Clang assert with [[msvc::no_unique_address]]: (BaseLayout.getNonVirtualSize() == CharUnits::Zero()), function layoutNonVirtualBase, file RecordLayoutBuilder.cpp, line 2946

[zmodem]

(From https://crbug.com/1507521)

Unreduced reproducer:
json_parser-744035.cpp.gz

$ build/bin/clang "-cc1" "-triple" "i386-pc-windows-msvc19.34.0" "-emit-obj" "-mrelax-all" "-mrelocation-model" "static" "-fmerge-all-constants" "-fno-delete-null-pointer-checks" "-mframe-pointer=all" "-relaxed-aliasing" "-fmath-errno" "-ffp-contract=off" "-fno-rounding-math" "-mconstructor-aliases" "-target-cpu" "pentium4" "-target-feature" "+sse3" "-mllvm" "-x86-asm-syntax=intel" "-tune-cpu" "generic" "-D_DEBUG" "-D_MT" "-D_DLL" "--dependent-lib=msvcrtd" "--dependent-lib=oldnames" "-fno-rtti-data" "-stack-protector" "2" "-fms-volatile" "-fno-dllexport-inlines" "-fdiagnostics-format" "msvc" "-cfguard-no-checks" "-gno-column-info" "-gcodeview" "-gcodeview-ghash" "-gno-codeview-command-line" "-debug-info-kind=constructor" "-fdebug-compilation-dir=." "-ffunction-sections" "-fcoverage-compilation-dir=." "-D" "BASE_IMPLEMENTATION" "-D" "IS_RAW_PTR_IMPL" "-D" "DCHECK_ALWAYS_ON=1" "-D" "USE_AURA=1" "-D" "_HAS_NODISCARD" "-D" "_CRT_NONSTDC_NO_WARNINGS" "-D" "_WINSOCK_DEPRECATED_NO_WARNINGS" "-D" "_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE" "-D" "CR_CLANG_REVISION=\"llvmorg-18-init-13481-ge469f847-0\"" "-D" "COMPONENT_BUILD" "-D" "CR_LIBCXX_REVISION=3467ae2512627f51e25ee4a851a873c7a3083a6a" "-D" "__STD_C" "-D" "_CRT_RAND_S" "-D" "_CRT_SECURE_NO_DEPRECATE" "-D" "_SCL_SECURE_NO_DEPRECATE" "-D" "_ATL_NO_OPENGL" "-D" "_WINDOWS" "-D" "CERT_CHAIN_PARA_HAS_EXTRA_FIELDS" "-D" "PSAPI_VERSION=2" "-D" "WIN32" "-D" "_SECURE_ATL" "-D" "WINAPI_FAMILY=WINAPI_FAMILY_DESKTOP_APP" "-D" "WIN32_LEAN_AND_MEAN" "-D" "NOMINMAX" "-D" "_UNICODE" "-D" "UNICODE" "-D" "NTDDI_VERSION=NTDDI_WIN10_NI" "-D" "_WIN32_WINNT=0x0A00" "-D" "WINVER=0x0A00" "-D" "_DEBUG" "-D" "DYNAMIC_ANNOTATIONS_ENABLED=1" "-D" "BASE_USE_PERFETTO_CLIENT_LIBRARY=1" "-D" "ABSL_CONSUME_DLL" "-D" "BORINGSSL_SHARED_LIBRARY" "-D" "__WRL_ENABLE_FUNCTION_STATICS__" "-D" "__DATE__=" "-D" "__TIME__=" "-D" "__TIMESTAMP__=" "-D" "PROTOBUF_ALLOW_DEPRECATED=1" "-ffile-reproducible" "-O0" "-WCL4" "-Wimplicit-fallthrough" "-Wextra-semi" "-Wunreachable-code-aggressive" "-Wthread-safety" "-Wno-missing-field-initializers" "-Wno-unused-parameter" "-Wno-psabi" "-Wloop-analysis" "-Wno-unneeded-internal-declaration" "-Wno-nonportable-include-path" "-Wenum-compare-conditional" "-Wno-ignored-pragma-optimize" "-Wno-deprecated-builtins" "-Wno-bitfield-constant-conversion" "-Wno-deprecated-this-capture" "-Wno-invalid-offsetof" "-Wno-vla-extension" "-Wno-thread-safety-reference-return" "-Wshadow" "-Werror" "-Wno-builtin-macro-redefined" "-Wheader-hygiene" "-Wstring-conversion" "-Wtautological-overlap-compare" "-Wshorten-64-to-32" "-Wimplicit-int-conversion" "-Wsign-compare" "-Wsign-conversion" "-Wtautological-unsigned-zero-compare" "-Wexit-time-destructors" "-Wglobal-constructors" "-Wno-undefined-bool-conversion" "-Wno-tautological-undefined-compare" "-Wno-trigraphs" "-fdeprecated-macro" "-ferror-limit" "19" "-ftrivial-auto-var-init=pattern" "-fno-use-cxa-atexit" "-fms-extensions" "-fms-compatibility" "-fms-compatibility-version=19.34" "-std=c++20" "-fno-inline" "-fno-implicit-modules" "-Qn" "-fcolor-diagnostics" "-fuse-ctor-homing" "-mllvm" "-instcombine-lower-dbg-declare=0" "-mllvm" "-split-threshold-for-reg-with-hint=0" "-fcomplete-member-pointers" "-faddrsig" "-x" "c++" "json_parser-744035.cpp"

