On Tue, Feb 11, 2020 at 10:41:48AM +0100, Michel Dänzer wrote: > 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)? > Hi Michel, Can't this condition be true when UINT_MAX == ULONG_MAX? clang does not warn on a 32-bit x86 build from what I remember. Honestly, my understanding of overflow is pretty shoddy, this is mostly based on what I have heard from others. I sent a patch trying to remove that check but had it rejected: https://lore.kernel.org/lkml/20191123195321.41305-1-natechancellor@xxxxxxxxx/ Cheers, Nathan _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
