1 // SimpleSValBuilder.cpp - A basic SValBuilder -----------------------*- C++ -*-
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines SimpleSValBuilder, a basic implementation of SValBuilder.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h"
14 #include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
15 #include "clang/StaticAnalyzer/Core/PathSensitive/APSIntType.h"
16 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
17 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
18 #include "clang/StaticAnalyzer/Core/PathSensitive/SValVisitor.h"
19
20 using namespace clang;
21 using namespace ento;
22
23 namespace {
24 class SimpleSValBuilder : public SValBuilder {
25 public:
SimpleSValBuilder(llvm::BumpPtrAllocator & alloc,ASTContext & context,ProgramStateManager & stateMgr)26 SimpleSValBuilder(llvm::BumpPtrAllocator &alloc, ASTContext &context,
27 ProgramStateManager &stateMgr)
28 : SValBuilder(alloc, context, stateMgr) {}
~SimpleSValBuilder()29 ~SimpleSValBuilder() override {}
30
31 SVal evalMinus(NonLoc val) override;
32 SVal evalComplement(NonLoc val) override;
33 SVal evalBinOpNN(ProgramStateRef state, BinaryOperator::Opcode op,
34 NonLoc lhs, NonLoc rhs, QualType resultTy) override;
35 SVal evalBinOpLL(ProgramStateRef state, BinaryOperator::Opcode op,
36 Loc lhs, Loc rhs, QualType resultTy) override;
37 SVal evalBinOpLN(ProgramStateRef state, BinaryOperator::Opcode op,
38 Loc lhs, NonLoc rhs, QualType resultTy) override;
39
40 /// getKnownValue - evaluates a given SVal. If the SVal has only one possible
41 /// (integer) value, that value is returned. Otherwise, returns NULL.
42 const llvm::APSInt *getKnownValue(ProgramStateRef state, SVal V) override;
43
44 /// Recursively descends into symbolic expressions and replaces symbols
45 /// with their known values (in the sense of the getKnownValue() method).
46 SVal simplifySVal(ProgramStateRef State, SVal V) override;
47
48 SVal MakeSymIntVal(const SymExpr *LHS, BinaryOperator::Opcode op,
49 const llvm::APSInt &RHS, QualType resultTy);
50 };
51 } // end anonymous namespace
52
createSimpleSValBuilder(llvm::BumpPtrAllocator & alloc,ASTContext & context,ProgramStateManager & stateMgr)53 SValBuilder *ento::createSimpleSValBuilder(llvm::BumpPtrAllocator &alloc,
54 ASTContext &context,
55 ProgramStateManager &stateMgr) {
56 return new SimpleSValBuilder(alloc, context, stateMgr);
57 }
58
59 //===----------------------------------------------------------------------===//
60 // Transfer function for unary operators.
61 //===----------------------------------------------------------------------===//
62
evalMinus(NonLoc val)63 SVal SimpleSValBuilder::evalMinus(NonLoc val) {
64 switch (val.getSubKind()) {
65 case nonloc::ConcreteIntKind:
66 return val.castAs<nonloc::ConcreteInt>().evalMinus(*this);
67 default:
68 return UnknownVal();
69 }
70 }
71
evalComplement(NonLoc X)72 SVal SimpleSValBuilder::evalComplement(NonLoc X) {
73 switch (X.getSubKind()) {
74 case nonloc::ConcreteIntKind:
75 return X.castAs<nonloc::ConcreteInt>().evalComplement(*this);
76 default:
77 return UnknownVal();
78 }
79 }
80
81 //===----------------------------------------------------------------------===//
82 // Transfer function for binary operators.
83 //===----------------------------------------------------------------------===//
84
MakeSymIntVal(const SymExpr * LHS,BinaryOperator::Opcode op,const llvm::APSInt & RHS,QualType resultTy)85 SVal SimpleSValBuilder::MakeSymIntVal(const SymExpr *LHS,
86 BinaryOperator::Opcode op,
87 const llvm::APSInt &RHS,
88 QualType resultTy) {
89 bool isIdempotent = false;
90
91 // Check for a few special cases with known reductions first.
92 switch (op) {
93 default:
94 // We can't reduce this case; just treat it normally.
95 break;
96 case BO_Mul:
97 // a*0 and a*1
98 if (RHS == 0)
99 return makeIntVal(0, resultTy);
100 else if (RHS == 1)
101 isIdempotent = true;
102 break;
103 case BO_Div:
104 // a/0 and a/1
105 if (RHS == 0)
106 // This is also handled elsewhere.
107 return UndefinedVal();
108 else if (RHS == 1)
109 isIdempotent = true;
110 break;
111 case BO_Rem:
112 // a%0 and a%1
113 if (RHS == 0)
114 // This is also handled elsewhere.
115 return UndefinedVal();
116 else if (RHS == 1)
117 return makeIntVal(0, resultTy);
118 break;
119 case BO_Add:
120 case BO_Sub:
121 case BO_Shl:
122 case BO_Shr:
123 case BO_Xor:
124 // a+0, a-0, a<<0, a>>0, a^0
125 if (RHS == 0)
126 isIdempotent = true;
127 break;
128 case BO_And:
129 // a&0 and a&(~0)
130 if (RHS == 0)
131 return makeIntVal(0, resultTy);
132 else if (RHS.isAllOnesValue())
133 isIdempotent = true;
134 break;
135 case BO_Or:
136 // a|0 and a|(~0)
137 if (RHS == 0)
138 isIdempotent = true;
139 else if (RHS.isAllOnesValue()) {
140 const llvm::APSInt &Result = BasicVals.Convert(resultTy, RHS);
141 return nonloc::ConcreteInt(Result);
142 }
143 break;
144 }
145
146 // Idempotent ops (like a*1) can still change the type of an expression.
147 // Wrap the LHS up in a NonLoc again and let evalCast do the
148 // dirty work.
149 if (isIdempotent)
150 return evalCast(nonloc::SymbolVal(LHS), resultTy, QualType{});
151
152 // If we reach this point, the expression cannot be simplified.
153 // Make a SymbolVal for the entire expression, after converting the RHS.
154 const llvm::APSInt *ConvertedRHS = &RHS;
155 if (BinaryOperator::isComparisonOp(op)) {
156 // We're looking for a type big enough to compare the symbolic value
157 // with the given constant.
158 // FIXME: This is an approximation of Sema::UsualArithmeticConversions.
159 ASTContext &Ctx = getContext();
160 QualType SymbolType = LHS->getType();
161 uint64_t ValWidth = RHS.getBitWidth();
162 uint64_t TypeWidth = Ctx.getTypeSize(SymbolType);
163
164 if (ValWidth < TypeWidth) {
165 // If the value is too small, extend it.
166 ConvertedRHS = &BasicVals.Convert(SymbolType, RHS);
167 } else if (ValWidth == TypeWidth) {
168 // If the value is signed but the symbol is unsigned, do the comparison
169 // in unsigned space. [C99 6.3.1.8]
170 // (For the opposite case, the value is already unsigned.)
