[Bug tree-optimization/23414] New: function call not optimized away after unsafe-loop-optimizations

[Bug tree-optimization/23414] New: function call not optimized away after unsafe-loop-optimizations

[tkho at ucla dot edu]

I built the attached test case with -O2 -save-temps -funsafe-loop-optimizations.

The entire call to a() should be optimized away if the loop optimization works
right, but it's not.

The assembly shows these three useless instructions left in a():
a:
        pushl   %ebp
        movl    %esp, %ebp
        popl    %ebp
        ret

-- 
           Summary: function call not optimized away after unsafe-loop-
                    optimizations
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tkho at ucla dot edu
                CC: gcc-bugs at gcc dot gnu dot org
  GCC host triplet: i686-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23414

[Bug tree-optimization/23414] function call not optimized away after unsafe-loop-optimizations

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-16 01:05 -------
The three instructions are the setup of the frame pointer.

This is a dup of bug 13822.  Either use -fomit-frame-pointer or convince someone to turn on -fomit-
frame-pointer for x86 by default.

*** This bug has been marked as a duplicate of 13822 ***

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23414

[Bug tree-optimization/23414] function call not optimized away after unsafe-loop-optimizations

[tkho at ucla dot edu]

------- Additional Comments From tkho at ucla dot edu  2005-08-16 00:59 -------
Created an attachment (id=9501)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=9501&action=view)
testcase

gcc -O2 -save-temps -funsafe-loop-optimizations loop.c

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23414

[Bug tree-optimization/23414] function call not optimized away after unsafe-loop-optimizations

[tkho at ucla dot edu]

------- Additional Comments From tkho at ucla dot edu  2005-08-16 01:11 -------
Why is it that the call to b() is completely optimized away while the call to
a() still exists?

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23414

[Bug tree-optimization/23414] pure function is not dectected for functions with non infinite loops

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-16 01:23 -------
The issue here is more complex.  We are not dected the function with the loop as constant so we don't 
mark it as the function a as not having side effects.

The most ovbvious way to fix this would do the ipa optimizations on the ssa level where we can get the 
loop information and check to see if the loops are finite.

A simple example is even without -funsafe-loop-optimization:

void a(int start, int finish) {
  for (; start < finish; ++start) {
  }
}
int main() {
  int x = 0, y = 99;
  a(x, y);
}


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2005-08-16 01:23:37
               date|                            |
            Summary|function call not optimized |pure function is not
                   |away after unsafe-loop-     |dectected for functions with
                   |optimizations               |non infinite loops


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23414

[Bug tree-optimization/23414] const function is not dectected for functions with non infinite loops

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-08-16 01:25 -------
(In reply to comment #4)
> The most ovbvious way to fix this would do the ipa optimizations on the ssa level where we can get 
> the loop information and check to see if the loops are finite.

I should mention that will not happen until at least 4.2.0.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|pure function is not        |const function is not
                   |dectected for functions with|dectected for functions with
                   |non infinite loops          |non infinite loops


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23414

[Bug tree-optimization/23414] const function is not dectected for functions with non infinite loops

[tkoenig at gcc dot gnu dot org]

------- Comment #6 from tkoenig at gcc dot gnu dot org  2009-01-31 22:00 -------
Test case now generates this assembly:

.globl main
        .type   main, @function
main:
        pushl   %ebp
        movl    %esp, %ebp
#APP
# 18 "gaga.c" 1
        #start1
# 0 "" 2
# 20 "gaga.c" 1
        #end1
# 0 "" 2
# 22 "gaga.c" 1
        #start2
# 0 "" 2
# 24 "gaga.c" 1
        #end2
# 0 "" 2
# 26 "gaga.c" 1
        #start3
# 0 "" 2
# 30 "gaga.c" 1
        #end3
# 0 "" 2
#NO_APP
        popl    %ebp
        ret
        .size   main, .-main
        .ident  "GCC: (GNU) 4.4.0 20090124 (experimental)"
        .section        .note.GNU-stack,"",@progbits

Fixed.


-- 

tkoenig at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23414