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//===- ValueLattice.cpp - Value constraint 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
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ValueLattice.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/IR/Instructions.h"
namespace llvm {
Constant *
ValueLatticeElement::getCompare(CmpInst::Predicate Pred, Type *Ty,
const ValueLatticeElement &Other,
const DataLayout &DL) const {
// Not yet resolved.
if (isUnknown() || Other.isUnknown())
return nullptr;
// TODO: Can be made more precise, but always returning undef would be
// incorrect.
if (isUndef() || Other.isUndef())
return nullptr;
if (isConstant() && Other.isConstant())
return ConstantFoldCompareInstOperands(Pred, getConstant(),
Other.getConstant(), DL);
if (ICmpInst::isEquality(Pred)) {
// not(C) != C => true, not(C) == C => false.
if ((isNotConstant() && Other.isConstant() &&
getNotConstant() == Other.getConstant()) ||
(isConstant() && Other.isNotConstant() &&
getConstant() == Other.getNotConstant()))
return Pred == ICmpInst::ICMP_NE ? ConstantInt::getTrue(Ty)
: ConstantInt::getFalse(Ty);
}
// Integer constants are represented as ConstantRanges with single
// elements.
if (!isConstantRange() || !Other.isConstantRange())
return nullptr;
const auto &CR = getConstantRange();
const auto &OtherCR = Other.getConstantRange();
if (CR.icmp(Pred, OtherCR))
return ConstantInt::getTrue(Ty);
if (CR.icmp(CmpInst::getInversePredicate(Pred), OtherCR))
return ConstantInt::getFalse(Ty);
return nullptr;
}
static bool hasSingleValue(const ValueLatticeElement &Val) {
if (Val.isConstantRange() && Val.getConstantRange().isSingleElement())
// Integer constants are single element ranges
return true;
return Val.isConstant();
}
/// Combine two sets of facts about the same value into a single set of
/// facts. Note that this method is not suitable for merging facts along
/// different paths in a CFG; that's what the mergeIn function is for. This
/// is for merging facts gathered about the same value at the same location
/// through two independent means.
/// Notes:
/// * This method does not promise to return the most precise possible lattice
/// value implied by A and B. It is allowed to return any lattice element
/// which is at least as strong as *either* A or B (unless our facts
/// conflict, see below).
/// * Due to unreachable code, the intersection of two lattice values could be
/// contradictory. If this happens, we return some valid lattice value so as
/// not confuse the rest of LVI. Ideally, we'd always return Undefined, but
/// we do not make this guarantee. TODO: This would be a useful enhancement.
ValueLatticeElement
ValueLatticeElement::intersect(const ValueLatticeElement &Other) const {
if (isUnknown())
return *this;
if (Other.isUnknown())
return Other;
// If we gave up for one, but got a useable fact from the other, use it.
if (isOverdefined())
return Other;
if (Other.isOverdefined())
return *this;
// Can't get any more precise than constants.
if (hasSingleValue(*this))
return *this;
if (hasSingleValue(Other))
return Other;
// Could be either constant range or not constant here.
if (!isConstantRange() || !Other.isConstantRange()) {
// TODO: Arbitrary choice, could be improved
return *this;
}
// Intersect two constant ranges
ConstantRange Range =
getConstantRange().intersectWith(Other.getConstantRange());
// Note: An empty range is implicitly converted to unknown or undef depending
// on MayIncludeUndef internally.
return ValueLatticeElement::getRange(
std::move(Range), /*MayIncludeUndef=*/isConstantRangeIncludingUndef() ||
Other.isConstantRangeIncludingUndef());
}
raw_ostream &operator<<(raw_ostream &OS, const ValueLatticeElement &Val) {
if (Val.isUnknown())
return OS << "unknown";
if (Val.isUndef())
return OS << "undef";
if (Val.isOverdefined())
return OS << "overdefined";
if (Val.isNotConstant())
return OS << "notconstant<" << *Val.getNotConstant() << ">";
if (Val.isConstantRangeIncludingUndef())
return OS << "constantrange incl. undef <"
<< Val.getConstantRange(true).getLower() << ", "
<< Val.getConstantRange(true).getUpper() << ">";
if (Val.isConstantRange())
return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
<< Val.getConstantRange().getUpper() << ">";
return OS << "constant<" << *Val.getConstant() << ">";
}
} // end namespace llvm
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