[Bug rtl-optimization/49088] New: Combine fails to properly handle zero-extension and signed int constant

[Bug rtl-optimization/49088] New: Combine fails to properly handle zero-extension and signed int constant

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

           Summary: Combine fails to properly handle zero-extension and
                    signed int constant
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hjl.tools@gmail.com
                CC: ebotcazou@gcc.gnu.org


We have

(insn 5 2 7 2 (parallel [
            (set (reg/f:DI 61)
                (plus:DI (reg/f:DI 20 frame)
                    (const_int -64 [0xffffffffffffffc0])))
            (clobber (reg:CC 17 flags))
        ]) x.i:12 252 {*adddi_1}
     (expr_list:REG_UNUSED (reg:CC 17 flags)
        (nil)))
(insn 17 9 18 2 (parallel [
            (set (reg:SI 72)
                (plus:SI (subreg:SI (reg/f:DI 61) 0)
                    (const_int 6 [0x6])))
            (clobber (reg:CC 17 flags))
        ]) x.i:14 251 {*addsi_1}
     (expr_list:REG_DEAD (reg/f:DI 61)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

(insn 18 17 10 2 (set (reg:DI 73)
        (zero_extend:DI (reg:SI 72))) x.i:14 112 {*zero_extendsidi2_rex64}
     (expr_list:REG_DEAD (reg:SI 72)
        (nil)))

(insn 11 10 12 2 (set (reg:DI 68)
        (reg:DI 73)) x.i:14 62 {*movdi_internal_rex64}
     (expr_list:REG_DEAD (reg:DI 73)
        (nil)))

combine turns it into

(insn 18 17 10 2 (set (reg:DI 73) 
        (const_int 4294967238 [0xffffffc6])) x.i:14 62 {*movdi_internal_rex64}
     (nil))

(insn 11 10 12 2 (set (reg:DI 68)
        (plus:DI (reg/f:DI 20 frame)
            (reg:DI 73))) x.i:14 247 {*lea_1}
     (expr_list:REG_DEAD (reg:DI 73)
        (nil)))

"const_int -64" is signed, not unsigned.

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> 2011-05-20 17:19:26 UTC ---
We have

#10 0x0000000001121405 in simplify_and_const_int_1 (mode=DImode, 
    varop=0x7ffff0acbdf8, constop=4294967294)
    at /export/gnu/import/git/gcc-x32/gcc/combine.c:9413
9413      varop = force_to_mode (varop, mode, constop, 0);
(gdb) call debug_rtx (varop)
(subreg:DI (plus:SI (subreg:SI (reg/f:DI 20 frame) 0)
        (const_int -58 [0xffffffffffffffc6])) 0)
(gdb) p/x constop
$5 = 0xfffffffe
(gdb) p mode
$6 = DImode
(gdb) f 9
#9  0x000000000111db3a in force_to_mode (x=0x7ffff0acbdf8, mode=DImode, 
    mask=4294967294, just_select=0)
    at /export/gnu/import/git/gcc-x32/gcc/combine.c:8154
8154        return force_to_mode (SUBREG_REG (x), mode, mask, next_select);
(gdb) call debug_rtx (x)
(subreg:DI (plus:SI (subreg:SI (reg/f:DI 20 frame) 0)
        (const_int -58 [0xffffffffffffffc6])) 0)
(gdb) 

I think we need to adjust mask by sign-extend it.

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> 2011-05-20 18:27:51 UTC ---
(gdb) bt
#0  force_to_mode (x=0x7ffff0acbdf8, mode=DImode, mask=4294967294, 
    just_select=0) at /export/gnu/import/git/gcc-x32/gcc/combine.c:8154
#1  0x0000000001121405 in simplify_and_const_int_1 (mode=DImode, 
    varop=0x7ffff0acbdf8, constop=4294967294)
    at /export/gnu/import/git/gcc-x32/gcc/combine.c:9413
#2  0x00000000011216e4 in simplify_and_const_int (x=0x0, mode=DImode, 
    varop=0x7ffff0acbdf8, constop=4294967294)
    at /export/gnu/import/git/gcc-x32/gcc/combine.c:9511
#3  0x0000000001123c57 in simplify_shift_const_1 (code=LSHIFTRT, 
    result_mode=DImode, varop=0x7ffff0acbdf8, orig_count=32)
    at /export/gnu/import/git/gcc-x32/gcc/combine.c:10568
#4  0x0000000001123d45 in simplify_shift_const (x=0x0, code=LSHIFTRT, 
    result_mode=DImode, varop=0x7ffff0acbe10, count=32)
    at /export/gnu/import/git/gcc-x32/gcc/combine.c:10599
#5  0x000000000111a923 in expand_compound_operation (x=0x7ffff0c4ddb0)
    at /export/gnu/import/git/gcc-x32/gcc/combine.c:6916
(gdb) f 5
#5  0x000000000111a923 in expand_compound_operation (x=0x7ffff0c4ddb0)
    at /export/gnu/import/git/gcc-x32/gcc/combine.c:6916
6916          tem = simplify_shift_const (NULL_RTX, unsignedp ? LSHIFTRT :
ASHIFTRT,
(gdb) call debug_rtx (x)
(zero_extend:DI (plus:SI (subreg:SI (reg/f:DI 20 frame) 0)
        (const_int -58 [0xffffffffffffffc6])))
(gdb)

