//=- AnalysisBasedWarnings.cpp - Sema warnings based on libAnalysis -*- C++ -*-=//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines analysis_warnings::[Policy,Executor].
// Together they are used by Sema to issue warnings based on inexpensive
// static analysis algorithms in libAnalysis.
//
//===----------------------------------------------------------------------===//
#include "clang/Sema/AnalysisBasedWarnings.h"
#include "clang/Sema/SemaInternal.h"
#include "clang/Basic/SourceManager.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/ExprObjC.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/StmtObjC.h"
#include "clang/AST/StmtCXX.h"
#include "clang/Analysis/AnalysisContext.h"
#include "clang/Analysis/CFG.h"
#include "clang/Analysis/Analyses/ReachableCode.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/Support/Casting.h"
using namespace clang;
//===----------------------------------------------------------------------===//
// Unreachable code analysis.
//===----------------------------------------------------------------------===//
namespace {
class UnreachableCodeHandler : public reachable_code::Callback {
Sema &S;
public:
UnreachableCodeHandler(Sema &s) : S(s) {}
void HandleUnreachable(SourceLocation L, SourceRange R1, SourceRange R2) {
S.Diag(L, diag::warn_unreachable) << R1 << R2;
}
};
}
/// CheckUnreachable - Check for unreachable code.
static void CheckUnreachable(Sema &S, AnalysisContext &AC) {
UnreachableCodeHandler UC(S);
reachable_code::FindUnreachableCode(AC, UC);
}
//===----------------------------------------------------------------------===//
// Check for missing return value.
//===----------------------------------------------------------------------===//
enum ControlFlowKind {
UnknownFallThrough,
NeverFallThrough,
MaybeFallThrough,
AlwaysFallThrough,
NeverFallThroughOrReturn
};
/// CheckFallThrough - Check that we don't fall off the end of a
/// Statement that should return a value.
///
/// \returns AlwaysFallThrough iff we always fall off the end of the statement,
/// MaybeFallThrough iff we might or might not fall off the end,
/// NeverFallThroughOrReturn iff we never fall off the end of the statement or
/// return. We assume NeverFallThrough iff we never fall off the end of the
/// statement but we may return. We assume that functions not marked noreturn
/// will return.
static ControlFlowKind CheckFallThrough(AnalysisContext &AC) {
CFG *cfg = AC.getCFG();
if (cfg == 0) return UnknownFallThrough;
// The CFG leaves in dead things, and we don't want the dead code paths to
// confuse us, so we mark all live things first.
llvm::BitVector live(cfg->getNumBlockIDs());
unsigned count = reachable_code::ScanReachableFromBlock(cfg->getEntry(),
live);
bool AddEHEdges = AC.getAddEHEdges();
if (!AddEHEdges && count != cfg->getNumBlockIDs())
// When there are things remaining dead, and we didn't add EH edges
// from CallExprs to the catch clauses, we have to go back and
// mark them as live.
for (CFG::iterator I = cfg->begin(), E = cfg->end(); I != E; ++I) {
CFGBlock &b = **I;
if (!live[b.getBlockID()]) {
if (b.pred_begin() == b.pred_end()) {
if (b.getTerminator() && isa<CXXTryStmt>(b.getTerminator()))
// When not adding EH edges from calls, catch clauses
// can otherwise seem dead. Avoid noting them as dead.
count += reachable_code::ScanReachableFromBlock(b, live);
continue;
}
}
}
// Now we know what is live, we check the live precessors of the exit block
// and look for fall through paths, being careful to ignore normal returns,
// and exceptional paths.
bool HasLiveReturn = false;
bool HasFakeEdge = false;
bool HasPlainEdge = false;
bool HasAbnormalEdge = false;
for (CFGBlock::pred_iterator I=cfg->getExit().pred_begin(),
E = cfg->getExit().pred_end();
I != E;
++I) {
CFGBlock& B = **I;
if (!live[B.getBlockID()])
continue;
if (B.size() == 0) {
if (B.getTerminator() && isa<CXXTryStmt>(B.getTerminator())) {
HasAbnormalEdge = true;
continue;
}
// A labeled empty statement, or the entry block...
HasPlainEdge = true;
continue;
}
Stmt *S = B[B.size()-1];
if (isa<ReturnStmt>(S)) {
HasLiveReturn = true;
continue;
}
if (isa<ObjCAtThrowStmt>(S)) {
HasFakeEdge = true;
continue;
}
if (isa<CXXThrowExpr>(S)) {
HasFakeEdge = true;
continue;
}
if (const AsmStmt *AS = dyn_cast<AsmStmt>(S)) {
if (AS->isMSAsm()) {
HasFakeEdge = true;
HasLiveReturn = true;
continue;
}
}
if (isa<CXXTryStmt>(S)) {
HasAbnormalEdge = true;
continue;
}
bool NoReturnEdge = false;
if (CallExpr *C = dyn_cast<CallExpr>(S)) {
if (std::find(B.succ_begin(), B.succ_end(), &cfg->getExit())
== B.succ_end()) {
HasAbnormalEdge = true;
continue;
}
Expr *CEE = C->getCallee()->IgnoreParenCasts();
if (getFunctionExtInfo(CEE->getType()).getNoReturn()) {
NoReturnEdge = true;
HasFakeEdge = true;
} else if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(CEE)) {
ValueDecl *VD = DRE->getDecl();
if (VD->hasAttr<NoReturnAttr>()) {
NoReturnEdge = true;
HasFakeEdge = true;
}
}
}
// FIXME: Remove this hack once temporaries and their destructors are
// modeled correctly by the CFG.
