diff --git a/doc/release-notes/rl-2511.section.md b/doc/release-notes/rl-2511.section.md
index a8bd8ab82bf0..9c1b3029f8bc 100644
--- a/doc/release-notes/rl-2511.section.md
+++ b/doc/release-notes/rl-2511.section.md
@@ -26,7 +26,7 @@
 
 - GCC 9, 10, 11, and 12 have been removed, as they have reached end‐of‐life upstream and are no longer supported.
 
-- LLVM 12, 13, and 14 have been removed, as they have reached end‐of‐life upstream and are no longer supported.
+- LLVM 12, 13, 14, and 15 have been removed, as they have reached end‐of‐life upstream and are no longer supported.
 
 - GHCJS 8.10, exposed via `haskell.compiler.ghcjs` and `haskell.compiler.ghcjs810`, has been removed. Downstream users should migrate their projects to the new JavaScript backend of GHC proper which can be used via `pkgsCross.ghcjs` from Nixpkgs. Haskell packaging code, like `haskellPackages.mkDerivation`, `ghcWithPackages` and `hoogleWithPackages`, also no longer supports GHCJS.
 
diff --git a/pkgs/development/compilers/llvm/15/clang/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/15/clang/gnu-install-dirs.patch
deleted file mode 100644
index f767c56836d5..000000000000
--- a/pkgs/development/compilers/llvm/15/clang/gnu-install-dirs.patch
+++ /dev/null
@@ -1,105 +0,0 @@
-diff --git a/CMakeLists.txt b/CMakeLists.txt
-index c27beec313d7..480f13e73c9f 100644
---- a/CMakeLists.txt
-+++ b/CMakeLists.txt
-@@ -78,15 +78,17 @@ if(CLANG_BUILT_STANDALONE)
-   if (NOT LLVM_CONFIG_FOUND)
-     # Pull values from LLVMConfig.cmake.  We can drop this once the llvm-config
-     # path is removed.
--    set(MAIN_INCLUDE_DIR "${LLVM_INCLUDE_DIR}")
-+    set(INCLUDE_DIRS ${LLVM_INCLUDE_DIRS})
-     set(LLVM_OBJ_DIR "${LLVM_BINARY_DIR}")
-     # N.B. this is just a default value, the CACHE PATHs below can be overriden.
-     set(MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm")
-     set(TOOLS_BINARY_DIR "${LLVM_TOOLS_BINARY_DIR}")
-     set(LIBRARY_DIR "${LLVM_LIBRARY_DIR}")
-+  else()
-+    set(INCLUDE_DIRS "${LLVM_BINARY_DIR}/include" "${MAIN_INCLUDE_DIR}")
-   endif()
- 
--  set(LLVM_MAIN_INCLUDE_DIR "${MAIN_INCLUDE_DIR}" CACHE PATH "Path to llvm/include")
-+  set(LLVM_INCLUDE_DIRS ${INCLUDE_DIRS} CACHE PATH "Path to llvm/include and any other header dirs needed")
-   set(LLVM_BINARY_DIR "${LLVM_OBJ_ROOT}" CACHE PATH "Path to LLVM build tree")
-   set(LLVM_MAIN_SRC_DIR "${MAIN_SRC_DIR}" CACHE PATH "Path to LLVM source tree")
-   set(LLVM_TOOLS_BINARY_DIR "${TOOLS_BINARY_DIR}" CACHE PATH "Path to llvm/bin")
-@@ -128,7 +130,7 @@ if(CLANG_BUILT_STANDALONE)
-     set(LLVM_INCLUDE_TESTS ON)
-   endif()
- 
--  include_directories("${LLVM_BINARY_DIR}/include" "${LLVM_MAIN_INCLUDE_DIR}")
-+  include_directories(${LLVM_INCLUDE_DIRS})
-   link_directories("${LLVM_LIBRARY_DIR}")
- 
-   set( CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin )
-diff --git a/cmake/modules/AddClang.cmake b/cmake/modules/AddClang.cmake
-index 21ac332e4f5f..b16c314bd1e2 100644
---- a/cmake/modules/AddClang.cmake
-+++ b/cmake/modules/AddClang.cmake
-@@ -119,8 +119,8 @@ macro(add_clang_library name)
-         install(TARGETS ${lib}
-           COMPONENT ${lib}
-           ${export_to_clangtargets}
--          LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX}
--          ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX}
-+          LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}"
-+          ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}"
-           RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}")
- 
-         if (NOT LLVM_ENABLE_IDE)
-diff --git a/lib/Headers/CMakeLists.txt b/lib/Headers/CMakeLists.txt
-index 6e2060991b92..b9bc930d26b8 100644
---- a/lib/Headers/CMakeLists.txt
-+++ b/lib/Headers/CMakeLists.txt
-@@ -420,7 +420,7 @@ add_header_target("openmp-resource-headers" ${openmp_wrapper_files})
- add_header_target("windows-resource-headers" ${windows_only_files})
- add_header_target("utility-resource-headers" ${utility_files})
- 
--set(header_install_dir lib${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION}/include)
-+set(header_install_dir ${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION}/include)
- 
- #############################################################
- # Install rules for the catch-all clang-resource-headers target
-diff --git a/tools/libclang/CMakeLists.txt b/tools/libclang/CMakeLists.txt
-index 8d95d0900e8c..ebc70ff7526d 100644
---- a/tools/libclang/CMakeLists.txt
-+++ b/tools/libclang/CMakeLists.txt
-@@ -180,7 +180,7 @@ foreach(PythonVersion ${CLANG_PYTHON_BINDINGS_VERSIONS})
-           COMPONENT
-             libclang-python-bindings
-           DESTINATION
--            "lib${LLVM_LIBDIR_SUFFIX}/python${PythonVersion}/site-packages")
-+            "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}/python${PythonVersion}/site-packages")
- endforeach()
- if(NOT LLVM_ENABLE_IDE)
-   add_custom_target(libclang-python-bindings)
-diff --git a/tools/scan-build-py/CMakeLists.txt b/tools/scan-build-py/CMakeLists.txt
-index 061dc7ef4dd9..adc54b2edc32 100644
---- a/tools/scan-build-py/CMakeLists.txt
-+++ b/tools/scan-build-py/CMakeLists.txt
-@@ -88,7 +88,7 @@ foreach(lib ${LibScanbuild})
-                      DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/lib/libscanbuild/${lib})
-   list(APPEND Depends ${CMAKE_BINARY_DIR}/lib/libscanbuild/${lib})
-   install(PROGRAMS lib/libscanbuild/${lib}
--          DESTINATION lib/libscanbuild
-+          DESTINATION "${CMAKE_INSTALL_LIBDIR}/libscanbuild"
-           COMPONENT scan-build-py)
- endforeach()
- 
-@@ -106,7 +106,7 @@ foreach(resource ${LibScanbuildResources})
-                      DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/lib/libscanbuild/resources/${resource})
-   list(APPEND Depends ${CMAKE_BINARY_DIR}/lib/libscanbuild/resources/${resource})
-   install(PROGRAMS lib/libscanbuild/resources/${resource}
--          DESTINATION lib/libscanbuild/resources
-+          DESTINATION "${CMAKE_INSTALL_LIBDIR}/libscanbuild/resources"
-           COMPONENT scan-build-py)
- endforeach()
- 
-@@ -122,7 +122,7 @@ foreach(lib ${LibEar})
-                      DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/lib/libear/${lib})
-   list(APPEND Depends ${CMAKE_BINARY_DIR}/lib/libear/${lib})
-   install(PROGRAMS lib/libear/${lib}
--          DESTINATION lib/libear
-+          DESTINATION "${CMAKE_INSTALL_LIBDIR}/libear"
-           COMPONENT scan-build-py)
- endforeach()
- 
diff --git a/pkgs/development/compilers/llvm/15/compiler-rt/normalize-var.patch b/pkgs/development/compilers/llvm/15/compiler-rt/normalize-var.patch
deleted file mode 100644
index 135cf625ef78..000000000000
--- a/pkgs/development/compilers/llvm/15/compiler-rt/normalize-var.patch
+++ /dev/null
@@ -1,16 +0,0 @@
-diff --git a/compiler-rt/cmake/Modules/CompilerRTUtils.cmake b/compiler-rt/cmake/Modules/CompilerRTUtils.cmake
-index f1f46fb9599c..6f19e69507ba 100644
---- a/cmake/Modules/CompilerRTUtils.cmake
-+++ b/cmake/Modules/CompilerRTUtils.cmake
-@@ -302,8 +302,9 @@ macro(load_llvm_config)
-     # Get some LLVM variables from LLVMConfig.
-     include("${LLVM_CMAKE_PATH}/LLVMConfig.cmake")
- 
--    set(LLVM_LIBRARY_OUTPUT_INTDIR
--      ${LLVM_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX})
-+    get_filename_component(LLVM_LIBRARY_OUTPUT_INTDIR
-+      ${LLVM_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX}
-+      REALPATH)
-   endif()
- endmacro()
- 
diff --git a/pkgs/development/compilers/llvm/15/lld/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/15/lld/gnu-install-dirs.patch
deleted file mode 100644
index ea62b2ad50c7..000000000000
--- a/pkgs/development/compilers/llvm/15/lld/gnu-install-dirs.patch
+++ /dev/null
@@ -1,46 +0,0 @@
-diff --git a/CMakeLists.txt b/CMakeLists.txt
-index dcc649629a4b..58dca54642e4 100644
---- a/CMakeLists.txt
-+++ b/CMakeLists.txt
-@@ -70,13 +70,15 @@ if(LLD_BUILT_STANDALONE)
-   if (NOT LLVM_CONFIG_FOUND)
-     # Pull values from LLVMConfig.cmake.  We can drop this once the llvm-config
-     # path is removed.
--    set(MAIN_INCLUDE_DIR "${LLVM_INCLUDE_DIR}")
-+    set(INCLUDE_DIRS ${LLVM_INCLUDE_DIRS})
-     set(LLVM_OBJ_DIR "${LLVM_BINARY_DIR}")
-     # N.B. this is just a default value, the CACHE PATHs below can be overridden.
-     set(MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm")
-+  else()
-+    set(INCLUDE_DIRS "${LLVM_BINARY_DIR}/include" "${MAIN_INCLUDE_DIR}")
-   endif()
- 
--  set(LLVM_MAIN_INCLUDE_DIR "${MAIN_INCLUDE_DIR}" CACHE PATH "Path to llvm/include")
-+  set(LLVM_INCLUDE_DIRS ${INCLUDE_DIRS} CACHE PATH "Path to llvm/include and any other header dirs needed")
-   set(LLVM_BINARY_DIR "${LLVM_OBJ_ROOT}" CACHE PATH "Path to LLVM build tree")