171 if (RHS.isSigned() && !SymbolType->isSignedIntegerOrEnumerationType())
172 ConvertedRHS = &BasicVals.Convert(SymbolType, RHS);
173 }
174 } else
175 ConvertedRHS = &BasicVals.Convert(resultTy, RHS);
176
177 return makeNonLoc(LHS, op, *ConvertedRHS, resultTy);
178 }
179
180 // See if Sym is known to be a relation Rel with Bound.
isInRelation(BinaryOperator::Opcode Rel,SymbolRef Sym,llvm::APSInt Bound,ProgramStateRef State)181 static bool isInRelation(BinaryOperator::Opcode Rel, SymbolRef Sym,
182 llvm::APSInt Bound, ProgramStateRef State) {
183 SValBuilder &SVB = State->getStateManager().getSValBuilder();
184 SVal Result =
185 SVB.evalBinOpNN(State, Rel, nonloc::SymbolVal(Sym),
186 nonloc::ConcreteInt(Bound), SVB.getConditionType());
187 if (auto DV = Result.getAs<DefinedSVal>()) {
188 return !State->assume(*DV, false);
189 }
190 return false;
191 }
192
193 // See if Sym is known to be within [min/4, max/4], where min and max
194 // are the bounds of the symbol's integral type. With such symbols,
195 // some manipulations can be performed without the risk of overflow.
196 // assume() doesn't cause infinite recursion because we should be dealing
197 // with simpler symbols on every recursive call.
isWithinConstantOverflowBounds(SymbolRef Sym,ProgramStateRef State)198 static bool isWithinConstantOverflowBounds(SymbolRef Sym,
199 ProgramStateRef State) {
200 SValBuilder &SVB = State->getStateManager().getSValBuilder();
201 BasicValueFactory &BV = SVB.getBasicValueFactory();
202
203 QualType T = Sym->getType();
204 assert(T->isSignedIntegerOrEnumerationType() &&
205 "This only works with signed integers!");
206 APSIntType AT = BV.getAPSIntType(T);
207
208 llvm::APSInt Max = AT.getMaxValue() / AT.getValue(4), Min = -Max;
209 return isInRelation(BO_LE, Sym, Max, State) &&
210 isInRelation(BO_GE, Sym, Min, State);
211 }
212
213 // Same for the concrete integers: see if I is within [min/4, max/4].
isWithinConstantOverflowBounds(llvm::APSInt I)214 static bool isWithinConstantOverflowBounds(llvm::APSInt I) {
215 APSIntType AT(I);
216 assert(!AT.isUnsigned() &&
217 "This only works with signed integers!");
218
219 llvm::APSInt Max = AT.getMaxValue() / AT.getValue(4), Min = -Max;
220 return (I <= Max) && (I >= -Max);
221 }
222
223 static std::pair<SymbolRef, llvm::APSInt>
decomposeSymbol(SymbolRef Sym,BasicValueFactory & BV)224 decomposeSymbol(SymbolRef Sym, BasicValueFactory &BV) {
225 if (const auto *SymInt = dyn_cast<SymIntExpr>(Sym))
226 if (BinaryOperator::isAdditiveOp(SymInt->getOpcode()))
227 return std::make_pair(SymInt->getLHS(),
228 (SymInt->getOpcode() == BO_Add) ?
229 (SymInt->getRHS()) :
230 (-SymInt->getRHS()));
231
232 // Fail to decompose: "reduce" the problem to the "$x + 0" case.
233 return std::make_pair(Sym, BV.getValue(0, Sym->getType()));
234 }
235
236 // Simplify "(LSym + LInt) Op (RSym + RInt)" assuming all values are of the
237 // same signed integral type and no overflows occur (which should be checked
238 // by the caller).
doRearrangeUnchecked(ProgramStateRef State,BinaryOperator::Opcode Op,SymbolRef LSym,llvm::APSInt LInt,SymbolRef RSym,llvm::APSInt RInt)239 static NonLoc doRearrangeUnchecked(ProgramStateRef State,
240 BinaryOperator::Opcode Op,
241 SymbolRef LSym, llvm::APSInt LInt,
242 SymbolRef RSym, llvm::APSInt RInt) {
243 SValBuilder &SVB = State->getStateManager().getSValBuilder();
244 BasicValueFactory &BV = SVB.getBasicValueFactory();
245 SymbolManager &SymMgr = SVB.getSymbolManager();
246
247 QualType SymTy = LSym->getType();
248 assert(SymTy == RSym->getType() &&
249 "Symbols are not of the same type!");
250 assert(APSIntType(LInt) == BV.getAPSIntType(SymTy) &&
251 "Integers are not of the same type as symbols!");
252 assert(APSIntType(RInt) == BV.getAPSIntType(SymTy) &&
253 "Integers are not of the same type as symbols!");
254
255 QualType ResultTy;
256 if (BinaryOperator::isComparisonOp(Op))
257 ResultTy = SVB.getConditionType();
258 else if (BinaryOperator::isAdditiveOp(Op))
259 ResultTy = SymTy;
260 else
261 llvm_unreachable("Operation not suitable for unchecked rearrangement!");
262
263 // FIXME: Can we use assume() without getting into an infinite recursion?
264 if (LSym == RSym)
265 return SVB.evalBinOpNN(State, Op, nonloc::ConcreteInt(LInt),
266 nonloc::ConcreteInt(RInt), ResultTy)
267 .castAs<NonLoc>();
268
269 SymbolRef ResultSym = nullptr;
270 BinaryOperator::Opcode ResultOp;
271 llvm::APSInt ResultInt;
272 if (BinaryOperator::isComparisonOp(Op)) {
273 // Prefer comparing to a non-negative number.
274 // FIXME: Maybe it'd be better to have consistency in
275 // "$x - $y" vs. "$y - $x" because those are solver's keys.
276 if (LInt > RInt) {
277 ResultSym = SymMgr.getSymSymExpr(RSym, BO_Sub, LSym, SymTy);
278 ResultOp = BinaryOperator::reverseComparisonOp(Op);
279 ResultInt = LInt - RInt; // Opposite order!
280 } else {
281 ResultSym = SymMgr.getSymSymExpr(LSym, BO_Sub, RSym, SymTy);
282 ResultOp = Op;
283 ResultInt = RInt - LInt; // Opposite order!
284 }
285 } else {
286 ResultSym = SymMgr.getSymSymExpr(LSym, Op, RSym, SymTy);
287 ResultInt = (Op == BO_Add) ? (LInt + RInt) : (LInt - RInt);
288 ResultOp = BO_Add;
289 // Bring back the cosmetic difference.
290 if (ResultInt < 0) {
291 ResultInt = -ResultInt;
292 ResultOp = BO_Sub;
293 } else if (ResultInt == 0) {
294 // Shortcut: Simplify "$x + 0" to "$x".
