Fixed in https://reviews.llvm.org/rL309694. Will be backporting to current llvm.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/12d40bee4f87358d641f08f19fde65f2b9a503f2

commit 12d40bee4f87358d641f08f19fde65f2b9a503f2
Author: Manoj Gupta <manojgupta@google.com>
Date: Tue Aug 01 22:55:11 2017

llvm: Cherry-pick 3 fixes from upstream.

Pick these 2 fixes for Linux kernel build issues (llvm + llvm-next).
commit f6fecfacea8ecde288b680a68823aaf1d08b5beb
commit 9330fda9a0ef108d03334f20319508e409bb356d

Pick this for fixing ARM ABI issues (llvm-next only).
commit c9c456edbdc7004d08581528219ee59362e59e8e

Fix details:
commit f6fecfacea8ecde288b680a68823aaf1d08b5beb
Author:     Manoj Gupta <manojgupta@google.com>
CommitDate: Tue Aug 1 15:39:12 2017 +0000

    [X86] Fix a crash in FEntryInserter Pass.

    Summary:
    FEntryInserter pass unconditionally derefs the first Instruction
    in the first Basic Block. The pass crashes when the first
    BasicBlock is empty. Fix the crash by not dereferencing the basic
    Block iterator. This fixes an issue observed when building Linux kernel
    4.4 with clang.

    Fixes PR33971.

commit 9330fda9a0ef108d03334f20319508e409bb356d
Author:     Eli Friedman <efriedma@codeaurora.org>
AuthorDate: Tue Jul 4 00:52:24 2017 +0000
Commit:     Eli Friedman <efriedma@codeaurora.org>
CommitDate: Tue Jul 4 00:52:24 2017 +0000

    [Sema] Make BreakContinueFinder handle nested loops.

    We don't care about break or continue statements that aren't
    associated with the current loop, so make sure the visitor
    doesn't find them.

    Fixes https://bugs.llvm.org/show_bug.cgi?id=32648 .

    Differential Revision: https://reviews.llvm.org/D34568

commit c9c456edbdc7004d08581528219ee59362e59e8e
Author: Peter Smith <peter.smith@linaro.org>
Date:   Thu Jul 27 10:43:53 2017 +0000

    [CodeGen][ARM] ARM runtime helper functions are not always soft-fp

    Re-commit r309257 with less precise register checks in arm-float-helpers.c
    test.

BUG= chromium:751126 
BUG=chromium:709711
TEST=llvm builds with/without USE="llvm-next".
TEST=squawks 4.4 kernel builds with clang with asserts enabled.
TEST=Reported warning in 709711 is fixed.

Change-Id: I278d383da563e80fb659948a49e8df64e84b2b28
Reviewed-on: https://chromium-review.googlesource.com/592401
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Trybot-Ready: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Luis Lozano <llozano@chromium.org>

[add] https://crrev.com/12d40bee4f87358d641f08f19fde65f2b9a503f2/sys-devel/llvm/files/cherry/c9c456edbdc7004d08581528219ee59362e59e8e.patch
[rename] https://crrev.com/12d40bee4f87358d641f08f19fde65f2b9a503f2/sys-devel/clang/clang-5.0_pre300080_p20170801.ebuild
[rename] https://crrev.com/12d40bee4f87358d641f08f19fde65f2b9a503f2/sys-devel/llvm/llvm-5.0_pre300080_p20170801.ebuild
[add] https://crrev.com/12d40bee4f87358d641f08f19fde65f2b9a503f2/sys-devel/llvm/files/cherry/f6fecfacea8ecde288b680a68823aaf1d08b5beb.patch

mka@ Can you retry with llvm-next build and check if the issue is fixed? 

mka@ please verify that this is fixed.

