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//===--- BranchCloneCheck.cpp - clang-tidy --------------------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "BranchCloneCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"
#include "clang/Analysis/CloneDetection.h"
#include "clang/Lex/Lexer.h"
#include "llvm/Support/Casting.h"
using namespace clang;
using namespace clang::ast_matchers;
/// Returns true when the statements are Type I clones of each other.
static bool areStatementsIdentical(const Stmt *LHS, const Stmt *RHS,
const ASTContext &Context) {
llvm::FoldingSetNodeID DataLHS, DataRHS;
LHS->Profile(DataLHS, Context, false);
RHS->Profile(DataRHS, Context, false);
return (DataLHS == DataRHS);
namespace {
/// A branch in a switch may consist of several statements; while a branch in
/// an if/else if/else chain is one statement (which may be a CompoundStmt).
using SwitchBranch = llvm::SmallVector<const Stmt *, 2>;
} // anonymous namespace
/// Determines if the bodies of two branches in a switch statements are Type I
/// clones of each other. This function only examines the body of the branch
/// and ignores the `case X:` or `default:` at the start of the branch.
static bool areSwitchBranchesIdentical(const SwitchBranch LHS,
const SwitchBranch RHS,
const ASTContext &Context) {
if (LHS.size() != RHS.size())
return false;
for (size_t I = 0, Size = LHS.size(); I < Size; I++) {
// NOTE: We strip goto labels and annotations in addition to stripping
// the `case X:` or `default:` labels, but it is very unlikely that this
// would cause false positives in real-world code.
if (!areStatementsIdentical(LHS[I]->stripLabelLikeStatements(),
RHS[I]->stripLabelLikeStatements(), Context)) {
return false;
return true;
namespace clang {
namespace tidy {
namespace bugprone {
void BranchCloneCheck::registerMatchers(MatchFinder *Finder) {
ifStmt(unless(allOf(isConstexpr(), isInTemplateInstantiation())),
Finder->addMatcher(switchStmt().bind("switch"), this);
Finder->addMatcher(conditionalOperator().bind("condOp"), this);
void BranchCloneCheck::check(const MatchFinder::MatchResult &Result) {
const ASTContext &Context = *Result.Context;
if (const auto *IS = Result.Nodes.getNodeAs<IfStmt>("if")) {
const Stmt *Then = IS->getThen();
assert(Then && "An IfStmt must have a `then` branch!");
const Stmt *Else = Result.Nodes.getNodeAs<Stmt>("else");
assert(Else && "We only look for `if` statements with an `else` branch!");
if (!isa<IfStmt>(Else)) {
// Just a simple if with no `else if` branch.
if (areStatementsIdentical(Then->IgnoreContainers(),
Else->IgnoreContainers(), Context)) {
diag(IS->getBeginLoc(), "if with identical then and else branches");
diag(IS->getElseLoc(), "else branch starts here", DiagnosticIDs::Note);
// This is the complicated case when we start an if/else if/else chain.
// To find all the duplicates, we collect all the branches into a vector.
llvm::SmallVector<const Stmt *, 4> Branches;
const IfStmt *Cur = IS;
while (true) {
// Store the `then` branch.
Else = Cur->getElse();
// The chain ends if there is no `else` branch.
if (!Else)
// Check if there is another `else if`...
Cur = dyn_cast<IfStmt>(Else);
if (!Cur) {
// ...this is just a plain `else` branch at the end of the chain.
size_t N = Branches.size();
llvm::BitVector KnownAsClone(N);
for (size_t I = 0; I + 1 < N; I++) {
// We have already seen Branches[i] as a clone of an earlier branch.
if (KnownAsClone[I])
int NumCopies = 1;
for (size_t J = I + 1; J < N; J++) {
if (KnownAsClone[J] ||
Branches[J]->IgnoreContainers(), Context))
KnownAsClone[J] = true;
if (NumCopies == 2) {
// We report the first occurrence only when we find the second one.
"repeated branch in conditional chain");
SourceLocation End =
Lexer::getLocForEndOfToken(Branches[I]->getEndLoc(), 0,
*Result.SourceManager, getLangOpts());
if (End.isValid()) {
diag(End, "end of the original", DiagnosticIDs::Note);
diag(Branches[J]->getBeginLoc(), "clone %0 starts here",
<< (NumCopies - 1);
if (const auto *CO = Result.Nodes.getNodeAs<ConditionalOperator>("condOp")) {
// We do not try to detect chains of ?: operators.
if (areStatementsIdentical(CO->getTrueExpr(), CO->getFalseExpr(), Context))
"conditional operator with identical true and false expressions");
if (const auto *SS = Result.Nodes.getNodeAs<SwitchStmt>("switch")) {
const CompoundStmt *Body = dyn_cast_or_null<CompoundStmt>(SS->getBody());
// Code like
// switch (x) case 0: case 1: foobar();
// is legal and calls foobar() if and only if x is either 0 or 1;
// but we do not try to distinguish branches in such code.
if (!Body)
// We will first collect the branches of the switch statements. For the
// sake of simplicity we say that branches are delimited by the SwitchCase
// (`case:` or `default:`) children of Body; that is, we ignore `case:` or
// `default:` labels embedded inside other statements and we do not follow
// the effects of `break` and other manipulation of the control-flow.
llvm::SmallVector<SwitchBranch, 4> Branches;
for (const Stmt *S : Body->body()) {
// If this is a `case` or `default`, we start a new, empty branch.
if (isa<SwitchCase>(S))
// There may be code before the first branch (which can be dead code
// and can be code reached either through goto or through case labels
// that are embedded inside e.g. inner compound statements); we do not
// store those statements in branches.
if (!Branches.empty())
auto *End = Branches.end();
auto *BeginCurrent = Branches.begin();
while (BeginCurrent < End) {
auto *EndCurrent = BeginCurrent + 1;
while (EndCurrent < End &&
areSwitchBranchesIdentical(*BeginCurrent, *EndCurrent, Context)) {
// At this point the iterator range {BeginCurrent, EndCurrent} contains a
// complete family of consecutive identical branches.
if (EndCurrent > BeginCurrent + 1) {
"switch has %0 consecutive identical branches")
<< static_cast<int>(std::distance(BeginCurrent, EndCurrent));
SourceLocation EndLoc = (EndCurrent - 1)->back()->getEndLoc();
// If the case statement is generated from a macro, it's SourceLocation
// may be invalid, resulting in an assertion failure down the line.
// While not optimal, try the begin location in this case, it's still
// better then nothing.
if (EndLoc.isInvalid())
EndLoc = (EndCurrent - 1)->back()->getBeginLoc();
if (EndLoc.isMacroID())
EndLoc = Context.getSourceManager().getExpansionLoc(EndLoc);
EndLoc = Lexer::getLocForEndOfToken(EndLoc, 0, *Result.SourceManager,
if (EndLoc.isValid()) {
diag(EndLoc, "last of these clones ends here", DiagnosticIDs::Note);
BeginCurrent = EndCurrent;
llvm_unreachable("No if statement and no switch statement.");
} // namespace bugprone
} // namespace tidy
} // namespace clang