diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index c450ee5a3d72e..d52bd84814aec 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -867,6 +867,11 @@ option(LLVM_INSTALL_GTEST
   "Install the llvm gtest library.  This should be on if you want to do
    stand-alone builds of the other projects and run their unit tests." OFF)
 
+option(LLVM_ENABLE_EXPENSIVE_CMAKE_CHECKS
+  "Enable use of expensive CMake checks for unused source files" ON)
+option(LLVM_ENABLE_LIT_CONVENIENCE_TARGETS
+  "Enable use of convenience targets for all subdirectories of a LIT test suite" ON)
+
 option(LLVM_BUILD_BENCHMARKS "Add LLVM benchmark targets to the list of default
 targets. If OFF, benchmarks still could be built using Benchmarks target." OFF)
 option(LLVM_INCLUDE_BENCHMARKS "Generate benchmark targets. If OFF, benchmarks can't be built." ON)
@@ -1027,9 +1032,18 @@ endif()
 find_package(Python3 ${LLVM_MINIMUM_PYTHON_VERSION} REQUIRED
     COMPONENTS Interpreter)
 
+set(LLVM_TOOLCHAIN_CHECK_CACHE "" CACHE PATH
+  "Path to where a generated *.cmake cache file will be saved.")
+
+include(LLVMCacheSnapshot)
 # All options referred to from HandleLLVMOptions have to be specified
 # BEFORE this include, otherwise options will not be correctly set on
-# first cmake run
+# first cmake run.
+if(LLVM_TOOLCHAIN_CHECK_CACHE AND EXISTS "${LLVM_TOOLCHAIN_CHECK_CACHE}")
+  include("${LLVM_TOOLCHAIN_CHECK_CACHE}")
+elseif(LLVM_TOOLCHAIN_CHECK_CACHE)
+  llvm_get_list_of_existing_cache_variables(cache_before)
+endif()
 include(config-ix)
 
 # By default, we target the host, but this can be overridden at CMake
@@ -1081,6 +1095,12 @@ endif()
 
 include(HandleLLVMOptions)
 
+if(LLVM_TOOLCHAIN_CHECK_CACHE AND NOT EXISTS "${LLVM_TOOLCHAIN_CHECK_CACHE}")
+  llvm_list_of_new_cache_variables_and_values(cache_before cache_new_pairs)
+  list(JOIN cache_new_pairs "\n" cache_new_pairs_joined)
+  file(WRITE "${LLVM_TOOLCHAIN_CHECK_CACHE}" "${cache_new_pairs_joined}")
+endif()
+
 ######
 
 # Configure all of the various header file fragments LLVM uses which depend on
diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index 80e59a4df2433..f26dd7aa549c5 100644
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -3,17 +3,18 @@ include(LLVMDistributionSupport)
 include(LLVMProcessSources)
 include(LLVM-Config)
 include(DetermineGCCCompatible)
+include(CheckLinkerFlag)
 
 # get_subproject_title(titlevar)
 #   Set ${outvar} to the title of the current LLVM subproject (Clang, MLIR ...)
-# 
+#
 # The title is set in the subproject's top-level using the variable
 # LLVM_SUBPROJECT_TITLE. If it does not exist, it is assumed it is LLVM itself.
 # The title is not semantically significant, but use to create folders in
 # CMake-generated IDE projects (Visual Studio/XCode).
 function(get_subproject_title outvar)
   if (LLVM_SUBPROJECT_TITLE)
-    set(${outvar} "${LLVM_SUBPROJECT_TITLE}" PARENT_SCOPE) 
+    set(${outvar} "${LLVM_SUBPROJECT_TITLE}" PARENT_SCOPE)
   else ()
     set(${outvar} "LLVM" PARENT_SCOPE)
   endif ()
@@ -269,7 +270,6 @@ if (NOT DEFINED LLVM_LINKER_DETECTED AND NOT WIN32)
   endif()
 
   if("${CMAKE_SYSTEM_NAME}" MATCHES "Darwin")
-    include(CheckLinkerFlag)
     # Linkers that support Darwin allow a setting to internalize all symbol exports,
     # aiding in reducing binary size and often is applicable for executables.
     check_linker_flag(C "-Wl,-no_exported_symbols" LLVM_LINKER_SUPPORTS_NO_EXPORTED_SYMBOLS)
@@ -289,8 +289,23 @@ if (NOT DEFINED LLVM_LINKER_DETECTED AND NOT WIN32)
   endif()
 endif()
 