-   set(LLVM_MAIN_SRC_DIR "${MAIN_SRC_DIR}" CACHE PATH "Path to LLVM source tree")
- 
-@@ -95,7 +97,7 @@ if(LLD_BUILT_STANDALONE)
- 
-   set(PACKAGE_VERSION "${LLVM_PACKAGE_VERSION}")
- 
--  include_directories("${LLVM_BINARY_DIR}/include" ${LLVM_INCLUDE_DIRS})
-+  include_directories(${LLVM_INCLUDE_DIRS})
-   link_directories(${LLVM_LIBRARY_DIRS})
- 
-   if(LLVM_INCLUDE_TESTS)
-diff --git a/cmake/modules/AddLLD.cmake b/cmake/modules/AddLLD.cmake
-index d3924f7243d4..42a7cd62281c 100644
---- a/cmake/modules/AddLLD.cmake
-+++ b/cmake/modules/AddLLD.cmake
-@@ -18,8 +18,8 @@ macro(add_lld_library name)
-     install(TARGETS ${name}
-       COMPONENT ${name}
-       ${export_to_lldtargets}
--      LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX}
--      ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX}
-+      LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}"
-+      ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}"
-       RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}")
- 
-     if (${ARG_SHARED} AND NOT CMAKE_CONFIGURATION_TYPES)
diff --git a/pkgs/development/compilers/llvm/15/lldb/procfs.patch b/pkgs/development/compilers/llvm/15/lldb/procfs.patch
deleted file mode 100644
index 7b200e86505c..000000000000
--- a/pkgs/development/compilers/llvm/15/lldb/procfs.patch
+++ /dev/null
@@ -1,46 +0,0 @@
---- a/source/Plugins/Process/Linux/Procfs.h
-+++ b/source/Plugins/Process/Linux/Procfs.h
-@@ -10,6 +10,13 @@
- // sys/procfs.h on Android/Linux for all supported architectures.
- 
- #include <sys/ptrace.h>
-+#include <asm/ptrace.h>
-+
-+// on i686 preprocessor symbols with these register names are defined as
-+// numeric constants; these symbols clash with identifier names used in
-+// `llvm/Support/VirtualFileSystem.h` and `llvm/ADT/SmallVector.h`
-+#undef FS
-+#undef CS
- 
- #include "lldb/lldb-types.h"
- 
-@@ -17,23 +24,13 @@
- 
- #include <vector>
- 
--#ifdef __ANDROID__
--#if defined(__arm64__) || defined(__aarch64__)
--typedef unsigned long elf_greg_t;
--typedef elf_greg_t
--    elf_gregset_t[(sizeof(struct user_pt_regs) / sizeof(elf_greg_t))];
--typedef struct user_fpsimd_state elf_fpregset_t;
--#ifndef NT_FPREGSET
--#define NT_FPREGSET NT_PRFPREG
--#endif // NT_FPREGSET
--#elif defined(__mips__)
--#ifndef NT_FPREGSET
--#define NT_FPREGSET NT_PRFPREG
--#endif // NT_FPREGSET
--#endif
--#else // __ANDROID__
-+#if !defined(__GLIBC__) && defined(__powerpc__)
-+#define pt_regs musl_pt_regs
-+#include <sys/procfs.h>
-+#undef pt_regs
-+#else
- #include <sys/procfs.h>
--#endif // __ANDROID__
-+#endif
- 
- namespace lldb_private {
- namespace process_linux {
diff --git a/pkgs/development/compilers/llvm/15/lldb/resource-dir.patch b/pkgs/development/compilers/llvm/15/lldb/resource-dir.patch
deleted file mode 100644
index e0db80afeb9f..000000000000
--- a/pkgs/development/compilers/llvm/15/lldb/resource-dir.patch
+++ /dev/null
@@ -1,13 +0,0 @@
-diff --git a/lldb/cmake/modules/LLDBConfig.cmake b/lldb/cmake/modules/LLDBConfig.cmake
-index 37364341ff8b..7f74c1a3e257 100644
---- a/cmake/modules/LLDBConfig.cmake
-+++ b/cmake/modules/LLDBConfig.cmake
-@@ -257,7 +257,7 @@ if (NOT TARGET clang-resource-headers)
-   # Iterate over the possible places where the external resource directory
-   # could be and pick the first that exists.
-   foreach(CANDIDATE "${Clang_DIR}/../.." "${LLVM_DIR}" "${LLVM_LIBRARY_DIRS}"
--                    "${LLVM_BUILD_LIBRARY_DIR}"
-+                    "${LLVM_BUILD_LIBRARY_DIR}" "@clangLibDir@"
-                     "${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}")
-     # Build the resource directory path by appending 'clang/<version number>'.
-     set(CANDIDATE_RESOURCE_DIR "${CANDIDATE}/clang/${LLDB_CLANG_RESOURCE_DIR_NAME}")
diff --git a/pkgs/development/compilers/llvm/15/llvm/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/15/llvm/gnu-install-dirs.patch
deleted file mode 100644
index 0ef317af8cc7..000000000000
--- a/pkgs/development/compilers/llvm/15/llvm/gnu-install-dirs.patch
+++ /dev/null
@@ -1,138 +0,0 @@
-diff --git a/CMakeLists.txt b/CMakeLists.txt
-index 45399dc0537e..5d946e9e6583 100644
---- a/CMakeLists.txt
-+++ b/CMakeLists.txt
-@@ -942,7 +942,7 @@ if (NOT TENSORFLOW_AOT_PATH STREQUAL "")
-   add_subdirectory(${TENSORFLOW_AOT_PATH}/xla_aot_runtime_src
-     ${CMAKE_ARCHIVE_OUTPUT_DIRECTORY}/tf_runtime)
-   install(TARGETS tf_xla_runtime EXPORT LLVMExports
--    ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX} COMPONENT tf_xla_runtime)
-+    ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX} COMPONENT tf_xla_runtime)
-   set_property(GLOBAL APPEND PROPERTY LLVM_EXPORTS tf_xla_runtime)
-   # Once we add more modules, we should handle this more automatically.
-   if (DEFINED LLVM_OVERRIDE_MODEL_HEADER_INLINERSIZEMODEL)
-diff --git a/cmake/modules/AddLLVM.cmake b/cmake/modules/AddLLVM.cmake
-index 057431208322..56f0dcb258da 100644
---- a/cmake/modules/AddLLVM.cmake
-+++ b/cmake/modules/AddLLVM.cmake
-@@ -844,8 +844,8 @@ macro(add_llvm_library name)
-       get_target_export_arg(${name} LLVM export_to_llvmexports ${umbrella})
-       install(TARGETS ${name}
-               ${export_to_llvmexports}
--              LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX} COMPONENT ${name}
--              ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX} COMPONENT ${name}
-+              LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" COMPONENT ${name}
-+              ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" COMPONENT ${name}
-               RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}" COMPONENT ${name})
- 
-       if (NOT LLVM_ENABLE_IDE)
-@@ -2007,7 +2007,7 @@ function(llvm_install_library_symlink name dest type)
-   set(full_name ${CMAKE_${type}_LIBRARY_PREFIX}${name}${CMAKE_${type}_LIBRARY_SUFFIX})
-   set(full_dest ${CMAKE_${type}_LIBRARY_PREFIX}${dest}${CMAKE_${type}_LIBRARY_SUFFIX})
- 
--  set(output_dir lib${LLVM_LIBDIR_SUFFIX})
-+  set(output_dir ${CMAKE_INSTALL_FULL_LIBDIR}${LLVM_LIBDIR_SUFFIX})
-   if(WIN32 AND "${type}" STREQUAL "SHARED")
-     set(output_dir "${CMAKE_INSTALL_BINDIR}")
-   endif()
-@@ -2271,15 +2271,15 @@ function(llvm_setup_rpath name)
- 
-   if (APPLE)
-     set(_install_name_dir INSTALL_NAME_DIR "@rpath")
--    set(_install_rpath "@loader_path/../lib${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
-+    set(_install_rpath "@loader_path/../${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
-   elseif(${CMAKE_SYSTEM_NAME} MATCHES "AIX" AND BUILD_SHARED_LIBS)
-     # $ORIGIN is not interpreted at link time by aix ld.
-     # Since BUILD_SHARED_LIBS is only recommended for use by developers,
-     # hardcode the rpath to build/install lib dir first in this mode.
-     # FIXME: update this when there is better solution.
--    set(_install_rpath "${LLVM_LIBRARY_OUTPUT_INTDIR}" "${CMAKE_INSTALL_PREFIX}/lib${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
-+    set(_install_rpath "${LLVM_LIBRARY_OUTPUT_INTDIR}" "${CMAKE_INSTALL_FULL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
-   elseif(UNIX)
--    set(_install_rpath "\$ORIGIN/../lib${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
-+    set(_install_rpath "\$ORIGIN/../${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
-     if(${CMAKE_SYSTEM_NAME} MATCHES "(FreeBSD|DragonFly)")
-       set_property(TARGET ${name} APPEND_STRING PROPERTY
-                    LINK_FLAGS " -Wl,-z,origin ")
-diff --git a/cmake/modules/AddOCaml.cmake b/cmake/modules/AddOCaml.cmake
-index 891c9e6d618c..8d963f3b0069 100644
---- a/cmake/modules/AddOCaml.cmake
-+++ b/cmake/modules/AddOCaml.cmake
-@@ -147,9 +147,9 @@ function(add_ocaml_library name)
-   endforeach()
- 
-   if( APPLE )
--    set(ocaml_rpath "@executable_path/../../../lib${LLVM_LIBDIR_SUFFIX}")
-+    set(ocaml_rpath "@executable_path/../../../${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}")
-   elseif( UNIX )
--    set(ocaml_rpath "\\$ORIGIN/../../../lib${LLVM_LIBDIR_SUFFIX}")
-+    set(ocaml_rpath "\\$ORIGIN/../../../${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}")
-   endif()
-   list(APPEND ocaml_flags "-ldopt" "-Wl,-rpath,${ocaml_rpath}")
- 
-diff --git a/cmake/modules/CMakeLists.txt b/cmake/modules/CMakeLists.txt
-index d4b0ab959148..26ed981fd09f 100644
---- a/cmake/modules/CMakeLists.txt
-+++ b/cmake/modules/CMakeLists.txt
-@@ -128,7 +128,7 @@ set(LLVM_CONFIG_INCLUDE_DIRS
-   )
- list(REMOVE_DUPLICATES LLVM_CONFIG_INCLUDE_DIRS)
- 
--extend_path(LLVM_CONFIG_LIBRARY_DIR "\${LLVM_INSTALL_PREFIX}" "lib\${LLVM_LIBDIR_SUFFIX}")
-+extend_path(LLVM_CONFIG_LIBRARY_DIR "\${LLVM_INSTALL_PREFIX}" "${CMAKE_INSTALL_LIBDIR}\${LLVM_LIBDIR_SUFFIX}")
- set(LLVM_CONFIG_LIBRARY_DIRS
-   "${LLVM_CONFIG_LIBRARY_DIR}"
-   # FIXME: Should there be other entries here?