295 return nonloc::SymbolVal(ResultSym);
296 }
297 }
298 const llvm::APSInt &PersistentResultInt = BV.getValue(ResultInt);
299 return nonloc::SymbolVal(
300 SymMgr.getSymIntExpr(ResultSym, ResultOp, PersistentResultInt, ResultTy));
301 }
302
303 // Rearrange if symbol type matches the result type and if the operator is a
304 // comparison operator, both symbol and constant must be within constant
305 // overflow bounds.
shouldRearrange(ProgramStateRef State,BinaryOperator::Opcode Op,SymbolRef Sym,llvm::APSInt Int,QualType Ty)306 static bool shouldRearrange(ProgramStateRef State, BinaryOperator::Opcode Op,
307 SymbolRef Sym, llvm::APSInt Int, QualType Ty) {
308 return Sym->getType() == Ty &&
309 (!BinaryOperator::isComparisonOp(Op) ||
310 (isWithinConstantOverflowBounds(Sym, State) &&
311 isWithinConstantOverflowBounds(Int)));
312 }
313
tryRearrange(ProgramStateRef State,BinaryOperator::Opcode Op,NonLoc Lhs,NonLoc Rhs,QualType ResultTy)314 static Optional<NonLoc> tryRearrange(ProgramStateRef State,
315 BinaryOperator::Opcode Op, NonLoc Lhs,
316 NonLoc Rhs, QualType ResultTy) {
317 ProgramStateManager &StateMgr = State->getStateManager();
318 SValBuilder &SVB = StateMgr.getSValBuilder();
319
320 // We expect everything to be of the same type - this type.
321 QualType SingleTy;
322
323 auto &Opts =
324 StateMgr.getOwningEngine().getAnalysisManager().getAnalyzerOptions();
325
326 // FIXME: After putting complexity threshold to the symbols we can always
327 // rearrange additive operations but rearrange comparisons only if
328 // option is set.
329 if(!Opts.ShouldAggressivelySimplifyBinaryOperation)
330 return None;
331
332 SymbolRef LSym = Lhs.getAsSymbol();
333 if (!LSym)
334 return None;
335
336 if (BinaryOperator::isComparisonOp(Op)) {
337 SingleTy = LSym->getType();
338 if (ResultTy != SVB.getConditionType())
339 return None;
340 // Initialize SingleTy later with a symbol's type.
341 } else if (BinaryOperator::isAdditiveOp(Op)) {
342 SingleTy = ResultTy;
343 if (LSym->getType() != SingleTy)
344 return None;
345 } else {
346 // Don't rearrange other operations.
347 return None;
348 }
349
350 assert(!SingleTy.isNull() && "We should have figured out the type by now!");
351
352 // Rearrange signed symbolic expressions only
353 if (!SingleTy->isSignedIntegerOrEnumerationType())
354 return None;
355
356 SymbolRef RSym = Rhs.getAsSymbol();
357 if (!RSym || RSym->getType() != SingleTy)
358 return None;
359
360 BasicValueFactory &BV = State->getBasicVals();
361 llvm::APSInt LInt, RInt;
362 std::tie(LSym, LInt) = decomposeSymbol(LSym, BV);
363 std::tie(RSym, RInt) = decomposeSymbol(RSym, BV);
364 if (!shouldRearrange(State, Op, LSym, LInt, SingleTy) ||
365 !shouldRearrange(State, Op, RSym, RInt, SingleTy))
366 return None;
367
368 // We know that no overflows can occur anymore.
369 return doRearrangeUnchecked(State, Op, LSym, LInt, RSym, RInt);
370 }
371
evalBinOpNN(ProgramStateRef state,BinaryOperator::Opcode op,NonLoc lhs,NonLoc rhs,QualType resultTy)372 SVal SimpleSValBuilder::evalBinOpNN(ProgramStateRef state,
373 BinaryOperator::Opcode op,
374 NonLoc lhs, NonLoc rhs,
375 QualType resultTy) {
376 NonLoc InputLHS = lhs;
377 NonLoc InputRHS = rhs;
378
379 // Handle trivial case where left-side and right-side are the same.
380 if (lhs == rhs)
381 switch (op) {
382 default:
383 break;
384 case BO_EQ:
385 case BO_LE:
386 case BO_GE:
387 return makeTruthVal(true, resultTy);
388 case BO_LT:
389 case BO_GT:
390 case BO_NE:
391 return makeTruthVal(false, resultTy);
392 case BO_Xor:
393 case BO_Sub:
394 if (resultTy->isIntegralOrEnumerationType())
395 return makeIntVal(0, resultTy);
396 return evalCast(makeIntVal(0, /*isUnsigned=*/false), resultTy,
397 QualType{});
398 case BO_Or:
399 case BO_And:
400 return evalCast(lhs, resultTy, QualType{});
401 }
402
403 while (1) {
404 switch (lhs.getSubKind()) {
405 default:
406 return makeSymExprValNN(op, lhs, rhs, resultTy);
407 case nonloc::PointerToMemberKind: {
408 assert(rhs.getSubKind() == nonloc::PointerToMemberKind &&
409 "Both SVals should have pointer-to-member-type");
410 auto LPTM = lhs.castAs<nonloc::PointerToMember>(),
411 RPTM = rhs.castAs<nonloc::PointerToMember>();
412 auto LPTMD = LPTM.getPTMData(), RPTMD = RPTM.getPTMData();
413 switch (op) {
414 case BO_EQ:
415 return makeTruthVal(LPTMD == RPTMD, resultTy);
416 case BO_NE:
417 return makeTruthVal(LPTMD != RPTMD, resultTy);
418 default:
419 return UnknownVal();
420 }
421 }
422 case nonloc::LocAsIntegerKind: {
423 Loc lhsL = lhs.castAs<nonloc::LocAsInteger>().getLoc();
424 switch (rhs.getSubKind()) {
425 case nonloc::LocAsIntegerKind:
426 // FIXME: at the moment the implementation
427 // of modeling "pointers as integers" is not complete.
428 if (!BinaryOperator::isComparisonOp(op))
429 return UnknownVal();
430 return evalBinOpLL(state, op, lhsL,
431 rhs.castAs<nonloc::LocAsInteger>().getLoc(),
432 resultTy);
433 case nonloc::ConcreteIntKind: {
434 // FIXME: at the moment the implementation
435 // of modeling "pointers as integers" is not complete.
436 if (!BinaryOperator::isComparisonOp(op))
437 return UnknownVal();
438 // Transform the integer into a location and compare.
439 // FIXME: This only makes sense for comparisons. If we want to, say,
440 // add 1 to a LocAsInteger, we'd better unpack the Loc and add to it,
441 // then pack it back into a LocAsInteger.