if (CXXExprWithTemporaries *E = dyn_cast<CXXExprWithTemporaries>(S)) {
for (unsigned I = 0, N = E->getNumTemporaries(); I != N; ++I) {
const FunctionDecl *FD = E->getTemporary(I)->getDestructor();
if (FD->hasAttr<NoReturnAttr>() ||
FD->getType()->getAs<FunctionType>()->getNoReturnAttr()) {
NoReturnEdge = true;
HasFakeEdge = true;
break;
}
}
}
// FIXME: Add noreturn message sends.
if (NoReturnEdge == false)
HasPlainEdge = true;
}
if (!HasPlainEdge) {
if (HasLiveReturn)
return NeverFallThrough;
return NeverFallThroughOrReturn;
}
if (HasAbnormalEdge || HasFakeEdge || HasLiveReturn)
return MaybeFallThrough;
// This says AlwaysFallThrough for calls to functions that are not marked
// noreturn, that don't return. If people would like this warning to be more
// accurate, such functions should be marked as noreturn.
return AlwaysFallThrough;
}
namespace {
struct CheckFallThroughDiagnostics {
unsigned diag_MaybeFallThrough_HasNoReturn;
unsigned diag_MaybeFallThrough_ReturnsNonVoid;
unsigned diag_AlwaysFallThrough_HasNoReturn;
unsigned diag_AlwaysFallThrough_ReturnsNonVoid;
unsigned diag_NeverFallThroughOrReturn;
bool funMode;
static CheckFallThroughDiagnostics MakeForFunction(const Decl *Func) {
CheckFallThroughDiagnostics D;
D.diag_MaybeFallThrough_HasNoReturn =
diag::warn_falloff_noreturn_function;
D.diag_MaybeFallThrough_ReturnsNonVoid =
diag::warn_maybe_falloff_nonvoid_function;
D.diag_AlwaysFallThrough_HasNoReturn =
diag::warn_falloff_noreturn_function;
D.diag_AlwaysFallThrough_ReturnsNonVoid =
diag::warn_falloff_nonvoid_function;
// Don't suggest that virtual functions be marked "noreturn", since they
// might be overridden by non-noreturn functions.
bool isVirtualMethod = false;
if (const CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Func))
isVirtualMethod = Method->isVirtual();
if (!isVirtualMethod)
D.diag_NeverFallThroughOrReturn =
diag::warn_suggest_noreturn_function;
else
D.diag_NeverFallThroughOrReturn = 0;
D.funMode = true;
return D;
}
static CheckFallThroughDiagnostics MakeForBlock() {
CheckFallThroughDiagnostics D;
D.diag_MaybeFallThrough_HasNoReturn =
diag::err_noreturn_block_has_return_expr;
D.diag_MaybeFallThrough_ReturnsNonVoid =
diag::err_maybe_falloff_nonvoid_block;
D.diag_AlwaysFallThrough_HasNoReturn =
diag::err_noreturn_block_has_return_expr;
D.diag_AlwaysFallThrough_ReturnsNonVoid =
diag::err_falloff_nonvoid_block;
D.diag_NeverFallThroughOrReturn =
diag::warn_suggest_noreturn_block;
D.funMode = false;
return D;
}
bool checkDiagnostics(Diagnostic &D, bool ReturnsVoid,
bool HasNoReturn) const {
if (funMode) {
return (D.getDiagnosticLevel(diag::warn_maybe_falloff_nonvoid_function)
== Diagnostic::Ignored || ReturnsVoid)
&& (D.getDiagnosticLevel(diag::warn_noreturn_function_has_return_expr)
== Diagnostic::Ignored || !HasNoReturn)
&& (D.getDiagnosticLevel(diag::warn_suggest_noreturn_block)
== Diagnostic::Ignored || !ReturnsVoid);
}
// For blocks.
return ReturnsVoid && !HasNoReturn
&& (D.getDiagnosticLevel(diag::warn_suggest_noreturn_block)
== Diagnostic::Ignored || !ReturnsVoid);
}
};
}
/// CheckFallThroughForFunctionDef - Check that we don't fall off the end of a
/// function that should return a value. Check that we don't fall off the end
/// of a noreturn function. We assume that functions and blocks not marked
/// noreturn will return.
