[llvm-bugs] [Bug 24957] New: alignas with placement new operator generate invalid instruction with sse

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https://llvm.org/bugs/show_bug.cgi?id=24957

            Bug ID: 24957
           Summary: alignas with placement new operator generate invalid
                    instruction with sse
           Product: clang
           Version: 3.6
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: llvm at gyoo.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

When using alignas, clang will generate the mmx instruction if O1 optimization
or greater are used:
 movaps %xmm0,(%rbx)

But if the memory has been allocated with a new placement operator on a non
16-bytes alignment, it will crash with a coredump


Here a test case:

// clang -std=c++11 -lstdc++ -O0 -g align.cc            # ok
// clang -std=c++11 -lstdc++ -O1 -g align.cc            # coredump because of
MOVAPS on non-aligned 128 bits
// clang -std=c++11 -lstdc++ -O1 -mno-sse -g align.cc   # no more coredump

#include <iostream>


constexpr static int ALIGN_SIZE = 64;

class MyStruct
{
public:
    MyStruct()
    {
        std::cout << "MyStruct: " << this << " " << sizeof(*this) << std::endl
                  << "m_v1: " << &m_v1 << ", m_v2: " << &m_v2 << std::endl;
        m_v1 = 0;
        m_v2 = 0;
    }


private:
   alignas(ALIGN_SIZE) uint64_t m_v1;
   uint64_t m_v2;
};


int main()
{
    size_t offset = 1; // offset not a multiplier of 16 will crash

    char* ptr = new char[sizeof(MyStruct) + offset];
    MyStruct* myStruct = new (ptr+offset) MyStruct;

    return 0;
}

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