-diff --git a/docs/CMake.rst b/docs/CMake.rst
-index 879b7b231d4c..9c31d14e8950 100644
---- a/docs/CMake.rst
-+++ b/docs/CMake.rst
-@@ -250,7 +250,7 @@ description is in `LLVM-related variables`_ below.
- **LLVM_LIBDIR_SUFFIX**:STRING
-   Extra suffix to append to the directory where libraries are to be
-   installed. On a 64-bit architecture, one could use ``-DLLVM_LIBDIR_SUFFIX=64``
--  to install libraries to ``/usr/lib64``.
-+  to install libraries to ``/usr/lib64``. See also ``CMAKE_INSTALL_LIBDIR``.
- 
- **LLVM_PARALLEL_{COMPILE,LINK}_JOBS**:STRING
-   Building the llvm toolchain can use a lot of resources, particularly
-@@ -284,6 +284,10 @@ manual, or execute ``cmake --help-variable VARIABLE_NAME``.
-   The path to install executables, relative to the *CMAKE_INSTALL_PREFIX*.
-   Defaults to "bin".
- 
-+**CMAKE_INSTALL_LIBDIR**:PATH
-+  The path to install libraries, relative to the *CMAKE_INSTALL_PREFIX*.
-+  Defaults to "lib".
-+
- **CMAKE_INSTALL_INCLUDEDIR**:PATH
-   The path to install header files, relative to the *CMAKE_INSTALL_PREFIX*.
-   Defaults to "include".
-diff --git a/tools/llvm-config/BuildVariables.inc.in b/tools/llvm-config/BuildVariables.inc.in
-index 370005cd8d7d..7e790bc52111 100644
---- a/tools/llvm-config/BuildVariables.inc.in
-+++ b/tools/llvm-config/BuildVariables.inc.in
-@@ -23,6 +23,7 @@
- #define LLVM_CXXFLAGS "@LLVM_CXXFLAGS@"
- #define LLVM_BUILDMODE "@LLVM_BUILDMODE@"
- #define LLVM_LIBDIR_SUFFIX "@LLVM_LIBDIR_SUFFIX@"
-+#define LLVM_INSTALL_LIBDIR "@CMAKE_INSTALL_LIBDIR@"
- #define LLVM_INSTALL_INCLUDEDIR "@CMAKE_INSTALL_INCLUDEDIR@"
- #define LLVM_INSTALL_PACKAGE_DIR "@LLVM_INSTALL_PACKAGE_DIR@"
- #define LLVM_TARGETS_BUILT "@LLVM_TARGETS_BUILT@"
-diff --git a/tools/llvm-config/llvm-config.cpp b/tools/llvm-config/llvm-config.cpp
-index 2c6c55f89d38..f6d2068a0827 100644
---- a/tools/llvm-config/llvm-config.cpp
-+++ b/tools/llvm-config/llvm-config.cpp
-@@ -369,7 +369,11 @@ int main(int argc, char **argv) {
-       sys::fs::make_absolute(ActivePrefix, Path);
-       ActiveBinDir = std::string(Path.str());
-     }
--    ActiveLibDir = ActivePrefix + "/lib" + LLVM_LIBDIR_SUFFIX;
-+    {
-+      SmallString<256> Path(LLVM_INSTALL_LIBDIR LLVM_LIBDIR_SUFFIX);
-+      sys::fs::make_absolute(ActivePrefix, Path);
-+      ActiveLibDir = std::string(Path.str());
-+    }
-     {
-       SmallString<256> Path(LLVM_INSTALL_PACKAGE_DIR);
-       sys::fs::make_absolute(ActivePrefix, Path);
diff --git a/pkgs/development/compilers/llvm/15/llvm/lit-shell-script-runner-set-dyld-library-path.patch b/pkgs/development/compilers/llvm/15/llvm/lit-shell-script-runner-set-dyld-library-path.patch
deleted file mode 100644
index 32f1d13a9dc2..000000000000
--- a/pkgs/development/compilers/llvm/15/llvm/lit-shell-script-runner-set-dyld-library-path.patch
+++ /dev/null
@@ -1,26 +0,0 @@
-diff --git a/utils/lit/lit/TestRunner.py b/utils/lit/lit/TestRunner.py
-index 0242e0b75af3..d732011306f7 100644
---- a/utils/lit/lit/TestRunner.py
-+++ b/utils/lit/lit/TestRunner.py
-@@ -1029,6 +1029,12 @@ def executeScript(test, litConfig, tmpBase, commands, cwd):
-             f.write('@echo off\n')
-         f.write('\n@if %ERRORLEVEL% NEQ 0 EXIT\n'.join(commands))
-     else:
-+        # This env var is *purged* when invoking subprocesses so we have to
-+        # manually set it from within the bash script in order for the commands
-+        # in run lines to see this var:
-+        if "DYLD_LIBRARY_PATH" in test.config.environment:
-+            f.write(f'export DYLD_LIBRARY_PATH="{test.config.environment["DYLD_LIBRARY_PATH"]}"\n')
-+
-         for i, ln in enumerate(commands):
-             match = re.match(kPdbgRegex, ln)
-             if match:
-@@ -1363,7 +1369,7 @@ def applySubstitutions(script, substitutions, conditions={},
-         return processed
- 
-     process = processLine if recursion_limit is None else processLineToFixedPoint
--    
-+
-     return [unescapePercents(process(ln)) for ln in script]
- 
- 
diff --git a/pkgs/development/compilers/llvm/15/llvm/llvm-lit-cfg-add-libs-to-dylib-path.patch b/pkgs/development/compilers/llvm/15/llvm/llvm-lit-cfg-add-libs-to-dylib-path.patch
deleted file mode 100644
index d824516c0a16..000000000000
--- a/pkgs/development/compilers/llvm/15/llvm/llvm-lit-cfg-add-libs-to-dylib-path.patch
+++ /dev/null
@@ -1,79 +0,0 @@
-diff --git a/test/Unit/lit.cfg.py b/test/Unit/lit.cfg.py
-index 81e8dc04acea..479ff95681e2 100644
---- a/test/Unit/lit.cfg.py
-+++ b/test/Unit/lit.cfg.py
-@@ -3,6 +3,7 @@
- # Configuration file for the 'lit' test runner.
- 
- import os
-+import platform
- import subprocess
- 
- import lit.formats
-@@ -55,3 +56,26 @@ if sys.platform in ['win32', 'cygwin'] and os.path.isdir(config.shlibdir):
- # Win32 may use %SYSTEMDRIVE% during file system shell operations, so propogate.
- if sys.platform == 'win32' and 'SYSTEMDRIVE' in os.environ:
-     config.environment['SYSTEMDRIVE'] = os.environ['SYSTEMDRIVE']
-+
-+# Add the LLVM dynamic libs to the platform-specific loader search path env var:
-+#
-+# TODO: this is copied from `clang`'s `lit.cfg.py`; should unify..
-+def find_shlibpath_var():
-+    if platform.system() in ['Linux', 'FreeBSD', 'NetBSD', 'OpenBSD', 'SunOS']:
-+        yield 'LD_LIBRARY_PATH'
-+    elif platform.system() == 'Darwin':
-+        yield 'DYLD_LIBRARY_PATH'
-+    elif platform.system() == 'Windows':
-+        yield 'PATH'
-+    elif platform.system() == 'AIX':
-+        yield 'LIBPATH'
-+
-+for shlibpath_var in find_shlibpath_var():
-+    shlibpath = os.path.pathsep.join(
-+        (config.shlibdir,
-+         config.environment.get(shlibpath_var, '')))
-+    config.environment[shlibpath_var] = shlibpath
-+    break
-+else:
-+    lit_config.warning("unable to inject shared library path on '{}'"
-+                       .format(platform.system()))
-diff --git a/test/lit.cfg.py b/test/lit.cfg.py
-index 75a38b4c5dad..856fc75c9d74 100644
---- a/test/lit.cfg.py
-+++ b/test/lit.cfg.py
-@@ -42,6 +42,26 @@ llvm_config.with_environment('PATH', config.llvm_tools_dir, append_path=True)
- llvm_config.with_system_environment(
-     ['HOME', 'INCLUDE', 'LIB', 'TMP', 'TEMP'])
- 
-+# Add the LLVM dynamic libs to the platform-specific loader search path env var:
-+#
-+# TODO: this is copied from `clang`'s `lit.cfg.py`; should unify..
-+def find_shlibpath_var():
-+    if platform.system() in ['Linux', 'FreeBSD', 'NetBSD', 'OpenBSD', 'SunOS']:
-+        yield 'LD_LIBRARY_PATH'
-+    elif platform.system() == 'Darwin':
-+        yield 'DYLD_LIBRARY_PATH'
-+    elif platform.system() == 'Windows':
-+        yield 'PATH'
-+    elif platform.system() == 'AIX':
-+        yield 'LIBPATH'
-+
-+for shlibpath_var in find_shlibpath_var():
-+    shlibpath = config.llvm_shlib_dir
-+    llvm_config.with_environment(shlibpath_var, shlibpath, append_path = True)
-+    break
-+else:
-+    lit_config.warning("unable to inject shared library path on '{}'"
-+                       .format(platform.system()))
- 
- # Set up OCAMLPATH to include newly built OCaml libraries.
- top_ocaml_lib = os.path.join(config.llvm_lib_dir, 'ocaml')
-@@ -318,7 +338,7 @@ def have_cxx_shared_library():
- 
-     try:
-         readobj_cmd = subprocess.Popen(
--            [readobj_exe, '--needed-libs', readobj_exe], stdout=subprocess.PIPE)
-+            [readobj_exe, '--needed-libs', readobj_exe], stdout=subprocess.PIPE, env=config.environment)
-     except OSError:
-         print('could not exec llvm-readobj')
-         return False
diff --git a/pkgs/development/compilers/llvm/15/llvm/no-pipes.patch b/pkgs/development/compilers/llvm/15/llvm/no-pipes.patch
deleted file mode 100644
index 5b3d94e21ff6..000000000000
--- a/pkgs/development/compilers/llvm/15/llvm/no-pipes.patch
+++ /dev/null
@@ -1,19 +0,0 @@
-diff --git a/test/Bindings/Go/lit.local.cfg b/test/Bindings/Go/lit.local.cfg
-index 91a0ad89..4da83a1a 100644
---- a/test/Bindings/Go/lit.local.cfg
-+++ b/test/Bindings/Go/lit.local.cfg
-@@ -1,5 +1,4 @@
- import os
--import pipes
- import shlex
- import sys
- 
-@@ -56,7 +55,7 @@ def fixup_compiler_path(compiler):
-     except (AttributeError, OSError):
-         pass
- 
--    return ' '.join([pipes.quote(arg) for arg in args])
-+    return ' '.join([shlex.quote(arg) for arg in args])
- 
- config.environment['CC'] = fixup_compiler_path(config.host_cc)
- config.environment['CXX'] = fixup_compiler_path(config.host_cxx)
diff --git a/pkgs/development/compilers/llvm/15/openmp/fix-find-tool.patch b/pkgs/development/compilers/llvm/15/openmp/fix-find-tool.patch
deleted file mode 100644
index 103b054ed176..000000000000
--- a/pkgs/development/compilers/llvm/15/openmp/fix-find-tool.patch
+++ /dev/null
@@ -1,18 +0,0 @@
-diff --git a/libomptarget/DeviceRTL/CMakeLists.txt b/libomptarget/DeviceRTL/CMakeLists.txt
