diff --git a/clang/tools/c-index-test/CMakeLists.txt b/clang/tools/c-index-test/CMakeLists.txt
index 41e80e66ffa7a..301d5ff8b7983 100644
--- a/clang/tools/c-index-test/CMakeLists.txt
+++ b/clang/tools/c-index-test/CMakeLists.txt
@@ -5,6 +5,9 @@ set(LLVM_LINK_COMPONENTS
 add_clang_executable(c-index-test
   c-index-test.c
   core_main.cpp
+
+  # Prevent CMake error with C source files.
+  DISABLE_PCH_REUSE
   )
 
 if(NOT MSVC)
diff --git a/clang/tools/clang-fuzzer/dictionary/CMakeLists.txt b/clang/tools/clang-fuzzer/dictionary/CMakeLists.txt
index 6b72b98f5e1c4..eec692a3b2e48 100644
--- a/clang/tools/clang-fuzzer/dictionary/CMakeLists.txt
+++ b/clang/tools/clang-fuzzer/dictionary/CMakeLists.txt
@@ -1,5 +1,8 @@
 set(CMAKE_CXX_FLAGS ${CXX_FLAGS_NOFUZZ})
 add_clang_executable(clang-fuzzer-dictionary
   dictionary.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
 
diff --git a/flang/CMakeLists.txt b/flang/CMakeLists.txt
index c01eb56d5e496..e21304d2e4da7 100644
--- a/flang/CMakeLists.txt
+++ b/flang/CMakeLists.txt
@@ -441,11 +441,6 @@ if (LLVM_COMPILER_IS_GCC_COMPATIBLE)
   if (BUILD_SHARED_LIBS AND NOT (CMAKE_CXX_COMPILER_ID MATCHES "Clang"))
    set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -fno-semantic-interposition")
   endif()
-
-  # GCC requires this flag in order for precompiled headers to work with ccache
-  if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND NOT CMAKE_DISABLE_PRECOMPILE_HEADERS)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpch-preprocess")
-  endif()
 endif()
 
 # Clang on Darwin enables non-POSIX extensions by default, which allows the
@@ -456,11 +451,6 @@ if (APPLE)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D_POSIX_C_SOURCE=200809")
 endif()
 
-# Clang requires this flag in order for precompiled headers to work with ccache
-if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT CMAKE_DISABLE_PRECOMPILE_HEADERS)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Xclang -fno-pch-timestamp")
-endif()
-
 list(REMOVE_DUPLICATES CMAKE_CXX_FLAGS)
 
 # Determine HOST_LINK_VERSION on Darwin.
diff --git a/flang/lib/Evaluate/CMakeLists.txt b/flang/lib/Evaluate/CMakeLists.txt
index 24a1c9004bc3b..472ecb6d8d079 100644
--- a/flang/lib/Evaluate/CMakeLists.txt
+++ b/flang/lib/Evaluate/CMakeLists.txt
@@ -66,15 +66,8 @@ add_flang_library(FortranEvaluate
   ${LIBPGMATH}
   ${QUADMATHLIB}
 
-  LINK_COMPONENTS
-  Support
-
-  DEPENDS
-  acc_gen
-  omp_gen
-)
-
-target_precompile_headers(FortranEvaluate PRIVATE
+  DISABLE_PCH_REUSE
+  PRECOMPILE_HEADERS
   [["flang/Evaluate/common.h"]]
   [["flang/Evaluate/call.h"]]
   [["flang/Evaluate/traverse.h"]]
@@ -86,4 +79,11 @@ target_precompile_headers(FortranEvaluate PRIVATE
   [["flang/Evaluate/integer.h"]]
   [["flang/Evaluate/expression.h"]]
   [["flang/Evaluate/tools.h"]]
+
+  LINK_COMPONENTS
+  Support
+
+  DEPENDS
+  acc_gen
+  omp_gen
 )
diff --git a/flang/lib/Frontend/CMakeLists.txt b/flang/lib/Frontend/CMakeLists.txt
index 4ebe497e65676..bd67ec444f358 100644
--- a/flang/lib/Frontend/CMakeLists.txt
+++ b/flang/lib/Frontend/CMakeLists.txt
@@ -13,6 +13,14 @@ add_flang_library(flangFrontend
   TextDiagnosticBuffer.cpp
   TextDiagnostic.cpp
 
