[Bug tree-optimization/30159] New: [4.3 Regression] gcc.c-torture/execute/20010422-1.c is miscompiled on sh-elf and mips-elf

[Bug tree-optimization/30159] New: [4.3 Regression] gcc.c-torture/execute/20010422-1.c is miscompiled on sh-elf and mips-elf

[kkojima at gcc dot gnu dot org]

On sh-elf, the function foo in 20010422-1.c

unsigned int foo(unsigned int x)
{
  if (x < 5)
    x = 4;
  else
    x = 8;
  return x;
}

is compiled to

foo:
        mov.l   r14,@-r15
        mov     r15,r14
        mov     #4,r1
        cmp/hi  r1,r1
        bf/s    .L6
        mov     #4,r0
        mov     #8,r0
.L6:
        mov     r14,r15
        mov.l   @r15+,r14
        rts
        nop

with -O1.  Thus the first parameter register r4 is ignored.
For mips-elf, foo is assembled to

foo:
        .frame  $sp,0,$31               # vars= 0, regs= 0/0, args= 0, gp= 0
        .mask   0x00000000,0
        .fmask  0x00000000,0
        .set    noreorder
        .set    nomacro

        sltu    $2,$2,5
        beq     $2,$0,$L2
        nop
        ...

with -O1 where $4 should be register for x.
It started after the patch

r119711 | amacleod | 2006-12-11 06:25:40 +0900 (Mon, 11 Dec 2006) | 103 lines

and the first tree dump which differs before and after this patch
is .099t.optimized:

[r119710 .099t.optimized]
;; Function foo (foo)

Analyzing Edge Insertions.
foo (x)
{
  unsigned int x.24;

<bb 2>:
  if (x <= 4) goto <L5>; else goto <L4>;

<L5>:;
  x.24 = 4;
  goto <bb 4> (<L2>);

<L4>:;
  x.24 = 8;

<L2>:;
  return x.24;

}

[r119711 .099t.optimized]
;; Function foo (foo)

Analyzing Edge Insertions.
foo (x)
{
  unsigned int x.24;

<bb 2>:
  if (x.24 <= 4) goto <L5>; else goto <L4>;

<L5>:;
  x = 4;
  goto <bb 4> (<L2>);

<L4>:;
  x = 8;

<L2>:;
  return x;

}


-- 
           Summary: [4.3 Regression] gcc.c-torture/execute/20010422-1.c is
                    miscompiled on sh-elf and mips-elf
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kkojima at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: sh-elf, mips-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30159

[Bug tree-optimization/30159] [4.3 Regression] gcc.c-torture/execute/20010422-1.c is miscompiled

[kkojima at gcc dot gnu dot org]

------- Comment #1 from kkojima at gcc dot gnu dot org  2006-12-12 13:01 -------
A slightly different test case

unsigned int foo(unsigned int x)
{
  if (x < 5)
    x = 4;
  else
    x = 8;
  return x;
}

int main(void)
{
  if (foo (4) != 4)
    abort ();
  if (foo (8) != 8)
    abort ();
  exit (0);
}

aborts on i686-pc-linux-gnu with -O1 and -O2.


-- 

kkojima at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
 GCC target triplet|sh-elf, mips-elf            |sh-elf, mips-elf, i686-pc-
                   |                            |linux-gnu
            Summary|[4.3 Regression] gcc.c-     |[4.3 Regression] gcc.c-
                   |torture/execute/20010422-1.c|torture/execute/20010422-1.c
                   |is miscompiled on sh-elf and|is miscompiled
                   |mips-elf                    |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30159

[Bug tree-optimization/30159] [4.3 Regression] gcc.c-torture/execute/20010422-1.c is miscompiled

[dnovillo at gcc dot gnu dot org]

------- Comment #2 from dnovillo at gcc dot gnu dot org  2006-12-12 13:51 -------

Adding Andrew to CC list.  Seems related to out-of-ssa changes.


-- 

dnovillo at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amacleod at redhat dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30159

[Bug tree-optimization/30159] [4.3 Regression] gcc.c-torture/execute/20010422-1.c is miscompiled

[amacleod at redhat dot com]

------- Comment #3 from amacleod at redhat dot com  2006-12-12 14:11 -------
Analyzing Edge Insertions.
foo (x)
{
  unsigned int x.24;

<bb 2>:
  if (x.24 <= 4) goto <L5>; else goto <L4>;

Yeah, this is clearly wrong. It looks like the coalescer somehow neglected to
coalesce the parameter to the first use in bb2, so it ended up getting the
wrong 'x' in the comparison. The x and x.24's should all be reversed.


-- 

amacleod at redhat dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |amacleod at redhat dot com
                   |dot org                     |
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2006-12-12 14:11:13
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30159

[Bug tree-optimization/30159] [4.3 Regression] gcc.c-torture/execute/20010422-1.c is miscompiled

[amacleod at gcc dot gnu dot org]

------- Comment #4 from amacleod at redhat dot com  2006-12-12 15:50 -------
Subject: Bug 30159

Author: amacleod
Date: Tue Dec 12 15:50:06 2006
New Revision: 119792

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=119792
Log:

2006-12-12  Andrew Macleod  <amacleod@redhat.com>

        PR tree-optimization/30159
        * tree-ssa-coalesce.c (coalesce_ssa_name): Process single ssa_name 
        functions in case a default_def coalesce is required.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/tree-ssa-coalesce.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30159

[Bug tree-optimization/30159] [4.3 Regression] gcc.c-torture/execute/20010422-1.c is miscompiled

[pinskia at gcc dot gnu dot org]

------- Comment #5 from pinskia at gcc dot gnu dot org  2006-12-12 19:53 -------
*** Bug 30178 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |danglin at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30159

[Bug tree-optimization/30159] [4.3 Regression] gcc.c-torture/execute/20010422-1.c is miscompiled

[kkojima at gcc dot gnu dot org]

------- Comment #6 from kkojima at gcc dot gnu dot org  2006-12-12 23:20 -------
The patch fixes the problem also on sh-elf and mips-elf.  Thanks!
BTW, I'm a bit surprised that current testcases didn't catch it on x86.
How about to add a new testcase?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30159

[Bug tree-optimization/30159] [4.3 Regression] gcc.c-torture/execute/20010422-1.c is miscompiled

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2006-12-13 05:42 -------
Fixed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30159