[Bug target/87421] New: GCC generates unaligned movdqa

[yshuiv7 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87421

            Bug ID: 87421
           Summary: GCC generates unaligned movdqa
           Product: gcc
           Version: 8.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yshuiv7 at gmail dot com
  Target Milestone: ---

C++ Test case:
struct A {
        unsigned int a1;
        long a5;
        unsigned int a6;
};
int fun(A *res);
int fun2(A *desc)
{
        A resource;
        fun(&resource);
        *desc = resource;
        return 0;
}

Target: amd64

Compiler flags:

g++ test.cc -c -O2 -fno-omit-frame-pointer -std=gnu++11

Compiles to:

0000000000000000 <_Z4fun2P1A>:
   // Assuming 16 bytes stack alignment
   0:   55                      push   %rbp              // rsp now aligns to
16 bytes + 8 bytes
   1:   48 89 e5                mov    %rsp,%rbp         // rbp also aligns to
16 + 8
   4:   53                      push   %rbx
   5:   48 89 fb                mov    %rdi,%rbx
   8:   48 8d 7d d0             lea    -0x30(%rbp),%rdi
   c:   48 83 ec 28             sub    $0x28,%rsp
  10:   64 48 8b 04 25 28 00    mov    %fs:0x28,%rax
  17:   00 00
  19:   48 89 45 e8             mov    %rax,-0x18(%rbp)
  1d:   31 c0                   xor    %eax,%eax
  1f:   e8 00 00 00 00          callq  24 <_Z4fun2P1A+0x24>
  24:   48 8b 45 e0             mov    -0x20(%rbp),%rax
  28:   66 0f 6f 45 d0          movdqa -0x30(%rbp),%xmm0 // rbp-0x30 is not
aligned to 16 bytes
  2d:   48 89 43 10             mov    %rax,0x10(%rbx)
  31:   0f 11 03                movups %xmm0,(%rbx)
  34:   48 8b 55 e8             mov    -0x18(%rbp),%rdx
  38:   64 48 33 14 25 28 00    xor    %fs:0x28,%rdx
  3f:   00 00
  41:   75 09                   jne    4c <_Z4fun2P1A+0x4c>
  43:   48 83 c4 28             add    $0x28,%rsp
  47:   31 c0                   xor    %eax,%eax
  49:   5b                      pop    %rbx
  4a:   5d                      pop    %rbp
  4b:   c3                      retq
  4c:   e8 00 00 00 00          callq  51 <_Z4fun2P1A+0x51>