[Bug c++/71644] New: gcc 6.1 generates movaps for unaligned memory

[justus at gmx dot li]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71644

            Bug ID: 71644
           Summary: gcc 6.1 generates movaps for unaligned memory
           Product: gcc
           Version: 6.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: justus at gmx dot li
  Target Milestone: ---

Created attachment 38757
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38757&action=edit
code for reproduction

compiling the code below using gcc 6.1.0 (on a x86_64 linux machine) or a
current svn snapshot genereates the expected two versions of Derived::Derived.
the problem is that in both the complete object constructor and the base object
construct 'movaps' is used to write both Derived::m2 and Derived::m3 at once,
but if Derived is the base of TestBug then Derived::m2 is not 16byte aligned
anymore. this results in a segfault.

-- gcc command
g++  -save-temps -Wall -Wextra -std=c++14 -ggdb -O3 -o /tmp/testbug
/tmp/testbug.cc

-- code -- 
#include <cstdint>
struct Base  {
    alignas(16) int64_t mAligned=0;
};

struct Derived : public virtual Base {
public:
    int64_t m1;
    int64_t m2{ 1234 };
    int64_t m3{ 2345 };

  __attribute__ ((noinline)) // or put ctor into different compilation unit
    Derived(){}
};

struct TestBug : public virtual Derived {};


int main() {
    Derived derived; // good
    TestBug testbug; // crashes because of using movaps on unaligned memory
}