https://bugs.llvm.org/show_bug.cgi?id=45420
Bug ID: 45420
Summary: clang-cl incorrectly interprets /Zp8 flag
Product: clang
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: C++
Assignee: unassignedclangb...@nondot.org
Reporter: an...@gaijin.team
CC: blitzrak...@gmail.com, dgre...@apple.com,
erik.pilking...@gmail.com, llvm-bugs@lists.llvm.org,
richard-l...@metafoo.co.uk
According to documentation,
https://docs.microsoft.com/en-us/cpp/build/reference/zp-struct-member-alignment?view=vs-2019
Visual studio interprets /Zp8 as a way to pack structure members, but it
doesn't not change alignment of such struct itself.
clang-cl interprets it similar to -fpack-struct=8, and so /Zp8 flag is working
significantly differently in msvc and clang-cl.
According to documentation WindowsSDK headers has to be compiled with /Zp8
flag, and so it can cause (and is causing in some projects) issues with using
clang-cl as replacement for msvc.
the following sample:
```
#include <emmintrin.h>
struct A{__m128 a[1];};
static_assert(alignof(A) == 16, "should be aligned");
```
won't compile with /Zp8 flag with clang-cl, but it will in msvc.
Run-time sample:
https://godbolt.org/z/qh7Dbg
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