Disabling here: https://chromium-review.googlesource.com/c/chromium/src/+/675383

This is a category of warnings broken out of -Wtautological-unsigned-zero-compare, see  Issue 763392 . We might want to try enabling that one whilst keeping this one disabled.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f4ac2785e42132e32c6737b7b39d40ce68f20c5c

commit f4ac2785e42132e32c6737b7b39d40ce68f20c5c
Author: Hans Wennborg <hans@chromium.org>
Date: Wed Sep 20 15:54:46 2017

Clang: Disable new -Wtautological-unsigned-enum-zero-compare warning

TBR=rnk

Bug:  767059 
Change-Id: I52b7fd023c6bad1dd507b23445d95aa8848d5e70
Reviewed-on: https://chromium-review.googlesource.com/675383
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503162}
[modify] https://crrev.com/f4ac2785e42132e32c6737b7b39d40ce68f20c5c/build/config/compiler/BUILD.gn

 Issue 767125  has been merged into this issue.

In the same vein, from r315614:

97/50566] CXX obj/base/base/memory_mapped_file_posix.o
FAILED: obj/base/base/memory_mapped_file_posix.o 
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF obj/base/base/memory_mapped_file_posix.o.d -DUSE_SYMBOLIZE -DV8_DEPRECATION_WARNINGS -DUSE_UDEV -DUSE_AURA=1 -DUSE_GLIB=1 -DUSE_NSS_CERTS=1 -DUSE_X11=1 -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -DCR_CLANG_REVISION=\"315623\" -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DCOMPONENT_BUILD -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DBASE_IMPLEMENTATION -DGLIB_VERSION_MAX_ALLOWED=GLIB_VERSION_2_32 -DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_26 -I../.. -Igen -I../../build/linux/debian_jessie_amd64-sysroot/usr/include/glib-2.0 -I../../build/linux/debian_jessie_amd64-sysroot/usr/lib/x86_64-linux-gnu/glib-2.0/include -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -funwind-tables -fPIC -pipe -B../../third_party/binutils/Linux_x64/Release/bin -pthread -fcolor-diagnostics -Xclang -mllvm -Xclang -instcombine-lower-dbg-declare=1 -no-canonical-prefixes -m64 -march=x86-64 -Wall -Werror -Wextra -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default -Wno-unneeded-internal-declaration -Wno-inconsistent-missing-override -Wno-undefined-var-template -Wno-nonportable-include-path -Wno-address-of-packed-member -Wno-unused-lambda-capture -Wno-user-defined-warnings -Wno-enum-compare-switch -Wno-tautological-unsigned-zero-compare -Wno-null-pointer-arithmetic -Wno-tautological-unsigned-enum-zero-compare -fomit-frame-pointer -g2 -ggnu-pubnames -fvisibility=hidden -Wheader-hygiene -Wstring-conversion -Wtautological-overlap-compare -Wno-char-subscripts -Wexit-time-destructors -Wexit-time-destructors -O2 -fno-ident -fdata-sections -ffunction-sections -std=gnu++14 -fno-rtti -nostdinc++ -isystem../../buildtools/third_party/libc++/trunk/include -isystem../../buildtools/third_party/libc++abi/trunk/include --sysroot=../../build/linux/debian_jessie_amd64-sysroot -fno-exceptions -fvisibility-inlines-hidden -c ../../base/files/memory_mapped_file_posix.cc -o obj/base/base/memory_mapped_file_posix.o
../../base/files/memory_mapped_file_posix.cc:60:23: error: comparison 'int64_t' (aka 'long') > 9223372036854775807 is always false [-Werror,-Wtautological-constant-compare]
        aligned_start > std::numeric_limits<off_t>::max() ||
        ~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../base/files/memory_mapped_file_posix.cc:61:45: error: comparison 'uint64_t' (aka 'unsigned long') > 18446744073709551615 is always false [-Werror,-Wtautological-constant-compare]
        static_cast<uint64_t>(aligned_size) >
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
../../base/files/memory_mapped_file_posix.cc:63:44: error: comparison 'uint64_t' (aka 'unsigned long') > 18446744073709551615 is always false [-Werror,-Wtautological-constant-compare]
        static_cast<uint64_t>(region.size) >
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
3 errors generated.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cfa6d963eb8a607c9885af92d43f74c61866a4d2

commit cfa6d963eb8a607c9885af92d43f74c61866a4d2
Author: Hans Wennborg <hans@chromium.org>
Date: Thu Oct 12 22:10:02 2017

Clang: disable new warning -Wtautological-constant-compare

This is a new warning in Clang r315614 and fires on e.g.:

    int64_t aligned_start = 0;
    int64_t aligned_size = 0;
    CalculateVMAlignedBoundaries(region.offset,
                                 region.size,
                                 &aligned_start,
                                 &aligned_size,
                                 &data_offset);