clang: /work/llvm-project/clang/lib/AST/RecordLayoutBuilder.cpp:2946: void (anonymous namespace)::MicrosoftRecordLayoutBuilder::layoutNonVirtualBase(const CXXRecordDecl *, const CXXRecordDecl *, const ASTRecordLayout &, const ASTRecordLayout *&): Assertion `BaseLayout.getNonVirtualSize() == CharUnits::Zero()' failed.

Comments on the crbug suggest it's the [[msvc::no_unique_address]] that's trigger this:

The assert is due to the second not_fn in https://chromium-review.googlesource.com/c/chromium/src/+/5067676/10/base/containers/flat_tree.h

It goes away if I remove the NO_UNIQUE_ADDRESS on https://source.chromium.org/chromium/chromium/src/+/main:base/containers/flat_tree.h;l=102?q=flat_tree.h which we started on using on msvc after https://chromium-review.googlesource.com/c/chromium/src/+/5026084

[zmodem]

Fully preprocessed:
a.ii.gz

$ build/bin/clang -cc1 -triple i386-pc-windows-msvc19.34.0 -emit-obj -target-cpu pentium4 -target-feature +sse3 -fdeprecated-macro -fno-use-cxa-atexit -fms-extensions -fms-compatibility -fms-compatibility-version=19.34 -std=c++20 -fcomplete-member-pointers -w /tmp/a.ii

[zmodem]

It seems to be the combination of [[msvc::no_unique_address]] and __declspec(empty_bases) that does it:

Reduced:

$ cat /tmp/x.ii
struct Empty {};

struct NUA {
  [[msvc::no_unique_address]] Empty e;
};

struct __declspec(empty_bases) Derived : NUA { } x;

$ build/bin/clang -cc1 -triple i386-pc-win32 -emit-obj -fms-extensions -w /tmp/x.ii
clang: /work/llvm-project/clang/lib/AST/RecordLayoutBuilder.cpp:2946: void (anonymous namespace)::MicrosoftRecordLayoutBuilder::layoutNonVirtualBase(const CXXRecordDecl *, const CXXRecordDecl *, const ASTRecordLayout &, const ASTRecordLayout *&): Assertion `BaseLayout.getNonVirtualSize() == CharUnits::Zero()' failed.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Hans (zmodem)

(From https://crbug.com/1507521)

