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Rewrite the TrailingObjects template to provide two new features: 

- Automatic alignment of the base type for the alignment requirements
   of the trailing types.

 - Support for an arbitrary numbers of trailing types, instead of only
   1 or 2, by using a variadic template implementation.

Upcoming commits to clang will take advantage of both of these features.

Differential Revision: http://reviews.llvm.org/D12439

llvm-svn: 256054
This commit is contained in:
James Y Knight 2015-12-18 22:54:37 +00:00
parent 31ccb51a7f
commit 64390b4238
2 changed files with 248 additions and 108 deletions
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318
llvm/include/llvm/Support/TrailingObjects.h
View File

@ -59,6 +59,27 @@
namespace llvm {
namespace trailing_objects_internal {
/// Helper template to calculate the max alignment requirement for a set of
/// objects.
template <typename First, typename... Rest> class AlignmentCalcHelper {
private:
enum {
FirstAlignment = AlignOf<First>::Alignment,
RestAlignment = AlignmentCalcHelper<Rest...>::Alignment,
};
public:
enum {
Alignment = FirstAlignment > RestAlignment ? FirstAlignment : RestAlignment
};
};
template <typename First> class AlignmentCalcHelper<First> {
public:
enum { Alignment = AlignOf<First>::Alignment };
};
/// The base class for TrailingObjects* classes.
class TrailingObjectsBase {
protected:
@ -70,64 +91,200 @@ protected:
template <typename T> struct OverloadToken {};
};
// Internally used to indicate that the user didn't supply this value,
// so the explicit-specialization for fewer args will be used.
class NoTrailingTypeArg {};
/// This helper template works-around MSVC 2013's lack of useful
/// alignas() support. The argument to LLVM_ALIGNAS(), in MSVC, is
/// required to be a literal integer. But, you *can* use template
/// specialization to select between a bunch of different LLVM_ALIGNAS
/// expressions...
template <int Align>
class TrailingObjectsAligner : public TrailingObjectsBase {};
template <>
class LLVM_ALIGNAS(1) TrailingObjectsAligner<1> : public TrailingObjectsBase {};
template <>
class LLVM_ALIGNAS(2) TrailingObjectsAligner<2> : public TrailingObjectsBase {};
template <>
class LLVM_ALIGNAS(4) TrailingObjectsAligner<4> : public TrailingObjectsBase {};
template <>
class LLVM_ALIGNAS(8) TrailingObjectsAligner<8> : public TrailingObjectsBase {};
template <>
class LLVM_ALIGNAS(16) TrailingObjectsAligner<16> : public TrailingObjectsBase {
};
template <>
class LLVM_ALIGNAS(32) TrailingObjectsAligner<32> : public TrailingObjectsBase {
};
// TODO: Consider using a single variadic implementation instead of
// multiple copies of the TrailingObjects template? [but, variadic
// template recursive implementations are annoying...]
// Just a little helper for transforming a type pack into the same
// number of a different type. e.g.:
// ExtractSecondType<Foo..., int>::type
template <typename Ty1, typename Ty2> struct ExtractSecondType {
typedef Ty2 type;
};
// TrailingObjectsImpl is somewhat complicated, because it is a
// recursively inheriting template, in order to handle the template
// varargs. Each level of inheritance picks off a single trailing type
// then recurses on the rest. The "Align", "BaseTy", and
// "TopTrailingObj" arguments are passed through unchanged through the
// recursion. "PrevTy" is, at each level, the type handled by the
// level right above it.
template <int Align, typename BaseTy, typename TopTrailingObj, typename PrevTy,
typename... MoreTys>
struct TrailingObjectsImpl {
// The main template definition is never used -- the two
// specializations cover all possibilities.
