[Bug tree-optimization/122608] New: `(a ? CST0 : CST1) OP CST3` is not optimized (for gimple COND)

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122608

            Bug ID: 122608
           Summary: `(a ? CST0 :  CST1) OP CST3` is not optimized (for
                    gimple COND)
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
```
__GIMPLE int f(int a)
{
  _Bool b;
  int t;
  b = a > 0;
  t = b ? 10 : 20;
  t = t + 20;
  return t;
}
```

I would have expected this be optimized down to `a > 0 ? 30 : 40` but it is not
currently.

I don't know how much this matters but sometimes VRP (and sccp) creates
COND_EXPR and you might end up with this IR (I don't have a C testcase where
this shows up though).

I noticed this when I saw the LLVM bug
https://github.com/llvm/llvm-project/issues/167014 .

I think clang produces select for ?: agressively rather than how the
gimplification handle it always via ifs.