    // Ensure that the casts in the mmap call below are sane.
    if (aligned_start < 0 || aligned_size < 0 ||
        aligned_start > std::numeric_limits<off_t>::max() ||
        static_cast<uint64_t>(aligned_size) >
            std::numeric_limits<size_t>::max() ||
        static_cast<uint64_t>(region.size) >
            std::numeric_limits<size_t>::max()) {
      DLOG(ERROR) << "Region bounds are not valid for mmap";
      return false;
    }

TBR=thakis

Bug:  767059 
Change-Id: I659664af603677195ba41d22de1098ca5084045b
Reviewed-on: https://chromium-review.googlesource.com/716875
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508497}
[modify] https://crrev.com/cfa6d963eb8a607c9885af92d43f74c61866a4d2/build/config/compiler/BUILD.gn

Probably should keep this open to decide if we want this warning, and if so, for the cleanup.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/26f095479802c277dbd8b2524cd1a27555fc714c

commit 26f095479802c277dbd8b2524cd1a27555fc714c
Author: Nico Weber <thakis@chromium.org>
Date: Thu Oct 12 22:44:03 2017

Revert "Clang: disable new warning -Wtautological-constant-compare"

This reverts commit cfa6d963eb8a607c9885af92d43f74c61866a4d2.

Reason for revert: was reverted again upstream

Original change's description:
> Clang: disable new warning -Wtautological-constant-compare
> 
> This is a new warning in Clang r315614 and fires on e.g.:
> 
>     int64_t aligned_start = 0;
>     int64_t aligned_size = 0;
>     CalculateVMAlignedBoundaries(region.offset,
>                                  region.size,
>                                  &aligned_start,
>                                  &aligned_size,
>                                  &data_offset);
> 
>     // Ensure that the casts in the mmap call below are sane.
>     if (aligned_start < 0 || aligned_size < 0 ||
>         aligned_start > std::numeric_limits<off_t>::max() ||
>         static_cast<uint64_t>(aligned_size) >
>             std::numeric_limits<size_t>::max() ||
>         static_cast<uint64_t>(region.size) >
>             std::numeric_limits<size_t>::max()) {
>       DLOG(ERROR) << "Region bounds are not valid for mmap";
>       return false;
>     }
> 
> TBR=thakis
> 
> Bug:  767059 
> Change-Id: I659664af603677195ba41d22de1098ca5084045b
> Reviewed-on: https://chromium-review.googlesource.com/716875
> Reviewed-by: Hans Wennborg <hans@chromium.org>
> Commit-Queue: Hans Wennborg <hans@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#508497}

TBR=thakis@chromium.org,hans@chromium.org

Change-Id: I8d2a4ecfc2d0d74ff700d3c6ec82b49ec5639641
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  767059 
Reviewed-on: https://chromium-review.googlesource.com/716463
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508511}
[modify] https://crrev.com/26f095479802c277dbd8b2524cd1a27555fc714c/build/config/compiler/BUILD.gn

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7360486c5ff6b2659fd13eef5d366c1e4e86dc98

commit 7360486c5ff6b2659fd13eef5d366c1e4e86dc98
Author: Nico Weber <thakis@chromium.org>
Date: Sun Oct 15 20:32:18 2017

Revert "Revert "Clang: disable new warning -Wtautological-constant-compare""

This reverts commit 26f095479802c277dbd8b2524cd1a27555fc714c.

Reason for revert: warning landed again

Original change's description:
> Revert "Clang: disable new warning -Wtautological-constant-compare"
> 
> This reverts commit cfa6d963eb8a607c9885af92d43f74c61866a4d2.
> 
> Reason for revert: was reverted again upstream
> 
> Original change's description:
> > Clang: disable new warning -Wtautological-constant-compare
> > 
> > This is a new warning in Clang r315614 and fires on e.g.:
> > 
> >     int64_t aligned_start = 0;
> >     int64_t aligned_size = 0;
> >     CalculateVMAlignedBoundaries(region.offset,
> >                                  region.size,
> >                                  &aligned_start,
> >                                  &aligned_size,
> >                                  &data_offset);
> > 
> >     // Ensure that the casts in the mmap call below are sane.
> >     if (aligned_start < 0 || aligned_size < 0 ||
> >         aligned_start > std::numeric_limits<off_t>::max() ||
> >         static_cast<uint64_t>(aligned_size) >
> >             std::numeric_limits<size_t>::max() ||
> >         static_cast<uint64_t>(region.size) >
> >             std::numeric_limits<size_t>::max()) {
> >       DLOG(ERROR) << "Region bounds are not valid for mmap";
> >       return false;
> >     }
> > 
> > TBR=thakis
> > 
> > Bug:  767059 
> > Change-Id: I659664af603677195ba41d22de1098ca5084045b
> > Reviewed-on: https://chromium-review.googlesource.com/716875
> > Reviewed-by: Hans Wennborg <hans@chromium.org>
> > Commit-Queue: Hans Wennborg <hans@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#508497}
> 
> TBR=thakis@chromium.org,hans@chromium.org
> 
> Change-Id: I8d2a4ecfc2d0d74ff700d3c6ec82b49ec5639641
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug:  767059 
> Reviewed-on: https://chromium-review.googlesource.com/716463
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Commit-Queue: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#508511}