-index ce66214822a2..6ab7b33c95da 100644
---- a/libomptarget/DeviceRTL/CMakeLists.txt
-+++ b/libomptarget/DeviceRTL/CMakeLists.txt
-@@ -27,10 +27,10 @@ endif()
- if (LLVM_DIR)
-   # Builds that use pre-installed LLVM have LLVM_DIR set.
-   # A standalone or LLVM_ENABLE_RUNTIMES=openmp build takes this route
--  find_program(CLANG_TOOL clang PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
-+  find_program(CLANG_TOOL clang PATHS ${LLVM_TOOLS_BINARY_DIR})
-   find_program(LINK_TOOL llvm-link PATHS ${LLVM_TOOLS_BINARY_DIR}
--    NO_DEFAULT_PATH)
--  find_program(OPT_TOOL opt PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
-+    )
-+  find_program(OPT_TOOL opt PATHS ${LLVM_TOOLS_BINARY_DIR})
-   if ((NOT CLANG_TOOL) OR (NOT LINK_TOOL) OR (NOT OPT_TOOL))
-     libomptarget_say("Not building DeviceRTL. Missing clang: ${CLANG_TOOL}, llvm-link: ${LINK_TOOL} or opt: ${OPT_TOOL}")
-     return()
diff --git a/pkgs/development/compilers/llvm/15/openmp/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/15/openmp/gnu-install-dirs.patch
deleted file mode 100644
index 77a93208832a..000000000000
--- a/pkgs/development/compilers/llvm/15/openmp/gnu-install-dirs.patch
+++ /dev/null
@@ -1,22 +0,0 @@
-diff --git a/CMakeLists.txt b/CMakeLists.txt
-index b6ddbe90516d..311ab1d50e7f 100644
---- a/CMakeLists.txt
-+++ b/CMakeLists.txt
-@@ -29,7 +29,7 @@ if (OPENMP_STANDALONE_BUILD)
-   set(OPENMP_LIBDIR_SUFFIX "" CACHE STRING
-     "Suffix of lib installation directory, e.g. 64 => lib64")
-   # Do not use OPENMP_LIBDIR_SUFFIX directly, use OPENMP_INSTALL_LIBDIR.
--  set(OPENMP_INSTALL_LIBDIR "lib${OPENMP_LIBDIR_SUFFIX}")
-+  set(OPENMP_INSTALL_LIBDIR "${CMAKE_INSTALL_LIBDIR}${OPENMP_LIBDIR_SUFFIX}")
- 
-   # Group test settings.
-   set(OPENMP_TEST_C_COMPILER ${CMAKE_C_COMPILER} CACHE STRING
-@@ -40,7 +40,7 @@ if (OPENMP_STANDALONE_BUILD)
- else()
-   set(OPENMP_ENABLE_WERROR ${LLVM_ENABLE_WERROR})
-   # If building in tree, we honor the same install suffix LLVM uses.
--  set(OPENMP_INSTALL_LIBDIR "lib${LLVM_LIBDIR_SUFFIX}")
-+  set(OPENMP_INSTALL_LIBDIR "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}")
- 
-   if (NOT MSVC)
-     set(OPENMP_TEST_C_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang)
diff --git a/pkgs/development/compilers/llvm/15/openmp/run-lit-directly.patch b/pkgs/development/compilers/llvm/15/openmp/run-lit-directly.patch
deleted file mode 100644
index 1e952fdc36a8..000000000000
--- a/pkgs/development/compilers/llvm/15/openmp/run-lit-directly.patch
+++ /dev/null
@@ -1,12 +0,0 @@
-diff --git a/cmake/OpenMPTesting.cmake b/cmake/OpenMPTesting.cmake
---- a/cmake/OpenMPTesting.cmake
-+++ b/cmake/OpenMPTesting.cmake
-@@ -185,7 +185,7 @@ function(add_openmp_testsuite target comment)
-   if (${OPENMP_STANDALONE_BUILD})
-     set(LIT_ARGS ${OPENMP_LIT_ARGS} ${ARG_ARGS})
-     add_custom_target(${target}
--      COMMAND ${PYTHON_EXECUTABLE} ${OPENMP_LLVM_LIT_EXECUTABLE} ${LIT_ARGS} ${ARG_UNPARSED_ARGUMENTS}
-+      COMMAND ${OPENMP_LLVM_LIT_EXECUTABLE} ${LIT_ARGS} ${ARG_UNPARSED_ARGUMENTS}
-       COMMENT ${comment}
-       DEPENDS ${ARG_DEPENDS}
-       USES_TERMINAL
diff --git a/pkgs/development/compilers/llvm/15/clang/purity.patch b/pkgs/development/compilers/llvm/16/clang/purity.patch
similarity index 100%
rename from pkgs/development/compilers/llvm/15/clang/purity.patch
rename to pkgs/development/compilers/llvm/16/clang/purity.patch
diff --git a/pkgs/development/compilers/llvm/15/compiler-rt/X86-support-extension.patch b/pkgs/development/compilers/llvm/16/compiler-rt/X86-support-extension.patch
similarity index 100%
rename from pkgs/development/compilers/llvm/15/compiler-rt/X86-support-extension.patch
rename to pkgs/development/compilers/llvm/16/compiler-rt/X86-support-extension.patch
diff --git a/pkgs/development/compilers/llvm/15/compiler-rt/armv6-scudo-libatomic.patch b/pkgs/development/compilers/llvm/16/compiler-rt/armv6-scudo-libatomic.patch
similarity index 100%
rename from pkgs/development/compilers/llvm/15/compiler-rt/armv6-scudo-libatomic.patch
rename to pkgs/development/compilers/llvm/16/compiler-rt/armv6-scudo-libatomic.patch
diff --git a/pkgs/development/compilers/llvm/15/compiler-rt/darwin-targetconditionals.patch b/pkgs/development/compilers/llvm/16/compiler-rt/darwin-targetconditionals.patch
similarity index 100%
rename from pkgs/development/compilers/llvm/15/compiler-rt/darwin-targetconditionals.patch
rename to pkgs/development/compilers/llvm/16/compiler-rt/darwin-targetconditionals.patch
diff --git a/pkgs/development/compilers/llvm/15/compiler-rt/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/16/compiler-rt/gnu-install-dirs.patch
similarity index 100%
rename from pkgs/development/compilers/llvm/15/compiler-rt/gnu-install-dirs.patch
rename to pkgs/development/compilers/llvm/16/compiler-rt/gnu-install-dirs.patch
diff --git a/pkgs/development/compilers/llvm/15/libunwind/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/16/libunwind/gnu-install-dirs.patch
similarity index 100%
rename from pkgs/development/compilers/llvm/15/libunwind/gnu-install-dirs.patch
rename to pkgs/development/compilers/llvm/16/libunwind/gnu-install-dirs.patch
diff --git a/pkgs/development/compilers/llvm/15/llvm/gnu-install-dirs-polly.patch b/pkgs/development/compilers/llvm/16/llvm/gnu-install-dirs-polly.patch
similarity index 100%
rename from pkgs/development/compilers/llvm/15/llvm/gnu-install-dirs-polly.patch
rename to pkgs/development/compilers/llvm/16/llvm/gnu-install-dirs-polly.patch
diff --git a/pkgs/development/compilers/llvm/15/llvm/polly-lit-cfg-add-libs-to-dylib-path.patch b/pkgs/development/compilers/llvm/16/llvm/polly-lit-cfg-add-libs-to-dylib-path.patch
similarity index 100%
rename from pkgs/development/compilers/llvm/15/llvm/polly-lit-cfg-add-libs-to-dylib-path.patch
rename to pkgs/development/compilers/llvm/16/llvm/polly-lit-cfg-add-libs-to-dylib-path.patch
diff --git a/pkgs/development/compilers/llvm/common/clang/clang-11-15-LLVMgold-path.patch b/pkgs/development/compilers/llvm/common/clang/clang-11-15-LLVMgold-path.patch
deleted file mode 100644
index 8f8991976f33..000000000000
--- a/pkgs/development/compilers/llvm/common/clang/clang-11-15-LLVMgold-path.patch
+++ /dev/null
@@ -1,13 +0,0 @@
-diff --git a/lib/Driver/ToolChains/CommonArgs.cpp b/lib/Driver/ToolChains/CommonArgs.cpp
-index 6b6e276b8ce7..7896542a1202 100644
---- a/lib/Driver/ToolChains/CommonArgs.cpp
-+++ b/lib/Driver/ToolChains/CommonArgs.cpp
-@@ -409,7 +409,7 @@ void tools::addLTOOptions(const ToolChain &ToolChain, const ArgList &Args,
- 
-     SmallString<1024> Plugin;
-     llvm::sys::path::native(
--        Twine(D.Dir) + "/../lib" CLANG_LIBDIR_SUFFIX "/LLVMgold" + Suffix,
-+        Twine("@libllvmLibdir@" "/LLVMgold") + Suffix,
-         Plugin);
-     CmdArgs.push_back(Args.MakeArgString(Plugin));
-   }
diff --git a/pkgs/development/compilers/llvm/common/clang/default.nix b/pkgs/development/compilers/llvm/common/clang/default.nix
index bfbabb48d480..cdd18429007b 100644
--- a/pkgs/development/compilers/llvm/common/clang/default.nix
+++ b/pkgs/development/compilers/llvm/common/clang/default.nix
@@ -60,26 +60,10 @@ stdenv.mkDerivation (
     })
     # Pass the correct path to libllvm
     ++ [
-      (replaceVars
-        (
-          if (lib.versionOlder release_version "16") then
-            ./clang-11-15-LLVMgold-path.patch
-          else
-            ./clang-at-least-16-LLVMgold-path.patch
-        )
-        {
-          libllvmLibdir = "${libllvm.lib}/lib";
-        }
-      )
+      (replaceVars ./clang-at-least-16-LLVMgold-path.patch {
+        libllvmLibdir = "${libllvm.lib}/lib";
+      })
     ]
-    # Backport version logic from Clang 16. This is needed by the following patch.
-    ++ lib.optional (lib.versions.major release_version == "15") (fetchpatch {
-      name = "clang-darwin-Use-consistent-version-define-stringifying-logic.patch";
-      url = "https://github.com/llvm/llvm-project/commit/60a33ded751c86fff9ac1c4bdd2b341fbe4b0649.patch?full_index=1";
-      includes = [ "lib/Basic/Targets/OSTargets.cpp" ];
-      stripLen = 1;
-      hash = "sha256-YVTSg5eZLz3po2AUczPNXCK26JA3CuTh6Iqp7hAAKIs=";
-    })
     # Backport `__ENVIRONMENT_OS_VERSION_MIN_REQUIRED__` support from Clang 17.
     # This is needed by newer SDKs (14+).
     ++ lib.optional (lib.versionOlder (lib.versions.major release_version) "17") (fetchpatch {
@@ -246,7 +230,6 @@ stdenv.mkDerivation (
           )
         ) "stackclashprotection"
         ++ lib.optional (!(targetPlatform.isx86_64 || targetPlatform.isAarch64)) "zerocallusedregs"
-        ++ lib.optional (lib.versionOlder release_version "16") "strictflexarrays3"
         ++ (finalAttrs.passthru.hardeningUnsupportedFlags or [ ]);
     };
 
