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//===--- InfiniteLoopCheck.cpp - clang-tidy -------------------------------===//
//
// 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 "InfiniteLoopCheck.h"
#include "../utils/Aliasing.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/Analysis/Analyses/ExprMutationAnalyzer.h"
using namespace clang::ast_matchers;
using clang::tidy::utils::hasPtrOrReferenceInFunc;
namespace clang {
namespace tidy {
namespace bugprone {
static internal::Matcher<Stmt>
loopEndingStmt(internal::Matcher<Stmt> Internal) {
// FIXME: Cover noreturn ObjC methods (and blocks?).
return stmt(anyOf(
mapAnyOf(breakStmt, returnStmt, gotoStmt, cxxThrowExpr).with(Internal),
callExpr(Internal, callee(functionDecl(isNoReturn())))));
}
/// Return whether `Var` was changed in `LoopStmt`.
static bool isChanged(const Stmt *LoopStmt, const VarDecl *Var,
ASTContext *Context) {
if (const auto *ForLoop = dyn_cast<ForStmt>(LoopStmt))
return (ForLoop->getInc() &&
ExprMutationAnalyzer(*ForLoop->getInc(), *Context)
.isMutated(Var)) ||
(ForLoop->getBody() &&
ExprMutationAnalyzer(*ForLoop->getBody(), *Context)
.isMutated(Var)) ||
(ForLoop->getCond() &&
ExprMutationAnalyzer(*ForLoop->getCond(), *Context).isMutated(Var));
return ExprMutationAnalyzer(*LoopStmt, *Context).isMutated(Var);
}
/// Return whether `Cond` is a variable that is possibly changed in `LoopStmt`.
static bool isVarThatIsPossiblyChanged(const Decl *Func, const Stmt *LoopStmt,
const Stmt *Cond, ASTContext *Context) {
if (const auto *DRE = dyn_cast<DeclRefExpr>(Cond)) {
if (const auto *Var = dyn_cast<VarDecl>(DRE->getDecl())) {
if (!Var->isLocalVarDeclOrParm())
return true;
if (Var->getType().isVolatileQualified())
return true;
if (!Var->getType().getTypePtr()->isIntegerType())
return true;
return hasPtrOrReferenceInFunc(Func, Var) ||
isChanged(LoopStmt, Var, Context);
// FIXME: Track references.
}
} else if (isa<MemberExpr, CallExpr,
ObjCIvarRefExpr, ObjCPropertyRefExpr, ObjCMessageExpr>(Cond)) {
// FIXME: Handle MemberExpr.
return true;
} else if (const auto *CE = dyn_cast<CastExpr>(Cond)) {
QualType T = CE->getType();
while (true) {
if (T.isVolatileQualified())
return true;
if (!T->isAnyPointerType() && !T->isReferenceType())
break;
T = T->getPointeeType();
}
}
return false;
}
/// Return whether at least one variable of `Cond` changed in `LoopStmt`.
static bool isAtLeastOneCondVarChanged(const Decl *Func, const Stmt *LoopStmt,
const Stmt *Cond, ASTContext *Context) {
if (isVarThatIsPossiblyChanged(Func, LoopStmt, Cond, Context))
return true;
for (const Stmt *Child : Cond->children()) {
if (!Child)
continue;
if (isAtLeastOneCondVarChanged(Func, LoopStmt, Child, Context))
return true;
}
return false;
}
/// Return the variable names in `Cond`.
static std::string getCondVarNames(const Stmt *Cond) {
if (const auto *DRE = dyn_cast<DeclRefExpr>(Cond)) {
if (const auto *Var = dyn_cast<VarDecl>(DRE->getDecl()))
return std::string(Var->getName());
}
std::string Result;
for (const Stmt *Child : Cond->children()) {
if (!Child)
continue;
std::string NewNames = getCondVarNames(Child);
if (!Result.empty() && !NewNames.empty())
Result += ", ";
Result += NewNames;
}
return Result;
}
static bool isKnownToHaveValue(const Expr &Cond, const ASTContext &Ctx,
bool ExpectedValue) {
if (Cond.isValueDependent()) {
if (const auto *BinOp = dyn_cast<BinaryOperator>(&Cond)) {
// Conjunctions (disjunctions) can still be handled if at least one
// conjunct (disjunct) is known to be false (true).