442 llvm::APSInt i = rhs.castAs<nonloc::ConcreteInt>().getValue();
443 // If the region has a symbolic base, pay attention to the type; it
444 // might be coming from a non-default address space. For non-symbolic
445 // regions it doesn't matter that much because such comparisons would
446 // most likely evaluate to concrete false anyway. FIXME: We might
447 // still need to handle the non-comparison case.
448 if (SymbolRef lSym = lhs.getAsLocSymbol(true))
449 BasicVals.getAPSIntType(lSym->getType()).apply(i);
450 else
451 BasicVals.getAPSIntType(Context.VoidPtrTy).apply(i);
452 return evalBinOpLL(state, op, lhsL, makeLoc(i), resultTy);
453 }
454 default:
455 switch (op) {
456 case BO_EQ:
457 return makeTruthVal(false, resultTy);
458 case BO_NE:
459 return makeTruthVal(true, resultTy);
460 default:
461 // This case also handles pointer arithmetic.
462 return makeSymExprValNN(op, InputLHS, InputRHS, resultTy);
463 }
464 }
465 }
466 case nonloc::ConcreteIntKind: {
467 llvm::APSInt LHSValue = lhs.castAs<nonloc::ConcreteInt>().getValue();
468
469 // If we're dealing with two known constants, just perform the operation.
470 if (const llvm::APSInt *KnownRHSValue = getKnownValue(state, rhs)) {
471 llvm::APSInt RHSValue = *KnownRHSValue;
472 if (BinaryOperator::isComparisonOp(op)) {
473 // We're looking for a type big enough to compare the two values.
474 // FIXME: This is not correct. char + short will result in a promotion
475 // to int. Unfortunately we have lost types by this point.
476 APSIntType CompareType = std::max(APSIntType(LHSValue),
477 APSIntType(RHSValue));
478 CompareType.apply(LHSValue);
479 CompareType.apply(RHSValue);
480 } else if (!BinaryOperator::isShiftOp(op)) {
481 APSIntType IntType = BasicVals.getAPSIntType(resultTy);
482 IntType.apply(LHSValue);
483 IntType.apply(RHSValue);
484 }
485
486 const llvm::APSInt *Result =
487 BasicVals.evalAPSInt(op, LHSValue, RHSValue);
488 if (!Result)
489 return UndefinedVal();
490
491 return nonloc::ConcreteInt(*Result);
492 }
493
494 // Swap the left and right sides and flip the operator if doing so
495 // allows us to better reason about the expression (this is a form
496 // of expression canonicalization).
497 // While we're at it, catch some special cases for non-commutative ops.
498 switch (op) {
499 case BO_LT:
500 case BO_GT:
501 case BO_LE:
502 case BO_GE:
503 op = BinaryOperator::reverseComparisonOp(op);
504 LLVM_FALLTHROUGH;
505 case BO_EQ:
506 case BO_NE:
507 case BO_Add:
508 case BO_Mul:
509 case BO_And:
510 case BO_Xor:
511 case BO_Or:
512 std::swap(lhs, rhs);
513 continue;
514 case BO_Shr:
515 // (~0)>>a
516 if (LHSValue.isAllOnesValue() && LHSValue.isSigned())
517 return evalCast(lhs, resultTy, QualType{});
518 LLVM_FALLTHROUGH;
519 case BO_Shl:
520 // 0<<a and 0>>a
521 if (LHSValue == 0)
522 return evalCast(lhs, resultTy, QualType{});
523 return makeSymExprValNN(op, InputLHS, InputRHS, resultTy);
524 case BO_Div:
525 // 0 / x == 0
526 case BO_Rem:
527 // 0 % x == 0
528 if (LHSValue == 0)
529 return makeZeroVal(resultTy);
530 LLVM_FALLTHROUGH;
531 default:
532 return makeSymExprValNN(op, InputLHS, InputRHS, resultTy);
533 }
534 }
535 case nonloc::SymbolValKind: {
536 // We only handle LHS as simple symbols or SymIntExprs.
537 SymbolRef Sym = lhs.castAs<nonloc::SymbolVal>().getSymbol();
538
539 // LHS is a symbolic expression.
540 if (const SymIntExpr *symIntExpr = dyn_cast<SymIntExpr>(Sym)) {
541
542 // Is this a logical not? (!x is represented as x == 0.)
543 if (op == BO_EQ && rhs.isZeroConstant()) {
544 // We know how to negate certain expressions. Simplify them here.
545
546 BinaryOperator::Opcode opc = symIntExpr->getOpcode();
547 switch (opc) {
548 default:
549 // We don't know how to negate this operation.
550 // Just handle it as if it were a normal comparison to 0.
551 break;
552 case BO_LAnd:
553 case BO_LOr:
554 llvm_unreachable("Logical operators handled by branching logic.");
555 case BO_Assign:
556 case BO_MulAssign:
557 case BO_DivAssign:
558 case BO_RemAssign:
559 case BO_AddAssign:
560 case BO_SubAssign:
561 case BO_ShlAssign:
562 case BO_ShrAssign:
563 case BO_AndAssign:
564 case BO_XorAssign:
565 case BO_OrAssign:
566 case BO_Comma:
567 llvm_unreachable("'=' and ',' operators handled by ExprEngine.");
568 case BO_PtrMemD:
569 case BO_PtrMemI:
570 llvm_unreachable("Pointer arithmetic not handled here.");
571 case BO_LT:
572 case BO_GT:
573 case BO_LE:
574 case BO_GE:
575 case BO_EQ:
576 case BO_NE:
577 assert(resultTy->isBooleanType() ||
578 resultTy == getConditionType());
579 assert(symIntExpr->getType()->isBooleanType() ||
580 getContext().hasSameUnqualifiedType(symIntExpr->getType(),
581 getConditionType()));
582 // Negate the comparison and make a value.
583 opc = BinaryOperator::negateComparisonOp(opc);
584 return makeNonLoc(symIntExpr->getLHS(), opc,
585 symIntExpr->getRHS(), resultTy);
586 }
587 }
588
589 // For now, only handle expressions whose RHS is a constant.
590 if (const llvm::APSInt *RHSValue = getKnownValue(state, rhs)) {
591 // If both the LHS and the current expression are additive,
592 // fold their constants and try again.
593 if (BinaryOperator::isAdditiveOp(op)) {
594 BinaryOperator::Opcode lop = symIntExpr->getOpcode();
595 if (BinaryOperator::isAdditiveOp(lop)) {
596 // Convert the two constants to a common type, then combine them.
597
598 // resultTy may not be the best type to convert to, but it's
599 // probably the best choice in expressions with mixed type
600 // (such as x+1U+2LL). The rules for implicit conversions should
601 // choose a reasonable type to preserve the expression, and will
602 // at least match how the value is going to be used.
