[Bug c/28727] New: Wrong code generated (assignment incorrectly optimized out)

[Bug c/28727] New: Wrong code generated (assignment incorrectly optimized out)

[qrczak at knm dot org dot pl]

The attached module, when compiled with -O2, has wrong code generated for the
last set_global_field call. The assembly shows:

        leal    4(%edx), %eax
        cmpl    marked_limit, %eax
        movl    BadArguments, %ecx
        movl    $record_12420+4, (%edx)
        movl    %eax, marked_top
        jbe     .L28
        movl    %ecx, record_12420+4
        call    gc
.L28:
        leave
        xorl    %eax, %eax
        ret

while the assignment of BadArguments (from %ecx) to record_12420+4 should be
performed unconditionally, as can be easily deduced from the source.

This is gcc-4.2.0-0.20060806r115974. The bug doesn't manifest without -O2 or
when the number of set_global_field calls is reduced.


-- 
           Summary: Wrong code generated (assignment incorrectly optimized
                    out)
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: qrczak at knm dot org dot pl
 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=28727

[Bug c/28727] Wrong code generated (assignment incorrectly optimized out)

[qrczak at knm dot org dot pl]

------- Comment #1 from qrczak at knm dot org dot pl  2006-08-14 19:00 -------
Created an attachment (id=12075)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12075&action=view)
Test case


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28727

[Bug middle-end/28727] Wrong code generated (assignment incorrectly optimized out)

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2006-08-14 19:10 -------
Most likely related to PR 28003.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |28003
           Keywords|                            |alias


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28727

[Bug middle-end/28727] Wrong code generated (assignment incorrectly optimized out)

[qrczak at knm dot org dot pl]

------- Comment #3 from qrczak at knm dot org dot pl  2006-08-26 19:15 -------
The problem seems to be caused by illegal type punning. Rewriting the code to
avoid pointer casts cures the bug, and -fno-strict-aliasing cures it too, so
gcc is probably correct.

Thanks to Michael Veksler for pointing this out.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28727

[Bug middle-end/28727] Wrong code generated (assignment incorrectly optimized out)

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2006-08-26 20:46 -------


*** This bug has been marked as a duplicate of 21920 ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28727