[Bug optimization/8776] loop invariants are not removed (most likely)

[Bug optimization/8776] loop invariants are not removed (most likely)

[dhazeghi@yahoo.com]

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8776


dhazeghi@yahoo.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
  GCC build triplet|                            |i686-pc-linux-gnu
   GCC host triplet|                            |i686-pc-linux-gnu
 GCC target triplet|                            |i686-linux-pc-gnu
   Last reconfirmed|0000-00-00 00:00:00         |2003-06-04 19:50:50
               date|                            |


------- Additional Comments From dhazeghi@yahoo.com  2003-06-04 19:50 -------
Hello,

your problem as stated is fixed on gcc 3.3 branch and mainline. Please note that -O9 is the same 
thing as -O3 (-On for n>3 is identical to -O3). Second, your code performs identically for me with 
-O3, -O3 -DSLOW1 and -O3 -DSLOW2 with gcc 3.3. With gcc mainline, things are somewhat more 
bizarre. With -O3, or -O3 -DSLOW1, the code is about 50% slower than with gcc 3.3, but with -O3 
-DSLOW2 it's the same speed as gcc 3.3 (ie faster than the with the other two options). Very 
strange.

Dara



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[Bug optimization/8776] loop invariants are not removed (most likely)

[pinskia at physics dot uc dot edu]

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8776


pinskia at physics dot uc dot edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug optimization/8776] [3.4 Regression] loop invariants are not removed (most likely)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-11-15 20:47 -------
There is a preformance regression here from 3.3, other than that the -DSLOW[12] stuff is 
fixed though, they alll preform the same.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|enhancement                 |normal
   Last reconfirmed|2003-06-04 19:50:50         |2003-11-15 20:47:31
               date|                            |
            Summary|loop invariants are not     |[3.4 Regression] loop
                   |removed (most likely)       |invariants are not removed
                   |                            |(most likely)
   Target Milestone|---                         |3.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8776

[Bug optimization/8776] loop invariants are not removed (most likely)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-12-28 03:56 -------
Here is the difference in the code:
--- temp.s      Sat Dec 27 22:51:13 2003
+++ temp1.s     Sat Dec 27 22:51:04 2003
@@ -5,21 +5,20 @@
        .type   main, @function
 main:
        pushl   %ebp
-       xorl    %edx, %edx
+       movl    $999999999, %eax
        movl    %esp, %ebp
        subl    $40, %esp
-       leal    -32(%ebp), %ecx
-       movl    $0, -16(%ebp)
+       leal    -32(%ebp), %edx
        andl    $-16, %esp
-       movl    $0, -20(%ebp)
+       movl    $0, -16(%ebp)
        subl    $16, %esp
+       movl    $0, -20(%ebp)
        movl    $0, -24(%ebp)
-       movl    $999999999, %eax
        .p2align 4,,15
 .L5:
-       movl    $0, (%ecx,%edx,8)
+       movl    $0, (%edx)
        decl    %eax
-       movl    $1072693248, 4(%ecx,%edx,8)
+       movl    $1072693248, 4(%edx)
        jns     .L5
        leave
        xorl    %eax, %eax

The main difference is the use of (%ecx,%edx,8) vs  (%edx)
But this does not produce any difference in performance (at least on pentium 4 or 
pentium 3):

tin:~/src/gnu/gcctest>time ./a.out
2.010u 0.000s 0:02.01 100.0%    0+0k 0+0io 69pf+0w
tin:~/src/gnu/gcctest>gcc -std=c99 -O3 pr8776.c -DSLOW2
tin:~/src/gnu/gcctest>!tim
time ./a.out
2.010u 0.000s 0:02.01 100.0%    0+0k 0+0io 69pf+0w
tin:~/src/gnu/gcctest>gcc -std=c99 -O3 pr8776.c -DSLOW1
tin:~/src/gnu/gcctest>!time
time ./a.out
2.010u 0.000s 0:02.01 100.0%    0+0k 0+0io 69pf+0w

So this is fixed on the mainline and 3.3.3.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
            Summary|[3.4 Regression] loop       |loop invariants are not
                   |invariants are not removed  |removed (most likely)
                   |(most likely)               |
   Target Milestone|3.4.0                       |3.3.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=8776