# add\_library/add\_executable sources do not depend on compiler executable
**URL:** https://discourse.cmake.org/t/add-library-add-executable-sources-do-not-depend-on-compiler-executable/15662
**Category:** Usage
**Created:** [May 26, 2026, 3:00am UTC](https://discourse.cmake.org/t/add-library-add-executable-sources-do-not-depend-on-compiler-executable/15662 "2026-05-26T03:00:22Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@wenju-he](https://discourse.cmake.org/u/wenju-he)
#### Post date: [May 26, 2026, 3:00am UTC](https://discourse.cmake.org/t/add-library-add-executable-sources-do-not-depend-on-compiler-executable/15662/1 "2026-05-26T03:00:22Z")
By default, CMake does not add the compiler executable as a dependency of compiled objects. Sources are rebuilt when they change, but not when the compiler changes.
This causes a concrete problem in toolchain bootstrap builds such as LLVM ([GitHub - llvm/llvm-project: The LLVM Project is a collection of modular and reusable compiler and toolchain technologies. · GitHub](https://github.com/llvm/llvm-project)):
- Step 1: Build clang using host compiler.
- Step 2: LLVM runtimes (libc, libclc, etc.) are configured as a separate CMake invocation via ExternalProject, using the just-built clang as CMAKE\_C\_COMPILER/CMAKE\_CXX\_COMPILER.
When clang is subsequently modified and rebuilt, the runtimes are not rebuilt because their object files have no dependency on the clang binary. This is especially critical for some runtimes that emit LLVM bitcode, where a compiler change must invalidate all outputs.
The behavior is probably related to the explanation provided in [When to reconfigure vs configure from scratch? Why? - #2 by ben.boeckel](https://discourse.cmake.org/t/when-to-reconfigure-vs-configure-from-scratch-why/3670/2), but it forces llvm-project to work around it by adding dependency on compiler executable manually.
Request: Could CMake provide an option or a variable — so that add\_library/add\_executable automatically adds compiler executable as an OBJECT\_DEPENDS for all compiled sources?
---
### Author:  [@ClausKlein](https://discourse.cmake.org/u/ClausKlein)
#### Post date: [May 26, 2026, 12:17pm UTC](https://discourse.cmake.org/t/add-library-add-executable-sources-do-not-depend-on-compiler-executable/15662/2 "2026-05-26T12:17:09Z")
which Generator do you use?
If `Ninja` is the Generator, all `llvm` headers are in the dependency list:
```bash
bash-5.3$ ninja -t deps | grep -w llvm | sort -u
# ...
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/algorithm
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/array
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/atomic
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/bitset
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cassert
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cctype
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cerrno
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/chrono
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cinttypes
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/climits
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/clocale
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cmath
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/compare
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/concepts
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/condition_variable
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/coroutine
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cstddef
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cstdint
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cstdio
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cstdlib
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cstring
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/ctime
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/ctype.h
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cwchar
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/cwctype
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/deque
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/errno.h
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/exception
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/format
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/functional
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/initializer_list
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/inttypes.h
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/ios
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/iosfwd
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/iostream
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/istream
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/iterator
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/limits
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/locale
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/math.h
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/memory
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/memory_resource
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/mutex
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/new
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/optional
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/ostream
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/print
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/queue
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/ranges
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/ratio
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/source_location
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/span
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/sstream
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/stddef.h
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/stdexcept
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/stdio.h
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/stdlib.h
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/streambuf
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/string
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/string.h
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/string_view
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/system_error
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/thread
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/tuple
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/type_traits
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/typeinfo
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/unordered_map
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/utility
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/variant
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/vector
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/version
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/wchar.h
/usr/local/Cellar/llvm/22.1.6/include/c++/v1/wctype.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/ __stdarg___ gnuc_va_list.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/ __stdarg___ va_copy.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stdarg_header_macro.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stdarg_va_arg.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stdarg_va_copy.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stdarg_va_list.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stddef_header_macro.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stddef_max_align_t.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stddef_null.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stddef_nullptr_t.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stddef_offsetof.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stddef_ptrdiff_t.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stddef_rsize_t.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stddef_size_t.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/__stddef_wchar_t.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/inttypes.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/limits.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/stdarg.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/stddef.h
/usr/local/Cellar/llvm/22.1.6/lib/clang/22/include/stdint.h
```
---
### Author:  [@wenju-he](https://discourse.cmake.org/u/wenju-he)
#### Post date: [May 27, 2026, 4:27am UTC](https://discourse.cmake.org/t/add-library-add-executable-sources-do-not-depend-on-compiler-executable/15662/3 "2026-05-27T04:27:52Z")
It should not be related to generator type. I can reproduce the issue using Ninja and Make generators.
It is not missing dependency on llvm headers. It is that just built clang isn’t in the dependency.
