[Bug 154] New: Compiler emits invalid assembly when compiled with -O2

[via D.gnu]

http://bugzilla.gdcproject.org/show_bug.cgi?id=154

            Bug ID: 154
           Summary: Compiler emits invalid assembly when compiled with -O2
           Product: GDC
           Version: 4.9.x
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: major
          Priority: Normal
         Component: gdc
          Assignee: ibuclaw at gdcproject.org
          Reporter: maor at weka.io

Using either the (almost) latest dev GDC (commit
5434139180a410f9fc79cabe0871b3601cee167f) or gdc-4.9 on Ubuntu Linux and X86_64
I get the following problem compiling the below code:

ulong /*RAX*/ exchangeAndAdd(ulong * counter /*RSI*/, ulong addition /*RDI*/)
{
    ulong retVal = void;
    asm {"
      mov  %2, %0;
      lock;
      xadd %0, (%1);

      "
      : "=r"(retVal)
      : "r"(counter), "r"(addition)
      : "memory"; }
    return retVal;
}

int main() {
  ulong a = 10;
  ulong b = exchangeAndAdd(&a, 2);
  assert(a==12);
  assert(b==10);
  return 0;
}

when compiling with no optimizations or with -O1 all is well, the
exchangeAndAdd assembly looks like:

  4065d9:       48 89 f0                mov    %rsi,%rax
  4065dc:       f0 48 0f c1 07          lock xadd %rax,(%rdi)
  4065e1:       c3                      retq 

it's called from main and everybody is happy.

when compiling with -O2 the exchangeAndAdd function assembly is the same but it
is also inlined into main like so (invalid assembly):

  406614:       ba 02 00 00 00          mov    $0x2,%edx
  406619:       48 c7 44 24 08 0a 00    movq   $0xa,0x8(%rsp)
  406620:       00 00 
  406622:       48 8d 44 24 08          lea    0x8(%rsp),%rax
  406627:       48 89 d0                mov    %rdx,%rax
  40662a:       f0 48 0f c1 00          lock xadd %rax,(%rax)

This obviously segfaults as rax is garbaged.

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