On Sat, Nov 23, 2019 at 12:05 PM Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > > Quoting Nathan Chancellor (2019-11-23 19:53:22) > > -Wtautological-compare was recently added to -Wall in LLVM, which > > exposed an if statement in i915 that is always false: > > > > ../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))) > > ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~ > > > > Since remain is an unsigned int, it can never be larger than UINT_MAX, > > which is less than ULONG_MAX / sizeof(struct drm_i915_gem_relocation_entry). > > Remove this statement to fix the warning. > > The check should remain as we do want to document the overflow > calculation, and it should represent the types used -- it's much easier What do you mean "represent the types used?" Are you concerned that the type of drm_i915_gem_exec_object2->relocation_count might change in the future? > to review a stub than trying to find a missing overflow check. If the > overflow cannot happen as the types are wide enough, no problem, the > compiler can remove the known false branch. What overflow are you trying to protect against here? > > Tautology here has a purpose for conveying information to the reader. Well leaving a warning unaddressed is also not a solution. Either replace it with a comment or turn off the warning for your subdir. The warning here looks valid to me; you have a guard for something that's impossible. -- Thanks, ~Nick Desaulniers _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