The new version builds working v4.4 kernels for arm64 and x86. However it crashes when building an upstream kernel for arm64:

  CC      arch/arm64/kernel/cpufeature.o
clang-5.0: /var/tmp/portage/sys-devel/llvm-5.0_pre300080_p20170801/work/llvm-5.0_pre300080_p20170801/tools/clang/lib/AST/ExprConstant.cpp:1108: clang::APValue &(anonymous namespace)::CallStackFrame::createTemporary(const void *, bool): Assertion `Result.isUninit() && "temporary created multiple times"' failed.
#0 0x00007f95033a92ef llvm::sys::PrintStackTrace(llvm::raw_ostream&) (/usr/bin/../lib64/libLLVM-5.0svn.so+0x84f2ef)
#1 0x00007f95033a9656 (/usr/bin/../lib64/libLLVM-5.0svn.so+0x84f656)
#2 0x00007f95022bddf0 (/lib64/libc.so.6+0x33df0)
#3 0x00007f95022bdd72 gsignal (/lib64/libc.so.6+0x33d72)
#4 0x00007f95022bfaaa abort (/lib64/libc.so.6+0x35aaa)
#5 0x00007f95022b6d77 (/lib64/libc.so.6+0x2cd77)
#6 0x00007f95022b6e22 (/lib64/libc.so.6+0x2ce22)
#7 0x000000000189f15b (/usr/bin/clang-5.0+0x189f15b)
#8 0x000000000188af1a (/usr/bin/clang-5.0+0x188af1a)
#9 0x000000000188f287 (/usr/bin/clang-5.0+0x188f287)
#10 0x00000000018d8461 (/usr/bin/clang-5.0+0x18d8461)
#11 0x0000000001887794 (/usr/bin/clang-5.0+0x1887794)
#12 0x00000000018cfde4 (/usr/bin/clang-5.0+0x18cfde4)
#13 0x000000000188ac6c (/usr/bin/clang-5.0+0x188ac6c)
#14 0x000000000188605a (/usr/bin/clang-5.0+0x188605a)
#15 0x0000000001888164 clang::Expr::EvaluateForOverflow(clang::ASTContext const&) const (/usr/bin/clang-5.0+0x1888164)
#16 0x0000000000f2983e clang::Sema::CheckCompletedExpr(clang::Expr*, clang::SourceLocation, bool) (/usr/bin/clang-5.0+0xf2983e)
#17 0x000000000116f8c1 clang::Sema::ActOnFinishFullExpr(clang::Expr*, clang::SourceLocation, bool, bool, bool) (/usr/bin/clang-5.0+0x116f8c1)
#18 0x0000000000fbd5f2 clang::Sema::AddInitializerToDecl(clang::Decl*, clang::Expr*, bool) (/usr/bin/clang-5.0+0xfbd5f2)
#19 0x0000000000cdcb78 clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/usr/bin/clang-5.0+0xcdcb78)
#20 0x0000000000cdad3f clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, unsigned int, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/usr/bin/clang-5.0+0xcdad3f)
#21 0x0000000000cc20d7 clang::Parser::ParseDeclOrFunctionDefInternal(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/usr/bin/clang-5.0+0xcc20d7)
#22 0x0000000000cc1a2a clang::Parser::ParseDeclarationOrFunctionDefinition(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/usr/bin/clang-5.0+0xcc1a2a)
#23 0x0000000000cc0c8b clang::Parser::ParseExternalDeclaration(clang::Parser::ParsedAttributesWithRange&, clang::ParsingDeclSpec*) (/usr/bin/clang-5.0+0xcc0c8b)
#24 0x0000000000cbf893 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&) (/usr/bin/clang-5.0+0xcbf893)
#25 0x0000000000cba94a clang::ParseAST(clang::Sema&, bool, bool) (/usr/bin/clang-5.0+0xcba94a)
#26 0x00000000009f9598 clang::FrontendAction::Execute() (/usr/bin/clang-5.0+0x9f9598)
#27 0x00000000009b1f11 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/usr/bin/clang-5.0+0x9b1f11)
#28 0x0000000000a876dc clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/usr/bin/clang-5.0+0xa876dc)
#29 0x00000000005ddde0 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/usr/bin/clang-5.0+0x5ddde0)
#30 0x00000000005dad3b main (/usr/bin/clang-5.0+0x5dad3b)
#31 0x00007f95022aa7b0 __libc_start_main (/lib64/libc.so.6+0x207b0)
#32 0x00000000005d8309 _start (/usr/bin/clang-5.0+0x5d8309)
Stack dump:
0.	Program arguments: /usr/bin/clang-5.0 -cc1 -triple aarch64-cros-linux-gnu -S -disable-free -main-file-name cpufeature.c -mrelocation-model static -mthread-model posix -mllvm -warn-stack-size=2048 -mdisable-fp-elim -relaxed-aliasing -mdisable-tail-calls -fmath-errno -masm-verbose -no-integrated-as -mconstructor-aliases -fuse-init-array -target-cpu generic -target-feature +neon -no-implicit-float -target-abi aapcs -backend-option -aarch64-enable-global-merge=false -dwarf-column-info -debug-info-kind=limited -dwarf-version=4 -debugger-tuning=gdb -coverage-notes-file /home/mka/linux/arch/arm64/kernel/cpufeature.gcno -nostdsysteminc -nobuiltininc -resource-dir /usr/lib64/clang/5.0.0 -isystem /usr/lib64/clang/5.0.0/include -include ./include/linux/kconfig.h -D _FORTIFY_SOURCE=2 -I ./arch/arm64/include -I ./arch/arm64/include/generated -I ./include -I ./arch/arm64/include/uapi -I ./arch/arm64/include/generated/uapi -I ./include/uapi -I ./include/generated/uapi -D __KERNEL__ -D CONFIG_BROKEN_GAS_INST=1 -D KBUILD_BASENAME="cpufeature" -D KBUILD_MODNAME="cpufeature" -isysroot ../../../usr/aarch64-cros-linux-gnu -O2 -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -Werror-implicit-function-declaration -Wno-format-security -Wno-unused-variable -Wno-format-invalid-specifier -Wno-gnu -Wno-address-of-packed-member -Wno-tautological-compare -Wdeclaration-after-statement -Wno-pointer-sign -Werror=implicit-int -Werror=strict-prototypes -Werror=date-time -Werror=incompatible-pointer-types -Wno-initializer-overrides -Wno-unused-value -Wno-format -Wno-sign-compare -Wno-format-zero-length -Wno-uninitialized -std=gnu89 -fno-dwarf-directory-asm -fdebug-compilation-dir /home/mka/linux -ferror-limit 19 -fmessage-length 0 -fwrapv -fallow-half-arguments-and-returns -fno-signed-char -fobjc-runtime=gcc -fno-common -fdiagnostics-show-option -fcolor-diagnostics -vectorize-loops -vectorize-slp -o /tmp/cpufeature-0af2ca.s -x c arch/arm64/kernel/cpufeature.c -dwarf-debug-flags /usr/bin/clang-5.0 --sysroot=../../../usr/aarch64-cros-linux-gnu -Qunused-arguments -grecord-gcc-switches -fno-stack-protector -fno-omit-frame-pointer -mlittle-endian -Qunused-arguments -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Werror-implicit-function-declaration -Wno-format-security -std=gnu89 -fno-PIE -mno-implicit-float -fno-asynchronous-unwind-tables -O2 --param allow-store-data-races=0 -Wframe-larger-than=2048 -fno-stack-protector --target=aarch64-cros-linux-gnu --gcc-toolchain=/usr -Wno-unused-variable -Wno-format-invalid-specifier -Wno-gnu -Wno-address-of-packed-member -Wno-tautological-compare -mno-global-merge -fno-integrated-as -fno-omit-frame-pointer -fno-optimize-sibling-calls -g -Wdeclaration-after-statement -Wno-pointer-sign -fno-strict-overflow -Werror=implicit-int -Werror=strict-prototypes -Werror=date-time -Werror=incompatible-pointer-types -Wno-initializer-overrides -Wno-unused-value -Wno-format -Wno-sign-compare -Wno-format-zero-length -Wno-uninitialized -B /usr/libexec/gcc/aarch64-cros-linux-gnu --target=aarch64-cros-linux-gnu -fcolor-diagnostics -D _FORTIFY_SOURCE=2 -nostdinc -isystem /usr/lib64/clang/5.0.0/include -I ./arch/arm64/include -I ./arch/arm64/include/generated -I ./include -I ./arch/arm64/include/uapi -I ./arch/arm64/include/generated/uapi -I ./include/uapi -I ./include/generated/uapi -include ./include/linux/kconfig.h -D __KERNEL__ -D CONFIG_BROKEN_GAS_INST=1 -D KBUILD_BASENAME="cpufeature" -D KBUILD_MODNAME="cpufeature" -c -o arch/arm64/kernel/cpufeature.o arch/arm64/kernel/cpufeature.c 
1.	arch/arm64/kernel/cpufeature.c:73:59: current parser token ';'
clang-5.0: error: unable to execute command: Aborted (core dumped)
clang-5.0: error: clang frontend command failed due to signal (use -v to see invocation)
Chromium OS 5.0_pre300080_p20170801 clang version 5.0.0 (/var/cache/chromeos-cache/distfiles/host/egit-src/clang.git 30060bff5b4cb49e17c27672d1aa60e6bc7a95e8) (/var/cache/chromeos-cache/distfiles/host/egit-src/llvm.git b903fddc562ccc622cabc4f08f5df2af90ceb251) (based on LLVM 5.0.0svn)
Target: aarch64-cros-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
clang-5.0: note: diagnostic msg: PLEASE submit a bug report to http://llvm.org/bugs/ and include the crash backtrace, preprocessed source, and associated run script.
clang-5.0: note: diagnostic msg: 
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang-5.0: note: diagnostic msg: /tmp/cpufeature-3d7652.c
clang-5.0: note: diagnostic msg: /tmp/cpufeature-3d7652.sh
clang-5.0: note: diagnostic msg: 

