On Fri, Feb 14, 2020 at 08:32:19AM +0000, Chris Wilson 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? > -Chris As noted in the commit message, I ran diff <(objdump -Dr) <(objdump -Dr) on objects files compiled with and without the patch with clang and gcc for x86_64 and gcc for i386 (i386 does not build with clang) and there was zero difference aside from the file names. At the end of the day, I do not really care how the warning get fixed, just that it does since it is the only one on x86_64 defconfig. Cheers, Nathan _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
