[Bug target/16890] [cygwin/mingw32] __m128 automatic variables misaligned

["matt dot daws at cantab dot net" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From matt dot daws at cantab dot net  2004-08-18 16:04 -------
As I have an interest in this family of bugs being fixed, I thought I'd chime in
here.  Firstly, with GCC 3.4.1, I cannot replicate the bug, and the assmebly
output is slightly different.  However, the MOVAPS and MULSS instructions are
the same.  I get the same result with GCC 3.3.3 (all using -O2 -msse), and using
MinGW, of course.

Now, my understanding of the assembly is as follows: in _main, the "andl $-16,
%esp" will align the stack to 16-bytes.  We then call __alloca and ___main,
which for the moment I'll assume do not mess with the stack.  Then we call _foo
which pushes 4 bytes to the stack.  Then, in _foo, we push %ebp, so 8 bytes are
now on the stack, and then set %ebp=%esp.  Thus %ebp+8 is aligned to a 16-byte
boundary.  This makes sense, as then the MOVAPS and MULSS instructions ARE aligned.

I don't see why your test case crashes then.  My only thought is that ___main
and __alloca somehow DO mess with the stack: this might explain how the binary
you produce dies and mine doesn't.

Can anyone confirm or correct my analysis?  Danny: I take it you are using gcc
3.5.0?

Thanks, --Matt Daws

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary| [cygwin/mingw32] __m128    |[cygwin/mingw32] __m128
                   |automatic variables         |automatic variables
                   |misaligned                  |misaligned


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16890