[Bug c/27136] New: Compile failure with -O -ffast-math

[Bug c/27136] New: Compile failure with -O -ffast-math

[trt at acm dot org]

This program, compiled -O -ffast-math, seems to consume infinite stack space

    /* -O -ffast-math */
    void foo()
    {
      double x;

      for (x = 2; x < 10; x *= x)
        ;
    }


-- 
           Summary: Compile failure with -O -ffast-math
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: trt at acm dot org
  GCC host triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1/4.2 Regression] Compile failure with -O -ffast-math

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-04-13 01:37 -------
Confirmed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|c                           |middle-end
     Ever Confirmed|0                           |1
           Keywords|                            |ice-on-valid-code
      Known to fail|                            |4.0.0 4.1.0 4.2.0
      Known to work|                            |3.4.0
   Last reconfirmed|0000-00-00 00:00:00         |2006-04-13 01:37:35
               date|                            |
            Summary|Compile failure with -O -   |[4.0/4.1/4.2 Regression]
                   |ffast-math                  |Compile failure with -O -
                   |                            |ffast-math
   Target Milestone|---                         |4.0.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1/4.2 Regression] Compile failure with -O -ffast-math

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2006-04-17 10:34 -------

#5  0x081a8738 in get_val_for (x=0xb7dedea0, base=0xb7d70480)
    at /space/rguenther/src/svn/gcc-4_1-branch/gcc/tree-ssa-loop-niter.c:1254
1254          val = fold (TREE_OPERAND (stmt, 1));
(gdb) call debug_generic_expr(stmt)
xD.1278_3 = __builtin_pow (4.0e+0, 2.0e+0)

which we don't evaluate at compile-time.  So loop_niter_by_eval builds
(gdb) call debug_generic_expr(expr)
__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow
(__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow
(__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow
(__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow
(__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow
(__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow
(__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow (__builtin_pow
(__builtin_pow ......

on which we punt at some point.  Now, we definitely should fold 4.0**2.0 at
compile time, too.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org, rakdver at gcc dot gnu
                   |                            |dot org
           Keywords|                            |missed-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1/4.2 Regression] Compile failure with -O -ffast-math

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2006-04-17 10:51 -------
Hmm, looks more like a tree sharing problem

Breakpoint 5, fold_ternary (code=CALL_EXPR, type=0xb7d5fa6c, op0=0xb7d55540,
    op1=0xb7dd9048, op2=0x0)
    at /space/rguenther/src/svn/gcc-4_1-branch/gcc/fold-const.c:9945
9945      tree arg0 = NULL_TREE, arg1 = NULL_TREE;
(gdb) call debug_tree(op1)
 <tree_list 0xb7dd9048
    value <call_expr 0xb7dd1028
        type <real_type 0xb7d5fa6c double sizes-gimplified DF
            size <integer_cst 0xb7d50540 constant invariant 64>
            unit size <integer_cst 0xb7d50558 constant invariant 8>
            align 64 symtab 0 alias set -1 precision 64
            pointer_to_this <pointer_type 0xb7d5fb80>>
        nothrow
        arg 0 <addr_expr 0xb7d55240 type <pointer_type 0xb7dcf3f4>
            readonly constant invariant arg 0 <function_decl 0xb7d80d80
__builtin_pow>>
        arg 1 <tree_list 0xb7dd67e0 value <call_expr 0xb7dd1028>
            chain <tree_list 0xb7dd67c8
                value <real_cst 0xb7dd6798 type <real_type 0xb7d5fa6c double>
                    constant invariant 2.0e+0>>>
        t.c:5>
    chain <tree_list 0xb7dd9030
        value <real_cst 0xb7dd9000 type <real_type 0xb7d5fa6c double>
            constant invariant 3.2e+1>>>

we are self-referencing and so built up an infinite chain of pow (pow (..., 2)


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|missed-optimization         |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1/4.2 Regression] Compile failure with -O -ffast-math

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2006-04-17 11:12 -------
1329            aval[j] = get_val_for (op[j], val[j]);
(gdb) call debug_generic_expr(val[0])
__builtin_pow (xD.1278_4, 2.0e+0)
(gdb) call debug_generic_expr(op[0])
xD.1278_3

Program received signal SIGSEGV, Segmentation fault.
0x08316db6 in operand_equal_p (arg0=0xb7dc0798, arg1=0xb7c556c0, flags=0)
    at /space/rguenther/src/svn/gcc-4_1-branch/gcc/fold-const.c:2423
2423      if (TYPE_UNSIGNED (TREE_TYPE (arg0)) != TYPE_UNSIGNED (TREE_TYPE
(arg1)))

I think the brute-force evaluation should stop as soon as val[i] is no longer
a constant.

get_val_for (x=0xb7d3aea0, base=0xb7d39028)
    at /space/rguenther/src/svn/gcc-4_1-branch/gcc/tree-ssa-loop-niter.c:1242

1246      if (TREE_CODE (stmt) == PHI_NODE)
(gdb) call debug_generic_expr(stmt)
xD.1278_3 = __builtin_pow (xD.1278_4, 2.0e+0)
(gdb) call debug_generic_expr(x)
xD.1278_3
(gdb) call debug_generic_expr(base)
__builtin_pow (xD.1278_4, 2.0e+0)

now, stmt is the same as the stmt of the first use.

