[Bug middle-end/32285] New: [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[Bug middle-end/32285] New: [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jakub at gcc dot gnu dot org]

extern void abort (void);

_Complex v = 3.0 + 1.0iF;

void
foo (_Complex z, int *x)
{
  if (z != v)
    abort ();
}

_Complex bar (_Complex z) __attribute__ ((pure));
_Complex
bar (_Complex z)
{
  return v;
}

int
baz (void)
{
  int a, i;
  for (i = 0; i < 6; i++)
    foo (bar (1.0iF * i), &a);
  return 0;
}

int
main ()
{
  baz ();
  return 0;
}

is miscompiled at -O1 -m32 or -O2 -m32.

This was fixed in 4.2 and on the trunk with PR25505 changes (the tree-nrv.c
change most importantly), NRV in this case is really a wrong thing to do,
as target is _Complex at virtual-outgoing-regs, but those are also used
for the call.  Furthermore GCC then incorrectly computes where the region
actually was:
(insn 26 25 27 2 (set (mem/i:DF (plus:SI (reg/f:SI 56 virtual-outgoing-args)
                (const_int 4 [0x4])) [0 S8 A32])
        (float_extend:DF (reg:SF 69))) -1 (nil)
    (nil))

(insn 27 26 28 2 (set (mem/i:DF (plus:SI (reg/f:SI 56 virtual-outgoing-args)
                (const_int 12 [0xc])) [0 S8 A32])
        (reg:DF 68)) -1 (nil)
    (nil))

(insn 28 27 29 2 (set (mem:SI (reg/f:SI 56 virtual-outgoing-args) [0 S4 A32])
        (reg/f:SI 56 virtual-outgoing-args)) -1 (nil)
    (nil))

(call_insn 29 28 30 2 (parallel [
            (call (mem:QI (symbol_ref:SI ("bar") [flags 0x3] <function_decl
0x2aaaaea20400 bar>) [0 S1 A8])
                (const_int 20 [0x14]))
            (set (reg/f:SI 7 sp)
                (plus:SI (reg/f:SI 7 sp)
                    (const_int 4 [0x4])))
        ]) -1 (nil)
    (expr_list:REG_EH_REGION (const_int 0 [0x0])
        (nil))
    (nil))

(insn 30 29 31 2 (parallel [
            (set (reg/f:SI 7 sp)
                (plus:SI (reg/f:SI 7 sp)
                    (const_int -4 [0xfffffffffffffffc])))
            (clobber (reg:CC 17 flags))
        ]) -1 (nil)
    (nil))

(insn 31 30 32 2 (set (reg:DF 70)
        (mem/c/i:DF (plus:SI (reg/f:SI 54 virtual-stack-vars)
                (const_int -32 [0xffffffffffffffe0])) [2 S8 A64])) -1 (nil)
    (nil))

(insn 32 31 33 2 (set (mem:DF (plus:SI (reg/f:SI 56 virtual-outgoing-args)
                (const_int 4 [0x4])) [0 S8 A8])
        (reg:DF 70)) -1 (nil)
    (nil))

(insn 33 32 34 2 (set (reg:DF 71)
        (mem/c/i:DF (plus:SI (reg/f:SI 54 virtual-stack-vars)
                (const_int -24 [0xffffffffffffffe8])) [2 S8 A64])) -1 (nil)
    (nil))

(insn 34 33 35 2 (set (mem:DF (plus:SI (reg/f:SI 56 virtual-outgoing-args)
                (const_int 12 [0xc])) [0 S8 A8])
        (reg:DF 71)) -1 (nil)
    (nil))

So, it stores the return value to %esp (== %ebp - 68 at that point) and
loads from %ebp - 40.


-- 
           Summary: [4.1 Regression] Miscompilation with pure _Complex
                    returning call inside another fn's argument list
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jakub at gcc dot gnu dot org
GCC target triplet: i686-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jakub at gcc dot gnu dot org]

------- Comment #1 from jakub at gcc dot gnu dot org  2007-06-11 15:43 -------
Looking at http://gcc.gnu.org/ml/gcc-patches/2006-09/msg00951.html
I'm slightly worried about backporting this to gcc-4_1-branch though.
Has that been resolved?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jconner at apple dot com]

------- Comment #2 from jconner at apple dot com  2007-06-11 16:06 -------
(In reply to comment #1)
> Looking at http://gcc.gnu.org/ml/gcc-patches/2006-09/msg00951.html
> I'm slightly worried about backporting this to gcc-4_1-branch though.
> Has that been resolved?

I recall being told that the problem was most likely the benchmarks, and that I
shouldn't worry about it.  Unfortunately, it must have been off-list, because I
can't find anything in the email archives.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2007-06-11 18:36 -------
Actually IIRC the machine's glibc was upgaded at the same time.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
           Keywords|                            |wrong-code
   Target Milestone|---                         |4.1.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jconner at apple dot com]

------- Comment #4 from jconner at apple dot com  2007-06-11 18:59 -------
Sorry, yes, reading back I wasn't being very clear.  I meant to say that the
impression I was left with was that it wasn't a result of my change, but of the
test environment, an idea which was supported by my own benchmarking results.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2007-06-12 10:05 -------
Confirmed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-06-12 10:05:44
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jakub at gcc dot gnu dot org]

------- Comment #6 from jakub at gcc dot gnu dot org  2007-06-13 15:22 -------
I see that PR25505 caused a bunch of code generation regressions.
On i?86, with -O2 -m32:
_Complex double foo (_Complex double x)
{
  return __builtin_cexp (x);
}
generated code got much worse, similarly:
elemental function specific__exp_c8 (parm)
   complex (kind=8), intent (in) :: parm
   complex (kind=8) :: specific__exp_c8
   specific__exp_c8 = exp (parm)
end function
In the above 2 cases, dest_safe_for_nrv_p is called on an SSA_NAME.  At least
in
these cases it should be safe to use SSA_NAME_VAR, shouldn't it?
A different testcase that regressed is:
struct P
{
  long long l;
  int a;
  unsigned int b;
  P(long long x) : l(x) {}
};