diff --git a/pkgs/development/compilers/llvm/common/common-let.nix b/pkgs/development/compilers/llvm/common/common-let.nix
index 6b334193e452..c310a8ab96fc 100644
--- a/pkgs/development/compilers/llvm/common/common-let.nix
+++ b/pkgs/development/compilers/llvm/common/common-let.nix
@@ -33,7 +33,7 @@ rec {
       ++ lib.platforms.x86
       ++ lib.platforms.riscv
       ++ lib.platforms.m68k
-      ++ lib.optionals (lib.versionAtLeast release_version "16") lib.platforms.loongarch64;
+      ++ lib.platforms.loongarch64;
   };
 
   releaseInfo =
diff --git a/pkgs/development/compilers/llvm/common/compiler-rt/armv7l-15.patch b/pkgs/development/compilers/llvm/common/compiler-rt/armv7l-15.patch
deleted file mode 100644
index ca1c2332abd9..000000000000
--- a/pkgs/development/compilers/llvm/common/compiler-rt/armv7l-15.patch
+++ /dev/null
@@ -1,32 +0,0 @@
-diff -ur a/cmake/builtin-config-ix.cmake b/cmake/builtin-config-ix.cmake
---- a/cmake/builtin-config-ix.cmake @llvm 15.0.6
-+++ b/cmake/builtin-config-ix.cmake
-@@ -46,7 +46,7 @@
- 
- set(ARM64 aarch64)
--set(ARM32 arm armhf armv6m armv7m armv7em armv7 armv7s armv7k armv8m.main armv8.1m.main)
-+set(ARM32 arm armhf armv6m armv7m armv7em armv7 armv7s armv7k armv7l armv8m.main armv8.1m.main)
- set(AVR avr)
- set(HEXAGON hexagon)
- set(X86 i386)
- set(X86_64 x86_64)
-diff -ur a/lib/builtins/CMakeLists.txt b/lib/builtins/CMakeLists.txt
---- a/lib/builtins/CMakeLists.txt @llvm 15.0.6
-+++ b/lib/builtins/CMakeLists.txt
-@@ -565,6 +565,7 @@
- set(armv7_SOURCES ${arm_SOURCES})
- set(armv7s_SOURCES ${arm_SOURCES})
- set(armv7k_SOURCES ${arm_SOURCES})
-+set(armv7l_SOURCES ${arm_SOURCES})
- set(arm64_SOURCES ${aarch64_SOURCES})
- 
- # macho_embedded archs
-@@ -734,7 +735,7 @@
-   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
-     if (CAN_TARGET_${arch})
-       # For ARM archs, exclude any VFP builtins if VFP is not supported
--      if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7m|armv7em|armv8m.main|armv8.1m.main)$")
-+      if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7l|armv7m|armv7em|armv8m.main|armv8.1m.main)$")
-         string(REPLACE ";" " " _TARGET_${arch}_CFLAGS "${TARGET_${arch}_CFLAGS}")
-         check_compile_definition(__VFP_FP__ "${CMAKE_C_FLAGS} ${_TARGET_${arch}_CFLAGS}" COMPILER_RT_HAS_${arch}_VFP)
-         if(NOT COMPILER_RT_HAS_${arch}_VFP)
diff --git a/pkgs/development/compilers/llvm/common/compiler-rt/default.nix b/pkgs/development/compilers/llvm/common/compiler-rt/default.nix
index 31def30e04ca..87b7d2f9da7d 100644
--- a/pkgs/development/compilers/llvm/common/compiler-rt/default.nix
+++ b/pkgs/development/compilers/llvm/common/compiler-rt/default.nix
@@ -41,10 +41,7 @@ let
   # TODO: Make this account for GCC having libstdcxx, which will help
   # use clean up the `cmakeFlags` rats nest below.
   haveLibcxx = stdenv.cc.libcxx != null;
-  isDarwinStatic =
-    stdenv.hostPlatform.isDarwin
-    && stdenv.hostPlatform.isStatic
-    && lib.versionAtLeast release_version "16";
+  isDarwinStatic = stdenv.hostPlatform.isDarwin && stdenv.hostPlatform.isStatic;
   inherit (stdenv.hostPlatform) isMusl isAarch64 isWindows;
   noSanitizers = !haveLibc || bareMetal || isMusl || isDarwinStatic || isWindows;
 in
@@ -97,10 +94,6 @@ stdenv.mkDerivation (finalAttrs: {
     # See: https://github.com/NixOS/nixpkgs/pull/186575
     ./darwin-plistbuddy-workaround.patch
   ]
-  ++
-    lib.optional (lib.versions.major release_version == "15")
-      # See: https://github.com/NixOS/nixpkgs/pull/194634#discussion_r999829893
-      ./armv7l-15.patch
   ++ lib.optionals (lib.versionOlder release_version "18") [
     # Fix build on armv6l
     ./armv6-scudo-no-yield.patch
@@ -191,7 +184,7 @@ stdenv.mkDerivation (finalAttrs: {
     (lib.cmakeFeature "COMPILER_RT_OS_DIR" "baremetal")
   ]
   ++ lib.optionals (stdenv.hostPlatform.isDarwin) (
-    lib.optionals (lib.versionAtLeast release_version "16") [
+    [
       (lib.cmakeFeature "CMAKE_LIPO" "${lib.getBin stdenv.cc.bintools.bintools}/bin/${stdenv.cc.targetPrefix}lipo")
     ]
     ++ lib.optionals (!haveLibcxx) [
@@ -255,16 +248,12 @@ stdenv.mkDerivation (finalAttrs: {
             --replace-fail 'find_program(CODESIGN codesign)' ""
         '';
 
