[Bug middle-end/33088] New: [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[Bug middle-end/33088] New: [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[jsm28 at gcc dot gnu dot org]

Since RTH's patch <http://gcc.gnu.org/ml/gcc-patches/2005-06/msg00860.html>,
stores to the real or imaginary part of a complex variable are represented
using a load of the other part and a COMPLEX_EXPR.

If the variable is not yet initialized, and the load of the other part does not
get optimized away, this can yield spurious floating-point exceptions (in
particular, loading a signaling NaN on the x87 raises the "invalid" exception).
 This can happen with -ffloat-store (I don't have any proof that this is
restricted to -ffloat-store, but haven't observed the problem without this
option).

I observed the problem originally as a failure of glibc's test-double, which is
built with -ffloat-store and forms complex values by setting the real and
imaginary parts separately.  The following testcase reproduces it on
i686-pc-linux-gnu, with trunk (-ffloat-store together with any of -O1 -O2 -O3
-Os), 4.2 branch (same options), 4.1 branch (-float-store -O1), but not for 4.0
(which predates the above mentioned patch) with any of those options.  An
equivalent x86-specific test could of course be written without use of
<fenv.h>.

#include <fenv.h>
#include <stdlib.h>

volatile int x[1024];

void __attribute__((noinline))
fill_stack (void)
{
  volatile int y[1024];
  int i;
  for (i = 0; i < 1024; i++)
    y[i] = 0x7ff00000;
  for (i = 0; i < 1024; i++)
    x[i] = y[i];
}

volatile _Complex double vc;

void __attribute__((noinline))
use_complex (_Complex double c)
{
  vc = c;
}

double t0, t1, t2, t3;

#define USE_COMPLEX(X, R, C) \
  do { __real__ X = R; __imag__ X = C; use_complex (X); } while (0)

void __attribute__((noinline))
use_stack (void)
{
  _Complex double a, b, c, d;
  USE_COMPLEX (a, t0, t1);
  USE_COMPLEX (b, t1, t2);
  USE_COMPLEX (c, t2, t3);
  USE_COMPLEX (d, t3, t0);
}

int
main (void)
{
  fill_stack ();
  feclearexcept (FE_INVALID);
  use_stack ();
  if (fetestexcept (FE_INVALID))
    abort ();
  exit (0);
}


-- 
           Summary: [4.1/4.2/4.3 Regression] spurious exceptions with -
                    ffloat-store
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jsm28 at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-08-17 09:27 -------
For one, I don't think " __real__ X = R; __imag__ X = C; " is really nice
looking.  Now if the person did:
 *(double*) &X = R; ((double*) & X)[1] = C; 

it might be a different story but then again X is still defined piece wise so
you will still get NaN.

I really don't think this is a bug as we have an uninitialized variables here
in the same way doing:
short a;
a = b&0xff|a;
a = (b<<8)&0xFF00|a;

Would be defined code.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[joseph at codesourcery dot com]

------- Comment #2 from joseph at codesourcery dot com  2007-08-17 10:37 -------
Subject: Re:  [4.1/4.2/4.3 Regression] spurious exceptions
 with -ffloat-store

On Fri, 17 Aug 2007, pinskia at gcc dot gnu dot org wrote:

> For one, I don't think " __real__ X = R; __imag__ X = C; " is really nice
> looking.  Now if the person did:
>  *(double*) &X = R; ((double*) & X)[1] = C; 
> 
> it might be a different story but then again X is still defined piece wise so
> you will still get NaN.

I think setting parts is cleaner than using casts like that, and safer 
(because of not involving arithmetic that GCC's liable to get wrong in 
cases involving -0) than R + C * I.

> I really don't think this is a bug as we have an uninitialized variables here
> in the same way doing:
> short a;
> a = b&0xff|a;
> a = (b<<8)&0xFF00|a;
> 
> Would be defined code.

I think setting the parts is valid GNU C (ISO C doesn't have the __real__ 
and __imag__ operators), and should be considered much like initializing a 
struct by parts, where it would definitely be incorrect to generate an 
exception from an uninitialized part.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[jsm28 at gcc dot gnu dot org]

-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.1.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[mmitchel at gcc dot gnu dot org]

------- Comment #3 from mmitchel at gcc dot gnu dot org  2007-09-28 03:59 -------
I think Joseph's code is valid.  All he's doing is initializing various parts
of complex numbers and then using them.  If using a fully initialized value
results in a floating-point exception, that's a bug.


