[Bug optimization/12792] New: {u,}int64_t variables are incorrectly reported as used uninitialized

[Bug optimization/12792] New: {u,}int64_t variables are incorrectly reported as used uninitialized

[chris at pin dot lu]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12792

           Summary: {u,}int64_t variables are incorrectly reported as used
                    uninitialized
           Product: gcc
           Version: 3.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: chris at pin dot lu
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i386-unknown-netbsdelf
  GCC host triplet: m68k--netbsdelf
GCC target triplet: m68k--netbsdelf

long long int and long long unsigned int variables trigger the following 
warning even though the variables are initialized:
longlongint.c: In function `main':
longlongint.c:7: warning: `blkno' might be used uninitialized in this function

reduced test case:
---- cut here ----
# 1 "longlongint.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "longlongint.c"

int printf (const char * __restrict, ...);

int
main(int argc, char **argv)
{
  long long int blkno;
  long long int t5;

  t5 = 1;

  blkno = t5 * t5;

  printf("%lld\n", blkno);

  return 0;
}
---- cut here ----
compilation command:
> cc -O1 -Wall longlongint.c -c                                                
longlongint.c: In function `main':
longlongint.c:7: warning: `blkno' might be used uninitialized in this function

There's no warning at -O0, there's a warning at Os, O1 and above.

[Bug optimization/12792] {u,}int64_t variables are incorrectly reported as used uninitialized

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12792


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic

[Bug optimization/12792] {u,}int64_t variables are incorrectly reported as used uninitialized

[mycroft at netbsd dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12792



------- Additional Comments From mycroft at netbsd dot org  2003-10-28 20:52 -------
Created an attachment (id=5014)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=5014&action=view)
proposed fix

The problem is thus:

* The {u,}mulsidi3 generate two parallel sets which modify the upper and lower
halves of the target register.

* life_analysis() does not track subregister modifications -- if you don't
modify the whole register with a single set, it considers the register
unused.

The simple, if klugy, solution to this is to stick an explicit clobber in.  It
seems to work.

While doing this, I noticed that constant folding was not happening for
32x32->64 multiplies.  This is because the parallel set generated by
{u,}mulsidi3 cannot be folded at all.  To solve this, I first expand to a
normal multiply, and then use a define_insn_and_split to convert it to the
parallel set after CSE and constant folding.

[Bug optimization/12792] {u,}int64_t variables are incorrectly reported as used uninitialized

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12792


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2003-10-30 05:04:33
               date|                            |


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-10-30 05:04 -------
The proper fix is to teach life_analysis about the two halves.

[Bug optimization/12792] {u,}int64_t variables are incorrectly reported as used uninitialized

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-11-20 08:01 -------
*** Bug 13136 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sami dot kantoluoto at
                   |                            |embedtronics dot fi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12792

[Bug optimization/12792] {u,}int64_t variables are incorrectly reported as used uninitialized

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-02-09 02:27 -------
Suspending as this is fixed on the tree-ssa by looking at the tree level instead of the rtl 
where all problems like this can occur.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |minor
             Status|NEW                         |SUSPENDED
   Target Milestone|---                         |tree-ssa


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12792

[Bug tree-optimization/12792] {u,}int64_t variables are incorrectly reported as used uninitialized

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-05-13 11:34 -------
Fixed for 3.5.0 by the merge of the tree-ssa.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|SUSPENDED                   |RESOLVED
          Component|rtl-optimization            |tree-optimization
         Resolution|                            |FIXED
   Target Milestone|tree-ssa                    |3.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12792