[Bug middle-end/65090] New: GCC produces instruction with bad alignment on SPARC when using -O

[Bug middle-end/65090] New: GCC produces instruction with bad alignment on SPARC when using -O

[dirk.bonne@inform-ac.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65090

            Bug ID: 65090
           Summary: GCC produces instruction with bad alignment on SPARC
                    when using -O
           Product: gcc
           Version: 4.7.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dirk.bonne@inform-ac.com

Created attachment 34789
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34789&action=edit
Complete source code

$ uname -a
SunOS uxs450 5.10 Generic_150400-17 sun4v sparc sun4v Solaris
$ g++-4.7 -v
Using built-in specs.
COLLECT_GCC=g++-4.7
COLLECT_LTO_WRAPPER=/opt/its/runtime/gcc/4.7/libexec/gcc/sparc-sun-solaris2.10/4.7.4/lto-wrapper
Target: sparc-sun-solaris2.10
Configured with:
/SSD/compile/toolsexternal/packages/gcc-4.7/work/gcc-4.7.4/configure
--prefix=/opt/its/runtime/gcc/4.7 --program-suffix=-4.7
--enable-languages=c,c++ --disable-multilib --disable-nls
--enable-threads=posix --enable-__cxa_atexit --enable-libstdcxx-debug
--with-gnu-as --with-gnu-ld
Thread model: posix
gcc version 4.7.4 (GCC) 

I got it down to two small files (see attachment). Reproduce it like this:

$ g++-4.7 -O -std=gnu++11 -c t.cc 
$ g++-4.7 -O -std=gnu++11 -c t2.cc 
$ g++-4.7 -O -std=gnu++11 -c t.cc 
$ g++-4.7 -O -std=gnu++11 -c t2.cc 
$ g++-4.7 -o t t.o t2.o
$ ./t 
Bus Error (core dumped)

The code generated for "somefunction" is broken:
00010a68 <_Z12somefunctionv>:
   10a68:       9d e3 bf 80     save  %sp, -128, %sp
   10a6c:       c0 27 bf e4     clr  [ %fp + -28 ]
   10a70:       c0 27 bf e8     clr  [ %fp + -24 ]
   10a74:       c0 27 bf ec     clr  [ %fp + -20 ]
   10a78:       c0 27 bf f0     clr  [ %fp + -16 ]
   10a7c:       c0 27 bf fb     clr  [ %fp + -5 ]
   ...

"%fp - 5" is not 4 bytes aligned and causes the bus error.

The function somefunction is in t.cc (attached), the relevant part is:
  struct X {
    size_t a = 0;
    std::vector<X*> vec_;

    X() {
      vec_.emplace_back(nullptr);
    }
  };
  void somefunction()
  {
    X cv;
    f2(string());
  }

[Bug middle-end/65090] GCC produces instruction with bad alignment on SPARC when using -O

[mikpelinux at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65090

--- Comment #1 from Mikael Pettersson <mikpelinux at gmail dot com> ---
I can reproduce the wrong-code with g++ 4.7.4 on sparc64-linux, but g++ 4.8.4
and 5 (current trunk) work.

[Bug middle-end/65090] GCC produces instruction with bad alignment on SPARC when using -O

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65090

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
4.7.x is no longer supported, so if that is the case, there is nothing to do.

[Bug middle-end/65090] GCC produces instruction with bad alignment on SPARC when using -O

[dirk.bonne@inform-ac.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65090

--- Comment #3 from Dirk Bonne <dirk.bonne@inform-ac.com> ---
The bug is elusive --- I then hope it is really gone from later versions and
not just hidden...

[Bug c++/65090] GCC produces instruction with bad alignment on SPARC when using -O

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65090

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-02-24
                 CC|                            |ebotcazou at gcc dot gnu.org
          Component|middle-end                  |c++
     Ever confirmed|0                           |1

--- Comment #4 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
4.9.x also works, but this nevertheless looks like a latent C++ bug to me:

  <<< Unknown tree: nullptr_type >>> D.29238;

  D.29238 = 0;

yields with mainline:

(insn 10 9 11 2 (set (mem/c:SI (plus:SI (reg/f:SI 104 virtual-stack-vars)
                (const_int -4 [0xfffffffffffffffc])) [0 D.29314+0 S4 A32])
        (const_int 0 [0])) t.cc:10 -1
     (nil))

But 32-bit alignment is forced by expand_one_stack_var_at, before it's 8-bit:

 <var_decl 0x7ffff583e870 D.29314
    type <nullptr_type 0x7ffff6e1bd20 decltype(nullptr) public unsigned type_6
SI
        size <integer_cst 0x7ffff6d0af00 constant 32>
        unit size <integer_cst 0x7ffff6d0af18 constant 4>
        align 8 symtab 0 alias set -1 canonical type 0x7ffff6e1bd20
        pointer_to_this <pointer_type 0x7ffff5f677e0> reference_to_this
<reference_type 0x7ffff5f675e8>>
    addressable used unsigned ignored SI file t.cc line 10 col 30 size
<integer_cst 0x7ffff6d0af00 32> unit size <integer_cst 0x7ffff6d0af18 4>
    align 8 context <function_decl 0x7ffff5f57870 __comp_ctor > abstract_origin
<var_decl 0x7ffff5f68090 D.25687>>

In other words giving SImode to NULLPTR_TYPE with only 8-bit alignment is a bit
dubious on strict-alignment platforms like SPARC.

[Bug c++/65090] GCC produces instruction with bad alignment on SPARC when using -O

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65090
Bug 65090 depends on bug 65945, which changed state.

Bug 65945 Summary: C++ alignment of nullptr_t is 1 and might cause unaligned stores to the frame
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65945

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

[Bug c++/65090] GCC produces instruction with bad alignment on SPARC when using -O

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65090

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |jason at gcc dot gnu.org
         Resolution|---                         |DUPLICATE
   Target Milestone|---                         |5.2

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed by the patch for 65945.

*** This bug has been marked as a duplicate of bug 65945 ***