-- 

mmitchel at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2007-11-15 15:53 -------
I cannot reproduce this problem with any of 4.1, 4.2 or 4.3.  But the issues
raised look related the CCP problem in PR34099.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[jakub at gcc dot gnu dot org]

------- Comment #5 from jakub at gcc dot gnu dot org  2007-11-16 14:50 -------
/usr/src/gcc/obj35/gcc/xgcc -B /usr/src/gcc/obj35/gcc/ -v 2>&1 | tail -n 1;
/usr/src/gcc/obj35/gcc/xgcc -B /usr/src/gcc/obj35/gcc/ -m32 -O2 -ffloat-store
-o pr33088{,.c} -lm; ./pr33088; echo $?
gcc version 4.3.0 20071115 (experimental) (GCC) 
Aborted
134

And I doubt any CCP changes would have anything to do with this.  The problem
is that the hole complex number is one gimple register and if either __real__
and
__imag__ setting isn't close enough to each other, or if -ffloat-store is used,
then this means GCC reads the unitialized value from memory using floating
point load and if there is a signalling NaN on the stack, already the load
signals.
And fill_stack fills the stack with 0x7ff000007ff00000, which is IEEE double
signalling NaN.

At -O0 this testcase doesn't trigger the abort, because the moves are done
using integer registers rather than FPU.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[joseph at codesourcery dot com]

------- Comment #6 from joseph at codesourcery dot com  2007-11-16 16:53 -------
Subject: Re:  [4.1/4.2/4.3 Regression] spurious exceptions
 with -ffloat-store

The failure still appears with a compiler from revision 130227, after the 
patch for PR 34099 was committed.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[ebotcazou at gcc dot gnu dot org]

------- Comment #8 from ebotcazou at gcc dot gnu dot org  2007-12-02 10:13 -------
Investigating.


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |ebotcazou at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-12-02 10:13:05         |2007-12-02 10:13:20
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[ebotcazou at gcc dot gnu dot org]

------- Comment #7 from ebotcazou at gcc dot gnu dot org  2007-12-02 10:13 -------
By Jakub.


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-12-02 10:13:05
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2007-12-03 11:13 -------
*** Bug 34321 has been marked as a duplicate of this bug. ***


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ismail at pardus dot org dot
                   |                            |tr


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[ismail at pardus dot org dot tr]

------- Comment #10 from ismail at pardus dot org dot tr  2007-12-03 11:17 -------
This breaks glibc 2.7 regression tests.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[ebotcazou at gcc dot gnu dot org]

------- Comment #11 from ebotcazou at gcc dot gnu dot org  2007-12-05 10:12 -------
We could probably get away with a kludge for -ffloat-store and optimization,
but currently the flag comes into play only very late (in TER) and I think
it's better to keep this.

So I think the approach to solving this is two-pronged:
- at -O0, do not promote the partial stores to total stores in the gimplifier,
- at -O1 or above, insert dummy initializations for "uninitialized" SSA names,
  this should be cleaned up at the RTL level (if -ffloat-store is not passed).


Andrew, IIRC you extended DECL_COMPLEX_GIMPLE_REG_P to DECL_GIMPLE_REG_P, can
vectors be affected by the same issue?


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[pinskia at gcc dot gnu dot org]

------- Comment #12 from pinskia at gcc dot gnu dot org  2007-12-05 10:44 -------
(In reply to comment #11)
> Andrew, IIRC you extended DECL_COMPLEX_GIMPLE_REG_P to DECL_GIMPLE_REG_P, can
> vectors be affected by the same issue?

No because vector types are not effected by -ffloat-store and there is no magic
in initializing vector piece wise as far as I know unless the vector type is
memory (as only BIT_FIELD_REF is optimized for the first element so far).

Thanks,
Andrew Pinski


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2/4.3 Regression] spurious exceptions with -ffloat-store

[ebotcazou at gcc dot gnu dot org]

------- Comment #13 from ebotcazou at gcc dot gnu dot org  2007-12-13 21:49 -------
Subject: Bug 33088

Author: ebotcazou
Date: Thu Dec 13 21:49:09 2007
New Revision: 130917

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=130917
Log:
        PR middle-end/33088
        * gimplify.c (gimplify_modify_expr_complex_part): Add note to comment.
        * tree-complex.c (init_dont_simulate_again): Return true if there are
        uninitialized loads generated by gimplify_modify_expr_complex_part.
        * tree-gimple.c (is_gimple_reg_type): Return false for complex types
        if not optimizing.
        * tree-ssa.c (ssa_undefined_value_p): New predicate extracted from...
        (warn_uninit): ...here.  Use ssa_undefined_value_p.
        * tree-ssa-pre.c (is_undefined_value): Delete.
        (phi_translate_1): Use ssa_undefined_value_p.
        (add_to_exp_gen): Likewise.
        (make_values_for_stmt): Likewise.
        * tree-flow.h (ssa_undefined_value_p): Declare.