+  DISABLE_PCH_REUSE
+  PRECOMPILE_HEADERS
+  [["flang/Parser/parsing.h"]]
+  [["flang/Parser/parse-tree.h"]]
+  [["flang/Parser/dump-parse-tree.h"]]
+  [["flang/Lower/PFTBuilder.h"]]
+  [["flang/Lower/Bridge.h"]]
+
   DEPENDS
   CUFDialect
   FIRDialect
@@ -78,11 +86,3 @@ add_flang_library(flangFrontend
   clangBasic
   clangOptions
 )
-
-target_precompile_headers(flangFrontend PRIVATE
-  [["flang/Parser/parsing.h"]]
-  [["flang/Parser/parse-tree.h"]]
-  [["flang/Parser/dump-parse-tree.h"]]
-  [["flang/Lower/PFTBuilder.h"]]
-  [["flang/Lower/Bridge.h"]]
-)
diff --git a/flang/lib/Lower/CMakeLists.txt b/flang/lib/Lower/CMakeLists.txt
index 230a56ab66ec5..f5424c78b9a98 100644
--- a/flang/lib/Lower/CMakeLists.txt
+++ b/flang/lib/Lower/CMakeLists.txt
@@ -38,6 +38,17 @@ add_flang_library(FortranLower
   Support/Utils.cpp
   SymbolMap.cpp
   VectorSubscripts.cpp
+
+  DISABLE_PCH_REUSE
+  PRECOMPILE_HEADERS
+  [["flang/Lower/ConvertExpr.h"]]
+  [["flang/Lower/SymbolMap.h"]]
+  [["flang/Lower/AbstractConverter.h"]]
+  [["flang/Lower/IterationSpace.h"]]
+  [["flang/Lower/CallInterface.h"]]
+  [["flang/Lower/BoxAnalyzer.h"]]
+  [["flang/Lower/PFTBuilder.h"]]
+  [["flang/Lower/DirectivesCommon.h"]]
   
   DEPENDS
   CUFAttrs
@@ -79,14 +90,3 @@ add_flang_library(FortranLower
   MLIRLLVMDialect
   MLIRSCFToControlFlow
 )
-
-target_precompile_headers(FortranLower PRIVATE
-  [["flang/Lower/ConvertExpr.h"]]
-  [["flang/Lower/SymbolMap.h"]]
-  [["flang/Lower/AbstractConverter.h"]]
-  [["flang/Lower/IterationSpace.h"]]
-  [["flang/Lower/CallInterface.h"]]
-  [["flang/Lower/BoxAnalyzer.h"]]
-  [["flang/Lower/PFTBuilder.h"]]
-  [["flang/Lower/DirectivesCommon.h"]]
-)
diff --git a/flang/lib/Parser/CMakeLists.txt b/flang/lib/Parser/CMakeLists.txt
index 20c6c2a7c8f80..e0479b0da3eb8 100644
--- a/flang/lib/Parser/CMakeLists.txt
+++ b/flang/lib/Parser/CMakeLists.txt
@@ -25,6 +25,14 @@ add_flang_library(FortranParser
   unparse.cpp
   user-state.cpp
 
+  DISABLE_PCH_REUSE
+  PRECOMPILE_HEADERS
+  [["flang/Parser/parsing.h"]]
+  [["flang/Parser/parse-tree.h"]]
+  [["flang/Parser/provenance.h"]]
+  [["flang/Parser/message.h"]]
+  [["flang/Parser/parse-tree-visitor.h"]]
+
   LINK_LIBS
   FortranSupport
 
@@ -37,11 +45,3 @@ add_flang_library(FortranParser
   omp_gen
   acc_gen
 )
-
-target_precompile_headers(FortranParser PRIVATE
-  [["flang/Parser/parsing.h"]]
-  [["flang/Parser/parse-tree.h"]]
-  [["flang/Parser/provenance.h"]]
-  [["flang/Parser/message.h"]]
-  [["flang/Parser/parse-tree-visitor.h"]]
-)
diff --git a/flang/lib/Semantics/CMakeLists.txt b/flang/lib/Semantics/CMakeLists.txt
index 109bc2dbb8569..44e6dfb4dd09f 100644
--- a/flang/lib/Semantics/CMakeLists.txt
+++ b/flang/lib/Semantics/CMakeLists.txt
@@ -53,6 +53,15 @@ add_flang_library(FortranSemantics
   type.cpp
   unparse-with-symbols.cpp
 