-  preConfigure =
-    lib.optionalString (lib.versionOlder release_version "16" && !haveLibc) ''
-      cmakeFlagsArray+=(-DCMAKE_C_FLAGS="-nodefaultlibs -ffreestanding")
-    ''
-    + lib.optionalString stdenv.hostPlatform.isDarwin ''
-      cmakeFlagsArray+=(
-        "-DDARWIN_macosx_CACHED_SYSROOT=$SDKROOT"
-        "-DDARWIN_macosx_OVERRIDE_SDK_VERSION=$(jq -r .Version "$SDKROOT/SDKSettings.json")"
-      )
-    '';
+  preConfigure = lib.optionalString stdenv.hostPlatform.isDarwin ''
+    cmakeFlagsArray+=(
+      "-DDARWIN_macosx_CACHED_SYSROOT=$SDKROOT"
+      "-DDARWIN_macosx_OVERRIDE_SDK_VERSION=$(jq -r .Version "$SDKROOT/SDKSettings.json")"
+    )
+  '';
 
   # Hack around weird upstream RPATH bug
   postInstall =
diff --git a/pkgs/development/compilers/llvm/common/default.nix b/pkgs/development/compilers/llvm/common/default.nix
index c431acde0c7b..4944ee75990c 100644
--- a/pkgs/development/compilers/llvm/common/default.nix
+++ b/pkgs/development/compilers/llvm/common/default.nix
@@ -115,11 +115,7 @@ let
     tools:
     let
       callPackage = newScope (tools // args // metadata);
-      clangVersion =
-        if (lib.versionOlder metadata.release_version "16") then
-          metadata.release_version
-        else
-          lib.versions.major metadata.release_version;
+      clangVersion = lib.versions.major metadata.release_version;
       mkExtraBuildCommands0 =
         cc:
         ''
@@ -401,20 +397,16 @@ let
       clangNoCompilerRt = tools.clangNoLibcNoRt;
       clangNoLibc = tools.clangNoLibcWithBasicRt;
       clangNoLibcxx = tools.clangWithLibcAndBasicRt;
-    }
-    // lib.optionalAttrs (lib.versionAtLeast metadata.release_version "16") {
+
       mlir = callPackage ./mlir { };
     }
     // lib.optionalAttrs (lib.versionAtLeast metadata.release_version "19") {
       bolt = callPackage ./bolt {
       };
     }
-    //
-      lib.optionalAttrs
-        (lib.versionAtLeast metadata.release_version "16" && lib.versionOlder metadata.release_version "22")
-        {
-          libclc = callPackage ./libclc { };
-        }
+    // lib.optionalAttrs (lib.versionOlder metadata.release_version "22") {
+      libclc = callPackage ./libclc { };
+    }
     // lib.optionalAttrs (lib.versionAtLeast metadata.release_version "20") {
       flang = callPackage ./flang {
         mlir = tools.mlir;
diff --git a/pkgs/development/compilers/llvm/common/libcxx/default.nix b/pkgs/development/compilers/llvm/common/libcxx/default.nix
index 3a5b777c0d64..73eee5aa84f0 100644
--- a/pkgs/development/compilers/llvm/common/libcxx/default.nix
+++ b/pkgs/development/compilers/llvm/common/libcxx/default.nix
@@ -64,8 +64,7 @@ let
     # https://github.com/llvm/llvm-project/issues/55245
     (lib.cmakeBool "LIBCXX_ENABLE_STATIC_ABI_LIBRARY" stdenv.hostPlatform.isWindows)
   ]
-  ++ lib.optionals (cxxabi == null && lib.versionAtLeast release_version "16") [
-    # Note: llvm < 16 doesn't support this flag (or it's broken); handled in postInstall instead.
+  ++ lib.optionals (cxxabi == null) [
     # Include libc++abi symbols within libc++.a for static linking libc++;
     # dynamic linking includes them through libc++.so being a linker script
     # which includes both shared objects.
@@ -96,11 +95,9 @@ let
   ++ lib.optionals useLLVM [
     (lib.cmakeBool "LIBCXX_USE_COMPILER_RT" true)
   ]
-  ++
-    lib.optionals (useLLVM && !stdenv.hostPlatform.isFreeBSD && lib.versionAtLeast release_version "16")
-      [
-        (lib.cmakeFeature "LIBCXX_ADDITIONAL_LIBRARIES" "unwind")
-      ]
+  ++ lib.optionals (useLLVM && !stdenv.hostPlatform.isFreeBSD) [
+    (lib.cmakeFeature "LIBCXX_ADDITIONAL_LIBRARIES" "unwind")
+  ]
   ++ lib.optionals stdenv.hostPlatform.isWasm [
     (lib.cmakeBool "LIBCXX_ENABLE_THREADS" false)
     (lib.cmakeBool "LIBCXX_ENABLE_FILESYSTEM" false)
@@ -163,37 +160,8 @@ stdenv.mkDerivation (
       patchShebangs utils/cat_files.py
     '';
 
-    patches = lib.optionals (lib.versionOlder release_version "16") (
-      lib.optional (lib.versions.major release_version == "15")
-        # See:
-        #   - https://reviews.llvm.org/D133566
-        #   - https://github.com/NixOS/nixpkgs/issues/214524#issuecomment-1429146432
-        # !!! Drop in LLVM 16+
-        (
-          fetchpatch {
-            url = "https://github.com/llvm/llvm-project/commit/57c7bb3ec89565c68f858d316504668f9d214d59.patch";
-            hash = "sha256-B07vHmSjy5BhhkGSj3e1E0XmMv5/9+mvC/k70Z29VwY=";
-          }
-        )
-      ++ [
-        (substitute {
-          src = ../libcxxabi/wasm.patch;
-          substitutions = [
-            "--replace-fail"
-            "/cmake/"
-            "/llvm/cmake/"
-          ];
-        })
-      ]
-      ++ lib.optional stdenv.hostPlatform.isMusl (substitute {
-        src = ./libcxx-0001-musl-hacks.patch;
-        substitutions = [
-          "--replace-fail"
-          "/include/"
-          "/libcxx/include/"
-        ];
-      })
-    );
+    # TODO: Remove on `staging`.
+    patches = [ ];
 
     nativeBuildInputs = [
       cmake
@@ -219,13 +187,13 @@ stdenv.mkDerivation (
         lndir ${lib.getLib cxxabi}/lib $out/lib
         libcxxabi=$out/lib/lib${cxxabi.libName}.a
       ''
-      # LIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY=ON doesn't work for LLVM < 16 or
+      # LIBCXX_STATICALLY_LINK_ABI_IN_STATIC_LIBRARY=ON doesn't work for
       # external cxxabi libraries so merge libc++abi.a into libc++.a ourselves.
 