get_val_for (x=0xb7d40104, base=0xb7d39028)
    at /space/rguenther/src/svn/gcc-4_1-branch/gcc/tree-ssa-loop-niter.c:1242
1242      if (!x)
(gdb) finish
Value returned is $11 = (union tree_node *) 0xb7d39028
(gdb) call debug_generic_expr($11)
__builtin_pow (xD.1278_4, 2.0e+0)
1253          SET_USE (op, val);

kaboom.  We just created a self-referencing tree here.  Now, either punt on
non-constant/SSA_NAME val, or unshare val, or punt earlier.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1/4.2 Regression] Compile failure with -O -ffast-math

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2006-04-17 11:18 -------
Now, the comment before get_val_for is confusing, as it says

   * if BASE is NULL_TREE, X must be a constant and we return X.

but we do

  if (!x)
    return base;

now, I believe a

  gcc_assert (is_gimple_min_invariant (base));

before this statement is what needs to hold.  So the caller needs to be fixed.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1/4.2 Regression] Compile failure with -O -ffast-math

[patchapp at dberlin dot org]

------- Comment #6 from patchapp at dberlin dot org  2006-04-17 13:10 -------
Subject: Bug number PR 27136

A patch for this bug has been added to the patch tracker.
The mailing list url for the patch is
http://gcc.gnu.org/ml/gcc-patches/2006-04/msg00623.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1/4.2 Regression] Compile failure with -O -ffast-math

[rguenth at gcc dot gnu dot org]

------- Comment #7 from rguenth at gcc dot gnu dot org  2006-05-07 13:07 -------
Subject: Bug 27136

Author: rguenth
Date: Sun May  7 13:07:22 2006
New Revision: 113601

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=113601
Log:
2006-05-07  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/27136
        * tree-ssa-loop-niter.c (get_val_for): Correct function
        comment, assert requirements.
        (loop_niter_by_eval): Stop processing if the iterated
        value did not simplify.

        * gcc.dg/torture/pr27136.c: New testcase.

Added:
    trunk/gcc/testsuite/gcc.dg/torture/pr27136.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-loop-niter.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1 Regression] Compile failure with -O -ffast-math

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2006-05-07 13:13 -------
Fixed on the mainline.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
      Known to fail|4.0.0 4.1.0 4.2.0           |4.0.0 4.1.0
      Known to work|3.4.0                       |3.4.0 4.2.0
   Last reconfirmed|2006-04-13 01:37:35         |2006-05-07 13:13:02
               date|                            |
            Summary|[4.0/4.1/4.2 Regression]    |[4.0/4.1 Regression] Compile
                   |Compile failure with -O -   |failure with -O -ffast-math
                   |ffast-math                  |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1 Regression] Compile failure with -O -ffast-math

[rguenth at gcc dot gnu dot org]

------- Comment #9 from rguenth at gcc dot gnu dot org  2006-05-09 15:56 -------
Subject: Bug 27136

Author: rguenth
Date: Tue May  9 15:56:12 2006
New Revision: 113656

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=113656
Log:
2006-05-09  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/27136
        * tree-ssa-loop-niter.c (get_val_for): Correct function
        comment, assert requirements.
        (loop_niter_by_eval): Stop processing if the iterated
        value did not simplify.

        * gcc.dg/torture/pr27136.c: New testcase.

Added:
    branches/gcc-4_1-branch/gcc/testsuite/gcc.dg/torture/pr27136.c
      - copied unchanged from r113601,
trunk/gcc/testsuite/gcc.dg/torture/pr27136.c
Modified:
    branches/gcc-4_1-branch/gcc/ChangeLog
    branches/gcc-4_1-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_1-branch/gcc/tree-ssa-loop-niter.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1 Regression] Compile failure with -O -ffast-math

[rguenth at gcc dot gnu dot org]

------- Comment #11 from rguenth at gcc dot gnu dot org  2006-05-09 16:02 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136

[Bug middle-end/27136] [4.0/4.1 Regression] Compile failure with -O -ffast-math

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2006-05-09 16:02 -------
Subject: Bug 27136

Author: rguenth
Date: Tue May  9 16:01:53 2006
New Revision: 113657

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=113657
Log:
2006-05-09  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/27136
        * tree-ssa-loop-niter.c (get_val_for): Correct function
        comment, assert requirements.
        (loop_niter_by_eval): Stop processing if the iterated
        value did not simplify.

        * gcc.dg/torture/pr27136.c: New testcase.

Added:
    branches/gcc-4_0-branch/gcc/testsuite/gcc.dg/torture/pr27136.c
      - copied unchanged from r113601,
trunk/gcc/testsuite/gcc.dg/torture/pr27136.c
Modified:
    branches/gcc-4_0-branch/gcc/ChangeLog
    branches/gcc-4_0-branch/gcc/testsuite/ChangeLog
    branches/gcc-4_0-branch/gcc/tree-ssa-loop-niter.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27136