+  DISABLE_PCH_REUSE
+  PRECOMPILE_HEADERS
+  [["flang/Semantics/semantics.h"]]
+  [["flang/Semantics/type.h"]]
+  [["flang/Semantics/openmp-modifiers.h"]]
+  [["flang/Semantics/expression.h"]]
+  [["flang/Semantics/tools.h"]]
+  [["flang/Semantics/symbol.h"]]
+
   DEPENDS
   acc_gen
   omp_gen
@@ -68,12 +77,3 @@ add_flang_library(FortranSemantics
   FrontendOpenACC
   TargetParser
 )
-
-target_precompile_headers(FortranSemantics PRIVATE
-  [["flang/Semantics/semantics.h"]]
-  [["flang/Semantics/type.h"]]
-  [["flang/Semantics/openmp-modifiers.h"]]
-  [["flang/Semantics/expression.h"]]
-  [["flang/Semantics/tools.h"]]
-  [["flang/Semantics/symbol.h"]]
-)
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index 9954053591d30..a539a2182efa5 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -313,6 +313,22 @@ if(LLVM_CCACHE_BUILD)
         set(CCACHE_PROGRAM "CCACHE_DIR=${LLVM_CCACHE_DIR} ${CCACHE_PROGRAM}")
       endif()
       set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ${CCACHE_PROGRAM})
+
+      if(NOT CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+        # ccache with PCH can lead to false-positives when only a macro
+        # definition changes with non-Clang compilers, because macro definitions
+        # are not compared in preprocessed mode.
+        # See: https://github.com/ccache/ccache/issues/1668
+        if(NOT DEFINED CMAKE_DISABLE_PRECOMPILE_HEADERS)
+          message(NOTICE "Using ccache with precompiled headers with non-Clang "
+            "compilers is not supported. CMAKE_DISABLE_PRECOMPILE_HEADERS will be set to ON. "
+            "Pass -DCMAKE_DISABLE_PRECOMPILE_HEADERS=OFF to override this.")
+          set(CMAKE_DISABLE_PRECOMPILE_HEADERS "ON")
+        elseif(NOT CMAKE_DISABLE_PRECOMPILE_HEADERS)
+          message(WARNING "Using ccache with precompiled headers with non-Clang "
+            "compilers is not supported.")
+        endif()
+      endif()
     else()
       # Until a way to reliably configure ccache on Windows is found,
       # disable precompiled headers for Windows + ccache builds
diff --git a/llvm/cmake/modules/AddLLVM.cmake b/llvm/cmake/modules/AddLLVM.cmake
index d938214f9d0df..fc038499940f2 100644
--- a/llvm/cmake/modules/AddLLVM.cmake
+++ b/llvm/cmake/modules/AddLLVM.cmake
@@ -79,6 +79,48 @@ function(llvm_update_compile_flags name)
   target_compile_definitions(${name} PRIVATE ${LLVM_COMPILE_DEFINITIONS})
 endfunction()
 
