1 //===--- LoopUnrolling.cpp - Unroll loops -----------------------*- 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 contains functions which are used to decide if a loop worth to be 10 /// unrolled. Moreover, these functions manages the stack of loop which is 11 /// tracked by the ProgramState. 12 /// 13 //===----------------------------------------------------------------------===// 14 15 #include "clang/ASTMatchers/ASTMatchers.h" 16 #include "clang/ASTMatchers/ASTMatchFinder.h" 17 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h" 18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 19 #include "clang/StaticAnalyzer/Core/PathSensitive/LoopUnrolling.h" 20 21 using namespace clang; 22 using namespace ento; 23 using namespace clang::ast_matchers; 24 25 static const int MAXIMUM_STEP_UNROLLED = 128; 26 27 struct LoopState { 28 private: 29 enum Kind { Normal, Unrolled } K; 30 const Stmt *LoopStmt; 31 const LocationContext *LCtx; 32 unsigned maxStep; 33 LoopState(Kind InK, const Stmt *S, const LocationContext *L, unsigned N) 34 : K(InK), LoopStmt(S), LCtx(L), maxStep(N) {} 35 36 public: 37 static LoopState getNormal(const Stmt *S, const LocationContext *L, 38 unsigned N) { 39 return LoopState(Normal, S, L, N); 40 } 41 static LoopState getUnrolled(const Stmt *S, const LocationContext *L, 42 unsigned N) { 43 return LoopState(Unrolled, S, L, N); 44 } 45 bool isUnrolled() const { return K == Unrolled; } 46 unsigned getMaxStep() const { return maxStep; } 47 const Stmt *getLoopStmt() const { return LoopStmt; } 48 const LocationContext *getLocationContext() const { return LCtx; } 49 bool operator==(const LoopState &X) const { 50 return K == X.K && LoopStmt == X.LoopStmt; 51 } 52 void Profile(llvm::FoldingSetNodeID &ID) const { 53 ID.AddInteger(K); 54 ID.AddPointer(LoopStmt); 55 ID.AddPointer(LCtx); 56 ID.AddInteger(maxStep); 57 } 58 }; 59 60 // The tracked stack of loops. The stack indicates that which loops the 61 // simulated element contained by. The loops are marked depending if we decided 62 // to unroll them. 63 // TODO: The loop stack should not need to be in the program state since it is 64 // lexical in nature. Instead, the stack of loops should be tracked in the 65 // LocationContext. 66 REGISTER_LIST_WITH_PROGRAMSTATE(LoopStack, LoopState) 67 68 namespace clang { 69 namespace ento { 70 71 static bool isLoopStmt(const Stmt *S) { 72 return S && (isa<ForStmt>(S) || isa<WhileStmt>(S) || isa<DoStmt>(S)); 73 } 74 75 ProgramStateRef processLoopEnd(const Stmt *LoopStmt, ProgramStateRef State) { 76 auto LS = State->get<LoopStack>(); 77 if (!LS.isEmpty() && LS.getHead().getLoopStmt() == LoopStmt) 78 State = State->set<LoopStack>(LS.getTail()); 79 return State; 80 } 81 82 static internal::Matcher<Stmt> simpleCondition(StringRef BindName) { 83 return binaryOperator(anyOf(hasOperatorName("<"), hasOperatorName(">"), 84 hasOperatorName("<="), hasOperatorName(">="), 85 hasOperatorName("!=")), 86 hasEitherOperand(ignoringParenImpCasts(declRefExpr( 87 to(varDecl(hasType(isInteger())).bind(BindName))))), 88 hasEitherOperand(ignoringParenImpCasts( 89 integerLiteral().bind("boundNum")))) 90 .bind("conditionOperator"); 91 } 92 93 static internal::Matcher<Stmt> 94 changeIntBoundNode(internal::Matcher<Decl> VarNodeMatcher) { 95 return anyOf( 96 unaryOperator(anyOf(hasOperatorName("--"), hasOperatorName("++")), 97 hasUnaryOperand(ignoringParenImpCasts( 98 declRefExpr(to(varDecl(VarNodeMatcher)))))), 99 