P foo (P);
P bar (P);

P foo (P x)
{
  P y = P (-1LL);
  y = bar (x);
  return y;
}

Here dest_safe_for_nrv_p is passed a RESULT_DECL and is again something
that ought to be optimized out, but is not any longer.

static bool
dest_safe_for_nrv_p (tree dest, location_t *loc)
{
  subvar_t subvar;

  while (handled_component_p (dest))
    dest = TREE_OPERAND (dest, 0);

  if (! SSA_VAR_P (dest))
    return false;

  if (TREE_CODE (dest) == SSA_NAME)
    dest = SSA_NAME_VAR (dest);

  if (is_call_clobbered (dest))
    return false;
  for (subvar = get_subvars_for_var (dest); subvar; subvar = subvar->next)
    if (is_call_clobbered (subvar->var))
      return false;
  return true;
}

handles all of these (i.e. doesn't regress on any of them).  I have verified
that
it e.g. refuses to NRV optimize:
struct P
{
  long long l;
  int a;
  unsigned int b;
  P(long long x) : l(x) {}
};

P foo (P);
P bar (P);
void baz (P *);

P foo (P x)
{
  P y = P (-1LL);
  baz (&y);
  y = bar (x);
  return y;
}
because the RESULT_DECL escapes.
It regresses on the initial testcase from this bugreport, so it would mean
writing a different bugfix (most probably in calls.c, check that the target
doesn't overlap with the arguments being pushed), but it might very well be
worth it.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jconner at apple dot com]

------- Comment #7 from jconner at apple dot com  2007-06-13 17:09 -------
(In reply to comment #6)
> I see that PR25505 caused a bunch of code generation regressions.
> On i?86, with -O2 -m32:
> ...

When you say regressions, I assume you mean size/performance, not correctness,
right?  If so, that's to be expected, as the previous tree-nrv implementation
was being overly permissive, and the new implementation is conservatively
pessimistic, as the comments indicate.  If I have introduced anything
incorrect, please let me know and I'd be glad to take a look.  Thanks!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jakub at gcc dot gnu dot org]

------- Comment #8 from jakub at gcc dot gnu dot org  2007-06-14 08:03 -------
Yes, I mean performance and size regressions.  But your changes to tree-nrv
never mentioned you found bugs in it and therefore are making NRV more strict,
on the contrary, PR25505 was fixing a performance/size issue where NRV was
too strict and your patch was meant to make it less strict, at least that's
what I understood from the gcc-patches thread.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
                URL|                            |http://gcc.gnu.org/ml/gcc-
                   |                            |patches/2007-
                   |                            |06/msg00973.html
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-06-12 10:05:44         |2007-06-15 08:50:04
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jakub at gcc dot gnu dot org]

------- Comment #9 from jakub at gcc dot gnu dot org  2007-06-15 11:27 -------
*** Bug 30493 has been marked as a duplicate of this bug. ***


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sam at sambromley dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jakub at gcc dot gnu dot org]

------- Comment #10 from jakub at gcc dot gnu dot org  2007-06-20 06:36 -------
Subject: Bug 32285

Author: jakub
Date: Wed Jun 20 06:35:55 2007
New Revision: 125873

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=125873
Log:
        PR middle-end/32285
        * calls.c (precompute_arguments): Also precompute CALL_EXPR arguments
        if ACCUMULATE_OUTGOING_ARGS.

        * gcc.c-torture/execute/20070614-1.c: New test.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/20070614-1.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/calls.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jakub at gcc dot gnu dot org]

------- Comment #11 from jakub at gcc dot gnu dot org  2007-06-20 06:44 -------
Subject: Bug 32285

Author: jakub
Date: Wed Jun 20 06:44:26 2007
New Revision: 125877

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=125877
Log:
        PR middle-end/32285
        * calls.c (precompute_arguments): Also precompute CALL_EXPR arguments
        if ACCUMULATE_OUTGOING_ARGS.

        * gcc.c-torture/execute/20070614-1.c: New test.

Added:
    branches/gcc-4_2-branch/gcc/testsuite/gcc.c-torture/execute/20070614-1.c
Modified:
    branches/gcc-4_2-branch/gcc/ChangeLog
    branches/gcc-4_2-branch/gcc/calls.c
    branches/gcc-4_2-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jakub at gcc dot gnu dot org]

------- Comment #12 from jakub at gcc dot gnu dot org  2007-06-20 06:50 -------
Subject: Bug 32285

Author: jakub
Date: Wed Jun 20 06:50:23 2007
New Revision: 125879

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=125879
Log:
        PR middle-end/32285
        * calls.c (precompute_arguments): Also precompute CALL_EXPR arguments
        if ACCUMULATE_OUTGOING_ARGS.

        * gcc.c-torture/execute/20070614-1.c: New test.

Added:
    branches/gcc-4_1-branch/gcc/testsuite/gcc.c-torture/execute/20070614-1.c
Modified:
    branches/gcc-4_1-branch/gcc/ChangeLog
    branches/gcc-4_1-branch/gcc/calls.c
    branches/gcc-4_1-branch/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285

[Bug middle-end/32285] [4.1 Regression] Miscompilation with pure _Complex returning call inside another fn's argument list

[jakub at gcc dot gnu dot org]

------- Comment #13 from jakub at gcc dot gnu dot org  2007-06-20 09:24 -------
Fixed in SVN, the performance regression caused by PR25550 patch is still
present though.


-- 

jakub at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32285