[libc-commits] [libc] [libc] Fix warnings emitted by GCC (PR #98751)

[via libc-commits]

overmighty wrote:

Remaining warnings when compiling with GCC 14.1.1 on x86-64:

```
In file included from /home/overmighty/projects/llvm-project/libc/test/UnitTest/Test.h:37,
                 from /home/overmighty/projects/llvm-project/libc/test/src/__support/CPP/type_traits_test.cpp:11:
/home/overmighty/projects/llvm-project/libc/test/src/__support/CPP/type_traits_test.cpp: In member function ‘virtual void __llvm_libc_19_0_0_git::cpp::LlvmLibcTypeTraitsTest_aligned_storage::Run()’:
/home/overmighty/projects/llvm-project/libc/test/src/__support/CPP/type_traits_test.cpp:122:13: warning: ISO C++ does not allow ‘alignof’ with a non-type [-Wpedantic]
  122 |   EXPECT_EQ(alignof(buf), alignof(S));
      |             ^~~~~~~
/home/overmighty/projects/llvm-project/libc/test/UnitTest/LibcTest.h:406:7: note: in definition of macro ‘LIBC_TEST_SCAFFOLDING_’
  406 |   if (TEST)                                                                    \
      |       ^~~~
/home/overmighty/projects/llvm-project/libc/test/UnitTest/LibcTest.h:420:29: note: in expansion of macro ‘LIBC_TEST_BINOP_’
  420 | #define EXPECT_EQ(LHS, RHS) LIBC_TEST_BINOP_(EQ, LHS, RHS, )
      |                             ^~~~~~~~~~~~~~~~
/home/overmighty/projects/llvm-project/libc/test/src/__support/CPP/type_traits_test.cpp:122:3: note: in expansion of macro ‘EXPECT_EQ’
  122 |   EXPECT_EQ(alignof(buf), alignof(S));
      |   ^~~~~~~~~
```

```
/home/overmighty/projects/llvm-project/libc/test/src/string/memory_utils/op_tests.cpp:198:26: warning: ignoring attributes on template argument ‘__m128i’ [-Wignored-attributes]
  198 |     generic::Bcmp<__m128i>,
      |                          ^
/home/overmighty/projects/llvm-project/libc/test/src/string/memory_utils/op_tests.cpp:201:26: warning: ignoring attributes on template argument ‘__m256i’ [-Wignored-attributes]
  201 |     generic::Bcmp<__m256i>,
      |                          ^
/home/overmighty/projects/llvm-project/libc/test/src/string/memory_utils/op_tests.cpp:281:28: warning: ignoring attributes on template argument ‘__m128i’ [-Wignored-attributes]
  281 |     generic::Memcmp<__m128i>, //
      |                            ^
/home/overmighty/projects/llvm-project/libc/test/src/string/memory_utils/op_tests.cpp:284:28: warning: ignoring attributes on template argument ‘__m256i’ [-Wignored-attributes]
  284 |     generic::Memcmp<__m256i>, //
      |                            ^
```

The attributes ignored seem to be `__aligned__(16)` and `__aligned__(32)`.

Notes without warnings:

```
In file included from /home/overmighty/projects/llvm-project/libc/src/stdio/printf_core/printf_main.cpp:15:
/home/overmighty/projects/llvm-project/libc/src/stdio/printf_core/parser.h: In instantiation of ‘__llvm_libc_19_0_0_git::cpp::optional<T> __llvm_libc_19_0_0_git::printf_core::Parser<ArgProvider>::get_arg_value(size_t) [with T = long double; ArgProvider = __llvm_libc_19_0_0_git::internal::ArgList; size_t = long unsigned int]’:
/home/overmighty/projects/llvm-project/libc/src/stdio/printf_core/parser.h:236:11:   required from ‘__llvm_libc_19_0_0_git::printf_core::FormatSection __llvm_libc_19_0_0_git::printf_core::Parser<ArgProvider>::get_next_section() [with ArgProvider = __llvm_libc_19_0_0_git::internal::ArgList]’
   52 |     auto temp = get_arg_value<arg_type>(index);                                \
      |                 ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
/home/overmighty/projects/llvm-project/libc/src/stdio/printf_core/printf_main.cpp:27:59:   required from here
   27 |   for (FormatSection cur_section = parser.get_next_section();
      |                                    ~~~~~~~~~~~~~~~~~~~~~~~^~
/home/overmighty/projects/llvm-project/libc/src/stdio/printf_core/parser.h:415:51: note: the ABI of passing union with ‘long double’ has changed in GCC 4.4
  415 |   template <class T> LIBC_INLINE cpp::optional<T> get_arg_value(size_t index) {
      |                                                   ^~~~~~~~~~~~~
```


https://github.com/llvm/llvm-project/pull/98751