+function(llvm_update_pch name)
+  if(LLVM_REQUIRES_RTTI OR LLVM_REQUIRES_EH)
+    # Non-default RTTI/EH results in incompatible flags, precluding PCH reuse.
+    set(ARG_DISABLE_PCH_REUSE ON)
+  endif()
+
+  # Find PCH with highest priority from dependencies. We reuse the first PCH
+  # with the highest priority. If the target has its own set of PCH, we give it
+  # a higher priority so that dependents will prefer the new PCH. We don't do
+  # transitive PCH reuse, because this causes too many unrelated naming
+  # collisions (e.g., in A -> B -> C{pch}, only B would reuse the PCH of C).
+  set(pch_priority 0)
+  llvm_map_components_to_libnames(libs
+    ${LLVM_LINK_COMPONENTS}
+  )
+  list(APPEND libs ${ARG_LINK_LIBS})
+  foreach(lib ${libs})
+    if(TARGET ${lib})
+      get_target_property(lib_pch_priority ${lib} LLVM_PCH_PRIORITY)
+      if(${lib_pch_priority} GREATER ${pch_priority})
+        set(pch_priority ${lib_pch_priority})
+        set(pch_reuse ${lib})
+      endif()
+    endif()
+  endforeach()
+
+  if(ARG_PRECOMPILE_HEADERS)
+    message(DEBUG "Adding PCH ${ARG_PRECOMPILE_HEADERS} for ${name} (prio ${pch_priority})")
+    target_precompile_headers(${name} PRIVATE $<$<COMPILE_LANGUAGE:CXX>:${ARG_PRECOMPILE_HEADERS}>)
+    if(NOT ARG_DISABLE_PCH_REUSE)
+      # Set priority so that dependants can reuse the PCH.
+      math(EXPR pch_priority "${pch_priority} + 1")
+      set_target_properties(${name} PROPERTIES LLVM_PCH_PRIORITY ${pch_priority})
+    endif()
+  elseif(pch_reuse AND NOT ARG_DISABLE_PCH_REUSE)
+    message(DEBUG "Using PCH ${pch_reuse} for ${name} (prio ${pch_priority})")
+    target_precompile_headers(${name} REUSE_FROM ${pch_reuse})
+  else()
+    message(DEBUG "Using NO PCH for ${name}")
+  endif()
+endfunction()
+
 function(add_llvm_symbol_exports target_name export_file)
   if("${CMAKE_SYSTEM_NAME}" MATCHES "Darwin")
     set(native_export_file "${target_name}.exports")
@@ -485,6 +527,13 @@ endfunction(set_windows_version_resource_properties)
 #     Corresponds to OUTPUT_NAME in target properties.
 #   DEPENDS targets...
 #     Same semantics as add_dependencies().
+#   PRECOMPILE_HEADERS include_directives...
+#     Pre-compiled C++ headers to use. PCH can be reused by dependants. If
+#     specified, no PCHs from dependencies will be reused.
+#   DISABLE_PCH_REUSE
+#     Disable reuse of pre-compiled headers in both directions: the library will
+#     not reuse the PCH of a dependency and a defined PCH will not be offered
+#     for reuse by dependants.
 #   LINK_COMPONENTS components...
 #     Same as the variable LLVM_LINK_COMPONENTS.
 #   LINK_LIBS lib_targets...
@@ -504,11 +553,12 @@ endfunction(set_windows_version_resource_properties)
 #   )
 function(llvm_add_library name)
   cmake_parse_arguments(ARG
-    "MODULE;SHARED;STATIC;OBJECT;DISABLE_LLVM_LINK_LLVM_DYLIB;SONAME;NO_INSTALL_RPATH;COMPONENT_LIB"
+    "MODULE;SHARED;STATIC;OBJECT;DISABLE_LLVM_LINK_LLVM_DYLIB;SONAME;NO_INSTALL_RPATH;COMPONENT_LIB;DISABLE_PCH_REUSE"
     "OUTPUT_NAME;PLUGIN_TOOL;ENTITLEMENTS;BUNDLE_PATH"
-    "ADDITIONAL_HEADERS;DEPENDS;LINK_COMPONENTS;LINK_LIBS;OBJLIBS"
+    "ADDITIONAL_HEADERS;PRECOMPILE_HEADERS;DEPENDS;LINK_COMPONENTS;LINK_LIBS;OBJLIBS"
     ${ARGN})
   list(APPEND LLVM_COMMON_DEPENDS ${ARG_DEPENDS})
+  list(APPEND LLVM_LINK_COMPONENTS ${ARG_LINK_COMPONENTS})
   if(ARG_ADDITIONAL_HEADERS)
     # Pass through ADDITIONAL_HEADERS.
     set(ARG_ADDITIONAL_HEADERS ADDITIONAL_HEADERS ${ARG_ADDITIONAL_HEADERS})
@@ -550,6 +600,7 @@ function(llvm_add_library name)
       ${ALL_FILES}
       )
     llvm_update_compile_flags(${obj_name})
+    llvm_update_pch(${obj_name})
     if(CMAKE_GENERATOR STREQUAL "Xcode")
       set(DUMMY_FILE ${CMAKE_CURRENT_BINARY_DIR}/Dummy.c)
       file(WRITE ${DUMMY_FILE} "// This file intentionally empty\n")
@@ -604,7 +655,7 @@ function(llvm_add_library name)
       ${output_name}
       OBJLIBS ${ALL_FILES} # objlib
       LINK_LIBS ${ARG_LINK_LIBS}
-      LINK_COMPONENTS ${ARG_LINK_COMPONENTS}
+      LINK_COMPONENTS ${LLVM_LINK_COMPONENTS}
       )
     set_target_properties(${name_static} PROPERTIES FOLDER "${subproject_title}/Libraries")
 
@@ -676,6 +727,11 @@ function(llvm_add_library name)
   # $<TARGET_OBJECTS> doesn't require compile flags.
   if(NOT obj_name)
     llvm_update_compile_flags(${name})
+    llvm_update_pch(${name})
+  else()
+    target_precompile_headers(${name} REUSE_FROM ${obj_name})
+    get_target_property(pch_priority ${obj_name} LLVM_PCH_PRIORITY)
+    set_target_properties(${name} PROPERTIES LLVM_PCH_PRIORITY ${pch_priority})
   endif()
   add_link_opts( ${name} )
   if(ARG_OUTPUT_NAME)
@@ -758,8 +814,7 @@ function(llvm_add_library name)
         target_compile_definitions(${name} PRIVATE LLVM_BUILD_STATIC)
       endif()
       llvm_map_components_to_libnames(llvm_libs
-       ${ARG_LINK_COMPONENTS}
-       ${LLVM_LINK_COMPONENTS}
+        ${LLVM_LINK_COMPONENTS}
        )
     endif()
   else()
@@ -770,7 +825,7 @@ function(llvm_add_library name)
     # It would be nice to verify that we have the dependencies for this library
     # name, but using get_property(... SET) doesn't suffice to determine if a
     # property has been set to an empty value.
-    set_property(TARGET ${name} PROPERTY LLVM_LINK_COMPONENTS ${ARG_LINK_COMPONENTS} ${LLVM_LINK_COMPONENTS})
+    set_property(TARGET ${name} PROPERTY LLVM_LINK_COMPONENTS ${LLVM_LINK_COMPONENTS})
 
