Author: Pierre Habouzit Date: 2020-01-14T19:48:33-08:00 New Revision: d18fbfc09720009c0dc6a1ddf315402ee0a7751d
URL: https://github.com/llvm/llvm-project/commit/d18fbfc09720009c0dc6a1ddf315402ee0a7751d DIFF: https://github.com/llvm/llvm-project/commit/d18fbfc09720009c0dc6a1ddf315402ee0a7751d.diff LOG: Relax the rules around objc_alloc and objc_alloc_init optimizations. Today the optimization is limited to: - `[ClassName alloc]` - `[self alloc]` when within a class method However it means that when code is written this way: ``` @interface MyObject - (id)copyWithZone:(NSZone *)zone { return [[self.class alloc] _initWith...]; } @end ``` ... then the optimization doesn't kick in and `+[NSObject alloc]` ends up in IMP caches where it could have been avoided. It turns out that `+alloc` -> `+[NSObject alloc]` is the most cached SEL/IMP pair in the entire platform which is rather silly). There's two theoretical risks allowing this optimization: 1. if the receiver is nil (which it can't be today), but it turns out that `objc_alloc()`/`objc_alloc_init()` cope with a nil receiver, 2. if the `Clas` type for the receiver is a lie. However, for such a code to work today (and not fail witn an unrecognized selector anyway) you'd have to have implemented the `-alloc` **instance method**. Fortunately, `objc_alloc()` doesn't assume that the receiver is a Class, it basically starts with a test that is similar to `if (receiver->isa->bits & hasDefaultAWZ) { /* fastpath */ }`. This bit is only set on metaclasses by the runtime, so if an instance is passed to this function by accident, its isa will fail this test, and `objc_alloc()` will gracefully fallback to `objc_msgSend()`. The one thing `objc_alloc()` doesn't support is tagged pointer instances. None of the tagged pointer classes implement an instance method called `'alloc'` (actually there's a single class in the entire Apple codebase that has such a method). Differential Revision: https://reviews.llvm.org/D71682 Radar-Id: rdar://problem/58058316 Reviewed-By: Akira Hatanaka Signed-off-by: Pierre Habouzit <phabou...@apple.com> Added: Modified: clang/lib/CodeGen/CGObjC.cpp clang/test/CodeGenObjC/objc-alloc-init.m Removed: ################################################################################ diff --git a/clang/lib/CodeGen/CGObjC.cpp b/clang/lib/CodeGen/CGObjC.cpp index c52aa6bb5496..90fca2836d99 100644 --- a/clang/lib/CodeGen/CGObjC.cpp +++ b/clang/lib/CodeGen/CGObjC.cpp @@ -461,38 +461,39 @@ tryEmitSpecializedAllocInit(CodeGenFunction &CGF, const ObjCMessageExpr *OME) { Sel.getNameForSlot(0) != "init") return None; - // Okay, this is '[receiver init]', check if 'receiver' is '[cls alloc]' or - // we are in an ObjC class method and 'receiver' is '[self alloc]'. + // Okay, this is '[receiver init]', check if 'receiver' is '[cls alloc]' + // with 'cls' a Class. auto *SubOME = dyn_cast<ObjCMessageExpr>(OME->getInstanceReceiver()->IgnoreParenCasts()); if (!SubOME) return None; Selector SubSel = SubOME->getSelector(); - // Check if we are in an ObjC class method and the receiver expression is - // 'self'. - const Expr *SelfInClassMethod = nullptr; - if (const auto *CurMD = dyn_cast_or_null<ObjCMethodDecl>(CGF.CurFuncDecl)) - if (CurMD->isClassMethod()) - if ((SelfInClassMethod = SubOME->getInstanceReceiver())) - if (!SelfInClassMethod->isObjCSelfExpr()) - SelfInClassMethod = nullptr; - - if ((SubOME->getReceiverKind() != ObjCMessageExpr::Class && - !SelfInClassMethod) || !SubOME->getType()->isObjCObjectPointerType() || + if (!SubOME->getType()->isObjCObjectPointerType() || !SubSel.isUnarySelector() || SubSel.getNameForSlot(0) != "alloc") return None; - llvm::Value *Receiver; - if (SelfInClassMethod) { - Receiver = CGF.EmitScalarExpr(SelfInClassMethod); - } else { + llvm::Value *Receiver = nullptr; + switch (SubOME->getReceiverKind()) { + case ObjCMessageExpr::Instance: + if (!SubOME->getInstanceReceiver()->getType()->isObjCClassType()) + return None; + Receiver = CGF.EmitScalarExpr(SubOME->getInstanceReceiver()); + break; + + case ObjCMessageExpr::Class: { QualType ReceiverType = SubOME->getClassReceiver(); const ObjCObjectType *ObjTy = ReceiverType->castAs<ObjCObjectType>(); const ObjCInterfaceDecl *ID = ObjTy->getInterface(); assert(ID && "null interface should be impossible here"); Receiver = CGF.CGM.getObjCRuntime().GetClass(CGF, ID); + break; + } + case ObjCMessageExpr::SuperInstance: + case ObjCMessageExpr::SuperClass: + return None; } + return CGF.EmitObjCAllocInit(Receiver, CGF.ConvertType(OME->getType())); } @@ -540,10 +541,7 @@ RValue CodeGenFunction::EmitObjCMessageExpr(const ObjCMessageExpr *E, switch (E->getReceiverKind()) { case ObjCMessageExpr::Instance: ReceiverType = E->getInstanceReceiver()->getType(); - if (auto *OMD = dyn_cast_or_null<ObjCMethodDecl>(CurFuncDecl)) - if (OMD->isClassMethod()) - if (E->getInstanceReceiver()->isObjCSelfExpr()) - isClassMessage = true; + isClassMessage = ReceiverType->isObjCClassType(); if (retainSelf) { TryEmitResult ter = tryEmitARCRetainScalarExpr(*this, E->getInstanceReceiver()); diff --git a/clang/test/CodeGenObjC/objc-alloc-init.m b/clang/test/CodeGenObjC/objc-alloc-init.m index c5c1a763b7c7..8370202748e6 100644 --- a/clang/test/CodeGenObjC/objc-alloc-init.m +++ b/clang/test/CodeGenObjC/objc-alloc-init.m @@ -22,21 +22,30 @@ void f() { } @interface Y : X ++(Class)class; +(void)meth; -(void)instanceMeth; @end @implementation Y ++(Class)class { + return self; +} +(void)meth { [[self alloc] init]; // OPTIMIZED: call i8* @objc_alloc_init( // NOT_OPTIMIZED: call i8* @objc_alloc( } ++ (void)meth2 { + [[[self class] alloc] init]; + // OPTIMIZED: call i8* @objc_alloc_init( + // NOT_OPTIMIZED: call i8* @objc_alloc( +} -(void)instanceMeth { // EITHER-NOT: call i8* @objc_alloc // EITHER: call {{.*}} @objc_msgSend // EITHER: call {{.*}} @objc_msgSend - [[self alloc] init]; + [[(id)self alloc] init]; } @end _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