TBR=thakis@chromium.org,hans@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug:  767059 
Change-Id: I8c89bac3795c7136f2ceaaf591b23a1dc767f4c8
Reviewed-on: https://chromium-review.googlesource.com/719944
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508959}
[modify] https://crrev.com/7360486c5ff6b2659fd13eef5d366c1e4e86dc98/build/config/compiler/BUILD.gn

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e83806f7408da1ea396f2eeae5da32905142d438

commit e83806f7408da1ea396f2eeae5da32905142d438
Author: Hans Wennborg <hans@chromium.org>
Date: Fri Nov 10 23:20:59 2017

Clang: re-enable -Wtautological-constant-out-of-range-compare

It was unintentionally disabled as part of disabling the new Clang
warning -Wtautological-constant-compare.

Bug:  767059 ,  783204 
Change-Id: I621f002f319cb395ecc30ca7ff9f132cefe0e5d4
Reviewed-on: https://chromium-review.googlesource.com/764035
Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515739}
[modify] https://crrev.com/e83806f7408da1ea396f2eeae5da32905142d438/build/config/compiler/BUILD.gn

The following revision refers to this bug:
  https://boringssl.googlesource.com/boringssl/+/6979c7e8eb0c96cbf57bd8f657d59a50f0487fcf

commit 6979c7e8eb0c96cbf57bd8f657d59a50f0487fcf
Author: David Benjamin <davidben@google.com>
Date: Tue Dec 05 19:34:47 2017

Disable Clang -Wtautological-constant-compare.

This is a recent Clang warning, but it's far too aggressive. The earlier
unsigned long silliness was worth fixing, but it otherwise complains on
32-bit platforms with:

  if (some_size_t > 0xffffffff) {
    ...
  }

which is unreasonable as, on 64-bit platforms, this check is meaningful
and requiring the programmer add ifdefs is error-prone. This matches
Chromium in  https://crbug.com/767059 .

Bug:  chromium:767059 
Change-Id: I0bb0f3a4b60f222e9d1b3c569471fbcf5518caed
Reviewed-on: https://boringssl-review.googlesource.com/23845
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

[modify] https://crrev.com/6979c7e8eb0c96cbf57bd8f657d59a50f0487fcf/CMakeLists.txt

error: unknown warning option '-Wno-tautological-constant-compare'; did you mean '-Wno-tautological-pointer-compare'? [-Werror,-Wunknown-warning-option]

This option isnt understood on clang for linux?

I'm seeing it in 2 build files
build/config/compiler/BUILD.gn
and
third_party/libxml/BUILD.gn

fbarchard: Which Clang for Linux? It's understood by the version Chromium uses.

I seem to still have an old version.  The roll script for libyuv says it should update chromium deps and clang
Clang version changed 313786:318667
Details: https://chromium.googlesource.com/chromium/src/+/ff3b31782d..e6bcf53038/tools/clang/scripts/update.py

This is the versoin

third_party/llvm-build/Release+Asserts/bin/clang++ --version
clang version 6.0.0 (trunk 313786)
Target: x86_64-unknown-linux-gnu
Thread model: posix

But chromium has a newer version:

third_party/llvm-build/Release+Asserts/bin/clang++ --version
clang version 6.0.0 (trunk 321204)
Target: x86_64-unknown-linux-gnu
Thread model: posix

tools/clang/scripts/update.py
Updating Clang to 313786-1...
Clang is already up to date.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c520a7b38d7781e13564a4559e41f9c9c47f51b3

commit c520a7b38d7781e13564a4559e41f9c9c47f51b3
Author: Nico Weber <thakis@chromium.org>
Date: Thu Feb 15 19:28:04 2018

Stop disabling warnings that are now off-by-default in clang.

Namely, Wtautological-unsigned-zero-compare and
Wtautological-unsigned-enum-zero-compare, see
http://llvm.org/viewvc/llvm-project?view=revision&revision=322901

If we have to disable them again in the future, it's probably better
to use -Wno-tautological-in-range-compare then.

Bug:  763392 , 767059 
Change-Id: I8374fc2b9854618052b784be0371f8744b057701
Reviewed-on: https://chromium-review.googlesource.com/922022
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537098}
[modify] https://crrev.com/c520a7b38d7781e13564a4559e41f9c9c47f51b3/build/config/compiler/BUILD.gn