[Bug tree-optimization/35468] New: LHS of assignment can be folded to a constant causing ICE

[Bug tree-optimization/35468] New: LHS of assignment can be folded to a constant causing ICE

[maddox at gcc dot gnu dot org]

The following testcase causes an ICE.  It is simply gcc.dg/980502-1.c
invoked with a different set of options, in particular, -fno-tree-dce.
Also included is the output of the final ccp pass.  Notice the (dead)
assignment '88 = 1'.  It looks like 'line[8]' in an lvalue context was
incorrectly folded to an rvalue.  I believe that the RTL phases choke on
this when DCE is not allowed to eliminate it.  I produced the output
below using trunk, but the issue shows up in 4.0.3 and probably elsewhere.

--- Contents of file 980502-1.c ---

char *const f(void)
{
        char *const line = "/dev/ptyXX";
        line[8] = 1;
        return line;
}

--- Failing compilation command ---

 ../rel/bin/gcc -v -save-temps  -c -O2 -fdump-tree-ccp -fno-tree-dce 980502-1.c
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../gcc/configure --with-gmp=/home/maddox/GCCLIBS
--with-mpfr=/home/maddox/GCCLIBS --build=i686-pc-linux-gnu
--host=i686-pc-linux-gnu --target=i686-pc-linux-gnu
--prefix=/home/maddox/trunk/rel --disable-bootstrap --disable-libmudflap
--disable-libgomp --enable-checking=yes,types
Thread model: posix
gcc version 4.4.0 20080304 (experimental) (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-O2' '-fdump-tree-ccp'
'-fno-tree-dce' '-mtune=generic'
 /home/maddox/trunk/rel/libexec/gcc/i686-pc-linux-gnu/4.4.0/cc1 -E -quiet -v
980502-1.c -mtune=generic -fdump-tree-ccp -fno-tree-dce -O2 -fpch-preprocess -o
980502-1.i
ignoring nonexistent directory
"/home/maddox/trunk/rel/lib/gcc/i686-pc-linux-gnu/4.4.0/../../../../i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /home/maddox/trunk/rel/include
 /home/maddox/trunk/rel/lib/gcc/i686-pc-linux-gnu/4.4.0/include
 /home/maddox/trunk/rel/lib/gcc/i686-pc-linux-gnu/4.4.0/include-fixed
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-O2' '-fdump-tree-ccp'
'-fno-tree-dce' '-mtune=generic'
 /home/maddox/trunk/rel/libexec/gcc/i686-pc-linux-gnu/4.4.0/cc1 -fpreprocessed
980502-1.i -quiet -dumpbase 980502-1.c -mtune=generic -auxbase 980502-1 -O2
-version -fdump-tree-ccp -fno-tree-dce -o 980502-1.s
GNU C (GCC) version 4.4.0 20080304 (experimental) (i686-pc-linux-gnu)
        compiled by GNU C version 4.0.3 (Ubuntu 4.0.3-1ubuntu5), GMP version
4.2.1, MPFR version 2.2.1.
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: b487bd365f366d1cb315758fb9e38dc9
980502-1.c: In function 'f':
980502-1.c:7: internal compiler error: in simplify_subreg, at
simplify-rtx.c:4936
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.

--- Contents of dump file 980502-1.c.056t.ccp2 ---

;; Function f (f)

f ()
{
<bb 2>:
  88 = 1;
  return &"/dev/ptyXX"[0];

}


-- 
           Summary: LHS of assignment can be folded to a constant causing
                    ICE
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: maddox 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=35468

[Bug tree-optimization/35468] LHS of assignment can be folded to a constant causing ICE

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2008-03-05 15:27 -------
This is done by several passes through the magics of fold_stmt_r:

    case ARRAY_REF:
      /* If we are not processing expressions found within an
         ADDR_EXPR, then we can fold constant array references.  */
      if (!*inside_addr_expr_p)
        t = fold_read_from_constant_string (expr);
      else
        t = NULL;
      break;

we should remember if we are visiting the LHS of an expression here.


-- 

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         |2008-03-05 15:27:56
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] LHS of assignment can be folded to a constant causing ICE

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2008-03-05 15:28 -------
Of course the testcase invokes undefined behavior at runtime.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code, wrong-
                   |                            |code


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] LHS of assignment can be folded to a constant causing ICE

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2008-03-06 10:10 -------
Actually, CCP propagates the invariant address in

  D.1547_2 = &"/dev/ptyXX"[8];
  *D.1547_2 ={v} 1;

which we cannot undo easily, so we indeed should fold the stmt to a
trap representation.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] LHS of assignment can be folded to a constant causing ICE

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2008-03-06 10:34 -------
Created an attachment (id=15268)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15268&action=view)
patch

