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//===- IntegerRangeAnalysis.cpp - Integer range analysis --------*- C++ -*-===//
//
// 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 defines the dataflow analysis class for integer range inference
// which is used in transformations over the `arith` dialect such as
// branch elimination or signed->unsigned rewriting
//
//===----------------------------------------------------------------------===//
#include "mlir/Analysis/DataFlow/IntegerRangeAnalysis.h"
#include "mlir/Analysis/DataFlow/ConstantPropagationAnalysis.h"
#include "mlir/Interfaces/InferIntRangeInterface.h"
#include "mlir/Interfaces/LoopLikeInterface.h"
#include "llvm/Support/Debug.h"
#include <optional>
#define DEBUG_TYPE "int-range-analysis"
using namespace mlir;
using namespace mlir::dataflow;
IntegerValueRange IntegerValueRange::getMaxRange(Value value) {
unsigned width = ConstantIntRanges::getStorageBitwidth(value.getType());
if (width == 0)
return {};
APInt umin = APInt::getMinValue(width);
APInt umax = APInt::getMaxValue(width);
APInt smin = width != 0 ? APInt::getSignedMinValue(width) : umin;
APInt smax = width != 0 ? APInt::getSignedMaxValue(width) : umax;
return IntegerValueRange{ConstantIntRanges{umin, umax, smin, smax}};
}
void IntegerValueRangeLattice::onUpdate(DataFlowSolver *solver) const {
Lattice::onUpdate(solver);
// If the integer range can be narrowed to a constant, update the constant
// value of the SSA value.
std::optional<APInt> constant = getValue().getValue().getConstantValue();
auto value = point.get<Value>();
auto *cv = solver->getOrCreateState<Lattice<ConstantValue>>(value);
if (!constant)
return solver->propagateIfChanged(
cv, cv->join(ConstantValue::getUnknownConstant()));
Dialect *dialect;
if (auto *parent = value.getDefiningOp())
dialect = parent->getDialect();
else
dialect = value.getParentBlock()->getParentOp()->getDialect();
solver->propagateIfChanged(
cv, cv->join(ConstantValue(IntegerAttr::get(value.getType(), *constant),
dialect)));
}
void IntegerRangeAnalysis::visitOperation(
Operation *op, ArrayRef<const IntegerValueRangeLattice *> operands,
ArrayRef<IntegerValueRangeLattice *> results) {
// If the lattice on any operand is unitialized, bail out.
if (llvm::any_of(operands, [](const IntegerValueRangeLattice *lattice) {
return lattice->getValue().isUninitialized();
})) {
return;
}
// Ignore non-integer outputs - return early if the op has no scalar
// integer results
bool hasIntegerResult = false;
for (auto it : llvm::zip(results, op->getResults())) {
Value value = std::get<1>(it);
if (value.getType().isIntOrIndex()) {
hasIntegerResult = true;
} else {
IntegerValueRangeLattice *lattice = std::get<0>(it);
propagateIfChanged(lattice,
lattice->join(IntegerValueRange::getMaxRange(value)));
}
}
if (!hasIntegerResult)
return;
auto inferrable = dyn_cast<InferIntRangeInterface>(op);
if (!inferrable)
return setAllToEntryStates(results);
LLVM_DEBUG(llvm::dbgs() << "Inferring ranges for " << *op << "\n");
SmallVector<ConstantIntRanges> argRanges(
llvm::map_range(operands, [](const IntegerValueRangeLattice *val) {
return val->getValue().getValue();
}));
auto joinCallback = [&](Value v, const ConstantIntRanges &attrs) {
auto result = dyn_cast<OpResult>(v);
if (!result)
return;
assert(llvm::is_contained(op->getResults(), result));
LLVM_DEBUG(llvm::dbgs() << "Inferred range " << attrs << "\n");
IntegerValueRangeLattice *lattice = results[result.getResultNumber()];
IntegerValueRange oldRange = lattice->getValue();
ChangeResult changed = lattice->join(IntegerValueRange{attrs});
// Catch loop results with loop variant bounds and conservatively make
// them [-inf, inf] so we don't circle around infinitely often (because
// the dataflow analysis in MLIR doesn't attempt to work out trip counts
// and often can't).
bool isYieldedResult = llvm::any_of(v.getUsers(), [](Operation *op) {
return op->hasTrait<OpTrait::IsTerminator>();
});
if (isYieldedResult && !oldRange.isUninitialized() &&
!(lattice->getValue() == oldRange)) {
LLVM_DEBUG(llvm::dbgs() << "Loop variant loop result detected\n");
changed |= lattice->join(IntegerValueRange::getMaxRange(v));
}
propagateIfChanged(lattice, changed);
};
inferrable.inferResultRanges(argRanges, joinCallback);
}
void IntegerRangeAnalysis::visitNonControlFlowArguments(
Operation *op, const RegionSuccessor &successor,
ArrayRef<IntegerValueRangeLattice *> argLattices, unsigned firstIndex) {
if (auto inferrable = dyn_cast<InferIntRangeInterface>(op)) {
LLVM_DEBUG(llvm::dbgs() << "Inferring ranges for " << *op << "\n");
// If the lattice on any operand is unitialized, bail out.