       # GNU binutils emits objects in LIFO order in MRI scripts so after the merge
       # the objects are in reversed order so a second MRI script is required so the
       # objects in the archive are listed in proper order (libc++.a, libc++abi.a)
-      + lib.optionalString (cxxabi != null || lib.versionOlder release_version "16") ''
+      + lib.optionalString (cxxabi != null) ''
         libcxxabi=''${libcxxabi-$out/lib/libc++abi.a}
         if [[ -f $out/lib/libc++.a && -e $libcxxabi ]]; then
           $AR -M <<MRI
@@ -264,7 +232,7 @@ stdenv.mkDerivation (
     };
   }
   // (
-    if (lib.versionOlder release_version "16" || lib.versionAtLeast release_version "17") then
+    if lib.versionAtLeast release_version "17" then
       {
         postPatch = ''
           cd runtimes
diff --git a/pkgs/development/compilers/llvm/common/libcxx/libcxx-0001-musl-hacks.patch b/pkgs/development/compilers/llvm/common/libcxx/libcxx-0001-musl-hacks.patch
deleted file mode 100644
index bcb5ad8cfb87..000000000000
--- a/pkgs/development/compilers/llvm/common/libcxx/libcxx-0001-musl-hacks.patch
+++ /dev/null
@@ -1,39 +0,0 @@
-From 1c936d7fda3275265e37f93697232a1ed652390f Mon Sep 17 00:00:00 2001
-From: Will Dietz <w@wdtz.org>
-Date: Sat, 9 Jul 2016 19:22:54 -0500
-Subject: [PATCH] musl fixes/hacks
-
-Conflicts:
-
-	include/__config
-	include/locale
-	src/locale.cpp
----
- include/locale |    4 ++--
- 1 files changed, 2 insertions(+), 2 deletions(-)
-
-diff --git a/include/locale b/include/locale
-index 3d804e8..9b01f5b 100644
---- a/include/locale
-+++ b/include/locale
-@@ -695,7 +695,7 @@ __num_get_signed_integral(const char* __a, const char* __a_end,
-         typename remove_reference<decltype(errno)>::type __save_errno = errno;
-         errno = 0;
-         char *__p2;
--        long long __ll = strtoll_l(__a, &__p2, __base, _LIBCPP_GET_C_LOCALE);
-+        long long __ll = strtoll(__a, &__p2, __base);
-         typename remove_reference<decltype(errno)>::type __current_errno = errno;
-         if (__current_errno == 0)
-             errno = __save_errno;
-@@ -735,7 +735,7 @@ __num_get_unsigned_integral(const char* __a, const char* __a_end,
-         typename remove_reference<decltype(errno)>::type __save_errno = errno;
-         errno = 0;
-         char *__p2;
--        unsigned long long __ll = strtoull_l(__a, &__p2, __base, _LIBCPP_GET_C_LOCALE);
-+        unsigned long long __ll = strtoull(__a, &__p2, __base);
-         typename remove_reference<decltype(errno)>::type __current_errno = errno;
-         if (__current_errno == 0)
-             errno = __save_errno;
--- 
-1.7.1
-
diff --git a/pkgs/development/compilers/llvm/common/libcxxabi/wasm.patch b/pkgs/development/compilers/llvm/common/libcxxabi/wasm.patch
deleted file mode 100644
index 4ebfe46aa813..000000000000
--- a/pkgs/development/compilers/llvm/common/libcxxabi/wasm.patch
+++ /dev/null
@@ -1,16 +0,0 @@
-diff --git a/cmake/modules/HandleLLVMOptions.cmake b/cmake/modules/HandleLLVMOptions.cmake
-index 15497d405e0..33f7f18193a 100644
---- a/cmake/modules/HandleLLVMOptions.cmake
-+++ b/cmake/modules/HandleLLVMOptions.cmake
-@@ -127,7 +127,10 @@ else(WIN32)
-       set(LLVM_HAVE_LINK_VERSION_SCRIPT 1)
-     endif()
-   else(FUCHSIA OR UNIX)
--    MESSAGE(SEND_ERROR "Unable to determine platform")
-+    if(${CMAKE_SYSTEM_NAME} MATCHES "Wasi")
-+    else()
-+      MESSAGE(SEND_ERROR "Unable to determine platform")
-+    endif()
-   endif(FUCHSIA OR UNIX)
- endif(WIN32)
- 
diff --git a/pkgs/development/compilers/llvm/common/lld/default.nix b/pkgs/development/compilers/llvm/common/lld/default.nix
index da9a59944761..be3ed102ab14 100644
--- a/pkgs/development/compilers/llvm/common/lld/default.nix
+++ b/pkgs/development/compilers/llvm/common/lld/default.nix
@@ -38,9 +38,7 @@ stdenv.mkDerivation (finalAttrs: {
   patches = [
     (getVersionFile "lld/gnu-install-dirs.patch")
   ]
-  ++ lib.optional (lib.versionAtLeast release_version "16" && lib.versionOlder release_version "18") (
-    getVersionFile "lld/add-table-base.patch"
-  )
+  ++ lib.optional (lib.versionOlder release_version "18") (getVersionFile "lld/add-table-base.patch")
   ++ lib.optional (lib.versions.major release_version == "18") (
     # https://github.com/llvm/llvm-project/pull/97122
     fetchpatch {
diff --git a/pkgs/development/compilers/llvm/common/lldb/default.nix b/pkgs/development/compilers/llvm/common/lldb/default.nix
index 24404d97de90..01461c352e7d 100644
--- a/pkgs/development/compilers/llvm/common/lldb/default.nix
+++ b/pkgs/development/compilers/llvm/common/lldb/default.nix
@@ -78,23 +78,7 @@ stdenv.mkDerivation (
           }).overrideAttrs
             (_: _: { name = "resource-dir.patch"; });
       in
-      lib.optionals (lib.versionOlder release_version "16") [
-        # Fixes for SWIG 4
-        (fetchpatch2 {
-          url = "https://github.com/llvm/llvm-project/commit/ba35c27ec9aa9807f5b4be2a0c33ca9b045accc7.patch?full_index=1";
-          stripLen = 1;
-          hash = "sha256-LXl+WbpmWZww5xMDrle3BM2Tw56v8k9LO1f1Z1/wDTs=";
-        })
-        (fetchpatch2 {
-          url = "https://github.com/llvm/llvm-project/commit/9ec115978ea2bdfc60800cd3c21264341cdc8b0a.patch?full_index=1";
-          stripLen = 1;
-          hash = "sha256-u0zSejEjfrH3ZoMFm1j+NVv2t5AP9cE5yhsrdTS1dG4=";
-        })
-
-        # FIXME: do we need this after 15?
-        (getVersionFile "lldb/procfs.patch")
-      ]
-      ++ lib.optional (lib.versionOlder release_version "18") (fetchpatch {
+      lib.optional (lib.versionOlder release_version "18") (fetchpatch {
         name = "libcxx-19-char_traits.patch";
         url = "https://github.com/llvm/llvm-project/commit/68744ffbdd7daac41da274eef9ac0d191e11c16d.patch";
         stripLen = 1;
@@ -140,8 +124,6 @@ stdenv.mkDerivation (
       libedit
       libxml2
       libllvm
-    ]
-    ++ lib.optionals (lib.versionAtLeast release_version "16") [
       # Starting with LLVM 16, the resource dir patch is no longer enough to get
       # libclang into the rpath of the lldb executables. By putting it into
       # buildInputs cc-wrapper will set up rpath correctly for us.
diff --git a/pkgs/development/compilers/llvm/common/llvm/default.nix b/pkgs/development/compilers/llvm/common/llvm/default.nix
index 903202cdc813..104bd84aa455 100644
--- a/pkgs/development/compilers/llvm/common/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/common/llvm/default.nix
@@ -178,16 +178,6 @@ stdenv.mkDerivation (
               stripLen = 1;
             }
           )
-      ++ lib.optionals (lib.versionOlder release_version "16") [
-        # Fix musl build.
-        (fetchpatch {
-          url = "https://github.com/llvm/llvm-project/commit/5cd554303ead0f8891eee3cd6d25cb07f5a7bf67.patch";
-          relative = "llvm";
-          hash = "sha256-XPbvNJ45SzjMGlNUgt/IgEvM2dHQpDOe6woUJY+nUYA=";
-        })
-        # Fix for Python 3.13
-        (getVersionFile "llvm/no-pipes.patch")
-      ]
       ++ lib.optionals (lib.versionOlder (lib.versions.major release_version) "17") [
         # fix RuntimeDyld usage on aarch64-linux (e.g. python312Packages.numba tests)
         # See also: https://github.com/numba/numba/issues/9109
@@ -308,18 +298,10 @@ stdenv.mkDerivation (
         +
           # This test tries to call `sw_vers` by absolute path (`/usr/bin/sw_vers`)
           # and thus fails under the sandbox:
-          (
-            if lib.versionAtLeast release_version "16" then
-              ''
-                substituteInPlace unittests/TargetParser/Host.cpp \
-                  --replace-fail '/usr/bin/sw_vers' "${(builtins.toString darwin.DarwinTools) + "/bin/sw_vers"}"
-              ''
-            else
-              ''
-                substituteInPlace unittests/Support/Host.cpp \
-                  --replace-fail '/usr/bin/sw_vers' "${(builtins.toString darwin.DarwinTools) + "/bin/sw_vers"}"
-              ''
-          )
+          ''
+            substituteInPlace unittests/TargetParser/Host.cpp \
+              --replace-fail '/usr/bin/sw_vers' "${(builtins.toString darwin.DarwinTools) + "/bin/sw_vers"}"
+          ''
         +
           # This test tries to call the intrinsics `@llvm.roundeven.f32` and
           # `@llvm.roundeven.f64` which seem to (incorrectly?) lower to `roundevenf`
@@ -331,7 +313,7 @@ stdenv.mkDerivation (
           #
           # TODO(@rrbutani): this seems to run fine on `aarch64-darwin`, why does it
           # pass there?
-          optionalString (lib.versionAtLeast release_version "16") ''
+          ''
             substituteInPlace test/ExecutionEngine/Interpreter/intrinsics.ll \
               --replace-fail "%roundeven32 = call float @llvm.roundeven.f32(float 0.000000e+00)" "" \
               --replace-fail "%roundeven64 = call double @llvm.roundeven.f64(double 0.000000e+00)" ""
@@ -346,67 +328,52 @@ stdenv.mkDerivation (
       +
         # dup of above patch with different conditions
         optionalString (stdenv.hostPlatform.isDarwin && stdenv.hostPlatform.isx86) (
-          optionalString (lib.versionOlder release_version "16") ''
-            substituteInPlace test/ExecutionEngine/Interpreter/intrinsics.ll \
-              --replace-fail "%roundeven32 = call float @llvm.roundeven.f32(float 0.000000e+00)" "" \
-              --replace-fail "%roundeven64 = call double @llvm.roundeven.f64(double 0.000000e+00)" ""
-
-          ''
-          +
-            # fails when run in sandbox
-            (
-              (optionalString (lib.versionAtLeast release_version "18") ''
-                substituteInPlace unittests/Support/VirtualFileSystemTest.cpp \
-                  --replace-fail "PhysicalFileSystemWorkingDirFailure" "DISABLED_PhysicalFileSystemWorkingDirFailure"
-              '')
-              +
-                # This test fails on darwin x86_64 because `sw_vers` reports a different
-                # macOS version than what LLVM finds by reading
-                # `/System/Library/CoreServices/SystemVersion.plist` (which is passed into
-                # the sandbox on macOS).
-                #
-                # The `sw_vers` provided by nixpkgs reports the macOS version associated
-                # with the `CoreFoundation` framework with which it was built. Because
-                # nixpkgs pins the SDK for `aarch64-darwin` and `x86_64-darwin` what
-                # `sw_vers` reports is not guaranteed to match the macOS version of the host
-                # that's building this derivation.
-                #
-                # Astute readers will note that we only _patch_ this test on aarch64-darwin
-                # (to use the nixpkgs provided `sw_vers`) instead of disabling it outright.
-                # So why does this test pass on aarch64?
-                #
-                # Well, it seems that `sw_vers` on aarch64 actually links against the _host_
-                # CoreFoundation framework instead of the nixpkgs provided one.
-                #
-                # Not entirely sure what the right fix is here. I'm assuming aarch64
-                # `sw_vers` doesn't intentionally link against the host `CoreFoundation`
-                # (still digging into how this ends up happening, will follow up) but that
-                # aside I think the more pertinent question is: should we be patching LLVM's
-                # macOS version detection logic to use `sw_vers` instead of reading host
-                # paths? This *is* a way in which details about builder machines can creep
-                # into the artifacts that are produced, affecting reproducibility, but it's
-                # not clear to me when/where/for what this even gets used in LLVM.
-                #
-                # TODO(@rrbutani): fix/follow-up
-                (
-                  if lib.versionAtLeast release_version "16" then
-                    ''
-                      substituteInPlace unittests/TargetParser/Host.cpp \
-                        --replace-fail "getMacOSHostVersion" "DISABLED_getMacOSHostVersion"
-                    ''
-                  else
-                    ''
-                      substituteInPlace unittests/Support/Host.cpp \
-                        --replace-fail "getMacOSHostVersion" "DISABLED_getMacOSHostVersion"
-                    ''
-                )
-              +
-                # This test fails with a `dysmutil` crash; have not yet dug into what's
-                # going on here (TODO(@rrbutani)).
-                lib.optionalString (lib.versionOlder release_version "19") ''
-                  rm test/tools/dsymutil/ARM/obfuscated.test
-                ''
-            )
+          # fails when run in sandbox
+          (
+            (optionalString (lib.versionAtLeast release_version "18") ''
+              substituteInPlace unittests/Support/VirtualFileSystemTest.cpp \
+                --replace-fail "PhysicalFileSystemWorkingDirFailure" "DISABLED_PhysicalFileSystemWorkingDirFailure"
+            '')
+            +
+              # This test fails on darwin x86_64 because `sw_vers` reports a different
+              # macOS version than what LLVM finds by reading
+              # `/System/Library/CoreServices/SystemVersion.plist` (which is passed into
+              # the sandbox on macOS).
+              #
+              # The `sw_vers` provided by nixpkgs reports the macOS version associated
+              # with the `CoreFoundation` framework with which it was built. Because
+              # nixpkgs pins the SDK for `aarch64-darwin` and `x86_64-darwin` what
+              # `sw_vers` reports is not guaranteed to match the macOS version of the host
+              # that's building this derivation.
+              #
+              # Astute readers will note that we only _patch_ this test on aarch64-darwin
+              # (to use the nixpkgs provided `sw_vers`) instead of disabling it outright.
+              # So why does this test pass on aarch64?
+              #
+              # Well, it seems that `sw_vers` on aarch64 actually links against the _host_
+              # CoreFoundation framework instead of the nixpkgs provided one.
+              #
+              # Not entirely sure what the right fix is here. I'm assuming aarch64
+              # `sw_vers` doesn't intentionally link against the host `CoreFoundation`
+              # (still digging into how this ends up happening, will follow up) but that
+              # aside I think the more pertinent question is: should we be patching LLVM's
+              # macOS version detection logic to use `sw_vers` instead of reading host
+              # paths? This *is* a way in which details about builder machines can creep
+              # into the artifacts that are produced, affecting reproducibility, but it's
+              # not clear to me when/where/for what this even gets used in LLVM.
+              #
+              # TODO(@rrbutani): fix/follow-up
+              ''
+                substituteInPlace unittests/TargetParser/Host.cpp \
+                  --replace-fail "getMacOSHostVersion" "DISABLED_getMacOSHostVersion"
+              ''
+            +
+              # This test fails with a `dysmutil` crash; have not yet dug into what's
+              # going on here (TODO(@rrbutani)).
+              lib.optionalString (lib.versionOlder release_version "19") ''
+                rm test/tools/dsymutil/ARM/obfuscated.test
+              ''
+          )
         )
       +
         # FileSystem permissions tests fail with various special bits
@@ -422,17 +389,13 @@ stdenv.mkDerivation (
       +
         # Fails in the presence of anti-virus software or other intrusion-detection software that
         # modifies the atime when run. See #284056.
-        lib.optionalString (lib.versionAtLeast release_version "16") (
-          ''
-            rm test/tools/llvm-objcopy/ELF/strip-preserve-atime.test
-          ''
-          + lib.optionalString (lib.versionOlder release_version "17") ''
-
-          ''
-        )
+        ''
+          rm test/tools/llvm-objcopy/ELF/strip-preserve-atime.test
+        ''
       +
         # timing-based tests are trouble
         lib.optionalString (lib.versionOlder release_version "17") ''
+
           rm utils/lit/tests/googletest-timeout.py
         ''
       +
diff --git a/pkgs/development/compilers/llvm/common/patches.nix b/pkgs/development/compilers/llvm/common/patches.nix
index ce241bf33184..735aa7b82b22 100644
--- a/pkgs/development/compilers/llvm/common/patches.nix
+++ b/pkgs/development/compilers/llvm/common/patches.nix
@@ -12,7 +12,7 @@
     }
     {
       before = "17";
-      path = ../15;
+      path = ../16;
     }
   ];
   "clang/aarch64-tblgen.patch" = [
@@ -24,7 +24,6 @@
   ];
   "lld/add-table-base.patch" = [
     {
-      after = "16";
       path = ../16;
     }
   ];
@@ -67,13 +66,13 @@
     }
     {
       before = "18";
-      path = ../15;
+      path = ../16;
     }
   ];
   "llvm/llvm-lit-cfg-add-libs-to-dylib-path.patch" = [
     {
       before = "17";
-      path = ../15;
+      path = ../16;
     }
     {
       after = "17";
@@ -86,25 +85,24 @@
       path = ../18;
     }
     {
-      after = "16";
       before = "18";
       path = ../16;
     }
   ];
   "llvm/polly-lit-cfg-add-libs-to-dylib-path.patch" = [
     {
-      path = ../15;
+      path = ../16;
     }
   ];
   "libunwind/gnu-install-dirs.patch" = [
     {
       before = "17";
-      path = ../15;
+      path = ../16;
     }
   ];
   "compiler-rt/X86-support-extension.patch" = [
     {
-      path = ../15;
+      path = ../16;
     }
   ];
   "compiler-rt/armv6-scudo-libatomic.patch" = [
@@ -114,50 +112,27 @@
     }
     {
       before = "19";
-      path = ../15;
+      path = ../16;
     }
   ];
   "compiler-rt/gnu-install-dirs.patch" = [
     {
       before = "17";
-      path = ../15;
+      path = ../16;
     }
     {
-      after = "16";
       path = ../17;
     }
   ];
   "compiler-rt/darwin-targetconditionals.patch" = [
     {
-      path = ../15;
+      path = ../16;
     }
   ];
   "compiler-rt/normalize-var.patch" = [
     {
-      after = "16";
       path = ../16;
     }
-    {
-      before = "16";
-      path = ../15;
-    }
-  ];
-  "lldb/procfs.patch" = [
-    {
-      path = ../15;
-    }
-  ];
-  "lldb/resource-dir.patch" = [
-    {
-      before = "16";
-      path = ../15;
-    }
-  ];
-  "llvm/no-pipes.patch" = [
-    {
-      before = "16";
-      path = ../15;
-    }
   ];
   "openmp/fix-find-tool.patch" = [
     {
@@ -168,13 +143,8 @@
   ];
   "openmp/run-lit-directly.patch" = [
     {
-      after = "16";
       path = ../16;
     }
-    {
-      before = "16";
-      path = ../15;
-    }
   ];
   "libclc/use-default-paths.patch" = [
     {
@@ -189,7 +159,6 @@
   ];
   "libclc/gnu-install-dirs.patch" = [
     {
-      after = "16";
       before = "21";
       path = ../16;
     }
diff --git a/pkgs/development/compilers/llvm/common/tblgen.nix b/pkgs/development/compilers/llvm/common/tblgen.nix
index c1b725be279f..0fa2f6269d6d 100644
--- a/pkgs/development/compilers/llvm/common/tblgen.nix
+++ b/pkgs/development/compilers/llvm/common/tblgen.nix
@@ -55,8 +55,6 @@ let
     "clang-tblgen"
     "llvm-tblgen"
     "clang-tidy-confusable-chars-gen"
-  ]
-  ++ lib.optionals (lib.versionAtLeast release_version "16") [
     "mlir-tblgen"
   ]
   ++ lib.optionals (lib.versionOlder release_version "20") [
@@ -95,16 +93,12 @@ let
     cmakeFlags = [
       # Projects with tablegen-like tools.
       "-DLLVM_ENABLE_PROJECTS=${
-        lib.concatStringsSep ";" (
-          [
-            "llvm"
-            "clang"
-            "clang-tools-extra"
-          ]
-          ++ lib.optionals (lib.versionAtLeast release_version "16") [
-            "mlir"
-          ]
-        )
+        lib.concatStringsSep ";" [
+          "llvm"
+          "clang"
+          "clang-tools-extra"
+          "mlir"
+        ]
       }"
     ]
     ++ devExtraCmakeFlags;
diff --git a/pkgs/development/compilers/llvm/default.nix b/pkgs/development/compilers/llvm/default.nix
index 19f8901f2bdc..014246d25bb2 100644
--- a/pkgs/development/compilers/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/default.nix
@@ -22,7 +22,6 @@
 }@packageSetArgs:
 let
   versions = {
-    "15.0.7".officialRelease.sha256 = "sha256-wjuZQyXQ/jsmvy6y1aksCcEDXGBjuhpgngF3XQJ/T4s=";
     "16.0.6".officialRelease.sha256 = "sha256-fspqSReX+VD+Nl/Cfq+tDcdPtnQPV1IRopNDfd5VtUs=";
     "17.0.6".officialRelease.sha256 = "sha256-8MEDLLhocshmxoEBRSKlJ/GzJ8nfuzQ8qn0X/vLA+ag=";
     "18.1.8".officialRelease.sha256 = "sha256-iiZKMRo/WxJaBXct9GdAcAT3cz9d9pnAcO1mmR6oPNE=";
diff --git a/pkgs/test/default.nix b/pkgs/test/default.nix
index 25c23371c565..b2cdbd98e990 100644
--- a/pkgs/test/default.nix
+++ b/pkgs/test/default.nix
@@ -19,6 +19,7 @@ with pkgs;
             (filter (n: n != "llvmPackages_12"))
             (filter (n: n != "llvmPackages_13"))
             (filter (n: n != "llvmPackages_14"))
+            (filter (n: n != "llvmPackages_15"))
           ];
           tests = lib.genAttrs pkgSets (
             name:
diff --git a/pkgs/top-level/aliases.nix b/pkgs/top-level/aliases.nix
index 75fd28c94099..557cc191c0c1 100644
--- a/pkgs/top-level/aliases.nix
+++ b/pkgs/top-level/aliases.nix
@@ -698,13 +698,11 @@ mapAliases {
   cyber = throw "cyber has been removed, as it does not build with supported Zig versions"; # Added 2025-08-09
 