********************
make[1]: *** [scripts/Makefile.build:303: arch/arm64/kernel/cpufeature.o] Error 254
make: *** [Makefile:1019: arch/arm64/kernel] Error 2

can you attach the two files /tmp/cpufeature-3d7652.c and /tmp/cpufeature-3d7652.sh

This is fixed in llvm ToT. Bisecting to find a fix.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/30623ca8daf7ce4f81e07765a5cdc3396b162505

commit 30623ca8daf7ce4f81e07765a5cdc3396b162505
Author: Manoj Gupta <manojgupta@google.com>
Date: Fri Aug 04 19:32:52 2017

llvm-next: Cherry Pick an upstream fix to fix a crash.

This is required to fix a clang crash while building an upstream kernel.

Upstream commit details:
commit 74dbb6c51a6706c959ed323673a7d1a9269720e0
Author: Richard Smith <richard-llvm@metafoo.co.uk>
Date:   Mon Jun 26 23:19:32 2017 +0000

    Revert r301742, which caused us to try to evaluate all full-expressions.

    Also add testcases for a bunch of expression forms that cause our evaluator to
    crash. See PR33140 and PR32864 for crashes that this was causing.

BUG= chromium:751126 
TEST=reported crash is fixed with llvm built with USE=llvm-next.

Change-Id: Ieff1da6b43b14a01c73b0bb1df7ccc9df733d449
Reviewed-on: https://chromium-review.googlesource.com/601005
Commit-Queue: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Manoj Gupta <manojgupta@chromium.org>
Trybot-Ready: Manoj Gupta <manojgupta@chromium.org>
Reviewed-by: Luis Lozano <llozano@chromium.org>

[rename] https://crrev.com/30623ca8daf7ce4f81e07765a5cdc3396b162505/sys-devel/llvm/llvm-5.0_pre300080_p20170801-r1.ebuild
[add] https://crrev.com/30623ca8daf7ce4f81e07765a5cdc3396b162505/sys-devel/llvm/files/cherry/74dbb6c51a6706c959ed323673a7d1a9269720e0.patch