603 APSIntType IntType = BasicVals.getAPSIntType(resultTy);
604 const llvm::APSInt &first = IntType.convert(symIntExpr->getRHS());
605 const llvm::APSInt &second = IntType.convert(*RHSValue);
606
607 const llvm::APSInt *newRHS;
608 if (lop == op)
609 newRHS = BasicVals.evalAPSInt(BO_Add, first, second);
610 else
611 newRHS = BasicVals.evalAPSInt(BO_Sub, first, second);
612
613 assert(newRHS && "Invalid operation despite common type!");
614 rhs = nonloc::ConcreteInt(*newRHS);
615 lhs = nonloc::SymbolVal(symIntExpr->getLHS());
616 op = lop;
617 continue;
618 }
619 }
620
621 // Otherwise, make a SymIntExpr out of the expression.
622 return MakeSymIntVal(symIntExpr, op, *RHSValue, resultTy);
623 }
624 }
625
626 // Does the symbolic expression simplify to a constant?
627 // If so, "fold" the constant by setting 'lhs' to a ConcreteInt
628 // and try again.
629 SVal simplifiedLhs = simplifySVal(state, lhs);
630 if (simplifiedLhs != lhs)
631 if (auto simplifiedLhsAsNonLoc = simplifiedLhs.getAs<NonLoc>()) {
632 lhs = *simplifiedLhsAsNonLoc;
633 continue;
634 }
635
636 // Is the RHS a constant?
637 if (const llvm::APSInt *RHSValue = getKnownValue(state, rhs))
638 return MakeSymIntVal(Sym, op, *RHSValue, resultTy);
639
640 if (Optional<NonLoc> V = tryRearrange(state, op, lhs, rhs, resultTy))
641 return *V;
642
643 // Give up -- this is not a symbolic expression we can handle.
644 return makeSymExprValNN(op, InputLHS, InputRHS, resultTy);
645 }
646 }
647 }
648 }
649
evalBinOpFieldRegionFieldRegion(const FieldRegion * LeftFR,const FieldRegion * RightFR,BinaryOperator::Opcode op,QualType resultTy,SimpleSValBuilder & SVB)650 static SVal evalBinOpFieldRegionFieldRegion(const FieldRegion *LeftFR,
651 const FieldRegion *RightFR,
652 BinaryOperator::Opcode op,
653 QualType resultTy,
654 SimpleSValBuilder &SVB) {
655 // Only comparisons are meaningful here!
656 if (!BinaryOperator::isComparisonOp(op))
657 return UnknownVal();
658
659 // Next, see if the two FRs have the same super-region.
660 // FIXME: This doesn't handle casts yet, and simply stripping the casts
661 // doesn't help.
662 if (LeftFR->getSuperRegion() != RightFR->getSuperRegion())
663 return UnknownVal();
664
665 const FieldDecl *LeftFD = LeftFR->getDecl();
666 const FieldDecl *RightFD = RightFR->getDecl();
667 const RecordDecl *RD = LeftFD->getParent();
668
669 // Make sure the two FRs are from the same kind of record. Just in case!
670 // FIXME: This is probably where inheritance would be a problem.
671 if (RD != RightFD->getParent())
672 return UnknownVal();
673
674 // We know for sure that the two fields are not the same, since that
675 // would have given us the same SVal.
676 if (op == BO_EQ)
677 return SVB.makeTruthVal(false, resultTy);
678 if (op == BO_NE)
679 return SVB.makeTruthVal(true, resultTy);
680
681 // Iterate through the fields and see which one comes first.
682 // [C99 6.7.2.1.13] "Within a structure object, the non-bit-field
683 // members and the units in which bit-fields reside have addresses that
684 // increase in the order in which they are declared."
685 bool leftFirst = (op == BO_LT || op == BO_LE);
686 for (const auto *I : RD->fields()) {
687 if (I == LeftFD)
688 return SVB.makeTruthVal(leftFirst, resultTy);
689 if (I == RightFD)
690 return SVB.makeTruthVal(!leftFirst, resultTy);
691 }
692
693 llvm_unreachable("Fields not found in parent record's definition");
694 }
695
696 // FIXME: all this logic will change if/when we have MemRegion::getLocation().
evalBinOpLL(ProgramStateRef state,BinaryOperator::Opcode op,Loc lhs,Loc rhs,QualType resultTy)697 SVal SimpleSValBuilder::evalBinOpLL(ProgramStateRef state,
698 BinaryOperator::Opcode op,
699 Loc lhs, Loc rhs,
700 QualType resultTy) {
701 // Only comparisons and subtractions are valid operations on two pointers.
702 // See [C99 6.5.5 through 6.5.14] or [C++0x 5.6 through 5.15].
703 // However, if a pointer is casted to an integer, evalBinOpNN may end up
704 // calling this function with another operation (PR7527). We don't attempt to
705 // model this for now, but it could be useful, particularly when the
706 // "location" is actually an integer value that's been passed through a void*.
707 if (!(BinaryOperator::isComparisonOp(op) || op == BO_Sub))
708 return UnknownVal();
709
710 // Special cases for when both sides are identical.
711 if (lhs == rhs) {
712 switch (op) {
713 default:
714 llvm_unreachable("Unimplemented operation for two identical values");
715 case BO_Sub:
716 return makeZeroVal(resultTy);
717 case BO_EQ:
718 case BO_LE:
719 case BO_GE:
720 return makeTruthVal(true, resultTy);
721 case BO_NE:
722 case BO_LT:
723 case BO_GT:
724 return makeTruthVal(false, resultTy);
725 }
726 }
727
728 switch (lhs.getSubKind()) {
729 default:
730 llvm_unreachable("Ordering not implemented for this Loc.");
731
732 case loc::GotoLabelKind:
733 // The only thing we know about labels is that they're non-null.
734 if (rhs.isZeroConstant()) {
735 switch (op) {
736 default:
737 break;
738 case BO_Sub:
739 return evalCast(lhs, resultTy, QualType{});
740 case BO_EQ:
741 case BO_LE:
742 case BO_LT:
743 return makeTruthVal(false, resultTy);
744 case BO_NE:
745 case BO_GT:
746 case BO_GE:
747 return makeTruthVal(true, resultTy);
748 }
749 }
750 // There may be two labels for the same location, and a function region may
751 // have the same address as a label at the start of the function (depending
752 // on the ABI).
753 // FIXME: we can probably do a comparison against other MemRegions, though.
754 // FIXME: is there a way to tell if two labels refer to the same location?
755 return UnknownVal();
756
757 case loc::ConcreteIntKind: {
758 // If one of the operands is a symbol and the other is a constant,
759 // build an expression for use by the constraint manager.
760 if (SymbolRef rSym = rhs.getAsLocSymbol()) {
761 // We can only build expressions with symbols on the left,
762 // so we need a reversible operator.
763 if (!BinaryOperator::isComparisonOp(op) || op == BO_Cmp)
764 return UnknownVal();
765
766 const llvm::APSInt &lVal = lhs.castAs<loc::ConcreteInt>().getValue();
767 op = BinaryOperator::reverseComparisonOp(op);
768 return makeNonLoc(rSym, op, lVal, resultTy);
769 }
770
771 // If both operands are constants, just perform the operation.
