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From: "rcopley at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/54412] New: Request for 32-byte stack alignment with -mavx on Windows
Date: Thu, 30 Aug 2012 01:10:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54412

             Bug #: 54412
           Summary: Request for 32-byte stack alignment with -mavx on
                    Windows
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: rcopley@gmail.com


Created attachment 28103
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28103
Self-contained C source, with AVX alignment bug on Windows

Code generated by GCC 4.7.1 for the Windows x86_64-w64-mingw32 target, with
"-mavx", can segfault due to alignment errors when the 32-byte ymm registers
are spilled onto the stack. May I please submit a feature request for 32-byte
stack alignment on this target where necessary?

Compiled for Windows with "gcc -O0 -m64 -mavx bug.c" using GCC 4.7.1 with the
MingGW W64 toolchain, the attached program segfaults. Specifically, it uses
vmovapd to copy the value of %ymm0 to a location on the stack before calling
f(), but doesn't align the location to 32 bytes as required by that
instruction. In contrast, the generated code for Linux (using GCC 4.6.3 from
Ubuntu) does explicitly align the stack to 32 bytes.

The lack of stack alignment on Windows has been noted before; see for
example http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001 and
http://stackoverflow.com/questions/5983389.