   # these are for convenience, not for backward compat., and shouldn't expire until the package is deprecated.
-  clang15Stdenv = lowPrio llvmPackages_15.stdenv; # preserve, reason: see above
   clang16Stdenv = lowPrio llvmPackages_16.stdenv; # preserve, reason: see above
   clang17Stdenv = lowPrio llvmPackages_17.stdenv; # preserve, reason: see above
   clang18Stdenv = lowPrio llvmPackages_18.stdenv; # preserve, reason: see above
   clang19Stdenv = lowPrio llvmPackages_19.stdenv; # preserve, reason: see above
 
-  clang-tools_15 = llvmPackages_15.clang-tools; # Added 2024-04-22
   clang-tools_16 = llvmPackages_16.clang-tools; # Added 2024-04-22
   clang-tools_17 = llvmPackages_17.clang-tools; # Added 2024-04-22
   clang-tools_18 = llvmPackages_18.clang-tools; # Added 2024-04-22
@@ -1507,6 +1505,14 @@ mapAliases {
   clang14Stdenv = throw "clang14Stdenv has been removed, as it is unmaintained and obsolete"; # Added 2025-08-10
   clang-tools_14 = throw "clang-tools_14 has been removed, as it is unmaintained and obsolete"; # Added 2025-08-10
 
+  llvmPackages_15 = throw "llvmPackages_15 has been removed, as it is unmaintained and obsolete"; # Added 2025-08-12
+  llvm_15 = throw "llvm_15 has been removed, as it is unmaintained and obsolete"; # Added 2025-08-12
+  lld_15 = throw "lld_15 has been removed, as it is unmaintained and obsolete"; # Added 2025-08-12
+  lldb_15 = throw "lldb_15 has been removed, as it is unmaintained and obsolete"; # Added 2025-08-12
+  clang_15 = throw "clang_15 has been removed, as it is unmaintained and obsolete"; # Added 2025-08-12
+  clang15Stdenv = throw "clang15Stdenv has been removed, as it is unmaintained and obsolete"; # Added 2025-08-12
+  clang-tools_15 = throw "clang-tools_15 has been removed, as it is unmaintained and obsolete"; # Added 2025-08-12
+
   lobster-two = throw "'lobster-two' has been renamed to/replaced by 'google-fonts'"; # Converted to throw 2024-10-17
   loc = throw "'loc' has been removed due to lack of upstream maintenance. Consider 'tokei' as an alternative."; # Added 2025-01-25
   loco-cli = loco; # Added 2025-02-24
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 31584910c6f6..5d096292c909 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -4633,7 +4633,6 @@ with pkgs;
   clang-manpages = llvmPackages.clang-manpages;
 
   clang = llvmPackages.clang;
-  clang_15 = llvmPackages_15.clang;
   clang_16 = llvmPackages_16.clang;
   clang_17 = llvmPackages_17.clang;
 
@@ -5362,17 +5361,14 @@ with pkgs;
   };
 
   lld = llvmPackages.lld;
-  lld_15 = llvmPackages_15.lld;
   lld_16 = llvmPackages_16.lld;
   lld_17 = llvmPackages_17.lld;
 
   lldb = llvmPackages.lldb;
-  lldb_15 = llvmPackages_15.lldb;
   lldb_16 = llvmPackages_16.lldb;
   lldb_17 = llvmPackages_17.lldb;
 
   llvm = llvmPackages.llvm;
-  llvm_15 = llvmPackages_15.llvm;
   llvm_16 = llvmPackages_16.llvm;
   llvm_17 = llvmPackages_17.llvm;
 
@@ -5390,7 +5386,6 @@ with pkgs;
     (rec {
       llvmPackagesSet = recurseIntoAttrs (callPackages ../development/compilers/llvm { });
 
-      llvmPackages_15 = llvmPackagesSet."15";
       llvmPackages_16 = llvmPackagesSet."16";
       llvmPackages_17 = llvmPackagesSet."17";
 
@@ -5425,7 +5420,6 @@ with pkgs;
 
       mkLLVMPackages = llvmPackagesSet.mkPackage;
     })
-    llvmPackages_15
     llvmPackages_16
     llvmPackages_17
     llvmPackages_18