clang 20.1.1/19.1.7 hangs when compiling a specific Mesa file `src/mesa/main/format_utils.c` for x86; compilation never finishes after 2 hours

[MIvanchev]

See the respective Mesa issue, https://gitlab.freedesktop.org/mesa/mesa/-/issues/12872, I'm suspecting this is more clang than Mesa.

[DimitryAndric]

When this hanging occurs, can you please send a SIGABRT to the clang instance? That should cause it to core dump, and write .sh and .cpp files, which you can then attach to this issue.

[MIvanchev]

Aye, let me try @DimitryAndric, thank you!

[MIvanchev]

@DimitryAndric I got the files but I can't attach them here for some reason. I've uploaded them to

https://raw.githubusercontent.com/MIvanchev/files/refs/heads/494225eb-553a-49e3-a069-cd380a9d9a76/format_utils-f42aff.c
https://raw.githubusercontent.com/MIvanchev/files/refs/heads/494225eb-553a-49e3-a069-cd380a9d9a76/format_utils-f42aff.sh

[DimitryAndric]

Hm, this test case appears to require an llvm build with polly enabled:

clang (LLVM option parsing): Unknown command line argument '-polly'.  Try: 'clang (LLVM option parsing) --help'
clang (LLVM option parsing): Did you mean '--color'?
clang (LLVM option parsing): Unknown command line argument '-polly-position=early'.  Try: 'clang (LLVM option parsing) --help'
clang (LLVM option parsing): Did you mean '--print-options=early'?
clang (LLVM option parsing): Unknown command line argument '-polly-vectorizer=stripmine'.  Try: 'clang (LLVM option parsing) --help'
clang (LLVM option parsing): Did you mean '--slp-vectorize-hor=stripmine'?

Unfortunately I don't have one lying around...

[MIvanchev]

@DimitryAndric you can remove the polly flags, it hangs regardless.

[DimitryAndric]

With my clang 19 here and the polly flags removed, it finishes in about 30 seconds:

+ /usr/bin/time -l clang -cc1 -triple i386-unknown-linux-gnu -emit-obj -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name format_utils.c -mrelocation-model pic -pic-level 2 -fhalf-no-semantic-interposition '-mframe-pointer=none' '-ffp-contract=on' -fno-rounding-math '-ffp-exception-behavior=ignore' -mfpmath sse -mconstructor-aliases '-funwind-tables=2' -enable-tlsdesc -target-cpu broadwell -target-feature +sse2 '-debugger-tuning=gdb' '-fdebug-compilation-dir=/build/mesa-25.0.2/build' -ffunction-sections -fdata-sections '-fcoverage-compilation-dir=/build/mesa-25.0.2/build' -sys-header-deps -D NDEBUG -D '_FILE_OFFSET_BITS=64' -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -D 'PACKAGE_VERSION="25.0.2"' -D 'PACKAGE_BUGREPORT="https://gitlab.freedesktop.org/mesa/mesa/-/issues"' -D 'HAVE_OPENGL=1' -D 'HAVE_OPENGL_ES_1=0' -D 'HAVE_OPENGL_ES_2=0' -D HAVE_ZINK -D HAVE_I915 -D HAVE_IRIS -D HAVE_CROCUS -D HAVE_NOUVEAU -D HAVE_R300 -D HAVE_R600 -D HAVE_RADEONSI -D HAVE_SWRAST -D 'VIDEO_CODEC_VC1DEC=0' -D 'VIDEO_CODEC_H264DEC=0' -D 'VIDEO_CODEC_H264ENC=0' -D 'VIDEO_CODEC_H265DEC=0' -D 'VIDEO_CODEC_H265ENC=0' -D 'VIDEO_CODEC_AV1DEC=1' -D 'VIDEO_CODEC_AV1ENC=1' -D 'VIDEO_CODEC_VP9DEC=1' -D HAVE_X11_PLATFORM -D HAVE_SURFACELESS_PLATFORM -D HAVE_DRM_PLATFORM -D HAVE_XCB_PLATFORM -D 'USE_LIBGLVND=0' -D GLX_INDIRECT_RENDERING -D GLX_DIRECT_RENDERING -D GLX_USE_DRM -D 'GLAPI_EXPORT_PROTO_ENTRY_POINTS=0' -D ALLOW_KCMP -D 'MESA_DEBUG=0' -D ENABLE_SHADER_CACHE -D HAVE___BUILTIN_BSWAP32 -D HAVE___BUILTIN_BSWAP64 -D HAVE___BUILTIN_CLZ -D HAVE___BUILTIN_CLZLL -D HAVE___BUILTIN_CTZ -D HAVE___BUILTIN_EXPECT -D HAVE___BUILTIN_FFS -D HAVE___BUILTIN_FFSLL -D HAVE___BUILTIN_POPCOUNT -D HAVE___BUILTIN_POPCOUNTLL -D HAVE___BUILTIN_UNREACHABLE -D HAVE___BUILTIN_TYPES_COMPATIBLE_P -D HAVE_FUNC_ATTRIBUTE_CONST -D HAVE_FUNC_ATTRIBUTE_FLATTEN -D HAVE_FUNC_ATTRIBUTE_MALLOC -D HAVE_FUNC_ATTRIBUTE_PURE -D HAVE_FUNC_ATTRIBUTE_UNUSED -D HAVE_FUNC_ATTRIBUTE_WARN_UNUSED_RESULT -D HAVE_FUNC_ATTRIBUTE_WEAK -D HAVE_FUNC_ATTRIBUTE_FORMAT -D HAVE_FUNC_ATTRIBUTE_PACKED -D HAVE_FUNC_ATTRIBUTE_RETURNS_NONNULL -D HAVE_FUNC_ATTRIBUTE_ALIAS -D HAVE_FUNC_ATTRIBUTE_NORETURN -D HAVE_FUNC_ATTRIBUTE_VISIBILITY -D HAVE_REALLOCARRAY -D HAVE_FMEMOPEN -D _GNU_SOURCE -D USE_SSE41 -D HAVE___BUILTIN_IA32_CLFLUSHOPT -D USE_GCC_ATOMIC_BUILTINS -D USE_X86_ASM -D MAJOR_IN_SYSMACROS -D HAS_SCHED_H -D HAS_SCHED_GETAFFINITY -D HAVE_LINUX_FUTEX_H -D HAVE_ENDIAN_H -D HAVE_DLFCN_H -D HAVE_SYS_SHM_H -D HAVE_CET_H -D HAVE_SYS_INOTIFY_H -D HAVE_LINUX_UDMABUF_H -D HAVE_STRTOF -D HAVE_MKOSTEMP -D HAVE_MEMFD_CREATE -D HAVE_RANDOM_R -D HAVE_FLOCK -D HAVE_STRTOK_R -D HAVE_GETRANDOM -D HAVE_POSIX_FALLOCATE -D HAVE_SECURE_GETENV -D HAVE_GNU_QSORT_R -D HAVE_STRUCT_TIMESPEC -D HAVE_PROGRAM_INVOCATION_NAME -D HAVE_ISSIGNALING -D HAVE_POSIX_MEMALIGN -D HAVE_DIRENT_D_TYPE -D HAVE_STRTOD_L -D HAVE_DLADDR -D HAVE_DL_ITERATE_PHDR -D SUPPORT_INTEL_INTEGRATED_GPUS -D HAVE_ZLIB -D HAVE_ZSTD -D HAVE_COMPRESSION -D HAVE_PTHREAD -D HAVE_PTHREAD_SETAFFINITY -D HAVE_LIBDRM -D HAVE_LIBUDEV -D 'MESA_LLVM_VERSION_STRING="20.1.1"' -D 'LLVM_IS_SHARED=0' -D 'LLVM_AVAILABLE=1' -D 'DRAW_LLVM_AVAILABLE=1' -D 'AMD_LLVM_AVAILABLE=1' -D 'GALLIVM_USE_ORCJIT=0' -D HAVE_SPIRV_TOOLS -D USE_LIBELF -D 'THREAD_SANITIZER=0' -D HAVE_LIBUNWIND -D HAVE_X11_DRM -D HAVE_DRI -D HAVE_DRI2 -D HAVE_DRI3_EXPLICIT_SYNC -D HAVE_DRISW_KMS -O3 -Wall -Winvalid-pch '-Werror=implicit-function-declaration' '-Werror=missing-prototypes' '-Werror=return-type' '-Werror=empty-body' '-Werror=incompatible-pointer-types' '-Werror=int-conversion' -Wimplicit-fallthrough -Wmisleading-indentation -Wno-missing-field-initializers -Wno-format-truncation -Wno-unknown-pragmas -Wno-microsoft-enum-value -Wno-unused-function '-Werror=format' -Wformat-security '-Werror=thread-safety' -Wno-unused-variable -Wno-unused-but-set-variable '-Werror=pointer-arith' '-Werror=vla' '-Werror=gnu-empty-initializer' '-std=c11' -ferror-limit 19 '-fvisibility=hidden' -pthread -mstackrealign '-fgnuc-version=4.2.1' -fskip-odr-check-in-gmf -fcolor-diagnostics -vectorize-loops -vectorize-slp '-flto=full' -flto-unit -ffat-lto-objects -ffat-lto-objects -faddrsig '-D__GCC_HAVE_DWARF2_CFI_ASM=1' -x c format_utils-f42aff.c
       31.19 real        30.31 user         0.14 sys
    161716  maximum resident set size
     73701  average shared memory size
       804  average unshared data size
       128  average unshared stack size
     29340  page reclaims
         0  page faults
         0  swaps
         0  block input operations
        16  block output operations
         0  messages sent
         0  messages received
         0  signals received
         3  voluntary context switches
       714  involuntary context switches

[MIvanchev]

I'm doing detailed tests again, but it seems you are right, it seems to caused by Polly... is this still the right repo for this bug?

P.S.
It's a shame because I moved to clang specifically to compile Mesa with Polly 😄

[DimitryAndric]

Well, I guess the polly developers can have a go at this bug, of course. First thing would be to minimize the test case, somehow. That's always a bit tricky with timeouts :)

[llvmbot]

@llvm/issue-subscribers-polly

Author: Mihail Ivanchev (MIvanchev)

See the respective Mesa issue, https://gitlab.freedesktop.org/mesa/mesa/-/issues/12872, I'm suspecting this is more clang than Mesa.