On Fri, 14 Feb 2020, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > Quoting Jani Nikula (2020-02-14 06:36:15) >> On Thu, 13 Feb 2020, Nathan Chancellor <natechancellor@xxxxxxxxx> wrote: >> > A recent commit in clang added -Wtautological-compare to -Wall, which is >> > enabled for i915 after -Wtautological-compare is disabled for the rest >> > of the kernel so we see the following warning on x86_64: >> > >> > ../drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c:1433:22: 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))) >> > ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~ >> > ../include/linux/compiler.h:78:42: note: expanded from macro 'unlikely' >> > # define unlikely(x) __builtin_expect(!!(x), 0) >> > ^ >> > 1 warning generated. >> > >> > It is not wrong in the case where ULONG_MAX > UINT_MAX but it does not >> > account for the case where this file is built for 32-bit x86, where >> > ULONG_MAX == UINT_MAX and this check is still relevant. >> > >> > Cast remain to unsigned long, which keeps the generated code the same >> > (verified with clang-11 on x86_64 and GCC 9.2.0 on x86 and x86_64) and >> > the warning is silenced so we can catch more potential issues in the >> > future. >> > >> > Link: https://github.com/ClangBuiltLinux/linux/issues/778 >> > Suggested-by: Michel Dänzer <michel@xxxxxxxxxxx> >> > Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx> >> >> Works for me as a workaround, > > But the whole point was that the compiler could see that it was > impossible and not emit the code. Doesn't this break that? It seems that goal and the warning are fundamentally incompatible. Back to the original patch? BR, Jani. -- Jani Nikula, Intel Open Source Graphics Center _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
