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Add utility for strictly applying EBO on MSVC #90

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Merged
saki7 merged 1 commit into from
Sep 19, 2026
Merged

Add utility for strictly applying EBO on MSVC #90

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66 changes: 57 additions & 9 deletions include/iris/config.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,27 @@

#include <version>

#if defined(_MSC_VER) && \
!defined(__clang__) && \
!defined(__INTEL_COMPILER) && !defined(__INTEL_LLVM_COMPILER)
# define IRIS_COMPILER_STRICTLY_MSVC 1
#else
# define IRIS_COMPILER_STRICTLY_MSVC 0
#endif

#if defined(_MSC_VER) && defined(__clang__)
# define IRIS_COMPILER_CLANG_CL 1
#else
# define IRIS_COMPILER_CLANG_CL 0
#endif

#if defined(_MSC_VER) && defined(__INTELLISENSE__)
# define IRIS_MSVC_INTELLISENSE 1
#else
# define IRIS_MSVC_INTELLISENSE 0
#endif


#if _MSC_VER
# include <CppCoreCheck/warnings.h>
# pragma warning(default: CPPCORECHECK_LIFETIME_WARNINGS)
Expand All @@ -18,26 +39,53 @@
# error "Too old MSVC version; we don't support this because it leads to ODR violation regarding the existence of [[(msvc::)no_unique_address]]"
#endif

#if _MSC_VER && __INTELLISENSE__ // Memory Layout view shows wrong layout without this workaround
#if IRIS_MSVC_INTELLISENSE // Memory Layout view shows wrong layout without this workaround
# define IRIS_NO_UNIQUE_ADDRESS [[msvc::no_unique_address, no_unique_address]]

#elif _MSC_VER // normal MSVC
#elif IRIS_COMPILER_STRICTLY_MSVC
# define IRIS_NO_UNIQUE_ADDRESS [[msvc::no_unique_address]]

#else // other compilers
#elif defined(_MSC_VER)
# if __has_cpp_attribute(msvc::no_unique_address)
# define IRIS_NO_UNIQUE_ADDRESS [[msvc::no_unique_address]]
# else
# define IRIS_NO_UNIQUE_ADDRESS [[no_unique_address]]
# endif

#else
# define IRIS_NO_UNIQUE_ADDRESS [[no_unique_address]]
#endif

#ifndef IRIS_LIFETIMEBOUND
# ifdef __clang__
# define IRIS_LIFETIMEBOUND [[clang::lifetimebound]]
# elifdef _MSC_VER
# define IRIS_LIFETIMEBOUND [[msvc::lifetimebound]]

#if IRIS_COMPILER_STRICTLY_MSVC
# define IRIS_EBO __declspec(empty_bases)

#elif IRIS_COMPILER_CLANG_CL
# if __has_declspec_attribute(empty_bases)
# define IRIS_EBO __declspec(empty_bases)
# else
# define IRIS_LIFETIMEBOUND
# define IRIS_EBO
# endif

#else
# define IRIS_EBO
#endif


#if IRIS_MSVC_INTELLISENSE
# define IRIS_LIFETIMEBOUND [[msvc::lifetimebound]]

#elif __has_cpp_attribute(clang::lifetimebound)
# define IRIS_LIFETIMEBOUND [[clang::lifetimebound]]

#elif __has_cpp_attribute(msvc::lifetimebound)
# define IRIS_LIFETIMEBOUND [[msvc::lifetimebound]]

#else
# define IRIS_LIFETIMEBOUND
#endif


#if __cpp_consteval >= 202211L
# define IRIS_CONSTEXPR_UP constexpr
#else
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43 changes: 43 additions & 0 deletions test/core.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,49 @@

namespace unit_test {

TEST_CASE("EBO")
{
// https://learn.microsoft.com/en-us/cpp/cpp/empty-bases

struct Empty1 {};
STATIC_CHECK(sizeof(Empty1) == 1);

struct Struct1 { char c; };
STATIC_CHECK(sizeof(Struct1) == 1);

struct Derived1 : Empty1 { char c; };
STATIC_CHECK(sizeof(Derived1) == 1);

struct Empty2 : Empty1 {};
struct Derived2 : Empty2 { char c; };
STATIC_CHECK(sizeof(Derived2) == 1);

struct Empty3 {};
struct Derived3 : Empty2, Empty3 { char c; };
struct Derived4 : Empty2, Empty3 { std::int32_t i; };
struct Struct2 : Struct1, Empty1 {};
STATIC_CHECK(sizeof(Struct2) == 1);

#if !IRIS_COMPILER_STRICTLY_MSVC
STATIC_CHECK(sizeof(Derived3) == 1);
STATIC_CHECK(sizeof(Derived4) == 4);
#endif

struct IRIS_EBO Derived3_fixed : Empty2, Empty3 { char c; };
STATIC_CHECK(sizeof(Derived3_fixed) == 1);

struct IRIS_EBO Derived4_fixed : Empty2, Empty3 { std::int32_t i; };
STATIC_CHECK(sizeof(Derived4_fixed) == 4);

struct IRIS_EBO Derived5 : Derived4 {};
#if !IRIS_COMPILER_STRICTLY_MSVC
STATIC_CHECK(sizeof(Derived5) == 4);
#endif

struct Derived5_fixed : Derived4_fixed {};
STATIC_CHECK(sizeof(Derived5_fixed) == 4);
}

TEST_CASE("pack_indexing")
{
STATIC_REQUIRE(std::is_same_v<iris::pack_indexing_t<0, int>, int>);
Expand Down
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