[Bug tree-optimization/112402] New: [11/12/13/14 Regression] Path splitting causes if-conversion miss

[Bug tree-optimization/112402] New: [11/12/13/14 Regression] Path splitting causes if-conversion miss

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112402

            Bug ID: 112402
           Summary: [11/12/13/14 Regression] Path splitting causes
                    if-conversion miss
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
            Blocks: 94274
  Target Milestone: ---

Similar to PR 68541 except instead of having a diamond, we just have a
triangle.

Testcase:
```
int
foo(signed char *p, int n)
{
  int s = 0;
  int i;

  for (i = 0; i < n; i++) {
    int t;
    if (p[i] >= 0)
      t=1;
    else
      t=-1;
    s+=t;
  }

  return s;
}
```

I noticed this while working on fixing PR 94274.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94274
[Bug 94274] fold phi whose incoming args are defined from binary operations

[Bug tree-optimization/112402] [11/12/13/14 Regression] Path splitting causes if-conversion miss

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112402

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.5

[Bug tree-optimization/112402] [11/12/13/14 Regression] Path splitting causes if-conversion miss

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112402

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the question is whether we should do more if-conversion on GIMPLE then (or
axe path splitting or move it to RTL)

[Bug tree-optimization/112402] [11/12/13/14 Regression] Path splitting causes if-conversion miss

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112402

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The orginal threads about patch splitting:
https://gcc.gnu.org/legacy-ml/gcc/2015-03/msg00057.html
https://gcc.gnu.org/pipermail/gcc/2015-May/217495.html

> or axe path splitting or move it to RTL
Jeff had a similar idea back in 2016 (I would assume while he was looking into
PR 68541):
https://gcc.gnu.org/pipermail/gcc-patches/2016-February/441651.html :
```
And if that's the case, then we may really be looking at something that 
belongs at the RTL level rather than at the tree/gimple level.  Sadly, 
it's harder to do things like duplicate blocks at the RTL level.
```
and also mentioned in (which was the heustrics added to fix PR 68541):
https://gcc.gnu.org/pipermail/gcc-patches/2016-February/441841.html

Maybe this is something for GCC 15 ... to move to this to RTL right during the
loop optimization phase after pass_rtl_doloop. There is still a CSE and DSE/DCE
passes afterwards too.

[Bug tree-optimization/112402] [11/12/13/14 Regression] Path splitting causes if-conversion miss

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112402

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |pinskia at gcc dot gnu.org
   Last reconfirmed|                            |2023-11-09
     Ever confirmed|0                           |1

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I have a patch which moves split paths to RTL like it should be.  Waiting on
legal though.

[Bug tree-optimization/112402] [11/12/13/14 Regression] Path splitting causes if-conversion miss

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112402

Jeffrey A. Law <law at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
                 CC|                            |law at gcc dot gnu.org