[Bug target/84377] gcc-7.3.0 miscompiles truncf128@@GLIBC_2.26 in libm.so

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84377

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The gimple level is the same:
```
  _5 = 281474976710655 >> j0_20;
  _6 = ~_5;
  _7 = (long long unsigned int) _6;
  _8 = _7 & _35;
  qw_u.parts64.msw = _8;
  qw_u.parts64.lsw = 0;
```

The place where it changes first between GCC 7.3 and 7.4 is IRA.