+if (NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
+  if(NOT LLVM_NO_DEAD_STRIP)
+    if("${CMAKE_SYSTEM_NAME}" MATCHES "SunOS" AND LLVM_LINKER_IS_SOLARISLD)
+      # Support for ld -z discard-unused=sections was only added in
+      # Solaris 11.4.  GNU ld ignores it, but warns every time.
+      check_linker_flag(CXX "-Wl,-z,discard-unused=sections" LINKER_SUPPORTS_Z_DISCARD_UNUSED)
+    endif()
+  endif()
+endif()
+
+# Check for existence of symbolic functions flag. Not supported
+# by the older BFD linker (such as on some OpenBSD archs), the
+# MinGW driver for LLD, and the Solaris native linker.
+check_linker_flag(CXX "-Wl,-Bsymbolic-functions"
+                  LLVM_LINKER_SUPPORTS_B_SYMBOLIC_FUNCTIONS)
+
 function(add_link_opts target_name)
-  include(CheckLinkerFlag)
   get_llvm_distribution(${target_name} in_distribution in_distribution_var)
   if(NOT in_distribution)
     # Don't LTO optimize targets that aren't part of any distribution.
@@ -320,9 +335,6 @@ function(add_link_opts target_name)
         set_property(TARGET ${target_name} APPEND_STRING PROPERTY
                      LINK_FLAGS " -Wl,-dead_strip")
       elseif("${CMAKE_SYSTEM_NAME}" MATCHES "SunOS" AND LLVM_LINKER_IS_SOLARISLD)
-        # Support for ld -z discard-unused=sections was only added in
-        # Solaris 11.4.  GNU ld ignores it, but warns every time.
-        check_linker_flag(CXX "-Wl,-z,discard-unused=sections" LINKER_SUPPORTS_Z_DISCARD_UNUSED)
         if (LINKER_SUPPORTS_Z_DISCARD_UNUSED)
           set_property(TARGET ${target_name} APPEND_STRING PROPERTY
                        LINK_FLAGS " -Wl,-z,discard-unused=sections")
@@ -349,12 +361,6 @@ function(add_link_opts target_name)
     set_property(TARGET ${target_name} APPEND_STRING PROPERTY
                  LINK_FLAGS " -Wl,-brtl")
   endif()
-
-  # Check for existence of symbolic functions flag. Not supported
-  # by the older BFD linker (such as on some OpenBSD archs), the
-  # MinGW driver for LLD, and the Solaris native linker.
-  check_linker_flag(CXX "-Wl,-Bsymbolic-functions"
-                    LLVM_LINKER_SUPPORTS_B_SYMBOLIC_FUNCTIONS)
 endfunction(add_link_opts)
 
 # Set each output directory according to ${CMAKE_CONFIGURATION_TYPES}.
@@ -645,11 +651,11 @@ function(llvm_add_library name)
   endif()
   set_target_properties(${name} PROPERTIES FOLDER "${subproject_title}/Libraries")
 
-  ## If were compiling with clang-cl use /Zc:dllexportInlines- to exclude inline 
+  ## If were compiling with clang-cl use /Zc:dllexportInlines- to exclude inline
   ## class members from being dllexport'ed to reduce compile time.
   ## This will also keep us below the 64k exported symbol limit
   ## https://blog.llvm.org/2018/11/30-faster-windows-builds-with-clang-cl_14.html
-  if(LLVM_BUILD_LLVM_DYLIB AND NOT LLVM_DYLIB_EXPORT_INLINES AND 
+  if(LLVM_BUILD_LLVM_DYLIB AND NOT LLVM_DYLIB_EXPORT_INLINES AND
      MSVC AND CMAKE_CXX_COMPILER_ID MATCHES Clang)
     target_compile_options(${name} PUBLIC /Zc:dllexportInlines-)
     if(TARGET ${obj_name})
@@ -1500,8 +1506,8 @@ macro(llvm_add_tool project name)
                 RUNTIME DESTINATION ${${project}_TOOLS_INSTALL_DIR}
                 COMPONENT ${name})
         if (LLVM_ENABLE_PDB)
-          install(FILES $<TARGET_PDB_FILE:${name}> 
-                DESTINATION "${${project}_TOOLS_INSTALL_DIR}" COMPONENT ${name} 
+          install(FILES $<TARGET_PDB_FILE:${name}>
+                DESTINATION "${${project}_TOOLS_INSTALL_DIR}" COMPONENT ${name}
                 OPTIONAL)
         endif()
 