     # This property is an internal property only used to make sure the
     # link step applied in LLVMBuildResolveComponentsLink uses the same
@@ -993,6 +1048,7 @@ macro(generate_llvm_objects name)
       ${ALL_FILES}
       )
     llvm_update_compile_flags(${obj_name})
+    llvm_update_pch(${obj_name})
     set(ALL_FILES "$<TARGET_OBJECTS:${obj_name}>")
     if(ARG_DEPENDS)
       add_dependencies(${obj_name} ${ARG_DEPENDS})
@@ -1032,7 +1088,7 @@ endmacro()
 
 macro(add_llvm_executable name)
   cmake_parse_arguments(ARG
-    "DISABLE_LLVM_LINK_LLVM_DYLIB;IGNORE_EXTERNALIZE_DEBUGINFO;NO_INSTALL_RPATH;SUPPORT_PLUGINS;EXPORT_SYMBOLS"
+    "DISABLE_LLVM_LINK_LLVM_DYLIB;IGNORE_EXTERNALIZE_DEBUGINFO;NO_INSTALL_RPATH;SUPPORT_PLUGINS;EXPORT_SYMBOLS;DISABLE_PCH_REUSE"
     "ENTITLEMENTS;BUNDLE_PATH"
     ""
     ${ARGN})
@@ -1070,9 +1126,23 @@ macro(add_llvm_executable name)
     set_windows_version_resource_properties(${name} ${windows_resource_file})
   endif()
 
+  # CMake position-independent code sets -fPIE for source files in executables.
+  # With LLVM_ENABLE_PIC, we add -fPIC to all source files, but -fPIE is added
+  # later and therefore wins. To avoid option mismatch between the PCH (-fPIC)
+  # and the executable (-fPIE), disable PCH reuse for PIE.
+  get_target_property(cmake_pie ${name} POSITION_INDEPENDENT_CODE)
+  if(${cmake_pie})
+    set(ARG_DISABLE_PCH_REUSE ON)
+  endif()
+
   # $<TARGET_OBJECTS> doesn't require compile flags.
   if(NOT LLVM_ENABLE_OBJLIB)
     llvm_update_compile_flags(${name})
+    llvm_update_pch(${name})
+  elseif(NOT ARG_DISABLE_PCH_REUSE)
+    target_precompile_headers(${name} REUSE_FROM ${obj_name})
+    get_target_property(pch_priority ${obj_name} LLVM_PCH_PRIORITY)
+    set_target_properties(${name} PROPERTIES LLVM_PCH_PRIORITY ${pch_priority})
   endif()
 
   if (ARG_SUPPORT_PLUGINS AND NOT "${CMAKE_SYSTEM_NAME}" MATCHES "AIX")
@@ -1780,7 +1850,7 @@ function(add_unittest test_suite test_name)
   endif()
 
   list(APPEND LLVM_LINK_COMPONENTS Support) # gtest needs it for raw_ostream
-  add_llvm_executable(${test_name} IGNORE_EXTERNALIZE_DEBUGINFO NO_INSTALL_RPATH ${ARGN})
+  add_llvm_executable(${test_name} IGNORE_EXTERNALIZE_DEBUGINFO NO_INSTALL_RPATH DISABLE_PCH_REUSE ${ARGN})
   get_subproject_title(subproject_title)
   set_target_properties(${test_name} PROPERTIES FOLDER "${subproject_title}/Tests/Unit")
 
diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index 8b7c8cd4028bd..63f7877e82364 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -1304,11 +1304,55 @@ if (LLVM_BUILD_INSTRUMENTED AND LLVM_BUILD_INSTRUMENTED_COVERAGE)
   message(FATAL_ERROR "LLVM_BUILD_INSTRUMENTED and LLVM_BUILD_INSTRUMENTED_COVERAGE cannot both be specified")
 endif()
 
