[Support] Replace deprecated std::aligned_union, NFCI.

[hahnjo]

All std::aligned_* are deprecated in C++23. Implement the replacement suggested in P1413R3 using alignas and std::max.

[llvmbot]

@llvm/pr-subscribers-llvm-support

Author: Jonas Hahnfeld (hahnjo)

Changes

All std::aligned_* are deprecated in C++23. Implement the replacement suggested in P1413R3 using alignas and std::max.

---

Full diff: https://github.com/llvm/llvm-project/pull/127417.diff

1 Files Affected:

• (modified) llvm/include/llvm/Support/AlignOf.h (+2-8)

diff --git a/llvm/include/llvm/Support/AlignOf.h b/llvm/include/llvm/Support/AlignOf.h
index f586d7f182aab..635bb8b101ef9 100644
--- a/llvm/include/llvm/Support/AlignOf.h
+++ b/llvm/include/llvm/Support/AlignOf.h
@@ -13,20 +13,14 @@
 #ifndef LLVM_SUPPORT_ALIGNOF_H
 #define LLVM_SUPPORT_ALIGNOF_H
 
-#include <type_traits>
+#include <algorithm>
 
 namespace llvm {
 
 /// A suitably aligned and sized character array member which can hold elements
 /// of any type.
-///
-/// This template is equivalent to std::aligned_union_t<1, ...>, but we cannot
-/// use it due to a bug in the MSVC x86 compiler:
-/// https://github.com/microsoft/STL/issues/1533
-/// Using `alignas` here works around the bug.
 template <typename T, typename... Ts> struct AlignedCharArrayUnion {
-  using AlignedUnion = std::aligned_union_t<1, T, Ts...>;
-  alignas(alignof(AlignedUnion)) char buffer[sizeof(AlignedUnion)];
+  alignas(T) alignas(Ts...) char buffer[std::max({sizeof(T), sizeof(Ts)...})];
 };
 
 } // end namespace llvm

[llvm-ci]

LLVM Buildbot has detected a new failure on builder openmp-offload-sles-build-only running on rocm-worker-hw-04-sles while building llvm at step 5 "compile-openmp".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/140/builds/17695