Unreduced reproducer:
json_parser-744035.cpp.gz

$ build/bin/clang "-cc1" "-triple" "i386-pc-windows-msvc19.34.0" "-emit-obj" "-mrelax-all" "-mrelocation-model" "static" "-fmerge-all-constants" "-fno-delete-null-pointer-checks" "-mframe-pointer=all" "-relaxed-aliasing" "-fmath-errno" "-ffp-contract=off" "-fno-rounding-math" "-mconstructor-aliases" "-target-cpu" "pentium4" "-target-feature" "+sse3" "-mllvm" "-x86-asm-syntax=intel" "-tune-cpu" "generic" "-D_DEBUG" "-D_MT" "-D_DLL" "--dependent-lib=msvcrtd" "--dependent-lib=oldnames" "-fno-rtti-data" "-stack-protector" "2" "-fms-volatile" "-fno-dllexport-inlines" "-fdiagnostics-format" "msvc" "-cfguard-no-checks" "-gno-column-info" "-gcodeview" "-gcodeview-ghash" "-gno-codeview-command-line" "-debug-info-kind=constructor" "-fdebug-compilation-dir=." "-ffunction-sections" "-fcoverage-compilation-dir=." "-D" "BASE_IMPLEMENTATION" "-D" "IS_RAW_PTR_IMPL" "-D" "DCHECK_ALWAYS_ON=1" "-D" "USE_AURA=1" "-D" "_HAS_NODISCARD" "-D" "_CRT_NONSTDC_NO_WARNINGS" "-D" "_WINSOCK_DEPRECATED_NO_WARNINGS" "-D" "_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE" "-D" "CR_CLANG_REVISION=\"llvmorg-18-init-13481-ge469f847-0\"" "-D" "COMPONENT_BUILD" "-D" "CR_LIBCXX_REVISION=3467ae2512627f51e25ee4a851a873c7a3083a6a" "-D" "__STD_C" "-D" "_CRT_RAND_S" "-D" "_CRT_SECURE_NO_DEPRECATE" "-D" "_SCL_SECURE_NO_DEPRECATE" "-D" "_ATL_NO_OPENGL" "-D" "_WINDOWS" "-D" "CERT_CHAIN_PARA_HAS_EXTRA_FIELDS" "-D" "PSAPI_VERSION=2" "-D" "WIN32" "-D" "_SECURE_ATL" "-D" "WINAPI_FAMILY=WINAPI_FAMILY_DESKTOP_APP" "-D" "WIN32_LEAN_AND_MEAN" "-D" "NOMINMAX" "-D" "_UNICODE" "-D" "UNICODE" "-D" "NTDDI_VERSION=NTDDI_WIN10_NI" "-D" "_WIN32_WINNT=0x0A00" "-D" "WINVER=0x0A00" "-D" "_DEBUG" "-D" "DYNAMIC_ANNOTATIONS_ENABLED=1" "-D" "BASE_USE_PERFETTO_CLIENT_LIBRARY=1" "-D" "ABSL_CONSUME_DLL" "-D" "BORINGSSL_SHARED_LIBRARY" "-D" "__WRL_ENABLE_FUNCTION_STATICS__" "-D" "__DATE__=" "-D" "__TIME__=" "-D" "__TIMESTAMP__=" "-D" "PROTOBUF_ALLOW_DEPRECATED=1" "-ffile-reproducible" "-O0" "-WCL4" "-Wimplicit-fallthrough" "-Wextra-semi" "-Wunreachable-code-aggressive" "-Wthread-safety" "-Wno-missing-field-initializers" "-Wno-unused-parameter" "-Wno-psabi" "-Wloop-analysis" "-Wno-unneeded-internal-declaration" "-Wno-nonportable-include-path" "-Wenum-compare-conditional" "-Wno-ignored-pragma-optimize" "-Wno-deprecated-builtins" "-Wno-bitfield-constant-conversion" "-Wno-deprecated-this-capture" "-Wno-invalid-offsetof" "-Wno-vla-extension" "-Wno-thread-safety-reference-return" "-Wshadow" "-Werror" "-Wno-builtin-macro-redefined" "-Wheader-hygiene" "-Wstring-conversion" "-Wtautological-overlap-compare" "-Wshorten-64-to-32" "-Wimplicit-int-conversion" "-Wsign-compare" "-Wsign-conversion" "-Wtautological-unsigned-zero-compare" "-Wexit-time-destructors" "-Wglobal-constructors" "-Wno-undefined-bool-conversion" "-Wno-tautological-undefined-compare" "-Wno-trigraphs" "-fdeprecated-macro" "-ferror-limit" "19" "-ftrivial-auto-var-init=pattern" "-fno-use-cxa-atexit" "-fms-extensions" "-fms-compatibility" "-fms-compatibility-version=19.34" "-std=c++20" "-fno-inline" "-fno-implicit-modules" "-Qn" "-fcolor-diagnostics" "-fuse-ctor-homing" "-mllvm" "-instcombine-lower-dbg-declare=0" "-mllvm" "-split-threshold-for-reg-with-hint=0" "-fcomplete-member-pointers" "-faddrsig" "-x" "c++" "json_parser-744035.cpp"

clang: /work/llvm-project/clang/lib/AST/RecordLayoutBuilder.cpp:2946: void (anonymous namespace)::MicrosoftRecordLayoutBuilder::layoutNonVirtualBase(const CXXRecordDecl *, const CXXRecordDecl *, const ASTRecordLayout &, const ASTRecordLayout *&): Assertion `BaseLayout.getNonVirtualSize() == CharUnits::Zero()' failed.

Comments on the crbug suggest it's the [[msvc::no_unique_address]] that's trigger this:

> The assert is due to the second not_fn in https://chromium-review.googlesource.com/c/chromium/src/+/5067676/10/base/containers/flat_tree.h
>
> It goes away if I remove the NO_UNIQUE_ADDRESS on https://source.chromium.org/chromium/chromium/src/+/main:base/containers/flat_tree.h;l=102?q=flat_tree.h which we started on using on msvc after https://chromium-review.googlesource.com/c/chromium/src/+/5026084