From here:
https://ci.chromium.org/buildbot/chromium.clang/ToTiOS/1517

FAILED: ios_clang_x86/obj/net/net_unittests_arch_executable_sources/bidirectional_stream_unittest.o 
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF ios_clang_x86/obj/net/net_unittests_arch_executable_sources/bidirectional_stream_unittest.o.d -DV8_DEPRECATION_WARNINGS -DNO_TCMALLOC -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -DCR_XCODE_VERSION=0920 -DCR_CLANG_REVISION=\"329768\" -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D_FORTIFY_SOURCE=2 -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DNS_BLOCK_ASSERTIONS=1 -DGTEST_API_= -DGTEST_HAS_POSIX_RE=0 -DGTEST_LANG_CXX11=1 -DGTEST_HAS_STD_TUPLE=1 -DGOOGLE_PROTOBUF_NO_RTTI -DGOOGLE_PROTOBUF_NO_STATIC_INITIALIZER -DHAVE_PTHREAD -DU_USING_ICU_NAMESPACE=0 -DU_ENABLE_DYLOAD=0 -DU_STATIC_IMPLEMENTATION -DICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE -DUCHAR_TYPE=uint16_t -DUNIT_TEST -I../.. -Iios_clang_x86/gen -I../../third_party/googletest/custom -I../../third_party/googletest/src/googletest/include -I../../third_party/protobuf/src -Iios_clang_x86/gen/protoc_out -I../../third_party/protobuf/src -I../../third_party/boringssl/src/include -I../../third_party/ced/src -I../../third_party/icu/source/common -I../../third_party/icu/source/i18n -I../../third_party/googletest/src/googlemock/include -I../../third_party/zlib -fno-strict-aliasing -fmerge-all-constants --param=ssp-buffer-size=4 -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -fcolor-diagnostics -no-canonical-prefixes -arch i386 -Wall -Werror -Wextra -Wimplicit-fallthrough -Wthread-safety -Wunguarded-availability -Wundeclared-selector -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-null-pointer-arithmetic -Wno-ignored-pragma-optimize -Oz -fno-omit-frame-pointer -gdwarf-2 -isysroot /b/c/xcode_ios_9c40b.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator11.2.sdk -stdlib=libc++ -mios-simulator-version-min=10.0 -fvisibility=hidden -Xclang -load -Xclang ../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.dylib -Xclang -add-plugin -Xclang find-bad-constructs -Xclang -plugin-arg-find-bad-constructs -Xclang no-realpath -Wheader-hygiene -Wstring-conversion -Wtautological-overlap-compare -std=c++14 -fno-exceptions -fno-rtti -fvisibility-inlines-hidden -c ../../net/http/bidirectional_stream_unittest.cc -o ios_clang_x86/obj/net/net_unittests_arch_executable_sources/bidirectional_stream_unittest.o
Assertion failed: (isReg() && "This is not a register operand!"), function getReg, file /b/c/b/ToTiOS/src/third_party/llvm/include/llvm/CodeGen/MachineOperand.h, line 344.
0  clang++                  0x000000010f5a55e8 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 40
1  clang++                  0x000000010f5a5ca6 SignalHandler(int) + 470
2  libsystem_platform.dylib 0x00007fffb146ebba _sigtramp + 26
3  libsystem_platform.dylib 000000000000000000 _sigtramp + 1320752224
4  libsystem_c.dylib        0x00007fffb12f5420 abort + 129
5  libsystem_c.dylib        0x00007fffb12bc893 basename_r + 0
6  clang++                  0x000000010e77fc34 (anonymous namespace)::X86FlagsCopyLoweringPass::runOnMachineFunction(llvm::MachineFunction&) + 8324
7  clang++                  0x000000010ed09d44 llvm::MachineFunctionPass::runOnFunction(llvm::Function&) + 180
8  clang++                  0x000000010eff99fd llvm::FPPassManager::runOnFunction(llvm::Function&) + 509
9  clang++                  0x000000010eff9c73 llvm::FPPassManager::runOnModule(llvm::Module&) + 67
10 clang++                  0x000000010effa1b0 llvm::legacy::PassManagerImpl::run(llvm::Module&) + 944
11 clang++                  0x000000010f793773 clang::EmitBackendOutput(clang::DiagnosticsEngine&, clang::HeaderSearchOptions const&, clang::CodeGenOptions const&, clang::TargetOptions const&, clang::LangOptions const&, llvm::DataLayout const&, llvm::Module*, clang::BackendAction, std::__1::unique_ptr<llvm::raw_pwrite_stream, std::__1::default_delete<llvm::raw_pwrite_stream> >) + 16723
12 clang++                  0x000000010f9c3b72 clang::BackendConsumer::HandleTranslationUnit(clang::ASTContext&) + 978
13 clang++                  0x000000010fc3a75c clang::MultiplexConsumer::HandleTranslationUnit(clang::ASTContext&) + 44
14 clang++                  0x00000001105a40a4 clang::ParseAST(clang::Sema&, bool, bool) + 516
15 clang++                  0x000000010fc1116c clang::FrontendAction::Execute() + 76
16 clang++                  0x000000010fbc9091 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) + 1233
17 clang++                  0x000000010fc5e498 clang::ExecuteCompilerInvocation(clang::CompilerInstance*) + 1736
18 clang++                  0x000000010dc8624b cc1_main(llvm::ArrayRef<char const*>, char const*, void*) + 1499
19 clang++                  0x000000010dc83ebd main + 10909
20 libdyld.dylib            0x00007fffb1261255 start + 1
21 libdyld.dylib            0x00000000000000b6 start + 1322905186


I'm guessing this is due to r329673