Like with this patch.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] LHS of assignment can be folded to a constant causing ICE

[rguenth at gcc dot gnu dot org]

------- Comment #5 from rguenth at gcc dot gnu dot org  2008-03-06 10:35 -------
(later)


-- 

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
   Last reconfirmed|2008-03-05 15:27:56         |2008-03-06 10:35:49
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] LHS of assignment can be folded to a constant causing ICE

[pinskia at gcc dot gnu dot org]

------- Comment #6 from pinskia at gcc dot gnu dot org  2008-08-11 01:01 -------
*** Bug 36532 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |matti dot niemenmaa+gccbugs
                   |                            |at iki dot fi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] LHS of assignment can be folded to a constant causing ICE

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2008-08-11 01:02 -------
This happens with the short testcase which does not need -fno-tree-dce and it
only needs -O0:
int main() {
        *"c" = 'x';
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] [4.2/4.3/4.4 Regression] LHS of assignment can be folded to a constant causing ICE

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
      Known to fail|                            |4.2.0 4.3.0 4.4.0
      Known to work|                            |4.1.0 4.0.1
            Summary|LHS of assignment can be    |[4.2/4.3/4.4 Regression] LHS
                   |folded to a constant causing|of assignment can be folded
                   |ICE                         |to a constant causing ICE
   Target Milestone|---                         |4.2.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] [4.2/4.3/4.4 Regression] LHS of assignment can be folded to a constant causing ICE

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] [4.2/4.3/4.4 Regression] LHS of assignment can be folded to a constant causing ICE

[rguenth at gcc dot gnu dot org]

------- Comment #8 from rguenth at gcc dot gnu dot org  2008-12-08 15:06 -------
Unassigning for now.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|rguenth at gcc dot gnu dot  |unassigned at gcc dot gnu
                   |org                         |dot org
             Status|ASSIGNED                    |NEW


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] [4.2/4.3/4.4 Regression] LHS of assignment can be folded to a constant causing ICE

[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/2008-
                   |                            |12/msg00535.html
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2008-03-06 10:35:49         |2008-12-09 14:09:32
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] [4.2/4.3/4.4 Regression] LHS of assignment can be folded to a constant causing ICE

[jakub at gcc dot gnu dot org]

------- Comment #9 from jakub at gcc dot gnu dot org  2008-12-09 16:57 -------
Subject: Bug 35468

Author: jakub
Date: Tue Dec  9 16:55:35 2008
New Revision: 142598

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=142598
Log:
        PR tree-optimization/35468
        * tree-ssa-ccp.c (fold_stmt_r): Don't fold reads from constant
        string on LHS.

        * gcc.dg/pr35468.c: New test.
        * gcc.c-torture/compile/pr35468.c: New test.

Added:
    trunk/gcc/testsuite/gcc.c-torture/compile/pr35468.c
    trunk/gcc/testsuite/gcc.dg/pr35468.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-ccp.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] [4.2/4.3 Regression] LHS of assignment can be folded to a constant causing ICE

[jakub at gcc dot gnu dot org]

------- Comment #10 from jakub at gcc dot gnu dot org  2008-12-09 17:09 -------
Fixed on the trunk.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|4.2.0 4.3.0 4.4.0           |4.2.0 4.3.0
      Known to work|4.1.0 4.0.1                 |4.1.0 4.0.1 4.4.0
            Summary|[4.2/4.3/4.4 Regression] LHS|[4.2/4.3 Regression] LHS of
                   |of assignment can be folded |assignment can be folded to
                   |to a constant causing ICE   |a constant causing ICE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] [4.3 Regression] LHS of assignment can be folded to a constant causing ICE

[jsm28 at gcc dot gnu dot org]

------- Comment #11 from jsm28 at gcc dot gnu dot org  2009-03-31 20:48 -------
Closing 4.2 branch.


-- 

jsm28 at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[4.2/4.3 Regression] LHS of |[4.3 Regression] LHS of
                   |assignment can be folded to |assignment can be folded to
                   |a constant causing ICE      |a constant causing ICE
   Target Milestone|4.2.5                       |4.3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] [4.3 Regression] LHS of assignment can be folded to a constant causing ICE

[rguenth at gcc dot gnu dot org]

------- Comment #12 from rguenth at gcc dot gnu dot org  2009-08-04 12:28 -------
GCC 4.3.4 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.4                       |4.3.5


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468

[Bug tree-optimization/35468] [4.3 Regression] LHS of assignment can be folded to a constant causing ICE

[rguenth at gcc dot gnu dot org]

------- Comment #13 from rguenth at gcc dot gnu dot org  2010-05-22 18:12 -------
GCC 4.3.5 is being released, adjusting target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.3.5                       |4.3.6


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35468