[Bug tree-optimization/42646] New: Jump threading breaks canonical loop forms

[Bug tree-optimization/42646] New: Jump threading breaks canonical loop forms

[joefoxreal at gmail dot com]

pass_dominator tries to thread jumps.But sometimes this will cause that the
loop's exit bb does not dominator its latch bb again. 

-------------------------------------
void
foo (int x)
{
 int i;

 for (i=0; i < 10 ; i++)
   if (x)
     {
       if (i == 0)
         fun_1 ();
       else
         fun_2 ();
     }
}
---------------------------------------
$ gcc -O3 -S foo.c
$ cat foo.s

       .file   "foo.c"
       .text
       .p2align 4,,15
.globl foo
       .type   foo, @function
foo:
       pushl   %ebp
       movl    %esp, %ebp
       pushl   %ebx
       movl    $1, %ebx
       subl    $4, %esp
       movl    8(%ebp), %eax
       testl   %eax, %eax
       jne     .L3
       addl    $4, %esp
       popl    %ebx
       popl    %ebp
       ret
       .p2align 4,,7
       .p2align 3
.L7:
       call    fun_1
.L5:
       addl    $1, %ebx
.L3:
       cmpl    $1, %ebx
       je      .L7
       call    fun_2
       cmpl    $9, %ebx
       jle     .L5
       addl    $4, %esp
       popl    %ebx
       popl    %ebp
       ret
       .size   foo, .-foo
       .ident  "GCC: (GNU) 4.5.0 20100107 (experimental)"
       .section        .note.GNU-stack,"",@progbits
-------------------------------------------
$ gcc -O3 -fno-tree-dominator-opts -S foo.c
$ cat foo.s

       .file   "foo.c"
       .text
       .p2align 4,,15
.globl foo
       .type   foo, @function
foo:
       pushl   %ebp
       movl    %esp, %ebp
       subl    $8, %esp
       movl    8(%ebp), %eax
       testl   %eax, %eax
       je      .L1
       call    fun_1
       call    fun_2
       .p2align 4,,5
       call    fun_2
       .p2align 4,,5
       call    fun_2
       .p2align 4,,5
       call    fun_2
       .p2align 4,,5
       call    fun_2
       .p2align 4,,5
       call    fun_2
       .p2align 4,,5
       call    fun_2
       .p2align 4,,5
       call    fun_2
       leave
       jmp     fun_2
       .p2align 4,,7
       .p2align 3
.L1:
       leave
       ret
       .size   foo, .-foo
       .ident  "GCC: (GNU) 4.5.0 20100107 (experimental)"
       .section        .note.GNU-stack,"",@progbits
-------------------------------------------
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/home/eric/install/trunk/libexec/gcc/i686-pc-linux-gnu/4.5.0/lto-wrapper
Target: i686-pc-linux-gnu
Configured with: ../trunk/configure --prefix=/home/eric/install/trunk
--with-gmp=/home/eric/install/generic
--with-mpfr=/home/eric/install/generic
--with-mpc=/home/eric/install/generic/ --enable-languages=c
Thread model: posix
gcc version 4.5.0 20100107 (experimental) (GCC)


-- 
           Summary: Jump threading breaks canonical loop forms
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: joefoxreal at gmail dot com
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42646

[Bug tree-optimization/42646] Jump threading breaks canonical loop forms

[joefoxreal at gmail dot com]

------- Comment #1 from joefoxreal at gmail dot com  2010-01-07 14:29 -------
Created an attachment (id=19498)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19498&action=view)
cfg of the function foo


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42646

[Bug tree-optimization/42646] Jump threading breaks canonical loop forms

[joefoxreal at gmail dot com]

------- Comment #2 from joefoxreal at gmail dot com  2010-01-08 01:40 -------
Created an attachment (id=19504)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19504&action=view)
the cfg of foo.c.079t.copyrename3


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42646

[Bug tree-optimization/42646] Jump threading breaks canonical loop forms

[joefoxreal at gmail dot com]

------- Comment #3 from joefoxreal at gmail dot com  2010-01-08 01:41 -------
Created an attachment (id=19505)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19505&action=view)
the cfg of foo.c.080t.dom1


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42646

[Bug tree-optimization/42646] Jump threading breaks canonical loop forms

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2010-01-08 11:52 -------
It just means that we shouldn't thread to the header but always to the latch
block.  Note that this restriction should probably be restricted to the
threading before loop optimizations.  Or the 1st jump threading should simply
avoid to thread over backedges (equivalent to removing the 1st DOM pass -
though
there is interesting fallout regarding jump-threading / loop header copying
pass ordering).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42646

[Bug tree-optimization/42646] Jump threading breaks canonical loop forms

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42646

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This seems to finally have been fixed on the trunk.