@@ -1535,8 +1541,8 @@ macro(add_llvm_example name)
   if( LLVM_BUILD_EXAMPLES )
     install(TARGETS ${name} RUNTIME DESTINATION "${LLVM_EXAMPLES_INSTALL_DIR}")
     if (LLVM_ENABLE_PDB)
-      install(FILES $<TARGET_PDB_FILE:${name}> 
-              DESTINATION "${LLVM_EXAMPLES_INSTALL_DIR}" COMPONENT ${name} 
+      install(FILES $<TARGET_PDB_FILE:${name}>
+              DESTINATION "${LLVM_EXAMPLES_INSTALL_DIR}" COMPONENT ${name}
               OPTIONAL)
     endif()
   endif()
@@ -1574,8 +1580,8 @@ macro(add_llvm_utility name)
               RUNTIME DESTINATION ${LLVM_UTILS_INSTALL_DIR}
               COMPONENT ${name})
       if (LLVM_ENABLE_PDB)
-        install(FILES $<TARGET_PDB_FILE:${name}> 
-                DESTINATION "${LLVM_UTILS_INSTALL_DIR}" COMPONENT ${name} 
+        install(FILES $<TARGET_PDB_FILE:${name}>
+                DESTINATION "${LLVM_UTILS_INSTALL_DIR}" COMPONENT ${name}
                 OPTIONAL)
       endif()
 
@@ -2192,6 +2198,9 @@ function(add_lit_testsuite target comment)
 endfunction()
 
 function(add_lit_testsuites project directory)
+  if(NOT LLVM_ENABLE_LIT_CONVENIENCE_TARGETS)
+    return()
+  endif()
   if (NOT LLVM_ENABLE_IDE)
     cmake_parse_arguments(ARG
       "EXCLUDE_FROM_CHECK_ALL"
diff --git a/llvm/cmake/modules/LLVMCacheSnapshot.cmake b/llvm/cmake/modules/LLVMCacheSnapshot.cmake
new file mode 100644
index 0000000000000..89d592a0a4165
--- /dev/null
+++ b/llvm/cmake/modules/LLVMCacheSnapshot.cmake
@@ -0,0 +1,51 @@
+# Example usage
+# llvm_get_cache_vars(before)
+# include(SomeModule)
+# llvm_diff_cache_vars("${before}" new_vars new_pairs)
+
+# message(STATUS "New cache variables: ${new_vars}")
+# message(STATUS "New cache vars and values:\n${new_pairs}")
+
+# get_list_of_existing_cache_variables(existing)
+function(llvm_get_list_of_existing_cache_variables out_var)
+  get_cmake_property(_all CACHE_VARIABLES)
+  if(NOT _all)
+    set(_all "")
+  endif()
+  set(${out_var} "${_all}" PARENT_SCOPE)
+endfunction()
+
+# list_of_new_cache_variables_and_values(existing new_vars_and_values)
+# - `existing` is the name of the var returned by the first helper
+# - `new_vars_and_values` will be a list like:  NAME=VALUE (TYPE=...);NAME2=VALUE2 (TYPE=...)
+function(llvm_list_of_new_cache_variables_and_values existing_list_var out_var)
+  # Existing (pre-include) snapshot
+  set(_before "${${existing_list_var}}")
+
+  # Current (post-include) snapshot
+  get_cmake_property(_after CACHE_VARIABLES)
+
+  # Compute new names
+  set(_new "${_after}")
+  if(_before)
+    list(REMOVE_ITEM _new ${_before})
+  endif()
+
+  # Pack "NAME=VALUE (TYPE=...)" for each new cache entry
+  set(_pairs "")
+  foreach(_k IN LISTS _new)
+    if(NOT "${_k}" MATCHES "^((C|CXX)_SUPPORTS|HAVE_|GLIBCXX_USE|SUPPORTS_FVISI)")
+      continue()
+    endif()
+    # Cache VALUE: dereference is fine here because cache entries read like normal vars
+    set(_val "${${_k}}")
+    # Cache TYPE (e.g., STRING, BOOL, PATH, FILEPATH, INTERNAL, UNINITIALIZED)
+    get_property(_type CACHE "${_k}" PROPERTY TYPE)
+    if(NOT _type)
+      set(_type "UNINITIALIZED")
+    endif()
+    list(APPEND _pairs "set(${_k} \"${_val}\" CACHE ${_type} \"\")")
+  endforeach()
+
+  set(${out_var} "${_pairs}" PARENT_SCOPE)
+endfunction()
diff --git a/llvm/cmake/modules/LLVMProcessSources.cmake b/llvm/cmake/modules/LLVMProcessSources.cmake
index 0670d60bf2afd..0bcce4c6c78ad 100644
--- a/llvm/cmake/modules/LLVMProcessSources.cmake
+++ b/llvm/cmake/modules/LLVMProcessSources.cmake
@@ -56,17 +56,25 @@ endfunction(find_all_header_files)
 function(llvm_process_sources OUT_VAR)
   cmake_parse_arguments(ARG "PARTIAL_SOURCES_INTENDED" "" "ADDITIONAL_HEADERS;ADDITIONAL_HEADER_DIRS" ${ARGN})
   set(sources ${ARG_UNPARSED_ARGUMENTS})
-  llvm_check_source_file_list(${sources})
 
