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//===-- ArrayExprVisitor.cpp ----------------------------------------------===//
//
// The KLEE Symbolic Virtual Machine
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "klee/Expr/ArrayExprVisitor.h"
#include "klee/Support/ErrorHandling.h"
#include <algorithm>
using namespace klee;
//------------------------------ HELPER FUNCTIONS ---------------------------//
bool ArrayExprHelper::isReadExprAtOffset(ref<Expr> e, const ReadExpr *base,
ref<Expr> offset) {
const ReadExpr *re = dyn_cast<ReadExpr>(e.get());
if (!re || (re->getWidth() != Expr::Int8))
return false;
return SubExpr::create(re->index, base->index) == offset;
}
ReadExpr *ArrayExprHelper::hasOrderedReads(const ConcatExpr &ce) {
const ReadExpr *base = dyn_cast<ReadExpr>(ce.getKid(0));
// right now, all Reads are byte reads but some
// transformations might change this
if (!base || base->getWidth() != Expr::Int8)
return nullptr;
// Get stride expr in proper index width.
Expr::Width idxWidth = base->index->getWidth();
ref<Expr> strideExpr = ConstantExpr::alloc(-1, idxWidth);
ref<Expr> offset = ConstantExpr::create(0, idxWidth);
ref<Expr> e = ce.getKid(1);
// concat chains are unbalanced to the right
while (e->getKind() == Expr::Concat) {
offset = AddExpr::create(offset, strideExpr);
if (!isReadExprAtOffset(e->getKid(0), base, offset))
return nullptr;
e = e->getKid(1);
}
offset = AddExpr::create(offset, strideExpr);
if (!isReadExprAtOffset(e, base, offset))
return nullptr;
return cast<ReadExpr>(e.get());
}
//--------------------------- INDEX-BASED OPTIMIZATION-----------------------//
ExprVisitor::Action
ConstantArrayExprVisitor::visitConcat(const ConcatExpr &ce) {
ReadExpr *base = ArrayExprHelper::hasOrderedReads(ce);
return base ? visitRead(*base) : Action::doChildren();
}
ExprVisitor::Action ConstantArrayExprVisitor::visitRead(const ReadExpr &re) {
// It is an interesting ReadExpr if it contains a concrete array
// that is read at a symbolic index
if (re.updates.root->isConstantArray() && !isa<ConstantExpr>(re.index)) {
for (const auto *un = re.updates.head.get(); un; un = un->next.get()) {
if (!isa<ConstantExpr>(un->index) || !isa<ConstantExpr>(un->value)) {
incompatible = true;
return Action::skipChildren();
}
}
IndexCompatibilityExprVisitor compatible;
compatible.visit(re.index);
if (compatible.isCompatible()) {
if (arrays.count(re.updates.root) > 0) {
const auto &indices = arrays[re.updates.root];
if (!indices.empty() && indices.front() != re.index) {
// Another possible index to resolve, currently unsupported
incompatible = true;
return Action::skipChildren();
}
}
arrays[re.updates.root].push_back(re.index);
} else if (compatible.hasInnerReads()) {
// This Read has an inner Read, we want to optimize the inner one
// to create a cascading effect during assignment evaluation
return Action::doChildren();
}
return Action::skipChildren();
} else if (re.updates.root->isSymbolicArray()) {
incompatible = true;
}
return Action::doChildren();
}
ExprVisitor::Action
IndexCompatibilityExprVisitor::visitRead(const ReadExpr &re) {
if (re.updates.head) {
compatible = false;
return Action::skipChildren();
} else if (re.updates.root->isConstantArray() &&
!isa<ConstantExpr>(re.index)) {
compatible = false;
inner = true;
return Action::skipChildren();
}
return Action::doChildren();
}
ExprVisitor::Action IndexCompatibilityExprVisitor::visitURem(const URemExpr &) {
compatible = false;
return Action::skipChildren();
}
