Thinking again, the method “can” be implemented I think. Forget it… — Mehdi
> On Nov 10, 2016, at 6:11 PM, Mehdi Amini <mehdi.am...@apple.com> wrote: > > Could we emit llvm.unreachable in this case? > > — > Mehdi > >> On Nov 10, 2016, at 5:01 PM, Richard Smith via cfe-commits >> <cfe-commits@lists.llvm.org> wrote: >> >> Author: rsmith >> Date: Thu Nov 10 19:01:31 2016 >> New Revision: 286534 >> >> URL: http://llvm.org/viewvc/llvm-project?rev=286534&view=rev >> Log: >> PR30937: don't devirtualize if we find that the callee is a pure virtual >> function. In that case, there is no requirement that the callee is actually >> defined, and the code may in fact be valid and have defined behavior if the >> virtual call is unreachable. >> >> Modified: >> cfe/trunk/lib/CodeGen/CGClass.cpp >> cfe/trunk/test/CodeGenCXX/devirtualize-virtual-function-calls.cpp >> >> Modified: cfe/trunk/lib/CodeGen/CGClass.cpp >> URL: >> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGClass.cpp?rev=286534&r1=286533&r2=286534&view=diff >> ============================================================================== >> --- cfe/trunk/lib/CodeGen/CGClass.cpp (original) >> +++ cfe/trunk/lib/CodeGen/CGClass.cpp Thu Nov 10 19:01:31 2016 >> @@ -2851,9 +2851,9 @@ CodeGenFunction::CanDevirtualizeMemberFu >> return false; >> >> // If the member function is marked 'final', we know that it can't be >> - // overridden and can therefore devirtualize it. >> + // overridden and can therefore devirtualize it unless it's pure virtual. >> if (MD->hasAttr<FinalAttr>()) >> - return true; >> + return !MD->isPure(); >> >> // If the base expression (after skipping derived-to-base conversions) is a >> // class prvalue, then we can devirtualize. >> @@ -2861,31 +2861,28 @@ CodeGenFunction::CanDevirtualizeMemberFu >> if (Base->isRValue() && Base->getType()->isRecordType()) >> return true; >> >> - // If the most derived class is marked final, we know that no subclass can >> - // override this member function and so we can devirtualize it. For >> example: >> - // >> - // struct A { virtual void f(); } >> - // struct B final : A { }; >> - // >> - // void f(B *b) { >> - // b->f(); >> - // } >> - // >> - if (const CXXRecordDecl *BestDynamicDecl = >> Base->getBestDynamicClassType()) { >> - if (BestDynamicDecl->hasAttr<FinalAttr>()) >> - return true; >> - >> - // There may be a method corresponding to MD in a derived class. If that >> - // method is marked final, we can devirtualize it. >> - const CXXMethodDecl *DevirtualizedMethod = >> - MD->getCorrespondingMethodInClass(BestDynamicDecl); >> - if (DevirtualizedMethod->hasAttr<FinalAttr>()) >> - return true; >> - } >> + // If we don't even know what we would call, we can't devirtualize. >> + const CXXRecordDecl *BestDynamicDecl = Base->getBestDynamicClassType(); >> + if (!BestDynamicDecl) >> + return false; >> + >> + // There may be a method corresponding to MD in a derived class. >> + const CXXMethodDecl *DevirtualizedMethod = >> + MD->getCorrespondingMethodInClass(BestDynamicDecl); >> + >> + // If that method is pure virtual, we can't devirtualize. If this code is >> + // reached, the result would be UB, not a direct call to the derived class >> + // function, and we can't assume the derived class function is defined. >> + if (DevirtualizedMethod->isPure()) >> + return false; >> + >> + // If that method is marked final, we can devirtualize it. >> + if (DevirtualizedMethod->hasAttr<FinalAttr>()) >> + return true; >> >> // Similarly, if the class itself is marked 'final' it can't be overridden >> // and we can therefore devirtualize the member function call. >> - if (MD->getParent()->hasAttr<FinalAttr>()) >> + if (BestDynamicDecl->hasAttr<FinalAttr>()) >> return true; >> >> if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Base)) { >> >> Modified: cfe/trunk/test/CodeGenCXX/devirtualize-virtual-function-calls.cpp >> URL: >> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/devirtualize-virtual-function-calls.cpp?rev=286534&r1=286533&r2=286534&view=diff >> ============================================================================== >> --- cfe/trunk/test/CodeGenCXX/devirtualize-virtual-function-calls.cpp >> (original) >> +++ cfe/trunk/test/CodeGenCXX/devirtualize-virtual-function-calls.cpp Thu >> Nov 10 19:01:31 2016 >> @@ -161,3 +161,37 @@ namespace test4 { >> p->fish.eat(); >> } >> } >> + >> +// Do not devirtualize to pure virtual function calls. >> +namespace test5 { >> + struct X { >> + virtual void f() = 0; >> + }; >> + struct Y {}; >> + // CHECK-LABEL: define {{.*}} @_ZN5test51f >> + void f(Y &y, X Y::*p) { >> + // CHECK-NOT: call {{.*}} @_ZN5test51X1fEv >> + // CHECK: call void % >> + (y.*p).f(); >> + }; >> + >> + struct Z final { >> + virtual void f() = 0; >> + }; >> + // CHECK-LABEL: define {{.*}} @_ZN5test51g >> + void g(Z &z) { >> + // CHECK-NOT: call {{.*}} @_ZN5test51Z1fEv >> + // CHECK: call void % >> + z.f(); >> + } >> + >> + struct Q { >> + virtual void f() final = 0; >> + }; >> + // CHECK-LABEL: define {{.*}} @_ZN5test51h >> + void h(Q &q) { >> + // CHECK-NOT: call {{.*}} @_ZN5test51Q1fEv >> + // CHECK: call void % >> + q.f(); >> + } >> +} >> >> >> _______________________________________________ >> cfe-commits mailing list >> cfe-commits@lists.llvm.org >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits > _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
