//===--- TransRetainReleaseDealloc.cpp - Transformations to ARC mode ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// removeRetainReleaseDealloc:
//
// Removes retain/release/autorelease/dealloc messages.
//
// return [[foo retain] autorelease];
// ---->
// return foo;
//
//===----------------------------------------------------------------------===//
#include "Transforms.h"
#include "Internals.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ParentMap.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Lex/Lexer.h"
#include "clang/Sema/SemaDiagnostic.h"
#include "llvm/ADT/StringSwitch.h"
using namespace clang;
using namespace arcmt;
using namespace trans;
namespace {
class RetainReleaseDeallocRemover :
public RecursiveASTVisitor<RetainReleaseDeallocRemover> {
Stmt *Body;
MigrationPass &Pass;
ExprSet Removables;
std::unique_ptr<ParentMap> StmtMap;
Selector DelegateSel, FinalizeSel;
public:
RetainReleaseDeallocRemover(MigrationPass &pass)
: Body(nullptr), Pass(pass) {
DelegateSel =
Pass.Ctx.Selectors.getNullarySelector(&Pass.Ctx.Idents.get("delegate"));
FinalizeSel =
Pass.Ctx.Selectors.getNullarySelector(&Pass.Ctx.Idents.get("finalize"));
}
void transformBody(Stmt *body, Decl *ParentD) {
Body = body;
collectRemovables(body, Removables);
StmtMap.reset(new ParentMap(body));
TraverseStmt(body);
}
bool VisitObjCMessageExpr(ObjCMessageExpr *E) {
switch (E->getMethodFamily()) {
default:
if (E->isInstanceMessage() && E->getSelector() == FinalizeSel)
break;
return true;
case OMF_autorelease:
if (isRemovable(E)) {
if (!isCommonUnusedAutorelease(E)) {
// An unused autorelease is badness. If we remove it the receiver
// will likely die immediately while previously it was kept alive
// by the autorelease pool. This is bad practice in general, leave it
// and emit an error to force the user to restructure their code.
Pass.TA.reportError("it is not safe to remove an unused 'autorelease' "
"message; its receiver may be destroyed immediately",
E->getLocStart(), E->getSourceRange());
return true;
}
}
// Pass through.
case OMF_retain:
case OMF_release:
if (E->getReceiverKind() == ObjCMessageExpr::Instance)
if (Expr *rec = E->getInstanceReceiver()) {
rec = rec->IgnoreParenImpCasts();
if (rec->getType().getObjCLifetime() == Qualifiers::OCL_ExplicitNone &&
(E->getMethodFamily() != OMF_retain || isRemovable(E))) {
std::string err = "it is not safe to remove '";
err += E->getSelector().getAsString() + "' message on "
"an __unsafe_unretained type";
Pass.TA.reportError(err, rec->getLocStart());
return true;
}
if (isGlobalVar(rec) &&
(E->getMethodFamily() != OMF_retain || isRemovable(E))) {
std::string err = "it is not safe to remove '";
err += E->getSelector().getAsString() + "' message on "
"a global variable";
Pass.TA.reportError(err, rec->getLocStart());
return true;
}
if (E->getMethodFamily() == OMF_release && isDelegateMessage(rec)) {
Pass.TA.reportError("it is not safe to remove 'retain' "
"message on the result of a 'delegate' message; "
"the object that was passed to 'setDelegate:' may not be "
"properly retained", rec->getLocStart());
return true;
}
}
case OMF_dealloc:
break;
}
switch (E->getReceiverKind()) {
default:
return true;
case ObjCMessageExpr::SuperInstance: {
Transaction Trans(Pass.TA);
clearDiagnostics(E->getSelectorLoc(0));
if (tryRemoving(E))
return true;
Pass.TA.replace(E->getSourceRange(), "self");
return true;
}
case ObjCMessageExpr::Instance:
break;
}
Expr *rec = E->getInstanceReceiver();
if (!rec) return true;
Transaction Trans(Pass.TA);
clearDiagnostics(E->getSelectorLoc(0));
ObjCMessageExpr *Msg = E;
Expr *RecContainer = Msg;
SourceRange RecRange = rec->getSourceRange();
checkForGCDOrXPC(Msg, RecContainer, rec, RecRange);
if (Msg->getMethodFamily() == OMF_release &&
isRemovable(RecContainer) && isInAtFinally(RecContainer)) {
// Change the -release to "receiver = nil" in a finally to avoid a leak
// when an exception is thrown.
Pass.TA.replace(RecContainer->getSourceRange(), RecRange);
std::string str = " = ";
str += getNilString(Pass.Ctx);
Pass.TA.insertAfterToken(RecRange.getEnd(), str);
return true;
}
if (!hasSideEffects(rec, Pass.Ctx)) {
if (tryRemoving(RecContainer))
return true;
}
Pass.TA.replace(RecContainer->getSourceRange(), RecRange);
return true;
}
private:
/// \brief Checks for idioms where an unused -autorelease is common.