if (!ExpectedValue && BinOp->getOpcode() == BO_LAnd)
return isKnownToHaveValue(*BinOp->getLHS(), Ctx, false) ||
isKnownToHaveValue(*BinOp->getRHS(), Ctx, false);
if (ExpectedValue && BinOp->getOpcode() == BO_LOr)
return isKnownToHaveValue(*BinOp->getLHS(), Ctx, true) ||
isKnownToHaveValue(*BinOp->getRHS(), Ctx, true);
if (BinOp->getOpcode() == BO_Comma)
return isKnownToHaveValue(*BinOp->getRHS(), Ctx, ExpectedValue);
} else if (const auto *UnOp = dyn_cast<UnaryOperator>(&Cond)) {
if (UnOp->getOpcode() == UO_LNot)
return isKnownToHaveValue(*UnOp->getSubExpr(), Ctx, !ExpectedValue);
} else if (const auto *Paren = dyn_cast<ParenExpr>(&Cond))
return isKnownToHaveValue(*Paren->getSubExpr(), Ctx, ExpectedValue);
else if (const auto *ImplCast = dyn_cast<ImplicitCastExpr>(&Cond))
return isKnownToHaveValue(*ImplCast->getSubExpr(), Ctx, ExpectedValue);
return false;
}
bool Result = false;
if (Cond.EvaluateAsBooleanCondition(Result, Ctx))
return Result == ExpectedValue;
return false;
}
void InfiniteLoopCheck::registerMatchers(MatchFinder *Finder) {
const auto LoopCondition = allOf(
hasCondition(
expr(forCallable(decl().bind("func"))).bind("condition")),
unless(hasBody(hasDescendant(
loopEndingStmt(forCallable(equalsBoundNode("func")))))));
Finder->addMatcher(mapAnyOf(whileStmt, doStmt, forStmt)
.with(LoopCondition)
.bind("loop-stmt"),
this);
}
void InfiniteLoopCheck::check(const MatchFinder::MatchResult &Result) {
const auto *Cond = Result.Nodes.getNodeAs<Expr>("condition");
const auto *LoopStmt = Result.Nodes.getNodeAs<Stmt>("loop-stmt");
const auto *Func = Result.Nodes.getNodeAs<Decl>("func");
if (isKnownToHaveValue(*Cond, *Result.Context, false))
return;
bool ShouldHaveConditionVariables = true;
if (const auto *While = dyn_cast<WhileStmt>(LoopStmt)) {
if (const VarDecl *LoopVarDecl = While->getConditionVariable()) {
if (const Expr *Init = LoopVarDecl->getInit()) {
ShouldHaveConditionVariables = false;
Cond = Init;
}
}
}
if (ExprMutationAnalyzer::isUnevaluated(LoopStmt, *LoopStmt, *Result.Context))
return;
if (isAtLeastOneCondVarChanged(Func, LoopStmt, Cond, Result.Context))
return;
std::string CondVarNames = getCondVarNames(Cond);
if (ShouldHaveConditionVariables && CondVarNames.empty())
return;
if (CondVarNames.empty()) {
diag(LoopStmt->getBeginLoc(),
"this loop is infinite; it does not check any variables in the"
" condition");
} else {
diag(LoopStmt->getBeginLoc(),
"this loop is infinite; none of its condition variables (%0)"
" are updated in the loop body")
<< CondVarNames;
}
}
} // namespace bugprone
} // namespace tidy
} // namespace clang
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