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

--- Comment #3 from H.J. Lu <hjl.tools at gmail dot com> 2011-05-20 19:01:14 UTC ---
This patch works:

diff --git a/gcc/combine.c b/gcc/combine.c
index 8af86f2..60c6e13 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -10184,6 +10184,7 @@ simplify_shift_const_1 (enum rtx_code code, enum
machine_mode result_mode,

         if (code == ASHIFTRT
        || (code == ROTATE && first_code == ASHIFTRT)
+       || (code == LSHIFTRT && first_code == ASHIFT)
        || GET_MODE_BITSIZE (mode) > HOST_BITS_PER_WIDE_INT
        || (GET_MODE (varop) != result_mode
            && (first_code == ASHIFTRT || first_code == LSHIFTRT

Does it make sense?

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.05.20 19:42:51
     Ever Confirmed|0                           |1

--- Comment #4 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-05-20 19:42:51 UTC ---
> combine turns it into
> 
> (insn 18 17 10 2 (set (reg:DI 73) 
>         (const_int 4294967238 [0xffffffc6])) x.i:14 62 {*movdi_internal_rex64}
>      (nil))
> 
> (insn 11 10 12 2 (set (reg:DI 68)
>         (plus:DI (reg/f:DI 20 frame)
>             (reg:DI 73))) x.i:14 247 {*lea_1}
>      (expr_list:REG_DEAD (reg:DI 73)
>         (nil)))
> 
> "const_int -64" is signed, not unsigned.

RTL constants are always sign-extended for their mode but RTL objects,
including constants, have no specific signedness, except for a few exceptions
like the SUBREG_PROMOTED_UNSIGNED_P flag.

That being said, the transformation looks indeed invalid.

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> 2011-05-20 20:12:10 UTC ---
The problem is

Breakpoint 3, force_to_mode (x=0x7ffff0acbde0, mode=DImode, mask=4294967295, 
    just_select=0) at /export/gnu/import/git/gcc-x32/gcc/combine.c:8325
8325          op1 = force_to_mode (XEXP (x, 1), mode, mask, next_select);
(gdb) call debug_rtx (x)
(plus:SI (subreg:SI (reg/f:DI 20 frame) 0)
    (const_int -58 [0xffffffffffffffc6]))
(gdb) 

      /* For most binary operations, just propagate into the operation and
         change the mode if we have an operation of that mode.  */

      op0 = force_to_mode (XEXP (x, 0), mode, mask, next_select);
      op1 = force_to_mode (XEXP (x, 1), mode, mask, next_select);

Shouldn't MASK be sign-extended to MODE here?

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

--- Comment #6 from H.J. Lu <hjl.tools at gmail dot com> 2011-05-20 20:59:43 UTC ---
Created attachment 24312
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24312
A patch

I am testing this patch.

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #24312|0                           |1
        is obsolete|                            |

--- Comment #7 from H.J. Lu <hjl.tools at gmail dot com> 2011-05-21 01:03:37 UTC ---
Created attachment 24314
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24314
A new testcase

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #24314|0                           |1
        is obsolete|                            |

--- Comment #8 from H.J. Lu <hjl.tools at gmail dot com> 2011-05-21 04:28:51 UTC ---
Created attachment 24315
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24315
An updated patch

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #24315|0                           |1
        is obsolete|                            |

--- Comment #9 from H.J. Lu <hjl.tools at gmail dot com> 2011-05-21 13:25:10 UTC ---
Created attachment 24318
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24318
A new patch

For binary operations, if X is narrower than MODE and we want all
the bits in X's mode, just use the operand when it is CONST_INT.

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

--- Comment #10 from hjl at gcc dot gnu.org <hjl at gcc dot gnu.org> 2011-05-27 13:38:45 UTC ---
Author: hjl
Date: Fri May 27 13:38:41 2011
New Revision: 174332

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=174332
Log:
Properly handle CONST_INT operands.

2011-05-21  H.J. Lu  <hongjiu.lu@intel.com>

    PR rtl-optimization/49088
    * combine.c (force_to_mode): If X is narrower than MODE and we
    want all the bits in X's mode, just use the operand when it
    is CONST_INT.

Modified:
    branches/x32/gcc/ChangeLog.x32
    branches/x32/gcc/combine.c

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

H.J. Lu <hjl.tools at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |DUPLICATE
   Target Milestone|---                         |4.7.0

--- Comment #11 from H.J. Lu <hjl.tools at gmail dot com> 2011-06-23 14:52:40 UTC ---
Dup

*** This bug has been marked as a duplicate of bug 49504 ***

[Bug rtl-optimization/49088] Combine fails to properly handle zero-extension and signed int constant

[hjl at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

--- Comment #12 from hjl at gcc dot gnu.org <hjl at gcc dot gnu.org> 2011-06-23 14:57:50 UTC ---
Author: hjl
Date: Thu Jun 23 14:57:45 2011
New Revision: 175335

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=175335
Log:
Revert the last change on force_to_mode.

2011-06-23  H.J. Lu  <hongjiu.lu@intel.com>

    PR rtl-optimization/49088
    * combine.c (force_to_mode): Revert the last change.

Modified:
    branches/x32/gcc/ChangeLog.x32
    branches/x32/gcc/combine.c