+if(NOT DEFINED CMAKE_DISABLE_PRECOMPILE_HEADERS)
+  if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+    # Pre-compiled headers with GCC (tested versions 14+15) provide very little
+    # compile-time improvements, but substantially increase the build dir size.
+    # Therefore, disable PCH with GCC by default.
+    message(NOTICE "Precompiled headers are disabled by default with GCC. "
+      "Pass -DCMAKE_DISABLE_PRECOMPILE_HEADERS=OFF to override.")
+    set(CMAKE_DISABLE_PRECOMPILE_HEADERS ON)
+  endif()
+  if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 18)
+    # Clang before version 18 has problems with mixed default visibility.
+    # Therefore, disable PCH with older Clang versions by default.
+    message(NOTICE "Precompiled headers are disabled by default with Clang <18. "
+      "Pass -DCMAKE_DISABLE_PRECOMPILE_HEADERS=OFF to override.")
+    set(CMAKE_DISABLE_PRECOMPILE_HEADERS ON)
+  endif()
+
+  # Warn on possibly unintended interactions with ccache/sccache if the user
+  # sets this via CMAKE_CXX_COMPILER_LAUNCHER (and not using LLVM_CCACHE_BUILD).
+  if(CMAKE_CXX_COMPILER_LAUNCHER MATCHES "ccache" AND NOT CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+    # ccache with PCH can lead to false-positives when only a macro
+    # definition changes with non-Clang compilers, because macro definitions
+    # are not compared in preprocessed mode.
+    # See: https://github.com/ccache/ccache/issues/1668
+    #
+    # It is unclear to what extent sccache supports PCH, but Clang seems to work
+    # fine.
+    # See: https://github.com/mozilla/sccache/issues/615
+    # See: https://github.com/mozilla/sccache/issues/2562
+    message(WARNING "Using sccache/ccache with precompiled headers with non-Clang "
+      "compilers is not supported and may lead to false positives. "
+      "Set CMAKE_DISABLE_PRECOMPILE_HEADERS to ON/OFF to silence this warning.")
+  endif()
+endif()
 if(NOT CMAKE_DISABLE_PRECOMPILE_HEADERS)
+  message(STATUS "Precompiled headers enabled.")
   # CMake weirdly marks all PCH as system headers. This undocumented variable
   # can be used to suppress the "#pragma clang system_header".
   # See: https://gitlab.kitware.com/cmake/cmake/-/issues/21219
   set(CMAKE_PCH_PROLOGUE "")
+  if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
+    # Clang requires this flag in order for precompiled headers to work with ccache.
+    append("-Xclang -fno-pch-timestamp" CMAKE_CXX_FLAGS)
+  elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+    # GCC requires this flag in order for precompiled headers to work with ccache.
+    append("-fpch-preprocess" CMAKE_CXX_FLAGS)
+  endif()
+else()
+  message(STATUS "Precompiled headers disabled.")
 endif()
 