-  # This adds .td and .h files to the Visual Studio solution:
-  add_td_sources(sources)
-  find_all_header_files(hdrs "${ARG_ADDITIONAL_HEADER_DIRS}")
-  if (hdrs)
-    set_source_files_properties(${hdrs} PROPERTIES HEADER_FILE_ONLY ON)
+  if(LLVM_ENABLE_EXPENSIVE_CMAKE_CHECKS)
+    llvm_check_source_file_list(${sources})
+  endif()
+
+  if(ARG_ADDITIONAL_HEADERS)
+    set_source_files_properties(${ARG_ADDITIONAL_HEADERS} PROPERTIES HEADER_FILE_ONLY ON)
+    list(APPEND sources ${ARG_ADDITIONAL_HEADERS})
   endif()
-  set_source_files_properties(${ARG_ADDITIONAL_HEADERS} PROPERTIES HEADER_FILE_ONLY ON)
-  list(APPEND sources ${ARG_ADDITIONAL_HEADERS} ${hdrs})
 
+  # This adds .td and .h files to the Visual Studio solution:
+  if(MSVC OR LLVM_ENABLE_EXPENSIVE_CMAKE_CHECKS)
+    add_td_sources(sources)
+    find_all_header_files(hdrs "${ARG_ADDITIONAL_HEADER_DIRS}")
+    if (hdrs)
+      set_source_files_properties(${hdrs} PROPERTIES HEADER_FILE_ONLY ON)
+    endif()
+    list(APPEND sources ${hdrs})
+  endif()
   set( ${OUT_VAR} ${sources} PARENT_SCOPE )
 endfunction(llvm_process_sources)
 
diff --git a/third-party/benchmark/cmake/AddCXXCompilerFlag.cmake b/third-party/benchmark/cmake/AddCXXCompilerFlag.cmake
index 858589e9775c6..1154311851f5d 100644
--- a/third-party/benchmark/cmake/AddCXXCompilerFlag.cmake
+++ b/third-party/benchmark/cmake/AddCXXCompilerFlag.cmake
@@ -27,20 +27,45 @@ function(mangle_compiler_flag FLAG OUTPUT)
   set(${OUTPUT} "${SANITIZED_FLAG}" PARENT_SCOPE)
 endfunction(mangle_compiler_flag)
 
+set(BENCHMARK_GCC_COMPATIBLE_FLAGS
+  -fno-exceptions
+  -fstrict-aliasing
+  -pedantic
+  -pedantic-errors
+  -Wall
+  -Werror
+  -Wextra
+  -Wfloat-equal
+  -Wno-deprecated
+  -Wno-deprecated-declarations
+  -Wold-style-cast
+  -Wshadow
+  -Wstrict-aliasing
+  -Wsuggest-override
+  )
+
+macro(_benchmark_populate_cxx_compiler_flag)
+  if(ARGC GREATER 1)
+    set(VARIANT ${ARGV1})
+    string(TOUPPER "_${VARIANT}" VARIANT)
+  else()
+    set(VARIANT "")
+  endif()
+  set(CMAKE_CXX_FLAGS${VARIANT} "${CMAKE_CXX_FLAGS${VARIANT}} ${BENCHMARK_CXX_FLAGS${VARIANT}} ${FLAG}" PARENT_SCOPE)
+endmacro()
+
 function(add_cxx_compiler_flag FLAG)
   mangle_compiler_flag("${FLAG}" MANGLED_FLAG)
+  if(LLVM_COMPILER_IS_GCC_COMPATIBLE AND "${FLAG}" IN_LIST BENCHMARK_GCC_COMPATIBLE_FLAGS)
+    _benchmark_populate_cxx_compiler_flag(${FLAG} ${VARIANT})
+    return()
+  endif()
   set(OLD_CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
   set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} ${FLAG}")
   check_cxx_compiler_flag("${FLAG}" ${MANGLED_FLAG})
   set(CMAKE_REQUIRED_FLAGS "${OLD_CMAKE_REQUIRED_FLAGS}")
   if(${MANGLED_FLAG})
-    if(ARGC GREATER 1)
-      set(VARIANT ${ARGV1})
-      string(TOUPPER "_${VARIANT}" VARIANT)
-    else()
-      set(VARIANT "")
-    endif()
-    set(CMAKE_CXX_FLAGS${VARIANT} "${CMAKE_CXX_FLAGS${VARIANT}} ${BENCHMARK_CXX_FLAGS${VARIANT}} ${FLAG}" PARENT_SCOPE)
+    _benchmark_populate_cxx_compiler_flag(${FLAG} ${VARIANT})
   endif()
 endfunction()