https://bugs.llvm.org/show_bug.cgi?id=41480
Bug ID: 41480
Summary: clang-cl: SIMD vector elements are unaligned in
Microsoft's std::array and std::tuple
Product: new-bugs
Version: 8.0
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: andreas.z...@ableton.com
CC: htmldevelo...@gmail.com, llvm-bugs@lists.llvm.org
As a result, code using std::array's and std::tuple's with SIMD vector elements
crashes due to unaligned memory access.
It seems that the behavior of "#pragma pack" is the underlying issue.
Microsoft's std::array and std::tuple are declared with #pragma pack(8)
(exactly "#pragma pack(push,_CRT_PACKING)"), and it seems that in clang-cl
"#pragma pack" beats alignment of SIMD types while in cl it's the other way
around.
To reproduce, compile the following example:
clang-cl -c
#include <emmintrin.h>
#include <array>
#include <tuple>
std::array<__m128, 1> arr;
static_assert(alignof(decltype(arr)) >= alignof(__m128), "unaligned array");
std::tuple<__m128> tpl;
static_assert(alignof(decltype(tpl)) >= alignof(__m128), "unaligned tuple");
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