 set(LLVM_THINLTO_CACHE_PATH "${PROJECT_BINARY_DIR}/lto.cache" CACHE STRING "Set ThinLTO cache path. This can be used when building LLVM from several different directiories.")
diff --git a/llvm/examples/OrcV2Examples/OrcV2CBindingsAddObjectFile/CMakeLists.txt b/llvm/examples/OrcV2Examples/OrcV2CBindingsAddObjectFile/CMakeLists.txt
index cc50112f326ea..a09ac0e8148d0 100644
--- a/llvm/examples/OrcV2Examples/OrcV2CBindingsAddObjectFile/CMakeLists.txt
+++ b/llvm/examples/OrcV2Examples/OrcV2CBindingsAddObjectFile/CMakeLists.txt
@@ -12,4 +12,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_example(OrcV2CBindingsAddObjectFile
   OrcV2CBindingsAddObjectFile.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
diff --git a/llvm/examples/OrcV2Examples/OrcV2CBindingsBasicUsage/CMakeLists.txt b/llvm/examples/OrcV2Examples/OrcV2CBindingsBasicUsage/CMakeLists.txt
index 0f18d6c24912f..9939bcf6e5ec9 100644
--- a/llvm/examples/OrcV2Examples/OrcV2CBindingsBasicUsage/CMakeLists.txt
+++ b/llvm/examples/OrcV2Examples/OrcV2CBindingsBasicUsage/CMakeLists.txt
@@ -12,4 +12,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_example(OrcV2CBindingsBasicUsage
   OrcV2CBindingsBasicUsage.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
diff --git a/llvm/examples/OrcV2Examples/OrcV2CBindingsDumpObjects/CMakeLists.txt b/llvm/examples/OrcV2Examples/OrcV2CBindingsDumpObjects/CMakeLists.txt
index 8e2c97d782062..e62f0256e3f86 100644
--- a/llvm/examples/OrcV2Examples/OrcV2CBindingsDumpObjects/CMakeLists.txt
+++ b/llvm/examples/OrcV2Examples/OrcV2CBindingsDumpObjects/CMakeLists.txt
@@ -12,4 +12,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_example(OrcV2CBindingsDumpObjects
   OrcV2CBindingsDumpObjects.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
diff --git a/llvm/examples/OrcV2Examples/OrcV2CBindingsIRTransforms/CMakeLists.txt b/llvm/examples/OrcV2Examples/OrcV2CBindingsIRTransforms/CMakeLists.txt
index af1b43e43e111..8fb344b5d523c 100644
--- a/llvm/examples/OrcV2Examples/OrcV2CBindingsIRTransforms/CMakeLists.txt
+++ b/llvm/examples/OrcV2Examples/OrcV2CBindingsIRTransforms/CMakeLists.txt
@@ -13,4 +13,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_example(OrcV2CBindingsIRTransforms
   OrcV2CBindingsIRTransforms.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
diff --git a/llvm/examples/OrcV2Examples/OrcV2CBindingsLazy/CMakeLists.txt b/llvm/examples/OrcV2Examples/OrcV2CBindingsLazy/CMakeLists.txt
index 52eb2d496fc23..4b415d0114d2e 100644
--- a/llvm/examples/OrcV2Examples/OrcV2CBindingsLazy/CMakeLists.txt
+++ b/llvm/examples/OrcV2Examples/OrcV2CBindingsLazy/CMakeLists.txt
@@ -12,4 +12,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_example(OrcV2CBindingsLazy
   OrcV2CBindingsLazy.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
diff --git a/llvm/examples/OrcV2Examples/OrcV2CBindingsMCJITLikeMemoryManager/CMakeLists.txt b/llvm/examples/OrcV2Examples/OrcV2CBindingsMCJITLikeMemoryManager/CMakeLists.txt
index 4cdc2b114e9a5..df7996519382c 100644
--- a/llvm/examples/OrcV2Examples/OrcV2CBindingsMCJITLikeMemoryManager/CMakeLists.txt
+++ b/llvm/examples/OrcV2Examples/OrcV2CBindingsMCJITLikeMemoryManager/CMakeLists.txt
@@ -12,4 +12,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_example(OrcV2CBindingsMCJITLikeMemoryManager
   OrcV2CBindingsMCJITLikeMemoryManager.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
diff --git a/llvm/examples/OrcV2Examples/OrcV2CBindingsRemovableCode/CMakeLists.txt b/llvm/examples/OrcV2Examples/OrcV2CBindingsRemovableCode/CMakeLists.txt
index 5b737557bb1ef..346aa5d62066d 100644
--- a/llvm/examples/OrcV2Examples/OrcV2CBindingsRemovableCode/CMakeLists.txt
+++ b/llvm/examples/OrcV2Examples/OrcV2CBindingsRemovableCode/CMakeLists.txt
@@ -12,4 +12,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_example(OrcV2CBindingsRemovableCode
   OrcV2CBindingsRemovableCode.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
diff --git a/llvm/examples/OrcV2Examples/OrcV2CBindingsVeryLazy/CMakeLists.txt b/llvm/examples/OrcV2Examples/OrcV2CBindingsVeryLazy/CMakeLists.txt
index 0bc9610b1ad7e..c71b2c20136d3 100644
--- a/llvm/examples/OrcV2Examples/OrcV2CBindingsVeryLazy/CMakeLists.txt
+++ b/llvm/examples/OrcV2Examples/OrcV2CBindingsVeryLazy/CMakeLists.txt
@@ -12,4 +12,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_example(OrcV2CBindingsVeryLazy
   OrcV2CBindingsVeryLazy.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
diff --git a/llvm/include/llvm/Support/pch.h b/llvm/include/llvm/Support/pch.h
new file mode 100644
index 0000000000000..ccfeceb231f61
--- /dev/null
+++ b/llvm/include/llvm/Support/pch.h
@@ -0,0 +1,75 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// Precompiled header for LLVMSupport.
+///
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/ADL.h"
+#include "llvm/ADT/APFloat.h"
+#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/APSInt.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/Hashing.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/Twine.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/FormatVariadic.h"
+#include "llvm/Support/JSON.h"
+#include "llvm/Support/SourceMgr.h"
+#include "llvm/Support/VersionTuple.h"
+#include "llvm/Support/YAMLTraits.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <array>
+#include <atomic>
+#include <bitset>
+#include <cassert>
+#include <chrono>
+#include <climits>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <cstring>
+#include <ctime>
+#include <deque>
+#include <functional>
+#include <initializer_list>
+#include <iterator>
+#include <limits>
+#include <list>
+#include <map>
+#include <memory>
+#include <mutex>
+#include <new>
+#include <optional>
+#include <queue>
+#include <set>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <system_error>
+#include <tuple>
+#include <type_traits>
+#include <unordered_map>
+#include <unordered_set>
+#include <utility>
+#include <variant>
+#include <vector>
diff --git a/llvm/lib/CMakeLists.txt b/llvm/lib/CMakeLists.txt
index 9af1854852436..f0faaff307997 100644
--- a/llvm/lib/CMakeLists.txt
+++ b/llvm/lib/CMakeLists.txt
@@ -3,8 +3,8 @@ include(LLVM-Build)
 # `Demangle', `Support' and `TableGen' libraries are added on the top-level
 # CMakeLists.txt
 