Here is the relevant piece of the build log for the reference

Step 5 (compile-openmp) failure: build (failure)
...
     for (const auto &[SC, _] : SuperClasses) {
                            ^
3.073 [6880/32/195] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Timer.cpp.o
3.083 [6879/32/196] Building CXX object lib/Option/CMakeFiles/LLVMOption.dir/Arg.cpp.o
3.091 [6878/32/197] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/Line.cpp.o
3.093 [6877/32/198] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/TimeProfiler.cpp.o
3.113 [6876/32/199] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/RecordName.cpp.o
3.114 [6875/32/200] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/RecordSerialization.cpp.o
3.131 [6874/32/201] Building CXX object lib/DebugInfo/CodeView/CMakeFiles/LLVMDebugInfoCodeView.dir/SimpleTypeSerializer.cpp.o
3.149 [6873/32/202] Building CXX object utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/CodeGenIntrinsics.cpp.o
FAILED: utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/CodeGenIntrinsics.cpp.o 
ccache /usr/bin/c++ -DGTEST_HAS_RTTI=0 -DLLVM_BUILD_STATIC -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Iutils/TableGen/Basic -I/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/utils/TableGen/Basic -Iinclude -I/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -fno-lifetime-dse -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wno-comment -Wno-misleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -std=c++1z -MD -MT utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/CodeGenIntrinsics.cpp.o -MF utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/CodeGenIntrinsics.cpp.o.d -o utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/CodeGenIntrinsics.cpp.o -c /home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/utils/TableGen/Basic/CodeGenIntrinsics.cpp
In file included from /home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/utils/TableGen/Basic/CodeGenIntrinsics.cpp:19:0:
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/TableGen/Record.h: In member function ‘bool llvm::Record::isSubClassOf(const llvm::Record*) const’:
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/TableGen/Record.h:1797:28: warning: unused variable ‘_’ [-Wunused-variable]
     for (const auto &[SC, _] : SuperClasses)
                            ^
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/TableGen/Record.h: In member function ‘bool llvm::Record::isSubClassOf(llvm::StringRef) const’:
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/TableGen/Record.h:1804:28: warning: unused variable ‘_’ [-Wunused-variable]
     for (const auto &[SC, _] : SuperClasses) {
                            ^
In file included from /home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/ADT/DenseMap.h:19:0,
                 from /home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/utils/TableGen/Basic/CodeGenIntrinsics.h:18,
                 from /home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/utils/TableGen/Basic/CodeGenIntrinsics.cpp:13:
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/Support/AlignOf.h: In instantiation of ‘struct llvm::AlignedCharArrayUnion<llvm::detail::DenseSetPair<llvm::StringRef> [4]>’:
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/ADT/DenseMap.h:1049:53:   required from ‘void llvm::SmallDenseMap<KeyT, ValueT, InlineBuckets, KeyInfoT, BucketT>::grow(unsigned int) [with KeyT = llvm::StringRef; ValueT = llvm::detail::DenseSetEmpty; unsigned int InlineBuckets = 4; KeyInfoT = llvm::DenseMapInfo<llvm::StringRef, void>; BucketT = llvm::detail::DenseSetPair<llvm::StringRef>]’
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/ADT/DenseMap.h:536:33:   required from ‘void llvm::DenseMapBase<DerivedT, KeyT, ValueT, KeyInfoT, BucketT>::grow(unsigned int) [with DerivedT = llvm::SmallDenseMap<llvm::StringRef, llvm::detail::DenseSetEmpty, 4, llvm::DenseMapInfo<llvm::StringRef, void>, llvm::detail::DenseSetPair<llvm::StringRef> >; KeyT = llvm::StringRef; ValueT = llvm::detail::DenseSetEmpty; KeyInfoT = llvm::DenseMapInfo<llvm::StringRef, void>; BucketT = llvm::detail::DenseSetPair<llvm::StringRef>]’
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/ADT/DenseMap.h:576:13:   required from ‘BucketT* llvm::DenseMapBase<DerivedT, KeyT, ValueT, KeyInfoT, BucketT>::InsertIntoBucketImpl(const LookupKeyT&, BucketT*) [with LookupKeyT = llvm::StringRef; DerivedT = llvm::SmallDenseMap<llvm::StringRef, llvm::detail::DenseSetEmpty, 4, llvm::DenseMapInfo<llvm::StringRef, void>, llvm::detail::DenseSetPair<llvm::StringRef> >; KeyT = llvm::StringRef; ValueT = llvm::detail::DenseSetEmpty; KeyInfoT = llvm::DenseMapInfo<llvm::StringRef, void>; BucketT = llvm::detail::DenseSetPair<llvm::StringRef>]’
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/ADT/DenseMap.h:543:37:   required from ‘BucketT* llvm::DenseMapBase<DerivedT, KeyT, ValueT, KeyInfoT, BucketT>::InsertIntoBucket(BucketT*, KeyArg&&, ValueArgs&& ...) [with KeyArg = const llvm::StringRef&; ValueArgs = {llvm::detail::DenseSetEmpty&}; DerivedT = llvm::SmallDenseMap<llvm::StringRef, llvm::detail::DenseSetEmpty, 4, llvm::DenseMapInfo<llvm::StringRef, void>, llvm::detail::DenseSetPair<llvm::StringRef> >; KeyT = llvm::StringRef; ValueT = llvm::detail::DenseSetEmpty; KeyInfoT = llvm::DenseMapInfo<llvm::StringRef, void>; BucketT = llvm::detail::DenseSetPair<llvm::StringRef>]’
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/ADT/DenseMap.h:262:33:   required from ‘std::pair<llvm::DenseMapIterator<KeyT, ValueT, KeyInfoT, BucketT>, bool> llvm::DenseMapBase<DerivedT, KeyT, ValueT, KeyInfoT, BucketT>::try_emplace(const KeyT&, Ts&& ...) [with Ts = {llvm::detail::DenseSetEmpty&}; DerivedT = llvm::SmallDenseMap<llvm::StringRef, llvm::detail::DenseSetEmpty, 4, llvm::DenseMapInfo<llvm::StringRef, void>, llvm::detail::DenseSetPair<llvm::StringRef> >; KeyT = llvm::StringRef; ValueT = llvm::detail::DenseSetEmpty; KeyInfoT = llvm::DenseMapInfo<llvm::StringRef, void>; BucketT = llvm::detail::DenseSetPair<llvm::StringRef>]’
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/ADT/DenseSet.h:215:39:   required from ‘std::pair<llvm::detail::DenseSetImpl<ValueT, MapTy, ValueInfoT>::Iterator, bool> llvm::detail::DenseSetImpl<ValueT, MapTy, ValueInfoT>::insert(const ValueT&) [with ValueT = llvm::StringRef; MapTy = llvm::SmallDenseMap<llvm::StringRef, llvm::detail::DenseSetEmpty, 4, llvm::DenseMapInfo<llvm::StringRef, void>, llvm::detail::DenseSetPair<llvm::StringRef> >; ValueInfoT = llvm::DenseMapInfo<llvm::StringRef, void>]’
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/utils/TableGen/Basic/CodeGenIntrinsics.cpp:111:35:   required from here
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/Support/AlignOf.h:23:77: internal compiler error: Segmentation fault
   alignas(T) alignas(Ts...) char buffer[std::max({sizeof(T), sizeof(Ts)...})];
                                                                             ^
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://bugs.opensuse.org/> for instructions.
3.173 [6873/31/203] Building CXX object lib/Option/CMakeFiles/LLVMOption.dir/Option.cpp.o
3.184 [6873/30/204] Building CXX object utils/TableGen/Basic/CMakeFiles/obj.LLVMTableGenBasic.dir/Attributes.cpp.o
In file included from /home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/utils/TableGen/Basic/Attributes.cpp:10:0:
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/TableGen/Record.h: In member function ‘bool llvm::Record::isSubClassOf(const llvm::Record*) const’:
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/TableGen/Record.h:1797:28: warning: unused variable ‘_’ [-Wunused-variable]
     for (const auto &[SC, _] : SuperClasses)
                            ^
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/TableGen/Record.h: In member function ‘bool llvm::Record::isSubClassOf(llvm::StringRef) const’:
/home/botworker/bbot/builds/openmp-offload-sles-build/llvm.src/llvm/include/llvm/TableGen/Record.h:1804:28: warning: unused variable ‘_’ [-Wunused-variable]
     for (const auto &[SC, _] : SuperClasses) {
                            ^

[jplehr]

Hi,
Can this be fixed forward for GCC 7.5 on SLES or should we revert in the meantime?
Thanks!

[hahnjo]

@jplehr I played a bit with Compiler Explorer and it seems the problem is alignas(Ts...), I couldn't get it to work with any parameter pack. But static constexpr std::size_t Align = std::max({alignof(T), alignof(Ts)...}); seems to work (https://godbolt.org/z/Mf3hzezPa) and should be fine because it's all power-of-two's. Do you have easy access to the bot / a similar machine? If not, I can commit and we revert if it still doesn't work...

[jplehr]

I don't mind if you land and we see if it fixes the issue and we revert in case it does not.

[hahnjo]

Pushed 6a5dd04, fingers crossed 🤞

[jplehr]

Looks good. Thank you for that quick fix!