ExprVisitor::Action IndexCompatibilityExprVisitor::visitSRem(const SRemExpr &) {
compatible = false;
return Action::skipChildren();
}
ExprVisitor::Action IndexCompatibilityExprVisitor::visitOr(const OrExpr &) {
compatible = false;
return Action::skipChildren();
}
ExprVisitor::Action
IndexTransformationExprVisitor::visitConcat(const ConcatExpr &ce) {
if (ReadExpr *re = dyn_cast<ReadExpr>(ce.getKid(0))) {
if (re->updates.root->hash() == array->hash() && width < ce.getWidth()) {
if (width == Expr::InvalidWidth)
width = ce.getWidth();
}
} else if (ReadExpr *re = dyn_cast<ReadExpr>(ce.getKid(1))) {
if (re->updates.root->hash() == array->hash() && width < ce.getWidth()) {
if (width == Expr::InvalidWidth)
width = ce.getWidth();
}
}
return Action::doChildren();
}
ExprVisitor::Action IndexTransformationExprVisitor::visitMul(const MulExpr &e) {
if (isa<ConstantExpr>(e.getKid(0)))
mul = e.getKid(0);
else if (isa<ConstantExpr>(e.getKid(0)))
mul = e.getKid(1);
return Action::doChildren();
}
//-------------------------- VALUE-BASED OPTIMIZATION------------------------//
ExprVisitor::Action ArrayReadExprVisitor::visitConcat(const ConcatExpr &ce) {
ReadExpr *base = ArrayExprHelper::hasOrderedReads(ce);
if (base) {
return inspectRead(const_cast<ConcatExpr *>(&ce), ce.getWidth(), *base);
}
return Action::doChildren();
}
ExprVisitor::Action ArrayReadExprVisitor::visitRead(const ReadExpr &re) {
return inspectRead(const_cast<ReadExpr *>(&re), re.getWidth(), re);
}
// This method is a mess because I want to avoid looping over the UpdateList
// values twice
ExprVisitor::Action ArrayReadExprVisitor::inspectRead(ref<Expr> hash,
Expr::Width width,
const ReadExpr &re) {
// pre(*): index is symbolic
if (!isa<ConstantExpr>(re.index)) {
if (readInfo.find(&re) == readInfo.end()) {
if (re.updates.root->isSymbolicArray() && !re.updates.head) {
return Action::doChildren();
}
if (re.updates.head) {
// Check preconditions on UpdateList nodes
bool hasConcreteValues = false;
for (const auto *un = re.updates.head.get(); un; un = un->next.get()) {
// Symbolic case - \inv(update): index is concrete
if (!isa<ConstantExpr>(un->index)) {
incompatible = true;
break;
} else if (!isa<ConstantExpr>(un->value)) {
// We tell the optimization that there is a symbolic value,
// otherwise we rely on the concrete optimization procedure
symbolic = true;
} else if (re.updates.root->isSymbolicArray() &&
isa<ConstantExpr>(un->value)) {
// We can optimize symbolic array, but only if they have
// at least one concrete value
hasConcreteValues = true;
}
}
// Symbolic case - if array is symbolic, then we need at least one
// concrete value
if (re.updates.root->isSymbolicArray()) {
if (hasConcreteValues)
symbolic = true;
else
incompatible = true;
}
if (incompatible)
return Action::skipChildren();
}
symbolic |= re.updates.root->isSymbolicArray();
reads.push_back(&re);
readInfo.emplace(&re, std::make_pair(hash, width));
}
return Action::skipChildren();
}
return Action::doChildren();
}
ExprVisitor::Action
ArrayValueOptReplaceVisitor::visitConcat(const ConcatExpr &ce) {
auto found = optimized.find(const_cast<ConcatExpr *>(&ce));
if (found != optimized.end()) {
return Action::changeTo((*found).second.get());
}
return Action::doChildren();
}
ExprVisitor::Action ArrayValueOptReplaceVisitor::visitRead(const ReadExpr &re) {
auto found = optimized.find(const_cast<ReadExpr *>(&re));
if (found != optimized.end()) {
return Action::changeTo((*found).second.get());
}
return Action::doChildren();
}
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