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