binaryOperator(isAssignmentOperator(), 100 hasLHS(ignoringParenImpCasts( 101 declRefExpr(to(varDecl(VarNodeMatcher))))))); 102 } 103 104 static internal::Matcher<Stmt> 105 callByRef(internal::Matcher<Decl> VarNodeMatcher) { 106 return callExpr(forEachArgumentWithParam( 107 declRefExpr(to(varDecl(VarNodeMatcher))), 108 parmVarDecl(hasType(references(qualType(unless(isConstQualified()))))))); 109 } 110 111 static internal::Matcher<Stmt> 112 assignedToRef(internal::Matcher<Decl> VarNodeMatcher) { 113 return declStmt(hasDescendant(varDecl( 114 allOf(hasType(referenceType()), 115 hasInitializer(anyOf( 116 initListExpr(has(declRefExpr(to(varDecl(VarNodeMatcher))))), 117 declRefExpr(to(varDecl(VarNodeMatcher))))))))); 118 } 119 120 static internal::Matcher<Stmt> 121 getAddrTo(internal::Matcher<Decl> VarNodeMatcher) { 122 return unaryOperator( 123 hasOperatorName("&"), 124 hasUnaryOperand(declRefExpr(hasDeclaration(VarNodeMatcher)))); 125 } 126 127 static internal::Matcher<Stmt> hasSuspiciousStmt(StringRef NodeName) { 128 return hasDescendant(stmt( 129 anyOf(gotoStmt(), switchStmt(), returnStmt(), 130 // Escaping and not known mutation of the loop counter is handled 131 // by exclusion of assigning and address-of operators and 132 // pass-by-ref function calls on the loop counter from the body. 133 changeIntBoundNode(equalsBoundNode(NodeName)), 134 callByRef(equalsBoundNode(NodeName)), 135 getAddrTo(equalsBoundNode(NodeName)), 136 assignedToRef(equalsBoundNode(NodeName))))); 137 } 138 139 static internal::Matcher<Stmt> forLoopMatcher() { 140 return forStmt( 141 hasCondition(simpleCondition("initVarName")), 142 // Initialization should match the form: 'int i = 6' or 'i = 42'. 143 hasLoopInit( 144 anyOf(declStmt(hasSingleDecl( 145 varDecl(allOf(hasInitializer(ignoringParenImpCasts( 146 integerLiteral().bind("initNum"))), 147 equalsBoundNode("initVarName"))))), 148 binaryOperator(hasLHS(declRefExpr(to(varDecl( 149 equalsBoundNode("initVarName"))))), 150 hasRHS(ignoringParenImpCasts( 151 integerLiteral().bind("initNum")))))), 152 // Incrementation should be a simple increment or decrement 153 // operator call. 154 hasIncrement(unaryOperator( 155 anyOf(hasOperatorName("++"), hasOperatorName("--")), 156 hasUnaryOperand(declRefExpr( 157 to(varDecl(allOf(equalsBoundNode("initVarName"), 158 hasType(isInteger())))))))), 159 unless(hasBody(hasSuspiciousStmt("initVarName")))).bind("forLoop"); 160 } 161 162 static bool isPossiblyEscaped(const VarDecl *VD, ExplodedNode *N) { 163 // Global variables assumed as escaped variables. 164 if (VD->hasGlobalStorage()) 165 return true; 166 167 while (!N->pred_empty()) { 168 // FIXME: getStmtForDiagnostics() does nasty things in order to provide 169 // a valid statement for body farms, do we need this behavior here? 170 const Stmt *S = N->getStmtForDiagnostics(); 171 if (!S) { 172 N = N->getFirstPred(); 173 continue; 174 } 175 176 if (const DeclStmt *DS = dyn_cast<DeclStmt>(S)) { 177 for (const Decl *D : DS->decls()) { 178 // Once we reach the declaration of the VD we can return. 