[Bug rtl-optimization/116179] [15 regression] -fcompare-debug -gno-statement-frontiers failure with -O3 when building mesa-24.1.4 since r15-1735-ge62ea4fb8ffcab (late combine)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116179

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Hmm:
```
      for (df_ref use = DF_REG_USE_CHAIN (REGNO(dest));
           use;
           use = DF_REF_NEXT_REG (use))
        {
          int ubbi = DF_REF_BB (use)->index;
          if (bitmap_bit_p (reachable, ubbi))
            bitmap_set_bit (need_new, ubbi);
        }

```

I think this should check if the use was not a debug insn.
that is `!DEBUG_INSN_P (DF_REF_INSN (use))` .

Let me check that tomorrow.


What late_combine1 is doing is ok, I think just exposing the latent bug in this
code.