lib/Sema/AnalysisBasedWarnings.cpp - platform/external/clang - Gitiles

 //=- 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 "Sema.h"
 #include "AnalysisBasedWarnings.h"
 #include "clang/Basic/SourceManager.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 { NeverFallThrough = 0, MaybeFallThrough = 1,
   AlwaysFallThrough = 2, NeverFallThroughOrReturn = 3 };

 /// 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)
     // FIXME: This should be NeverFallThrough
     return NeverFallThroughOrReturn;

   // 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 (B.succ_begin()[0] != &cfg->getExit()) {
         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: 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;
 }

 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 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.
   if (S.getDiagnostics().hasErrorOccurred())
     return;

   // Do not do any analysis for declarations in system headers if we are
   // going to just ignore them.
   if (S.getDiagnostics().getSuppressSystemWarnings() &&
       S.SourceMgr.isInSystemHeader(D->getLocation()))
     return;

   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
     // For function templates, class templates and member function templates
     // we'll do the analysis at instantiation time.
     if (FD->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, 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);
 }
	//=- 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 "Sema.h"
	#include "AnalysisBasedWarnings.h"
	#include "clang/Basic/SourceManager.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 { NeverFallThrough = 0, MaybeFallThrough = 1,
	AlwaysFallThrough = 2, NeverFallThroughOrReturn = 3 };

	/// 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)
	// FIXME: This should be NeverFallThrough
	return NeverFallThroughOrReturn;

	// 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 (B.succ_begin()[0] != &cfg->getExit()) {
	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: 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;
	}

	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 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.
	if (S.getDiagnostics().hasErrorOccurred())
	return;

	// Do not do any analysis for declarations in system headers if we are
	// going to just ignore them.
	if (S.getDiagnostics().getSuppressSystemWarnings() &&
	S.SourceMgr.isInSystemHeader(D->getLocation()))
	return;

	if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
	// For function templates, class templates and member function templates
	// we'll do the analysis at instantiation time.
	if (FD->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, 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);
	}