[Bug tree-optimization/35452] New: erasing uncessary warning for basic block frequency computation

[Bug tree-optimization/35452] New: erasing uncessary warning for basic block frequency computation

[zhouyi04 at ios dot cn]

When compiling program like following:
int
fn(int s) {
  int i;

  i = 2;

  if (s)
   i = 1;

  if (s)
   printf("%d\n", i);


  return 0;
}

#cc1 -O2 -fdump-tree-vrp-all hello.c
There will be:
Jumps threaded: 1
Removing basic block 3
;; basic block 3, loop depth 0, count 0
;; prev block 7, next block 4
;; pred:
;; succ:       4 [100.0%]  (fallthru,exec)
Invalid sum of incoming frequencies 0, should be 5000
<L0>:;
in hello.c.055t.vrp1 etc.


A patch:
--- gcc/gcc/tree-cfgcleanup.c~  Sat Jan  5 14:45:30 2008
+++ gcc/gcc/tree-cfgcleanup.c   Tue Mar  4 11:11:49 2008
@@ -427,6 +427,9 @@
       else
        s = redirect_edge_and_branch (e, dest);

+      bb->frequency -= EDGE_FREQUENCY(e);
+      bb->count -= e->count;
+
       if (s == e)
        {
          /* Create arguments for the phi nodes, since the edge was not


Anyone help me to regression test it, because I am not able to 
regression it in current juncture :-)


-- 
           Summary: erasing uncessary warning for basic block frequency
                    computation
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: zhouyi04 at ios dot cn
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35452

[Bug tree-optimization/35452] erasing uncessary warning for basic block frequency computation

[zhouyi04 at ios dot cn]

------- Comment #1 from zhouyi04 at ios dot cn  2008-03-05 07:03 -------
(In reply to comment #0)
Sorry there are some problem with 1st patch because the edge e
maybe removed after redirection.
 2    4
 | \ /
 \  5
  \ |
    6
In function redirect_edge_succ_nodup, the edge from 5 to 6 will
be removed because there exists one from 2 to 6.

following is correct patch:
--- gcc/gcc/tree-cfgcleanup.c~  Wed Mar  5 14:13:00 2008
+++ gcc/gcc/tree-cfgcleanup.c   Wed Mar  5 14:13:52 2008
@@ -418,6 +418,10 @@
     {
       bitmap_set_bit (cfgcleanup_altered_bbs, e->src->index);

+
+      bb->frequency -= EDGE_FREQUENCY(e);
+      bb->count -= e->count;
+
       if (e->flags & EDGE_ABNORMAL)
        {
          /* If there is an abnormal edge, redirect it anyway, and

#########################################################
By the way, the frequency and count of forwarder block's succor will not be
affected because he is the only child of the forwarder block.

Anyone help me regression test it please


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35452

[Bug tree-optimization/35452] erasing uncessary warning for basic block frequency computation

[steven at gcc dot gnu dot org]

------- Comment #2 from steven at gcc dot gnu dot org  2009-04-18 20:01 -------
Similar as what is said in commen #0, the detailed vrp1 dump of trunk today
has:

Removing basic block 3
;; basic block 3, loop depth 0, count 0
;; prev block 7, next block 4
;; pred:
;; succ:       8 [100.0%]  (fallthru,exec)
Invalid sum of incoming frequencies 0, should be 5000
goto <bb 8>;

Note the *Removing* basic block.  The CFG branch probabilities have already
been updated at this point.  The edge redirection functions do not take care of
this (often only the caller knows how the profile/predictions should be
updated).  You can see in the dump at the end what the function looks like
after vrp1, and you'll notice the branch probabilities are OK.

So there is no bug -> INVALID.

But thanks for the report.  It took me a little while to figure out what is
going on.  We should probably not dump this "Invalid sum" blah-blah for blocks
that we are about to remove.


-- 

steven at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35452