};
template <int Align, typename BaseTy, typename TopTrailingObj, typename PrevTy,
typename NextTy, typename... MoreTys>
struct TrailingObjectsImpl<Align, BaseTy, TopTrailingObj, PrevTy, NextTy,
MoreTys...>
: public TrailingObjectsImpl<Align, BaseTy, TopTrailingObj, NextTy,
MoreTys...> {
typedef TrailingObjectsImpl<Align, BaseTy, TopTrailingObj, NextTy, MoreTys...>
ParentType;
// Ensure the methods we inherit are not hidden.
using ParentType::getTrailingObjectsImpl;
using ParentType::additionalSizeToAllocImpl;
static void verifyTrailingObjectsAssertions() {
static_assert(llvm::AlignOf<PrevTy>::Alignment >=
llvm::AlignOf<NextTy>::Alignment,
"A trailing object requires more alignment than the previous "
"trailing object provides");
ParentType::verifyTrailingObjectsAssertions();
}
// These two functions are helper functions for
// TrailingObjects::getTrailingObjects. They recurse to the left --
// the result for each type in the list of trailing types depends on
// the result of calling the function on the type to the
// left. However, the function for the type to the left is
// implemented by a *subclass* of this class, so we invoke it via
// the TopTrailingObj, which is, via the
// curiously-recurring-template-pattern, the most-derived type in
// this recursion, and thus, contains all the overloads.
static const NextTy *
getTrailingObjectsImpl(const BaseTy *Obj,
TrailingObjectsBase::OverloadToken<NextTy>) {
return reinterpret_cast<const NextTy *>(
TopTrailingObj::getTrailingObjectsImpl(
Obj, TrailingObjectsBase::OverloadToken<PrevTy>()) +
TopTrailingObj::callNumTrailingObjects(
Obj, TrailingObjectsBase::OverloadToken<PrevTy>()));
}
static NextTy *
getTrailingObjectsImpl(BaseTy *Obj,
TrailingObjectsBase::OverloadToken<NextTy>) {
return reinterpret_cast<NextTy *>(
TopTrailingObj::getTrailingObjectsImpl(
Obj, TrailingObjectsBase::OverloadToken<PrevTy>()) +
TopTrailingObj::callNumTrailingObjects(
Obj, TrailingObjectsBase::OverloadToken<PrevTy>()));
}
// Helper function for TrailingObjects::additionalSizeToAlloc: this
// function recurses to superclasses, each of which requires one
// fewer size_t argument, and adds its own size.
static LLVM_CONSTEXPR size_t additionalSizeToAllocImpl(
size_t Count1,
typename ExtractSecondType<MoreTys, size_t>::type... MoreCounts) {
return sizeof(NextTy) * Count1 + additionalSizeToAllocImpl(MoreCounts...);
}
};
// The base case of the TrailingObjectsImpl inheritance recursion,
// when there's no more trailing types.
template <int Align, typename BaseTy, typename TopTrailingObj, typename PrevTy>
struct TrailingObjectsImpl<Align, BaseTy, TopTrailingObj, PrevTy>
: public TrailingObjectsAligner<Align> {
// This is a dummy method, only here so the "using" doesn't fail --
// it will never be called, because this function recurses backwards
// up the inheritance chain to subclasses.
static void getTrailingObjectsImpl();
static LLVM_CONSTEXPR size_t additionalSizeToAllocImpl() { return 0; }
static void verifyTrailingObjectsAssertions() {}
};
} // end namespace trailing_objects_internal
// Finally, the main type defined in this file, the one intended for users...
