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[CodeGen] Devirtualize calls to methods marked final in a derived class 

If we see a virtual method call to Base::foo() but can infer that the
object is an instance of Derived, and that 'foo' is marked 'final' in
Derived, we can devirtualize the call to Derived::foo().

Differential Revision: https://reviews.llvm.org/D25813

llvm-svn: 284766
This commit is contained in:
Vedant Kumar 2016-10-20 18:44:14 +00:00
parent b625d17db8
commit 2d38ae6c41
3 changed files with 45 additions and 24 deletions
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22
clang/lib/CodeGen/CGClass.cpp
View File

@ -2873,6 +2873,11 @@ CodeGenFunction::CanDevirtualizeMemberFunctionCall(const Expr *Base,
if (getLangOpts().AppleKext)
return false;
// If the member function is marked 'final', we know that it can't be
// overridden and can therefore devirtualize it.
if (MD->hasAttr<FinalAttr>())
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:
//
@ -2883,14 +2888,17 @@ CodeGenFunction::CanDevirtualizeMemberFunctionCall(const Expr *Base,
// b->f();
// }
//
const CXXRecordDecl *MostDerivedClassDecl = Base->getBestDynamicClassType();
if (MostDerivedClassDecl->hasAttr<FinalAttr>())
return true;
if (const CXXRecordDecl *BestDynamicDecl = Base->getBestDynamicClassType()) {
if (BestDynamicDecl->hasAttr<FinalAttr>())
return true;
// If the member function is marked 'final', we know that it can't be
// overridden and can therefore devirtualize it.
if (MD->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;
}
// Similarly, if the class itself is marked 'final' it can't be overridden
// and we can therefore devirtualize the member function call.

16
clang/test/CodeGenCXX/devirtualize-virtual-function-calls-final.cpp
View File

@ -225,3 +225,19 @@ namespace Test9 {
return -static_cast<RA&>(*x);
}
}
namespace Test10 {
struct A {
virtual int f();
};
struct B : A {
int f() final;
};
// CHECK-LABEL: define i32 @_ZN6Test101fEPNS_1BE
int f(B *b) {
// CHECK: call i32 @_ZN6Test101B1fEv
return static_cast<A *>(b)->f();
}
}

31
clang/test/CodeGenCXX/ubsan-devirtualized-calls.cpp
View File

@ -16,9 +16,6 @@ struct Derived2 final : Base1, Base2 {
void f1() override {}
};
// PR13127 documents some missed devirtualization opportunities, including
// devirt for methods marked 'final'. We can enable the checks marked 'PR13127'
// if we implement this in the frontend.
struct Derived3 : Base1 {
void f1() override /* nofinal */ {}
};
@ -30,10 +27,10 @@ struct Derived4 final : Base1 {
// CHECK: [[UBSAN_TI_DERIVED1_1:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI8Derived1 to i8*
// CHECK: [[UBSAN_TI_DERIVED2_1:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI8Derived2 to i8*
// CHECK: [[UBSAN_TI_DERIVED2_2:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI8Derived2 to i8*
// PR13127: [[UBSAN_TI_DERIVED3:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI8Derived3 to i8*
// PR13127: [[UBSAN_TI_BASE1:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI5Base1 to i8*
// PR13127: [[UBSAN_TI_DERIVED4_1:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI8Derived4 to i8*
// PR13127: [[UBSAN_TI_DERIVED4_2:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI8Derived4 to i8*
// CHECK: [[UBSAN_TI_DERIVED3:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI8Derived3 to i8*
// CHECK: [[UBSAN_TI_BASE1:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI5Base1 to i8*
// CHECK: [[UBSAN_TI_DERIVED4_1:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI8Derived4 to i8*
// CHECK: [[UBSAN_TI_DERIVED4_2:@[0-9]+]] = private unnamed_addr global {{.*}} i8* bitcast {{.*}} @_ZTI8Derived4 to i8*
// CHECK-LABEL: define void @_Z2t1v
void t1() {
@ -59,26 +56,26 @@ void t3() {
// CHECK-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_DERIVED2_2]] {{.*}}, i{{[0-9]+}} %[[D2_2]]
}
// PR13127-LABEL: define void @_Z2t4v
// CHECK-LABEL: define void @_Z2t4v
void t4() {
Base1 p;
Derived3 *badp = static_cast<Derived3 *>(&p); //< Check that &p isa Derived3.
// PR13127: %[[P1:[0-9]+]] = ptrtoint %struct.Derived3* {{%[0-9]+}} to i{{[0-9]+}}, !nosanitize
// PR13127-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_DERIVED3]] {{.*}}, i{{[0-9]+}} %[[P1]]
// CHECK: %[[P1:[0-9]+]] = ptrtoint %struct.Derived3* {{%[0-9]+}} to i{{[0-9]+}}, !nosanitize
// CHECK-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_DERIVED3]] {{.*}}, i{{[0-9]+}} %[[P1]]
static_cast<Base1 *>(badp)->f1(); //< No devirt, test 'badp isa Base1'.
// PR13127: %[[BADP1:[0-9]+]] = ptrtoint %struct.Base1* {{%[0-9]+}} to i{{[0-9]+}}, !nosanitize
// PR13127-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_BASE1]] {{.*}}, i{{[0-9]+}} %[[BADP1]]
// CHECK: %[[BADP1:[0-9]+]] = ptrtoint %struct.Base1* {{%[0-9]+}} to i{{[0-9]+}}, !nosanitize
// CHECK-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_BASE1]] {{.*}}, i{{[0-9]+}} %[[BADP1]]
}
// PR13127-LABEL: define void @_Z2t5v
// CHECK-LABEL: define void @_Z2t5v
void t5() {
Base1 p;
Derived4 *badp = static_cast<Derived4 *>(&p); //< Check that &p isa Derived4.
// PR13127: %[[P1:[0-9]+]] = ptrtoint %struct.Derived4* {{%[0-9]+}} to i{{[0-9]+}}, !nosanitize
// PR13127-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_DERIVED4_1]] {{.*}}, i{{[0-9]+}} %[[P1]]
// CHECK: %[[P1:[0-9]+]] = ptrtoint %struct.Derived4* {{%[0-9]+}} to i{{[0-9]+}}, !nosanitize
// CHECK-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_DERIVED4_1]] {{.*}}, i{{[0-9]+}} %[[P1]]
static_cast<Base1 *>(badp)->f1(); //< Devirt Base1::f1 to Derived4::f1.
// PR13127: %[[BADP1:[0-9]+]] = ptrtoint %struct.Derived4* {{%[0-9]+}} to i{{[0-9]+}}, !nosanitize
// PR13127-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_DERIVED4_2]] {{.*}}, i{{[0-9]+}} %[[BADP1]]
// CHECK: %[[BADP1:[0-9]+]] = ptrtoint %struct.Derived4* {{%[0-9]+}} to i{{[0-9]+}}, !nosanitize
// CHECK-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_DERIVED4_2]] {{.*}}, i{{[0-9]+}} %[[BADP1]]
}