[Bug c/19857] New: alignment check of SSE constant fails in simple test program

[Bug c/19857] New: alignment check of SSE constant fails in simple test program

[gcc-bugzilla at gcc dot gnu dot org]

When I compile a simple test program that declares an SSE constant and checks
that it is 8-byte aligned (see below), the alignment check fails in the
gcc 4.0 snapshot (it succeeds in 3.3.5).

I'm not sure whether the constant is actually misaligned or the alignment
check itself is miscompiled...changing the check slightly makes it succeed.

Environment:
System: Linux fftw.org 2.6.3-1-686-smp #2 SMP Tue Feb 24 20:29:08 EST 2004 i686 GNU/Linux
Architecture: i686

	
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ../configure --prefix=/home/stevenj/gcc4

How-To-Repeat:

Compile the following code with 'gcc -O3 -msse -o bug bug.c' and run
with './bug && echo ok' ... output *should* be "ok" (ALIGNED==true),
but is not.

(Yes, the way the alignment check is performed looks kinda weird...it
is distilled from other code (www.fftw.org), obviously...but it should
still pass for any 8-byte aligned quantity.)

Thanks for looking into this,

Steven G. Johnson


typedef float V __attribute__ ((vector_size (16)));
union fvec {
     float f[4];
     V v;
};

typedef unsigned int uintptr_t;
#define ALIGNMENT 8
#define TAINT_BIT 1
#define UNTAINT(p) ((float *) (((uintptr_t) (p)) & ~(uintptr_t)3))
#define PTRINT(p) ((uintptr_t)(p))
#define ALIGNED(p) \
  (((PTRINT(UNTAINT(p)) % ALIGNMENT) == 0) && !(PTRINT(p) & TAINT_BIT))

const union fvec foo = {{-0.0, 0.0, -0.0, 0.0}};

int main(void)
{
     return !ALIGNED(&foo);
}

-- 
           Summary: alignment check of SSE constant fails in simple test
                    program
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: stevenj at fftw dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19857

[Bug regression/19857] [4.0 Regression] alignment check of SSE constant fails in simple test program

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.0 Regression alignment   |[4.0 Regression] alignment
                   |check of SSE constant fails |check of SSE constant fails
                   |in simple test program      |in simple test program


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19857

[Bug regression/19857] [4.0 Regression alignment check of SSE constant fails in simple test program

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|critical                    |normal
          Component|c                           |regression
           Keywords|                            |wrong-code
            Summary|alignment check of SSE      |[4.0 Regression alignment
                   |constant fails in simple    |check of SSE constant fails
                   |test program                |in simple test program
   Target Milestone|---                         |4.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19857

[Bug middle-end/19857] [4.0 Regression] alignment check of SSE constant fails in simple test program

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-02-09 21:24 -------
Confirmed, here is a testcase which uses abort:
typedef float V __attribute__ ((vector_size (16)));
typedef __SIZE_TYPE__ uintptr_t;
V foo;
void abort (void);

int main(void)
{
  V *foo2 = &foo;
  if (!(((((uintptr_t)(((float *) (((uintptr_t) foo2) & ~(uintptr_t)3)))) % 8) == 0) && !(((uintptr_t)foo2) & 1)))
   abort ();
  return 0;
}





-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |19858
              nThis|                            |
             Status|UNCONFIRMED                 |NEW
          Component|regression                  |middle-end
     Ever Confirmed|                            |1
  GCC build triplet|i686-pc-linux-gnu           |
   GCC host triplet|i686-pc-linux-gnu           |
 GCC target triplet|i686-pc-linux-gnu           |
      Known to fail|                            |4.0.0
      Known to work|                            |3.3.2
   Last reconfirmed|0000-00-00 00:00:00         |2005-02-09 21:24:32
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19857

[Bug middle-end/19857] [4.0 Regression] alignment check of SSE constant fails in simple test program

[jakub at gcc dot gnu dot org]

------- Additional Comments From jakub at gcc dot gnu dot org  2005-02-10 17:21 -------
This looks like fold_truthop bug, will look at it.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2005-02-09 21:24:32         |2005-02-10 17:21:35
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19857

[Bug middle-end/19857] [4.0 Regression] alignment check of SSE constant fails in simple test program

[jakub at gcc dot gnu dot org]

------- Additional Comments From jakub at gcc dot gnu dot org  2005-02-10 18:07 -------
Actually, I see there multiple problems elsewhere.
First is on
int i;
int foo (void)
{
  return i & ~(unsigned int)3;
}
First is that
          if (change)
            return fold (build2 (BIT_AND_EXPR, type,
                                 fold_convert (type, and0),
                                 fold_convert (type, and1)));
folds (int) ((unsigned)i & ~(unsigned)3) into i & (int)~(unsigned)3 where
(int)~(unsigned)3 is -4 with TREE_OVERFLOW set.  But there is no overflow
in the original program, so we shouldn't IMHO create one as part of this
optimization.

Another problem is that
    case POINTER_TYPE:
    case REFERENCE_TYPE:
      if (integer_zerop (expr))
        expr = integer_zero_node;
      else
        expr = fold (build1 (CONVERT_EXPR,
                             lang_hooks.types.type_for_size (POINTER_SIZE, 0),
                             expr));

      return convert_to_integer (type, expr);
unconditionally converts to signed type as wide as pointer (== intptr_t) instead
of considering TYPE_UNSIGNED (type).

As the result of these 2, fold_truthop is presented with ll_mask and ll_and_mask
TREE_OVERFLOW -4 and given that gets confused into believing the whole comparison
is always 0.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19857

[Bug middle-end/19857] [4.0 Regression] alignment check of SSE constant fails in simple test program

[jakub at gcc dot gnu dot org]

------- Additional Comments From jakub at gcc dot gnu dot org  2005-02-15 11:42 -------
Patch here: <http://gcc.gnu.org/ml/gcc-patches/2005-02/msg00810.html>

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19857

[Bug middle-end/19857] [4.0 Regression] alignment check of SSE constant fails in simple test program

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2005-02-16 13:54 -------
Subject: Bug 19857

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	jakub@gcc.gnu.org	2005-02-16 13:54:31

Modified files:
	gcc            : ChangeLog convert.c fold-const.c 
	gcc/testsuite  : ChangeLog 
Added files:
	gcc/testsuite/gcc.c-torture/execute: 20050215-1.c 
	gcc/testsuite/gcc.dg/tree-ssa: 20050215-1.c 

Log message:
	PR middle-end/19857
	* fold-const.c (fold): Don't optimize (T)(x & cst) to
	(T)x & (T)cst if (T)cst overflows.
	* convert.c (convert_to_integer) <case POINTER_TYPE>: Pass
	TYPE_UNSIGNED (type) as type_for_size's UNSIGNEDP argument.
	
	* gcc.dg/tree-ssa/20050215-1.c: New test.
	* gcc.c-torture/execute/20050215-1.c: New test.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.diff?cvsroot=gcc&r1=2.7491&r2=2.7492
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/convert.c.diff?cvsroot=gcc&r1=1.54&r2=1.55
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/fold-const.c.diff?cvsroot=gcc&r1=1.512&r2=1.513
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.5039&r2=1.5040
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.c-torture/execute/20050215-1.c.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/gcc.dg/tree-ssa/20050215-1.c.diff?cvsroot=gcc&r1=NONE&r2=1.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19857

[Bug middle-end/19857] [4.0 Regression] alignment check of SSE constant fails in simple test program

[jakub at gcc dot gnu dot org]

------- Additional Comments From jakub at gcc dot gnu dot org  2005-02-16 13:58 -------
Fixed.

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19857