[llvm] r256054 - Rewrite the TrailingObjects template to provide two new features:
James Y Knight via llvm-commits
llvm-commits at lists.llvm.org
Fri Dec 18 14:54:37 PST 2015
Author: jyknight
Date: Fri Dec 18 16:54:37 2015
New Revision: 256054
URL: http://llvm.org/viewvc/llvm-project?rev=256054&view=rev
Log:
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
Modified:
llvm/trunk/include/llvm/Support/TrailingObjects.h
llvm/trunk/unittests/Support/TrailingObjectsTest.cpp
Modified: llvm/trunk/include/llvm/Support/TrailingObjects.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/TrailingObjects.h?rev=256054&r1=256053&r2=256054&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/TrailingObjects.h (original)
+++ llvm/trunk/include/llvm/Support/TrailingObjects.h Fri Dec 18 16:54:37 2015
@@ -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 {};
-
-// TODO: Consider using a single variadic implementation instead of
-// multiple copies of the TrailingObjects template? [but, variadic
-// template recursive implementations are annoying...]
-
-/// 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:
+/// 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 {
+};
+
+// 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;
+
// 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...);
}
};
Modified: llvm/trunk/unittests/Support/TrailingObjectsTest.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/TrailingObjectsTest.cpp?rev=256054&r1=256053&r2=256054&view=diff
==============================================================================
--- llvm/trunk/unittests/Support/TrailingObjectsTest.cpp (original)
+++ llvm/trunk/unittests/Support/TrailingObjectsTest.cpp Fri Dec 18 16:54:37 2015
@@ -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));
+}
}
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