772 if (Optional<loc::ConcreteInt> rInt = rhs.getAs<loc::ConcreteInt>()) {
773 SVal ResultVal =
774 lhs.castAs<loc::ConcreteInt>().evalBinOp(BasicVals, op, *rInt);
775 if (Optional<NonLoc> Result = ResultVal.getAs<NonLoc>())
776 return evalCast(*Result, resultTy, QualType{});
777
778 assert(!ResultVal.getAs<Loc>() && "Loc-Loc ops should not produce Locs");
779 return UnknownVal();
780 }
781
782 // Special case comparisons against NULL.
783 // This must come after the test if the RHS is a symbol, which is used to
784 // build constraints. The address of any non-symbolic region is guaranteed
785 // to be non-NULL, as is any label.
786 assert(rhs.getAs<loc::MemRegionVal>() || rhs.getAs<loc::GotoLabel>());
787 if (lhs.isZeroConstant()) {
788 switch (op) {
789 default:
790 break;
791 case BO_EQ:
792 case BO_GT:
793 case BO_GE:
794 return makeTruthVal(false, resultTy);
795 case BO_NE:
796 case BO_LT:
797 case BO_LE:
798 return makeTruthVal(true, resultTy);
799 }
800 }
801
802 // Comparing an arbitrary integer to a region or label address is
803 // completely unknowable.
804 return UnknownVal();
805 }
806 case loc::MemRegionValKind: {
807 if (Optional<loc::ConcreteInt> rInt = rhs.getAs<loc::ConcreteInt>()) {
808 // If one of the operands is a symbol and the other is a constant,
809 // build an expression for use by the constraint manager.
810 if (SymbolRef lSym = lhs.getAsLocSymbol(true)) {
811 if (BinaryOperator::isComparisonOp(op))
812 return MakeSymIntVal(lSym, op, rInt->getValue(), resultTy);
813 return UnknownVal();
814 }
815 // Special case comparisons to NULL.
816 // This must come after the test if the LHS is a symbol, which is used to
817 // build constraints. The address of any non-symbolic region is guaranteed
818 // to be non-NULL.
819 if (rInt->isZeroConstant()) {
820 if (op == BO_Sub)
821 return evalCast(lhs, resultTy, QualType{});
822
823 if (BinaryOperator::isComparisonOp(op)) {
824 QualType boolType = getContext().BoolTy;
825 NonLoc l = evalCast(lhs, boolType, QualType{}).castAs<NonLoc>();
826 NonLoc r = makeTruthVal(false, boolType).castAs<NonLoc>();
827 return evalBinOpNN(state, op, l, r, resultTy);
828 }
829 }
830
831 // Comparing a region to an arbitrary integer is completely unknowable.
832 return UnknownVal();
833 }
834
835 // Get both values as regions, if possible.
836 const MemRegion *LeftMR = lhs.getAsRegion();
837 assert(LeftMR && "MemRegionValKind SVal doesn't have a region!");
838
839 const MemRegion *RightMR = rhs.getAsRegion();
840 if (!RightMR)
841 // The RHS is probably a label, which in theory could address a region.
842 // FIXME: we can probably make a more useful statement about non-code
843 // regions, though.
844 return UnknownVal();
845
846 const MemRegion *LeftBase = LeftMR->getBaseRegion();
847 const MemRegion *RightBase = RightMR->getBaseRegion();
848 const MemSpaceRegion *LeftMS = LeftBase->getMemorySpace();
849 const MemSpaceRegion *RightMS = RightBase->getMemorySpace();
850 const MemSpaceRegion *UnknownMS = MemMgr.getUnknownRegion();
851
852 // If the two regions are from different known memory spaces they cannot be
853 // equal. Also, assume that no symbolic region (whose memory space is
854 // unknown) is on the stack.
855 if (LeftMS != RightMS &&
856 ((LeftMS != UnknownMS && RightMS != UnknownMS) ||
857 (isa<StackSpaceRegion>(LeftMS) || isa<StackSpaceRegion>(RightMS)))) {
858 switch (op) {
859 default:
860 return UnknownVal();
861 case BO_EQ:
862 return makeTruthVal(false, resultTy);
863 case BO_NE:
864 return makeTruthVal(true, resultTy);
865 }
866 }
867
868 // If both values wrap regions, see if they're from different base regions.
869 // Note, heap base symbolic regions are assumed to not alias with
870 // each other; for example, we assume that malloc returns different address
871 // on each invocation.
872 // FIXME: ObjC object pointers always reside on the heap, but currently
873 // we treat their memory space as unknown, because symbolic pointers
874 // to ObjC objects may alias. There should be a way to construct
875 // possibly-aliasing heap-based regions. For instance, MacOSXApiChecker
876 // guesses memory space for ObjC object pointers manually instead of
877 // relying on us.
878 if (LeftBase != RightBase &&
879 ((!isa<SymbolicRegion>(LeftBase) && !isa<SymbolicRegion>(RightBase)) ||
880 (isa<HeapSpaceRegion>(LeftMS) || isa<HeapSpaceRegion>(RightMS))) ){
881 switch (op) {
882 default:
883 return UnknownVal();
884 case BO_EQ:
885 return makeTruthVal(false, resultTy);
886 case BO_NE:
887 return makeTruthVal(true, resultTy);
888 }
889 }
890
891 // Handle special cases for when both regions are element regions.
892 const ElementRegion *RightER = dyn_cast<ElementRegion>(RightMR);
893 const ElementRegion *LeftER = dyn_cast<ElementRegion>(LeftMR);
894 if (RightER && LeftER) {
895 // Next, see if the two ERs have the same super-region and matching types.
896 // FIXME: This should do something useful even if the types don't match,
897 // though if both indexes are constant the RegionRawOffset path will
898 // give the correct answer.
899 if (LeftER->getSuperRegion() == RightER->getSuperRegion() &&
900 LeftER->getElementType() == RightER->getElementType()) {
901 // Get the left index and cast it to the correct type.
902 // If the index is unknown or undefined, bail out here.
903 SVal LeftIndexVal = LeftER->getIndex();
904 Optional<NonLoc> LeftIndex = LeftIndexVal.getAs<NonLoc>();
905 if (!LeftIndex)
906 return UnknownVal();
907 LeftIndexVal = evalCast(*LeftIndex, ArrayIndexTy, QualType{});
908 LeftIndex = LeftIndexVal.getAs<NonLoc>();
909 if (!LeftIndex)
910 return UnknownVal();
911
912 // Do the same for the right index.
913 SVal RightIndexVal = RightER->getIndex();
914 Optional<NonLoc> RightIndex = RightIndexVal.getAs<NonLoc>();
915 if (!RightIndex)
916 return UnknownVal();
917 RightIndexVal = evalCast(*RightIndex, ArrayIndexTy, QualType{});
918 RightIndex = RightIndexVal.getAs<NonLoc>();
919 if (!RightIndex)
920 return UnknownVal();
921
922 // Actually perform the operation.