Ninja reproduce steps:
```auto
cd llvm-project-llvmorg-22.1.6/build
cmake -GNinja -DLLVM_ENABLE_PROJECTS="clang" -DLLVM_ENABLE_RUNTIMES="libc" -DLLVM_TARGETS_TO_BUILD="X86" -DCMAKE_BUILD_TYPE=Release -DLLVM_LIBC_FULL_BUILD=OFF ../llvm
ninja
ls -l ./bin/clang-22
-rwxr-x--- 1 wenjuhe icg_src 152354624 May 27 02:21 ./bin/clang-22*
ls -l ./runtimes/runtimes-bins/libc/lib/libllvmlibc.a
-rw-r----- 1 wenjuhe icg_src 5923336 May 27 02:22 ./runtimes/runtimes-bins/libc/lib/libllvmlibc.a
touch ../llvm/lib/Transforms/Scalar/LICM.cpp
ninja
ls -l ./bin/clang-22
-rwxr-x--- 1 wenjuhe icg_src 152354624 May 27 04:51 ./bin/clang-22*
ls -l ./runtimes/runtimes-bins/libc/lib/libllvmlibc.a
-rw-r----- 1 wenjuhe icg_src 5923336 May 27 02:22 ./runtimes/runtimes-bins/libc/lib/libllvmlibc.a
ninja -C runtimes/runtimes-bins -t deps|grep "build/bin/clang"
```
We can see that timestamp of just-built clang is updated after rebuild, but timestamp of libc library libllvmlibc.a isn’t updated.
However, libllvmlibc.a is built using just-built clang. For example, Unix Makefiles generator output file `runtimes/runtimes-bins/compile_commands.json` has content:
```auto
{
"directory": "/localdisk2/wenjuhe/tmp5/llvm-project-llvmorg-22.1.6/build-make/runtimes/runtimes-bins/libc/src/__support",
"command": "/localdisk2/wenjuhe/tmp5/llvm-project-llvmorg-22.1.6/build-make/bin/clang++ --target=x86_64-unknown-linux-gnu -DLIBC_NAMESPACE= __llvm_libc_22_1_6_ -I/localdisk2/wenjuhe/tmp5/llvm-project-llvmorg-22.1.6/libc -I/localdisk2/wenjuhe/tmp5/llvm-project-llvmorg-22.1.6/build-make/runtimes/runtimes-bins/libc -isystem /localdisk2/wenjuhe/tmp5/llvm-project-llvmorg-22.1.6/build-make/runtimes/runtimes-bins/libc/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wno-pass-failed -Wmisleading-indentation -Wctad-maybe-unsupported -ffunction-sections -fdata-sections -O3 -DNDEBUG -std=gnu++17 -DLIBC_QSORT_IMPL=LIBC_QSORT_QUICK_SORT -DLIBC_COPT_STRING_LENGTH_IMPL=clang_vector -DLIBC_COPT_FIND_FIRST_CHARACTER_IMPL=word -DLIBC_ADD_NULL_CHECKS -DLIBC_ERRNO_MODE=LIBC_ERRNO_MODE_DEFAULT -DLIBC_THREAD_MODE=LIBC_THREAD_MODE_PLATFORM -DLIBC_CONF_WCTYPE_MODE=LIBC_WCTYPE_MODE_ASCII -DLIBC_COPT_RAW_MUTEX_DEFAULT_SPIN_COUNT=100 -fpie -ffixed-point -fno-builtin -fno-exceptions -fno-lax-vector-conversions -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-rtti -ftrivial-auto-var-init=pattern -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -Wall -Wextra -Werror -Wconversion -Wno-sign-conversion -Wdeprecated -Wno-c99-extensions -Wno-gnu-imaginary-constant -Wno-pedantic -Wimplicit-fallthrough -Wwrite-strings -Wextra-semi -Wnewline-eof -Wnonportable-system-include-path -Wstrict-prototypes -Wthread-safety -Wglobal-constructors -DLIBC_FREELIST_MALLOC_SIZE= -o CMakeFiles/libc.src.__ support.freelist_heap.dir/freelist_heap.cpp.o -c /localdisk2/wenjuhe/tmp5/llvm-project-llvmorg-22.1.6/libc/src/__support/freelist_heap.cpp",
"file": "/localdisk2/wenjuhe/tmp5/llvm-project-llvmorg-22.1.6/libc/src/__support/freelist_heap.cpp",
"output": "libc/src/ __support/CMakeFiles/libc.src.__ support.freelist_heap.dir/freelist_heap.cpp.o"
},
```
The intention is that rebuild of clang should trigger rebuild of libc library.
The last command outputs empty, meaning that libc library has no dependency on clang executable.
---
### Author:  [@wenju-he](https://discourse.cmake.org/u/wenju-he)
#### Post date: [June 16, 2026, 11:07am UTC](https://discourse.cmake.org/t/add-library-add-executable-sources-do-not-depend-on-compiler-executable/15662/4 "2026-06-16T11:07:57Z")
Kindly ping. Does this feature request make sense as an opt-in feature for bootstrap build scenario? The core issue is that CMake does not register compiler as a build dependency, which breaks when a newly built compiler is updated in bootstrap step.
---
### Author:  [@vito.gamberini](https://discourse.cmake.org/u/vito.gamberini)
#### Post date: [June 29, 2026, 6:19pm UTC](https://discourse.cmake.org/t/add-library-add-executable-sources-do-not-depend-on-compiler-executable/15662/5 "2026-06-29T18:19:41Z")
The compiler is not a build dependency in effectively all CMake projects which are not LLVM or extending LLVM.
It’s opt-in for those use-cases. That’s why the capacity to manually add dependencies exists, for exceptions to the normal rules.