-add_subdirectory(ABI)
 add_subdirectory(IR)
+add_subdirectory(ABI)
 add_subdirectory(FuzzMutate)
 add_subdirectory(FileCheck)
 add_subdirectory(InterfaceStub)
diff --git a/llvm/lib/Support/CMakeLists.txt b/llvm/lib/Support/CMakeLists.txt
index 099b0e55579be..b4e39fced3853 100644
--- a/llvm/lib/Support/CMakeLists.txt
+++ b/llvm/lib/Support/CMakeLists.txt
@@ -135,7 +135,6 @@ if (UNIX AND "${CMAKE_SYSTEM_NAME}" MATCHES "AIX")
 endif()
 
 add_subdirectory(BLAKE3)
-add_subdirectory(LSP)
 
 add_llvm_component_library(LLVMSupport
   ABIBreak.cpp
@@ -322,6 +321,9 @@ add_llvm_component_library(LLVMSupport
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/Support
   ${Backtrace_INCLUDE_DIRS}
 
+  PRECOMPILE_HEADERS
+  [["llvm/Support/pch.h"]]
+
   LINK_LIBS
   ${system_libs} ${imported_libs} ${delayload_flags}
 
@@ -396,3 +398,6 @@ target_include_directories(LLVMSupport
   PRIVATE
   ${LLVM_THIRD_PARTY_DIR}/siphash/include
 )
+
+# SupportLSP depends on Support and therefore must be included afterwards.
+add_subdirectory(LSP)
diff --git a/llvm/tools/llvm-c-test/CMakeLists.txt b/llvm/tools/llvm-c-test/CMakeLists.txt
index 939164e636216..99d79443f1bc4 100644
--- a/llvm/tools/llvm-c-test/CMakeLists.txt
+++ b/llvm/tools/llvm-c-test/CMakeLists.txt
@@ -53,6 +53,9 @@ add_llvm_tool(llvm-c-test
   metadata.c
   object.c
   targets.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
 
 if(USE_LLVM_DYLIB)
diff --git a/llvm/utils/count/CMakeLists.txt b/llvm/utils/count/CMakeLists.txt
index cfd1f4a85d8a1..94250a2ef6374 100644
--- a/llvm/utils/count/CMakeLists.txt
+++ b/llvm/utils/count/CMakeLists.txt
@@ -4,4 +4,7 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_utility(count
   count.c
+
+  # No C++ files, prevent CMake error.
+  DISABLE_PCH_REUSE
   )
diff --git a/mlir/test/CAPI/CMakeLists.txt b/mlir/test/CAPI/CMakeLists.txt
index d45142510a496..313a3a8d9ba46 100644
--- a/mlir/test/CAPI/CMakeLists.txt
+++ b/mlir/test/CAPI/CMakeLists.txt
@@ -8,6 +8,8 @@ function(_add_capi_test_executable name)
     )
   add_llvm_executable(${name}
     PARTIAL_SOURCES_INTENDED
+    # No C++ files, prevent CMake error.
+    DISABLE_PCH_REUSE
     ${ARG_UNPARSED_ARGUMENTS})
   set_target_properties(${name} PROPERTIES FOLDER "MLIR/Tests")
   set_target_properties(${name} PROPERTIES EXCLUDE_FROM_ALL ON)
diff --git a/polly/lib/CMakeLists.txt b/polly/lib/CMakeLists.txt
index 41c3b97764ac7..6f6e4d5782dfb 100644
--- a/polly/lib/CMakeLists.txt
+++ b/polly/lib/CMakeLists.txt
@@ -91,6 +91,10 @@ add_llvm_pass_plugin(Polly
   Transform/MatmulOptimizer.cpp
   ${POLLY_HEADER_FILES}
 
+  # Polly unconditionally uses -fno-rtti -fno-exceptions. This can be
+  # incompatible with PCH if LLVM is built with RTTI or exceptions.
+  DISABLE_PCH_REUSE
+
   LINK_COMPONENTS
   ${POLLY_COMPONENTS}
   )