static void CheckFallThroughForBody(Sema &S, const Decl *D, const Stmt *Body,
QualType BlockTy,
const CheckFallThroughDiagnostics& CD,
AnalysisContext &AC) {
bool ReturnsVoid = false;
bool HasNoReturn = false;
if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
ReturnsVoid = FD->getResultType()->isVoidType();
HasNoReturn = FD->hasAttr<NoReturnAttr>() ||
FD->getType()->getAs<FunctionType>()->getNoReturnAttr();
}
else if (const ObjCMethodDecl *MD = dyn_cast<ObjCMethodDecl>(D)) {
ReturnsVoid = MD->getResultType()->isVoidType();
HasNoReturn = MD->hasAttr<NoReturnAttr>();
}
else if (isa<BlockDecl>(D)) {
if (const FunctionType *FT =
BlockTy->getPointeeType()->getAs<FunctionType>()) {
if (FT->getResultType()->isVoidType())
ReturnsVoid = true;
if (FT->getNoReturnAttr())
HasNoReturn = true;
}
}
Diagnostic &Diags = S.getDiagnostics();
// Short circuit for compilation speed.
if (CD.checkDiagnostics(Diags, ReturnsVoid, HasNoReturn))
return;
// FIXME: Function try block
if (const CompoundStmt *Compound = dyn_cast<CompoundStmt>(Body)) {
switch (CheckFallThrough(AC)) {
case UnknownFallThrough:
break;
case MaybeFallThrough:
if (HasNoReturn)
S.Diag(Compound->getRBracLoc(),
CD.diag_MaybeFallThrough_HasNoReturn);
else if (!ReturnsVoid)
S.Diag(Compound->getRBracLoc(),
CD.diag_MaybeFallThrough_ReturnsNonVoid);
break;
case AlwaysFallThrough:
if (HasNoReturn)
S.Diag(Compound->getRBracLoc(),
CD.diag_AlwaysFallThrough_HasNoReturn);
else if (!ReturnsVoid)
S.Diag(Compound->getRBracLoc(),
CD.diag_AlwaysFallThrough_ReturnsNonVoid);
break;
case NeverFallThroughOrReturn:
if (ReturnsVoid && !HasNoReturn && CD.diag_NeverFallThroughOrReturn)
S.Diag(Compound->getLBracLoc(),
CD.diag_NeverFallThroughOrReturn);
break;
case NeverFallThrough:
break;
}
}
}
//===----------------------------------------------------------------------===//
// AnalysisBasedWarnings - Worker object used by Sema to execute analysis-based
// warnings on a function, method, or block.
//===----------------------------------------------------------------------===//
clang::sema::AnalysisBasedWarnings::Policy::Policy() {
enableCheckFallThrough = 1;
enableCheckUnreachable = 0;
}
clang::sema::AnalysisBasedWarnings::AnalysisBasedWarnings(Sema &s) : S(s) {
Diagnostic &D = S.getDiagnostics();
DefaultPolicy.enableCheckUnreachable = (unsigned)
(D.getDiagnosticLevel(diag::warn_unreachable) != Diagnostic::Ignored);
}
void clang::sema::
AnalysisBasedWarnings::IssueWarnings(sema::AnalysisBasedWarnings::Policy P,
const Decl *D, QualType BlockTy) {
assert(BlockTy.isNull() || isa<BlockDecl>(D));
// We avoid doing analysis-based warnings when there are errors for
// two reasons:
// (1) The CFGs often can't be constructed (if the body is invalid), so
// don't bother trying.
// (2) The code already has problems; running the analysis just takes more
// time.
Diagnostic &Diags = S.getDiagnostics();
if (Diags.hasErrorOccurred() || Diags.hasFatalErrorOccurred())
return;
// Do not do any analysis for declarations in system headers if we are
// going to just ignore them.
if (Diags.getSuppressSystemWarnings() &&
S.SourceMgr.isInSystemHeader(D->getLocation()))
return;
// For code in dependent contexts, we'll do this at instantiation time.
if (cast<DeclContext>(D)->isDependentContext())
return;
const Stmt *Body = D->getBody();
assert(Body);
// Don't generate EH edges for CallExprs as we'd like to avoid the n^2
// explosion for destrutors that can result and the compile time hit.
AnalysisContext AC(D, 0, false);
// Warning: check missing 'return'
if (P.enableCheckFallThrough) {
const CheckFallThroughDiagnostics &CD =
(isa<BlockDecl>(D) ? CheckFallThroughDiagnostics::MakeForBlock()
: CheckFallThroughDiagnostics::MakeForFunction(D));
CheckFallThroughForBody(S, D, Body, BlockTy, CD, AC);
}
// Warning: check for unreachable code
if (P.enableCheckUnreachable)
CheckUnreachable(S, AC);
}
void clang::sema::
AnalysisBasedWarnings::IssueWarnings(sema::AnalysisBasedWarnings::Policy P,
const BlockExpr *E) {
return IssueWarnings(P, E->getBlockDecl(), E->getType());
}
void clang::sema::
AnalysisBasedWarnings::IssueWarnings(sema::AnalysisBasedWarnings::Policy P,
const ObjCMethodDecl *D) {
return IssueWarnings(P, D, QualType());
}
void clang::sema::
AnalysisBasedWarnings::IssueWarnings(sema::AnalysisBasedWarnings::Policy P,
const FunctionDecl *D) {
return IssueWarnings(P, D, QualType());
}
