Re: [PATCH v2] drm/i915: Disable -Wtautological-constant-out-of-range-compare

Michel Dänzer
2020-02-11T09:41:54Z

On 2020-02-11 7:13 a.m., Nathan Chancellor wrote:
> A recent commit in clang added -Wtautological-compare to -Wall, which is
> enabled for i915 so we see the following warning:
>
> ../drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c:1485:22: warning:
> result of comparison of constant 576460752303423487 with expression of
> type 'unsigned int' is always false
> [-Wtautological-constant-out-of-range-compare]
> if (unlikely(remain > N_RELOC(ULONG_MAX)))
> ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
>
> This warning only happens on x86_64 but that check is relevant for
> 32-bit x86 so we cannot remove it.

That's suprising. AFAICT N_RELOC(ULONG_MAX) works out to the same value
in both cases, and remain is a 32-bit value in both cases. How can it be
larger than N_RELOC(ULONG_MAX) on 32-bit (but not on 64-bit)?

--
Earthling Michel Dänzer | https://redhat.com
Libre software enthusiast | Mesa and X developer