extend this to store's and other memref dereferencing ops.
bool getMemoryRegion(OpPointer<LoadOp> loadOp, FlatAffineConstraints *region) {
OperationStmt *opStmt = dyn_cast<OperationStmt>(loadOp->getOperation());
// Only in MLFunctions.
if (!opStmt)
return false;
unsigned rank = loadOp->getMemRefType().getRank();
MLFuncBuilder b(opStmt);
auto idMap = b.getMultiDimIdentityMap(rank);
SmallVector<MLValue *, 4> indices;
for (auto *index : loadOp->getIndices()) {
indices.push_back(cast<MLValue>(index));
}
// Initialize 'srcValueMap' and compose with reachable AffineApplyOps.
AffineValueMap srcValueMap(idMap, indices);
forwardSubstituteReachableOps(&srcValueMap);
AffineMap srcMap = srcValueMap.getAffineMap();
region->reset(8, 8, srcMap.getNumInputs() + 1, srcMap.getNumDims(),
srcMap.getNumSymbols());
// Add equality constraints.
AffineMap map = srcValueMap.getAffineMap();
unsigned numDims = map.getNumDims();
unsigned numSymbols = map.getNumSymbols();
// Add inEqualties for loop lower/upper bounds.
for (unsigned i = 0; i < numDims + numSymbols; ++i) {
if (auto *loop = dyn_cast<ForStmt>(srcValueMap.getOperand(i))) {
if (!loop->hasConstantBounds())
return false;
// Add lower bound and upper bounds.
region->addConstantLowerBound(i, loop->getConstantLowerBound());
region->addConstantUpperBound(i, loop->getConstantUpperBound());
} else {
// Has to be a valid symbol.
auto *symbol = cast<MLValue>(srcValueMap.getOperand(i));
assert(symbol->isValidSymbol());
// Check if the symbols is a constant.
if (auto *opStmt = symbol->getDefiningStmt()) {
if (auto constOp = opStmt->dyn_cast<ConstantIndexOp>()) {
region->setIdToConstant(i, constOp->getValue());
}
}
}
}
// Add access function equalities to connect loop IVs to data dimensions.
region->addDimsForMap(0, srcValueMap.getAffineMap());
// Eliminate the loop IVs.
for (unsigned i = 0, e = srcValueMap.getNumOperands(); i < e; i++) {
region->FourierMotzkinEliminate(srcMap.getNumResults());
}
assert(region->getNumDimIds() == rank);
return true;
}
void MemRefBoundCheck::visitOperationStmt(OperationStmt *opStmt) {
// TODO(bondhugula): extend this to store's and other memref dereferencing
// op's.
if (auto loadOp = opStmt->dyn_cast<LoadOp>()) {
FlatAffineConstraints memoryRegion;
if (!getMemoryRegion(loadOp, &memoryRegion))
return;
unsigned rank = loadOp->getMemRefType().getRank();
// For each dimension, check for out of bounds.
for (unsigned r = 0; r < rank; r++) {
FlatAffineConstraints ucst(memoryRegion);
// Intersect memory region with constraint capturing out of bounds,
// and check if the constraint system is feasible. If it is, there is at
// least one point out of bounds.
SmallVector<int64_t, 4> ineq(rank + 1, 0);
// d_i >= memref dim size.
ucst.addConstantLowerBound(r, loadOp->getMemRefType().getDimSize(r));
LLVM_DEBUG(llvm::dbgs() << "System to check for overflow:\n");
LLVM_DEBUG(ucst.dump());
//
if (!ucst.isEmpty()) {
loadOp->emitOpError(
"memref out of upper bound access along dimension #" +
Twine(r + 1));
}
// Check for less than negative index.
FlatAffineConstraints lcst(memoryRegion);
std::fill(ineq.begin(), ineq.end(), 0);
// d_i <= -1;
lcst.addConstantUpperBound(r, -1);
LLVM_DEBUG(llvm::dbgs() << "System to check for underflow:\n");
LLVM_DEBUG(lcst.dump());
if (!lcst.isEmpty()) {
loadOp->emitOpError(
"memref out of lower bound access along dimension #" +
Twine(r + 1));
}
}
}
}
PassResult MemRefBoundCheck::runOnMLFunction(MLFunction *f) {
return walk(f), success();
}
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