/// See the file comment for details on the usage of the
/// TrailingObjects type.
template <typename BaseTy, typename... TrailingTys>
class TrailingObjects : private trailing_objects_internal::TrailingObjectsImpl<
trailing_objects_internal::AlignmentCalcHelper<
TrailingTys...>::Alignment,
BaseTy, TrailingObjects<BaseTy, TrailingTys...>,
BaseTy, TrailingTys...> {
template <int A, typename B, typename T, typename P, typename... M>
friend struct trailing_objects_internal::TrailingObjectsImpl;
template <typename... Tys> class Foo {};
typedef trailing_objects_internal::TrailingObjectsImpl<
trailing_objects_internal::AlignmentCalcHelper<TrailingTys...>::Alignment,
BaseTy, TrailingObjects<BaseTy, TrailingTys...>, BaseTy, TrailingTys...>
ParentType;
using TrailingObjectsBase = trailing_objects_internal::TrailingObjectsBase;
using ParentType::getTrailingObjectsImpl;
/// This is the two-type version of the TrailingObjects template; see
/// file docstring for details.
template <typename BaseTy, typename TrailingTy1,
typename TrailingTy2 = NoTrailingTypeArg>
class TrailingObjects : public TrailingObjectsBase {
private:
// Contains static_assert statements for the alignment of the
// types. Must not be at class-level, because BaseTy isn't complete
// at class instantiation time, but will be by the time this
// function is instantiated.
// function is instantiated. Recurses through the superclasses.
static void verifyTrailingObjectsAssertions() {
static_assert(llvm::AlignOf<BaseTy>::Alignment >=
llvm::AlignOf<TrailingTy1>::Alignment,
"TrailingTy1 requires more alignment than BaseTy provides");
static_assert(
llvm::AlignOf<TrailingTy1>::Alignment >=
llvm::AlignOf<TrailingTy2>::Alignment,
"TrailingTy2 requires more alignment than TrailingTy1 provides");
#ifdef LLVM_IS_FINAL
static_assert(LLVM_IS_FINAL(BaseTy), "BaseTy must be final.");
#endif
ParentType::verifyTrailingObjectsAssertions();
}
// The next four functions are internal helpers for getTrailingObjects.
static const TrailingTy1 *getTrailingObjectsImpl(const BaseTy *Obj,
OverloadToken<TrailingTy1>) {
return reinterpret_cast<const TrailingTy1 *>(Obj + 1);
// These two methods are the base of the recursion for this method.
static const BaseTy *
getTrailingObjectsImpl(const BaseTy *Obj,
TrailingObjectsBase::OverloadToken<BaseTy>) {
return Obj;
}
static TrailingTy1 *getTrailingObjectsImpl(BaseTy *Obj,
OverloadToken<TrailingTy1>) {
return reinterpret_cast<TrailingTy1 *>(Obj + 1);
static BaseTy *
getTrailingObjectsImpl(BaseTy *Obj,
TrailingObjectsBase::OverloadToken<BaseTy>) {
return Obj;
}
static const TrailingTy2 *getTrailingObjectsImpl(const BaseTy *Obj,
OverloadToken<TrailingTy2>) {
return reinterpret_cast<const TrailingTy2 *>(
getTrailingObjectsImpl(Obj, OverloadToken<TrailingTy1>()) +
Obj->numTrailingObjects(OverloadToken<TrailingTy1>()));
// callNumTrailingObjects simply calls numTrailingObjects on the
// provided Obj -- except when the type being queried is BaseTy
// itself. There is always only one of the base object, so that case
// is handled here. (An additional benefit of indirecting through
// this function is that consumers only say "friend
// TrailingObjects", and thus, only this class itself can call the
// numTrailingObjects function.)
static size_t
callNumTrailingObjects(const BaseTy *Obj,
TrailingObjectsBase::OverloadToken<BaseTy>) {
return 1;
}
static TrailingTy2 *getTrailingObjectsImpl(BaseTy *Obj,
OverloadToken<TrailingTy2>) {
return reinterpret_cast<TrailingTy2 *>(
getTrailingObjectsImpl(Obj, OverloadToken<TrailingTy1>()) +
Obj->numTrailingObjects(OverloadToken<TrailingTy1>()));
template <typename T>
static size_t callNumTrailingObjects(const BaseTy *Obj,
TrailingObjectsBase::OverloadToken<T>) {
return Obj->numTrailingObjects(TrailingObjectsBase::OverloadToken<T>());
}
protected:
public:
// make this (privately inherited) class public.
using TrailingObjectsBase::OverloadToken;
/// Returns a pointer to the trailing object array of the given type
/// (which must be one of those specified in the class template). The
/// array may have zero or more elements in it.