923 // evalBinOpNN expects the two indexes to already be the right type.
924 return evalBinOpNN(state, op, *LeftIndex, *RightIndex, resultTy);
925 }
926 }
927
928 // Special handling of the FieldRegions, even with symbolic offsets.
929 const FieldRegion *RightFR = dyn_cast<FieldRegion>(RightMR);
930 const FieldRegion *LeftFR = dyn_cast<FieldRegion>(LeftMR);
931 if (RightFR && LeftFR) {
932 SVal R = evalBinOpFieldRegionFieldRegion(LeftFR, RightFR, op, resultTy,
933 *this);
934 if (!R.isUnknown())
935 return R;
936 }
937
938 // Compare the regions using the raw offsets.
939 RegionOffset LeftOffset = LeftMR->getAsOffset();
940 RegionOffset RightOffset = RightMR->getAsOffset();
941
942 if (LeftOffset.getRegion() != nullptr &&
943 LeftOffset.getRegion() == RightOffset.getRegion() &&
944 !LeftOffset.hasSymbolicOffset() && !RightOffset.hasSymbolicOffset()) {
945 int64_t left = LeftOffset.getOffset();
946 int64_t right = RightOffset.getOffset();
947
948 switch (op) {
949 default:
950 return UnknownVal();
951 case BO_LT:
952 return makeTruthVal(left < right, resultTy);
953 case BO_GT:
954 return makeTruthVal(left > right, resultTy);
955 case BO_LE:
956 return makeTruthVal(left <= right, resultTy);
957 case BO_GE:
958 return makeTruthVal(left >= right, resultTy);
959 case BO_EQ:
960 return makeTruthVal(left == right, resultTy);
961 case BO_NE:
962 return makeTruthVal(left != right, resultTy);
963 }
964 }
965
966 // At this point we're not going to get a good answer, but we can try
967 // conjuring an expression instead.
968 SymbolRef LHSSym = lhs.getAsLocSymbol();
969 SymbolRef RHSSym = rhs.getAsLocSymbol();
970 if (LHSSym && RHSSym)
971 return makeNonLoc(LHSSym, op, RHSSym, resultTy);
972
973 // If we get here, we have no way of comparing the regions.
974 return UnknownVal();
975 }
976 }
977 }
978
evalBinOpLN(ProgramStateRef state,BinaryOperator::Opcode op,Loc lhs,NonLoc rhs,QualType resultTy)979 SVal SimpleSValBuilder::evalBinOpLN(ProgramStateRef state,
980 BinaryOperator::Opcode op, Loc lhs,
981 NonLoc rhs, QualType resultTy) {
982 if (op >= BO_PtrMemD && op <= BO_PtrMemI) {
983 if (auto PTMSV = rhs.getAs<nonloc::PointerToMember>()) {
984 if (PTMSV->isNullMemberPointer())
985 return UndefinedVal();
986
987 auto getFieldLValue = [&](const auto *FD) -> SVal {
988 SVal Result = lhs;
989
990 for (const auto &I : *PTMSV)
991 Result = StateMgr.getStoreManager().evalDerivedToBase(
992 Result, I->getType(), I->isVirtual());
993
994 return state->getLValue(FD, Result);
995 };
996
997 if (const auto *FD = PTMSV->getDeclAs<FieldDecl>()) {
998 return getFieldLValue(FD);
999 }
1000 if (const auto *FD = PTMSV->getDeclAs<IndirectFieldDecl>()) {
1001 return getFieldLValue(FD);
1002 }
1003 }
1004
1005 return rhs;
1006 }
1007
1008 assert(!BinaryOperator::isComparisonOp(op) &&
1009 "arguments to comparison ops must be of the same type");
1010
1011 // Special case: rhs is a zero constant.
1012 if (rhs.isZeroConstant())
1013 return lhs;
1014
1015 // Perserve the null pointer so that it can be found by the DerefChecker.
1016 if (lhs.isZeroConstant())
1017 return lhs;
1018
1019 // We are dealing with pointer arithmetic.
1020
1021 // Handle pointer arithmetic on constant values.
1022 if (Optional<nonloc::ConcreteInt> rhsInt = rhs.getAs<nonloc::ConcreteInt>()) {
1023 if (Optional<loc::ConcreteInt> lhsInt = lhs.getAs<loc::ConcreteInt>()) {
1024 const llvm::APSInt &leftI = lhsInt->getValue();
1025 assert(leftI.isUnsigned());
1026 llvm::APSInt rightI(rhsInt->getValue(), /* isUnsigned */ true);
1027
1028 // Convert the bitwidth of rightI. This should deal with overflow
1029 // since we are dealing with concrete values.
1030 rightI = rightI.extOrTrunc(leftI.getBitWidth());
1031
1032 // Offset the increment by the pointer size.
1033 llvm::APSInt Multiplicand(rightI.getBitWidth(), /* isUnsigned */ true);
1034 QualType pointeeType = resultTy->getPointeeType();
1035 Multiplicand = getContext().getTypeSizeInChars(pointeeType).getQuantity();
1036 rightI *= Multiplicand;
1037
1038 // Compute the adjusted pointer.
1039 switch (op) {
1040 case BO_Add:
1041 rightI = leftI + rightI;
1042 break;
1043 case BO_Sub:
1044 rightI = leftI - rightI;
1045 break;
1046 default:
1047 llvm_unreachable("Invalid pointer arithmetic operation");
1048 }
1049 return loc::ConcreteInt(getBasicValueFactory().getValue(rightI));
1050 }
1051 }
1052
1053 // Handle cases where 'lhs' is a region.
1054 if (const MemRegion *region = lhs.getAsRegion()) {
1055 rhs = convertToArrayIndex(rhs).castAs<NonLoc>();
1056 SVal index = UnknownVal();
1057 const SubRegion *superR = nullptr;
1058 // We need to know the type of the pointer in order to add an integer to it.
1059 // Depending on the type, different amount of bytes is added.
1060 QualType elementType;
1061
1062 if (const ElementRegion *elemReg = dyn_cast<ElementRegion>(region)) {
1063 assert(op == BO_Add || op == BO_Sub);
1064 index = evalBinOpNN(state, op, elemReg->getIndex(), rhs,
1065 getArrayIndexType());
1066 superR = cast<SubRegion>(elemReg->getSuperRegion());
1067 elementType = elemReg->getElementType();
1068 }
1069 else if (isa<SubRegion>(region)) {
1070 assert(op == BO_Add || op == BO_Sub);
1071 index = (op == BO_Add) ? rhs : evalMinus(rhs);
1072 superR = cast<SubRegion>(region);
1073 // TODO: Is this actually reliable? Maybe improving our MemRegion
1074 // hierarchy to provide typed regions for all non-void pointers would be
1075 // better. For instance, we cannot extend this towards LocAsInteger
1076 // operations, where result type of the expression is integer.