///
/// Returns true for this idiom which is common in property
/// setters:
///
/// [backingValue autorelease];
/// backingValue = [newValue retain]; // in general a +1 assign
///
/// For these as well:
///
/// [[var retain] autorelease];
/// return var;
///
bool isCommonUnusedAutorelease(ObjCMessageExpr *E) {
if (isPlusOneAssignBeforeOrAfterAutorelease(E))
return true;
if (isReturnedAfterAutorelease(E))
return true;
return false;
}
bool isReturnedAfterAutorelease(ObjCMessageExpr *E) {
Expr *Rec = E->getInstanceReceiver();
if (!Rec)
return false;
Decl *RefD = getReferencedDecl(Rec);
if (!RefD)
return false;
Stmt *nextStmt = getNextStmt(E);
if (!nextStmt)
return false;
// Check for "return <variable>;".
if (ReturnStmt *RetS = dyn_cast<ReturnStmt>(nextStmt))
return RefD == getReferencedDecl(RetS->getRetValue());
return false;
}
bool isPlusOneAssignBeforeOrAfterAutorelease(ObjCMessageExpr *E) {
Expr *Rec = E->getInstanceReceiver();
if (!Rec)
return false;
Decl *RefD = getReferencedDecl(Rec);
if (!RefD)
return false;
Stmt *prevStmt, *nextStmt;
std::tie(prevStmt, nextStmt) = getPreviousAndNextStmt(E);
return isPlusOneAssignToVar(prevStmt, RefD) ||
isPlusOneAssignToVar(nextStmt, RefD);
}
bool isPlusOneAssignToVar(Stmt *S, Decl *RefD) {
if (!S)
return false;
// Check for "RefD = [+1 retained object];".
if (BinaryOperator *Bop = dyn_cast<BinaryOperator>(S)) {
if (RefD != getReferencedDecl(Bop->getLHS()))
return false;
if (isPlusOneAssign(Bop))
return true;
return false;
}
if (DeclStmt *DS = dyn_cast<DeclStmt>(S)) {
if (DS->isSingleDecl() && DS->getSingleDecl() == RefD) {
if (VarDecl *VD = dyn_cast<VarDecl>(RefD))
return isPlusOne(VD->getInit());
}
return false;
}
return false;
}
Stmt *getNextStmt(Expr *E) {
return getPreviousAndNextStmt(E).second;
}
std::pair<Stmt *, Stmt *> getPreviousAndNextStmt(Expr *E) {
Stmt *prevStmt = nullptr, *nextStmt = nullptr;
if (!E)
return std::make_pair(prevStmt, nextStmt);
Stmt *OuterS = E, *InnerS;
do {
InnerS = OuterS;
OuterS = StmtMap->getParent(InnerS);
}
while (OuterS && (isa<ParenExpr>(OuterS) ||
isa<CastExpr>(OuterS) ||
isa<ExprWithCleanups>(OuterS)));
if (!OuterS)
return std::make_pair(prevStmt, nextStmt);
Stmt::child_iterator currChildS = OuterS->child_begin();
Stmt::child_iterator childE = OuterS->child_end();
Stmt::child_iterator prevChildS = childE;
for (; currChildS != childE; ++currChildS) {
if (*currChildS == InnerS)
break;
prevChildS = currChildS;
}
if (prevChildS != childE) {
prevStmt = *prevChildS;
if (prevStmt)
prevStmt = prevStmt->IgnoreImplicit();
}
if (currChildS == childE)
return std::make_pair(prevStmt, nextStmt);
++currChildS;
if (currChildS == childE)
return std::make_pair(prevStmt, nextStmt);
nextStmt = *currChildS;
if (nextStmt)
nextStmt = nextStmt->IgnoreImplicit();
return std::make_pair(prevStmt, nextStmt);
}
Decl *getReferencedDecl(Expr *E) {
if (!E)
return nullptr;
E = E->IgnoreParenCasts();
if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E)) {
switch (ME->getMethodFamily()) {
case OMF_copy:
case OMF_autorelease:
case OMF_release:
case OMF_retain:
return getReferencedDecl(ME->getInstanceReceiver());
default:
return nullptr;
}
}
if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
return DRE->getDecl();
if (MemberExpr *ME = dyn_cast<MemberExpr>(E))
return ME->getMemberDecl();
if (ObjCIvarRefExpr *IRE = dyn_cast<ObjCIvarRefExpr>(E))
return IRE->getDecl();
return nullptr;
}
/// \brief Check if the retain/release is due to a GCD/XPC macro that are
/// defined as:
///
/// #define dispatch_retain(object) ({ dispatch_object_t _o = (object); _dispatch_object_validate(_o); (void)[_o retain]; })
/// #define dispatch_release(object) ({ dispatch_object_t _o = (object); _dispatch_object_validate(_o); [_o release]; })
/// #define xpc_retain(object) ({ xpc_object_t _o = (object); _xpc_object_validate(_o); [_o retain]; })
/// #define xpc_release(object) ({ xpc_object_t _o = (object); _xpc_object_validate(_o); [_o release]; })
///
/// and return the top container which is the StmtExpr and the macro argument
/// expression.
