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 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. Tautology here has a purpose for conveying information to the reader. -Chris _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