@ -135,8 +292,9 @@ protected:
verifyTrailingObjectsAssertions();
// Forwards to an impl function with overloads, since member
// function templates can't be specialized.
return getTrailingObjectsImpl(static_cast<const BaseTy *>(this),
OverloadToken<T>());
return this->getTrailingObjectsImpl(
static_cast<const BaseTy *>(this),
TrailingObjectsBase::OverloadToken<T>());
}
/// Returns a pointer to the trailing object array of the given type
@ -146,8 +304,8 @@ protected:
verifyTrailingObjectsAssertions();
// Forwards to an impl function with overloads, since member
// function templates can't be specialized.
return getTrailingObjectsImpl(static_cast<BaseTy *>(this),
OverloadToken<T>());
return this->getTrailingObjectsImpl(
static_cast<BaseTy *>(this), TrailingObjectsBase::OverloadToken<T>());
}
/// Returns the size of the trailing data, if an object were
@ -156,73 +314,25 @@ protected:
/// base object. The template arguments must be the same as those
/// used in the class; they are supplied here redundantly only so
/// that it's clear what the counts are counting in callers.
template <typename Ty1, typename Ty2,
typename std::enable_if<std::is_same<Ty1, TrailingTy1>::value &&
std::is_same<Ty2, TrailingTy2>::value,
int>::type = 0>
static LLVM_CONSTEXPR size_t additionalSizeToAlloc(size_t Count1, size_t Count2) {
return sizeof(TrailingTy1) * Count1 + sizeof(TrailingTy2) * Count2;
template <typename... Tys>
static LLVM_CONSTEXPR typename std::enable_if<
std::is_same<Foo<TrailingTys...>, Foo<Tys...>>::value, size_t>::type
additionalSizeToAlloc(
typename trailing_objects_internal::ExtractSecondType<
TrailingTys, size_t>::type... Counts) {
return ParentType::additionalSizeToAllocImpl(Counts...);
}
/// Returns the total size of an object if it were allocated with the
/// given trailing object counts. This is the same as
/// additionalSizeToAlloc, except it *does* include the size of the base
/// object.
template <typename Ty1, typename Ty2>
static LLVM_CONSTEXPR size_t totalSizeToAlloc(size_t Count1, size_t Count2) {
return sizeof(BaseTy) + additionalSizeToAlloc<Ty1, Ty2>(Count1, Count2);
}
};
/// This is the one-type version of the TrailingObjects template. See
/// the two-type version for more documentation.
template <typename BaseTy, typename TrailingTy1>
class TrailingObjects<BaseTy, TrailingTy1, NoTrailingTypeArg>
: public TrailingObjectsBase {
private:
static void verifyTrailingObjectsAssertions() {
static_assert(llvm::AlignOf<BaseTy>::Alignment >=
llvm::AlignOf<TrailingTy1>::Alignment,
"TrailingTy1 requires more alignment than BaseTy provides");
#ifdef LLVM_IS_FINAL
static_assert(LLVM_IS_FINAL(BaseTy), "BaseTy must be final.");
#endif
}
static const TrailingTy1 *getTrailingObjectsImpl(const BaseTy *Obj,
OverloadToken<TrailingTy1>) {
return reinterpret_cast<const TrailingTy1 *>(Obj + 1);
}
static TrailingTy1 *getTrailingObjectsImpl(BaseTy *Obj,
OverloadToken<TrailingTy1>) {
return reinterpret_cast<TrailingTy1 *>(Obj + 1);
}
protected:
template <typename T> const T *getTrailingObjects() const {
verifyTrailingObjectsAssertions();
return getTrailingObjectsImpl(static_cast<const BaseTy *>(this),