void checkForGCDOrXPC(ObjCMessageExpr *Msg, Expr *&RecContainer,
Expr *&Rec, SourceRange &RecRange) {
SourceLocation Loc = Msg->getExprLoc();
if (!Loc.isMacroID())
return;
SourceManager &SM = Pass.Ctx.getSourceManager();
StringRef MacroName = Lexer::getImmediateMacroName(Loc, SM,
Pass.Ctx.getLangOpts());
bool isGCDOrXPC = llvm::StringSwitch<bool>(MacroName)
.Case("dispatch_retain", true)
.Case("dispatch_release", true)
.Case("xpc_retain", true)
.Case("xpc_release", true)
.Default(false);
if (!isGCDOrXPC)
return;
StmtExpr *StmtE = nullptr;
Stmt *S = Msg;
while (S) {
if (StmtExpr *SE = dyn_cast<StmtExpr>(S)) {
StmtE = SE;
break;
}
S = StmtMap->getParent(S);
}
if (!StmtE)
return;
Stmt::child_range StmtExprChild = StmtE->children();
if (!StmtExprChild)
return;
CompoundStmt *CompS = dyn_cast_or_null<CompoundStmt>(*StmtExprChild);
if (!CompS)
return;
Stmt::child_range CompStmtChild = CompS->children();
if (!CompStmtChild)
return;
DeclStmt *DeclS = dyn_cast_or_null<DeclStmt>(*CompStmtChild);
if (!DeclS)
return;
if (!DeclS->isSingleDecl())
return;
VarDecl *VD = dyn_cast_or_null<VarDecl>(DeclS->getSingleDecl());
if (!VD)
return;
Expr *Init = VD->getInit();
if (!Init)
return;
RecContainer = StmtE;
Rec = Init->IgnoreParenImpCasts();
if (ExprWithCleanups *EWC = dyn_cast<ExprWithCleanups>(Rec))
Rec = EWC->getSubExpr()->IgnoreParenImpCasts();
RecRange = Rec->getSourceRange();
if (SM.isMacroArgExpansion(RecRange.getBegin()))
RecRange.setBegin(SM.getImmediateSpellingLoc(RecRange.getBegin()));
if (SM.isMacroArgExpansion(RecRange.getEnd()))
RecRange.setEnd(SM.getImmediateSpellingLoc(RecRange.getEnd()));
}
void clearDiagnostics(SourceLocation loc) const {
Pass.TA.clearDiagnostic(diag::err_arc_illegal_explicit_message,
diag::err_unavailable,
diag::err_unavailable_message,
loc);
}
bool isDelegateMessage(Expr *E) const {
if (!E) return false;
E = E->IgnoreParenCasts();
// Also look through property-getter sugar.
if (PseudoObjectExpr *pseudoOp = dyn_cast<PseudoObjectExpr>(E))
E = pseudoOp->getResultExpr()->IgnoreImplicit();
if (ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(E))
return (ME->isInstanceMessage() && ME->getSelector() == DelegateSel);
return false;
}
bool isInAtFinally(Expr *E) const {
assert(E);
Stmt *S = E;
while (S) {
if (isa<ObjCAtFinallyStmt>(S))
return true;
S = StmtMap->getParent(S);
}
return false;
}
bool isRemovable(Expr *E) const {
return Removables.count(E);
}
bool tryRemoving(Expr *E) const {
if (isRemovable(E)) {
Pass.TA.removeStmt(E);
return true;
}
Stmt *parent = StmtMap->getParent(E);
if (ImplicitCastExpr *castE = dyn_cast_or_null<ImplicitCastExpr>(parent))
return tryRemoving(castE);
if (ParenExpr *parenE = dyn_cast_or_null<ParenExpr>(parent))
return tryRemoving(parenE);
if (BinaryOperator *
bopE = dyn_cast_or_null<BinaryOperator>(parent)) {
if (bopE->getOpcode() == BO_Comma && bopE->getLHS() == E &&
isRemovable(bopE)) {
Pass.TA.replace(bopE->getSourceRange(), bopE->getRHS()->getSourceRange());
return true;
}
}
return false;
}
};
} // anonymous namespace
void trans::removeRetainReleaseDeallocFinalize(MigrationPass &pass) {
BodyTransform<RetainReleaseDeallocRemover> trans(pass);
trans.TraverseDecl(pass.Ctx.getTranslationUnitDecl());
}