1077 if (resultTy->isAnyPointerType())
1078 elementType = resultTy->getPointeeType();
1079 }
1080
1081 // Represent arithmetic on void pointers as arithmetic on char pointers.
1082 // It is fine when a TypedValueRegion of char value type represents
1083 // a void pointer. Note that arithmetic on void pointers is a GCC extension.
1084 if (elementType->isVoidType())
1085 elementType = getContext().CharTy;
1086
1087 if (Optional<NonLoc> indexV = index.getAs<NonLoc>()) {
1088 return loc::MemRegionVal(MemMgr.getElementRegion(elementType, *indexV,
1089 superR, getContext()));
1090 }
1091 }
1092 return UnknownVal();
1093 }
1094
getKnownValue(ProgramStateRef state,SVal V)1095 const llvm::APSInt *SimpleSValBuilder::getKnownValue(ProgramStateRef state,
1096 SVal V) {
1097 V = simplifySVal(state, V);
1098 if (V.isUnknownOrUndef())
1099 return nullptr;
1100
1101 if (Optional<loc::ConcreteInt> X = V.getAs<loc::ConcreteInt>())
1102 return &X->getValue();
1103
1104 if (Optional<nonloc::ConcreteInt> X = V.getAs<nonloc::ConcreteInt>())
1105 return &X->getValue();
1106
1107 if (SymbolRef Sym = V.getAsSymbol())
1108 return state->getConstraintManager().getSymVal(state, Sym);
1109
1110 // FIXME: Add support for SymExprs.
1111 return nullptr;
1112 }
1113
simplifySVal(ProgramStateRef State,SVal V)1114 SVal SimpleSValBuilder::simplifySVal(ProgramStateRef State, SVal V) {
1115 // For now, this function tries to constant-fold symbols inside a
1116 // nonloc::SymbolVal, and does nothing else. More simplifications should
1117 // be possible, such as constant-folding an index in an ElementRegion.
1118
1119 class Simplifier : public FullSValVisitor<Simplifier, SVal> {
1120 ProgramStateRef State;
1121 SValBuilder &SVB;
1122
1123 // Cache results for the lifetime of the Simplifier. Results change every
1124 // time new constraints are added to the program state, which is the whole
1125 // point of simplifying, and for that very reason it's pointless to maintain
1126 // the same cache for the duration of the whole analysis.
1127 llvm::DenseMap<SymbolRef, SVal> Cached;
1128
1129 static bool isUnchanged(SymbolRef Sym, SVal Val) {
1130 return Sym == Val.getAsSymbol();
1131 }
1132
1133 SVal cache(SymbolRef Sym, SVal V) {
1134 Cached[Sym] = V;
1135 return V;
1136 }
1137
1138 SVal skip(SymbolRef Sym) {
1139 return cache(Sym, SVB.makeSymbolVal(Sym));
1140 }
1141
1142 public:
1143 Simplifier(ProgramStateRef State)
1144 : State(State), SVB(State->getStateManager().getSValBuilder()) {}
1145
1146 SVal VisitSymbolData(const SymbolData *S) {
1147 // No cache here.
1148 if (const llvm::APSInt *I =
1149 SVB.getKnownValue(State, SVB.makeSymbolVal(S)))
1150 return Loc::isLocType(S->getType()) ? (SVal)SVB.makeIntLocVal(*I)
1151 : (SVal)SVB.makeIntVal(*I);
1152 return SVB.makeSymbolVal(S);
1153 }
1154
1155 // TODO: Support SymbolCast. Support IntSymExpr when/if we actually
1156 // start producing them.
1157
1158 SVal VisitSymIntExpr(const SymIntExpr *S) {
1159 auto I = Cached.find(S);
1160 if (I != Cached.end())
1161 return I->second;
1162
1163 SVal LHS = Visit(S->getLHS());
1164 if (isUnchanged(S->getLHS(), LHS))
1165 return skip(S);
1166
1167 SVal RHS;
1168 // By looking at the APSInt in the right-hand side of S, we cannot
1169 // figure out if it should be treated as a Loc or as a NonLoc.
1170 // So make our guess by recalling that we cannot multiply pointers
1171 // or compare a pointer to an integer.
1172 if (Loc::isLocType(S->getLHS()->getType()) &&
1173 BinaryOperator::isComparisonOp(S->getOpcode())) {
1174 // The usual conversion of $sym to &SymRegion{$sym}, as they have
1175 // the same meaning for Loc-type symbols, but the latter form
1176 // is preferred in SVal computations for being Loc itself.
1177 if (SymbolRef Sym = LHS.getAsSymbol()) {
1178 assert(Loc::isLocType(Sym->getType()));
1179 LHS = SVB.makeLoc(Sym);
1180 }
1181 RHS = SVB.makeIntLocVal(S->getRHS());
1182 } else {
1183 RHS = SVB.makeIntVal(S->getRHS());
1184 }
1185
1186 return cache(
1187 S, SVB.evalBinOp(State, S->getOpcode(), LHS, RHS, S->getType()));
1188 }
1189
1190 SVal VisitSymSymExpr(const SymSymExpr *S) {
1191 auto I = Cached.find(S);
1192 if (I != Cached.end())
1193 return I->second;
1194
1195 // For now don't try to simplify mixed Loc/NonLoc expressions
1196 // because they often appear from LocAsInteger operations
1197 // and we don't know how to combine a LocAsInteger
1198 // with a concrete value.
1199 if (Loc::isLocType(S->getLHS()->getType()) !=
1200 Loc::isLocType(S->getRHS()->getType()))
1201 return skip(S);
1202
1203 SVal LHS = Visit(S->getLHS());
1204 SVal RHS = Visit(S->getRHS());
1205 if (isUnchanged(S->getLHS(), LHS) && isUnchanged(S->getRHS(), RHS))
1206 return skip(S);
1207
1208 return cache(
1209 S, SVB.evalBinOp(State, S->getOpcode(), LHS, RHS, S->getType()));
1210 }
1211
1212 SVal VisitSymExpr(SymbolRef S) { return nonloc::SymbolVal(S); }
1213
1214 SVal VisitMemRegion(const MemRegion *R) { return loc::MemRegionVal(R); }
1215
1216 SVal VisitNonLocSymbolVal(nonloc::SymbolVal V) {
1217 // Simplification is much more costly than computing complexity.
1218 // For high complexity, it may be not worth it.
1219 return Visit(V.getSymbol());
1220 }
1221
1222 SVal VisitSVal(SVal V) { return V; }
1223 };
1224
1225 // A crude way of preventing this function from calling itself from evalBinOp.
1226 static bool isReentering = false;
1227 if (isReentering)
1228 return V;
1229
1230 isReentering = true;
1231 SVal SimplifiedV = Simplifier(State).Visit(V);
1232 isReentering = false;
1233
1234 return SimplifiedV;
1235 }
1236