179 if (D->getCanonicalDecl() == VD) 180 return false; 181 } 182 } 183 // Check the usage of the pass-by-ref function calls and adress-of operator 184 // on VD and reference initialized by VD. 185 ASTContext &ASTCtx = 186 N->getLocationContext()->getAnalysisDeclContext()->getASTContext(); 187 auto Match = 188 match(stmt(anyOf(callByRef(equalsNode(VD)), getAddrTo(equalsNode(VD)), 189 assignedToRef(equalsNode(VD)))), 190 *S, ASTCtx); 191 if (!Match.empty()) 192 return true; 193 194 N = N->getFirstPred(); 195 } 196 llvm_unreachable("Reached root without finding the declaration of VD"); 197 } 198 199 bool shouldCompletelyUnroll(const Stmt *LoopStmt, ASTContext &ASTCtx, 200 ExplodedNode *Pred, unsigned &maxStep) { 201 202 if (!isLoopStmt(LoopStmt)) 203 return false; 204 205 // TODO: Match the cases where the bound is not a concrete literal but an 206 // integer with known value 207 auto Matches = match(forLoopMatcher(), *LoopStmt, ASTCtx); 208 if (Matches.empty()) 209 return false; 210 211 auto CounterVar = Matches[0].getNodeAs<VarDecl>("initVarName"); 212 llvm::APInt BoundNum = 213 Matches[0].getNodeAs<IntegerLiteral>("boundNum")->getValue(); 214 llvm::APInt InitNum = 215 Matches[0].getNodeAs<IntegerLiteral>("initNum")->getValue(); 216 auto CondOp = Matches[0].getNodeAs<BinaryOperator>("conditionOperator"); 217 if (InitNum.getBitWidth() != BoundNum.getBitWidth()) { 218 InitNum = InitNum.zextOrSelf(BoundNum.getBitWidth()); 219 BoundNum = BoundNum.zextOrSelf(InitNum.getBitWidth()); 220 } 221 222 if (CondOp->getOpcode() == BO_GE || CondOp->getOpcode() == BO_LE) 223 maxStep = (BoundNum - InitNum + 1).abs().getZExtValue(); 224 else 225 maxStep = (BoundNum - InitNum).abs().getZExtValue(); 226 227 // Check if the counter of the loop is not escaped before. 228 return !isPossiblyEscaped(CounterVar->getCanonicalDecl(), Pred); 229 } 230 231 bool madeNewBranch(ExplodedNode *N, const Stmt *LoopStmt) { 232 const Stmt *S = nullptr; 233 while (!N->pred_empty()) { 234 if (N->succ_size() > 1) 235 return true; 236 237 ProgramPoint P = N->getLocation(); 238 if (Optional<BlockEntrance> BE = P.getAs<BlockEntrance>()) 239 S = BE->getBlock()->getTerminatorStmt(); 240 241 if (S == LoopStmt) 242 return false; 243 244 N = N->getFirstPred(); 245 } 246 247 llvm_unreachable("Reached root without encountering the previous step"); 248 } 249 250 // updateLoopStack is called on every basic block, therefore it needs to be fast 251 ProgramStateRef updateLoopStack(const Stmt *LoopStmt, ASTContext &ASTCtx, 252 ExplodedNode *Pred, unsigned maxVisitOnPath) { 253 auto State = Pred->getState(); 254 auto LCtx = Pred->getLocationContext(); 255 256 if (!isLoopStmt(LoopStmt)) 257 return State; 258 259 auto LS = State->get<LoopStack>(); 260 if (!LS.isEmpty() && LoopStmt == LS.getHead().getLoopStmt() && 261 LCtx == LS.getHead().getLocationContext()) { 262 if (LS.getHead().isUnrolled() && madeNewBranch(Pred, LoopStmt)) { 263 State = State->set<LoopStack>(LS.getTail()); 264 State = State->add<LoopStack>( 265 LoopState::getNormal(LoopStmt, LCtx, maxVisitOnPath)); 266 } 267 return State; 268 } 269 unsigned maxStep; 270 if (!shouldCompletelyUnroll(LoopStmt, ASTCtx, Pred, maxStep)) { 271 State = State->add<LoopStack>( 272 LoopState::getNormal(LoopStmt, LCtx, maxVisitOnPath)); 273 return State; 274 } 275 276 unsigned outerStep = (LS.isEmpty() ? 1 : LS.getHead().getMaxStep()); 277 278 unsigned innerMaxStep = maxStep * outerStep; 279 if (innerMaxStep > MAXIMUM_STEP_UNROLLED) 280 State = State->add<LoopStack>( 281 LoopState::getNormal(LoopStmt, LCtx, maxVisitOnPath)); 282 else 283 State = State->add<LoopStack>( 284 LoopState::getUnrolled(LoopStmt, LCtx, innerMaxStep)); 285 return State; 286 } 287 288 bool isUnrolledState(ProgramStateRef State) { 289 auto LS = State->get<LoopStack>(); 290 if (LS.isEmpty() || !LS.getHead().isUnrolled()) 291 return false; 292 return true; 293 } 294 } 295 } 296