if (llvm::any_of(op->getOperands(), [&](Value value) {
return getLatticeElementFor(op, value)->getValue().isUninitialized();
}))
return;
SmallVector<ConstantIntRanges> argRanges(
llvm::map_range(op->getOperands(), [&](Value value) {
return getLatticeElementFor(op, value)->getValue().getValue();
}));
auto joinCallback = [&](Value v, const ConstantIntRanges &attrs) {
auto arg = dyn_cast<BlockArgument>(v);
if (!arg)
return;
if (!llvm::is_contained(successor.getSuccessor()->getArguments(), arg))
return;
LLVM_DEBUG(llvm::dbgs() << "Inferred range " << attrs << "\n");
IntegerValueRangeLattice *lattice = argLattices[arg.getArgNumber()];
IntegerValueRange oldRange = lattice->getValue();
ChangeResult changed = lattice->join(IntegerValueRange{attrs});
// Catch loop results with loop variant bounds and conservatively make
// them [-inf, inf] so we don't circle around infinitely often (because
// the dataflow analysis in MLIR doesn't attempt to work out trip counts
// and often can't).
bool isYieldedValue = llvm::any_of(v.getUsers(), [](Operation *op) {
return op->hasTrait<OpTrait::IsTerminator>();
});
if (isYieldedValue && !oldRange.isUninitialized() &&
!(lattice->getValue() == oldRange)) {
LLVM_DEBUG(llvm::dbgs() << "Loop variant loop result detected\n");
changed |= lattice->join(IntegerValueRange::getMaxRange(v));
}
propagateIfChanged(lattice, changed);
};
inferrable.inferResultRanges(argRanges, joinCallback);
return;
}
/// Given the results of getConstant{Lower,Upper}Bound() or getConstantStep()
/// on a LoopLikeInterface return the lower/upper bound for that result if
/// possible.
auto getLoopBoundFromFold = [&](std::optional<OpFoldResult> loopBound,
Type boundType, bool getUpper) {
unsigned int width = ConstantIntRanges::getStorageBitwidth(boundType);
if (loopBound.has_value()) {
if (loopBound->is<Attribute>()) {
if (auto bound =
dyn_cast_or_null<IntegerAttr>(loopBound->get<Attribute>()))
return bound.getValue();
} else if (auto value = loopBound->dyn_cast<Value>()) {
const IntegerValueRangeLattice *lattice =
getLatticeElementFor(op, value);
if (lattice != nullptr)
return getUpper ? lattice->getValue().getValue().smax()
: lattice->getValue().getValue().smin();
}
}
// Given the results of getConstant{Lower,Upper}Bound()
// or getConstantStep() on a LoopLikeInterface return the lower/upper
// bound
return getUpper ? APInt::getSignedMaxValue(width)
: APInt::getSignedMinValue(width);
};
// Infer bounds for loop arguments that have static bounds
if (auto loop = dyn_cast<LoopLikeOpInterface>(op)) {
std::optional<Value> iv = loop.getSingleInductionVar();
if (!iv) {
return SparseDataFlowAnalysis ::visitNonControlFlowArguments(
op, successor, argLattices, firstIndex);
}
std::optional<OpFoldResult> lowerBound = loop.getSingleLowerBound();
std::optional<OpFoldResult> upperBound = loop.getSingleUpperBound();
std::optional<OpFoldResult> step = loop.getSingleStep();
APInt min = getLoopBoundFromFold(lowerBound, iv->getType(),
/*getUpper=*/false);
APInt max = getLoopBoundFromFold(upperBound, iv->getType(),
/*getUpper=*/true);
// Assume positivity for uniscoverable steps by way of getUpper = true.
APInt stepVal =
getLoopBoundFromFold(step, iv->getType(), /*getUpper=*/true);
if (stepVal.isNegative()) {
std::swap(min, max);
} else {
// Correct the upper bound by subtracting 1 so that it becomes a <=
// bound, because loops do not generally include their upper bound.
max -= 1;
}
IntegerValueRangeLattice *ivEntry = getLatticeElement(*iv);
auto ivRange = ConstantIntRanges::fromSigned(min, max);
propagateIfChanged(ivEntry, ivEntry->join(IntegerValueRange{ivRange}));
return;
}
return SparseDataFlowAnalysis::visitNonControlFlowArguments(
op, successor, argLattices, firstIndex);
}
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