Added:
    trunk/gcc/testsuite/gcc.dg/complex-5.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/gimplify.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/uninit-13.c
    trunk/gcc/tree-complex.c
    trunk/gcc/tree-flow.h
    trunk/gcc/tree-gimple.c
    trunk/gcc/tree-ssa-pre.c
    trunk/gcc/tree-ssa.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2 regression] spurious exceptions with -ffloat-store

[ebotcazou at gcc dot gnu dot org]

------- Comment #14 from ebotcazou at gcc dot gnu dot org  2007-12-13 21:53 -------
Fixed on the mainline.  Not sure what to do for the branches, the fix is not
totally trivial.


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot gnu dot
                   |                            |org
         AssignedTo|ebotcazou at gcc dot gnu dot|unassigned at gcc dot gnu
                   |org                         |dot org
             Status|ASSIGNED                    |NEW
            Summary|[4.1/4.2/4.3 Regression]    |[4.1/4.2 regression]
                   |spurious exceptions with -  |spurious exceptions with -
                   |ffloat-store                |ffloat-store


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2 regression] spurious exceptions with -ffloat-store

[pinskia at gcc dot gnu dot org]

------- Comment #15 from pinskia at gcc dot gnu dot org  2008-03-13 17:00 -------
I think this patch causes invalid gimple to show up at -O0 .  With my patches
to detect invalid gimple shows that there are a lot of failures with complex
and -O0.  Did the definition of what is valid gimple for complex at -O0 change?


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.1.3                       |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.1/4.2 regression] spurious exceptions with -ffloat-store

[rguenther at suse dot de]

------- Comment #16 from rguenther at suse dot de  2008-03-13 17:02 -------
Subject: Re:  [4.1/4.2 regression] spurious exceptions
 with -ffloat-store

On Thu, 13 Mar 2008, pinskia at gcc dot gnu dot org wrote:

> ------- Comment #15 from pinskia at gcc dot gnu dot org  2008-03-13 17:00 -------
> I think this patch causes invalid gimple to show up at -O0 .  With my patches
> to detect invalid gimple shows that there are a lot of failures with complex
> and -O0.  Did the definition of what is valid gimple for complex at -O0 change?

No.  I also recognized that we still set DECL_IS_GIMPLE_REG but
is_gimple_reg says it is not.

We should go into SSA for -O0 as well and fix this for real.

Richard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.2 Regression] spurious exceptions with -ffloat-store

[rguenth at gcc dot gnu dot org]

------- Comment #17 from rguenth at gcc dot gnu dot org  2008-03-14 17:00 -------
WONTFIX on the 4.1 branch.  Downgrading severity for the 4.2 regression.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
      Known to fail|                            |4.1.3 4.2.3
      Known to work|                            |4.3.0
           Priority|P1                          |P2
            Summary|[4.1/4.2 regression]        |[4.2 Regression] spurious
                   |spurious exceptions with -  |exceptions with -ffloat-
                   |ffloat-store                |store


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.2 Regression] spurious exceptions with -ffloat-store

[jsm28 at gcc dot gnu dot org]

------- Comment #18 from jsm28 at gcc dot gnu dot org  2008-03-15 00:41 -------
Update milestone after 4.3.0 release.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.0                       |4.3.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.2 Regression] spurious exceptions with -ffloat-store

[jsm28 at gcc dot gnu dot org]

-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.1                       |4.2.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.2 Regression] spurious exceptions with -ffloat-store

[jsm28 at gcc dot gnu dot org]

------- Comment #19 from jsm28 at gcc dot gnu dot org  2008-05-19 20:23 -------
4.2.4 is being released, changing milestones to 4.2.5.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.2.4                       |4.2.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088

[Bug middle-end/33088] [4.2 Regression] spurious exceptions with -ffloat-store

[jsm28 at gcc dot gnu dot org]

------- Comment #20 from jsm28 at gcc dot gnu dot org  2009-03-30 22:15 -------
Closing 4.2 branch, fixed in 4.3.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
      Known to fail|4.1.3 4.2.3                 |4.1.3 4.2.3 4.2.5
         Resolution|                            |FIXED
   Target Milestone|4.2.5                       |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33088