[clang] [clang][bytecode] Use tailcalls via `[[clang::musttail]]` (PR #173756)

Mon Mar 23 05:52:41 PDT 2026

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-win-fast` running on `as-builder-3` while building `clang` at step 6 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/2/builds/47463

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (build-unified-tree) failure: build (failure)
...
[4367/4434] Linking CXX executable bin\sanstats.exe
[4368/4434] Linking CXX executable bin\obj2yaml.exe
[4369/4434] Linking CXX executable bin\sancov.exe
[4370/4434] Building CXX object tools\clang\lib\AST\CMakeFiles\obj.clangAST.dir\ByteCode\EvalEmitter.cpp.obj
[4371/4434] Linking CXX executable bin\llvm-lto2.exe
[4372/4434] Linking CXX executable bin\llvm-split.exe
[4373/4434] Linking CXX executable bin\llvm-opt-fuzzer.exe
[4374/4434] Linking CXX executable bin\llvm-reduce.exe
[4375/4434] Linking CXX executable bin\opt.exe
[4376/4434] Building CXX object tools\clang\lib\AST\CMakeFiles\obj.clangAST.dir\ByteCode\Interp.cpp.obj
FAILED: tools/clang/lib/AST/CMakeFiles/obj.clangAST.dir/ByteCode/Interp.cpp.obj 
C:\ninja\ccache.exe C:\PROGRA~1\MICROS~2\2022\COMMUN~1\VC\Tools\MSVC\1444~1.352\bin\Hostx64\x64\cl.exe  /nologo /TP -DCLANG_BUILD_STATIC -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\clang\lib\AST -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\clang\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\include -IC:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\llvm\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:preprocessor /Zc:__cplusplus /Oi /bigobj /permissive- /W4 -wd4146 -wd4244 -wd4267 -wd4456 -wd4457 -wd4458 -wd4459 -wd4624 -wd4100 -wd4127 -wd4505 -wd4702 -wd4245 -wd4310 -wd4701 -wd4703 -wd4389 -wd4805 -wd4577 -wd4319 -wd4324 -wd4251 -wd4275 -w14062 -we4238 /Gw /O2 /Ob2 /DNDEBUG -MD /EHs-c- /GR- -std:c++17 /showIncludes /Fotools\clang\lib\AST\CMakeFiles\obj.clangAST.dir\ByteCode\Interp.cpp.obj /Fdtools\clang\lib\AST\CMakeFiles\obj.clangAST.dir\ /FS -c C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\clang\lib\AST\ByteCode\Interp.cpp
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\clang\lib\AST\ByteCode\Interp.cpp(2572) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(44984) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(38081) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\llvm-project\clang\lib\AST\ByteCode\Interp.cpp(1583) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27231) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27245) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27259) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27273) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27287) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27301) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27315) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27329) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27343) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27357) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27371) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27399) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(27427) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1754) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1740) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1852) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1726) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1838) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1824) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1712) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1810) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1796) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1782) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1768) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1908) : error C4737: Unable to perform required tail call. Performance may be degraded.
C:\buildbot\as-builder-3\llvm-clang-x86_64-win-fast\build\tools\clang\lib\AST\Opcodes.inc(1880) : error C4737: Unable to perform required tail call. Performance may be degraded.
[4377/4434] Generating export list for LLVM-C
[4378/4434] Building CXX object tools\clang\lib\AST\CMakeFiles\obj.clangAST.dir\ByteCode\Disasm.cpp.obj
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/173756