OverloadToken<T>());
}
template <typename T> T *getTrailingObjects() {
verifyTrailingObjectsAssertions();
return getTrailingObjectsImpl(static_cast<BaseTy *>(this),
OverloadToken<T>());
}
template <typename Ty1,
typename std::enable_if<std::is_same<Ty1, TrailingTy1>::value,
int>::type = 0>
static LLVM_CONSTEXPR size_t additionalSizeToAlloc(size_t Count1) {
return sizeof(TrailingTy1) * Count1;
}
template <typename Ty1>
static LLVM_CONSTEXPR size_t totalSizeToAlloc(size_t Count1) {
return sizeof(BaseTy) + additionalSizeToAlloc<Ty1>(Count1);
template <typename... Tys>
static LLVM_CONSTEXPR typename std::enable_if<
std::is_same<Foo<TrailingTys...>, Foo<Tys...>>::value, size_t>::type
totalSizeToAlloc(typename trailing_objects_internal::ExtractSecondType<
TrailingTys, size_t>::type... Counts) {
return sizeof(BaseTy) + ParentType::additionalSizeToAllocImpl(Counts...);
}
};

38
llvm/unittests/Support/TrailingObjectsTest.cpp
View File

@ -45,9 +45,10 @@ public:
using TrailingObjects::getTrailingObjects;
};
// Here, there are two singular optional object types appended.
// Note that it fails to compile without the alignment spec.
class LLVM_ALIGNAS(8) Class2 final : protected TrailingObjects<Class2, double, short> {
// Here, there are two singular optional object types appended. Note
// that the alignment of Class2 is automatically increased to account
// for the alignment requirements of the trailing objects.
class Class2 final : protected TrailingObjects<Class2, double, short> {
friend TrailingObjects;
bool HasShort, HasDouble;
@ -117,7 +118,9 @@ TEST(TrailingObjects, TwoArg) {
Class2 *C1 = Class2::create(4);
Class2 *C2 = Class2::create(0, 4.2);
EXPECT_EQ(sizeof(Class2), 8u); // due to alignment
EXPECT_EQ(sizeof(Class2), llvm::RoundUpToAlignment(sizeof(bool) * 2,
llvm::alignOf<double>()));
EXPECT_EQ(llvm::alignOf<Class2>(), llvm::alignOf<double>());
EXPECT_EQ((Class2::additionalSizeToAlloc<double, short>(1, 0)),
sizeof(double));
@ -144,4 +147,31 @@ TEST(TrailingObjects, TwoArg) {
delete C1;
delete C2;
}
// This test class is not trying to be a usage demo, just asserting
// that three args does actually work too (it's the same code as
// handles the second arg, so it's basically covered by the above, but
// just in case..)
class Class3 final : public TrailingObjects<Class3, double, short, bool> {
friend TrailingObjects;
size_t numTrailingObjects(OverloadToken<double>) const { return 1; }
size_t numTrailingObjects(OverloadToken<short>) const { return 1; }
};
TEST(TrailingObjects, ThreeArg) {
EXPECT_EQ((Class3::additionalSizeToAlloc<double, short, bool>(1, 1, 3)),
sizeof(double) + sizeof(short) + 3 * sizeof(bool));
EXPECT_EQ(sizeof(Class3),
llvm::RoundUpToAlignment(1, llvm::alignOf<double>()));
Class3 *C = reinterpret_cast<Class3 *>(::operator new(1000));
EXPECT_EQ(C->getTrailingObjects<double>(), reinterpret_cast<double *>(C + 1));
EXPECT_EQ(C->getTrailingObjects<short>(),
reinterpret_cast<short *>(reinterpret_cast<double *>(C + 1) + 1));
EXPECT_EQ(
C->getTrailingObjects<bool>(),
reinterpret_cast<bool *>(
reinterpret_cast<short *>(reinterpret_cast<double *>(C + 1) + 1) +
1));
}
}