Index: llvm/CMakeLists.txt
===================================================================
--- llvm/CMakeLists.txt
+++ llvm/CMakeLists.txt
@@ -931,6 +931,8 @@
 include(AddLLVM)
 include(TableGen)
 
+include(LLVMDistributionSupport)
+
 if( MINGW AND NOT "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" )
   # People report that -O3 is unreliable on MinGW. The traditional
   # build also uses -O2 for that reason:
@@ -1119,7 +1121,6 @@
 
 # This must be at the end of the LLVM root CMakeLists file because it must run
 # after all targets are created.
-include(LLVMDistributionSupport)
 llvm_distribution_add_targets()
 process_llvm_pass_plugins(GEN_CONFIG)
 
Index: llvm/cmake/modules/AddLLVM.cmake
===================================================================
--- llvm/cmake/modules/AddLLVM.cmake
+++ llvm/cmake/modules/AddLLVM.cmake
@@ -218,13 +218,30 @@
 endif()
 
 function(add_link_opts target_name)
+  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.
+    if (LLVM_ENABLE_LTO)
+      # We may consider avoiding LTO altogether by using -fembed-bitcode
+      # and teaching the linker to select machine code from .o files, see
+      # https://lists.llvm.org/pipermail/llvm-dev/2021-April/149843.html
+      if((UNIX OR MINGW) AND LLVM_USE_LINKER STREQUAL "lld")
+        set_property(TARGET ${target_name} APPEND_STRING PROPERTY
+                      LINK_FLAGS " -Wl,--lto-O0")
+      elseif(LINKER_IS_LLD_LINK)
+        set_property(TARGET ${target_name} APPEND_STRING PROPERTY
+                      LINK_FLAGS " /opt:lldlto=0")
+      endif()
+    endif()
+  endif()
+
   # Don't use linker optimizations in debug builds since it slows down the
   # linker in a context where the optimizations are not important.
   if (NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
 
     # Pass -O3 to the linker. This enabled different optimizations on different
     # linkers.
-    if(NOT (CMAKE_SYSTEM_NAME MATCHES "Darwin|SunOS|AIX|OS390" OR WIN32))
+    if(NOT (CMAKE_SYSTEM_NAME MATCHES "Darwin|SunOS|AIX|OS390" OR WIN32) AND in_distribution)
       set_property(TARGET ${target_name} APPEND_STRING PROPERTY
                    LINK_FLAGS " -Wl,-O3")
     endif()
Index: llvm/cmake/modules/LLVMDistributionSupport.cmake
===================================================================
--- llvm/cmake/modules/LLVMDistributionSupport.cmake
+++ llvm/cmake/modules/LLVMDistributionSupport.cmake
@@ -56,6 +56,49 @@
 # only defines other functions (i.e. it doesn't execute any more code directly).
 llvm_distribution_build_target_map()
 
+# Look up the distribution a particular target belongs to. By convention, the
+# project calling this should set the ${PROJECT}${distribution}_HAS_EXPORTS
+# global property to true if the target is in ${distribution} (${PROJECT} is the
+# project name in uppercase).
+# - target: The target to look up.
+# - in_distribution_var: The variable with this name is set in the caller's
+#   scope to indicate if the target is in any distribution. If no distributions
+#   have been configured, this will always be set to true.
+# - distribution_var: The variable with this name is set in the caller's scope
+#   to indicate the distribution name for the target. If the target belongs to
+#   the default (unnamed) distribution, or if no distributions have been
+#   configured, it's set to the empty string.
+# - UMBRELLA: The (optional) umbrella target that the target is a part of. For
+#   example, all LLVM libraries have the umbrella target llvm-libraries.
+function(get_llvm_distribution target in_distribution_var distribution_var)
+  if(NOT LLVM_DISTRIBUTION_COMPONENTS AND NOT LLVM_DISTRIBUTIONS)
+    set(${in_distribution_var} YES PARENT_SCOPE)
+    set(${distribution_var} "" PARENT_SCOPE)
+    return()
+  endif()
+
+  cmake_parse_arguments(ARG "" UMBRELLA "" ${ARGN})
+  get_property(distribution GLOBAL PROPERTY LLVM_DISTRIBUTION_FOR_${target})
+  if(ARG_UMBRELLA)
+    get_property(umbrella_distribution GLOBAL PROPERTY LLVM_DISTRIBUTION_FOR_${ARG_UMBRELLA})
+    if(distribution AND umbrella_distribution AND NOT distribution STREQUAL umbrella_distribution)
+      message(SEND_ERROR "Target ${target} has different distribution ${distribution} from its"
+                         " umbrella target ${ARG_UMBRELLA} distribution ${umbrella_distribution}")
+    elseif(NOT distribution)
+      set(distribution ${umbrella_distribution})
+    endif()
+  endif()
+  if(distribution)
+    set(${in_distribution_var} YES PARENT_SCOPE)
+    if(distribution STREQUAL "<DEFAULT>")
+      set(distribution "")
+    endif()
+    set(${distribution_var} "${distribution}" PARENT_SCOPE)
+  else()
+    set(${in_distribution_var} NO PARENT_SCOPE)
+  endif()
+endfunction()
+
 # Get the EXPORT argument to use for an install command for a target in a
 # project. As explained at the top of the file, the project export set for a
 # distribution is named ${project}{distribution}Targets (except for LLVM where
@@ -79,29 +122,11 @@
     set(suffix "Targets")
   endif()
 
-  if(NOT LLVM_DISTRIBUTION_COMPONENTS AND NOT LLVM_DISTRIBUTIONS)
-    set(${export_arg_var} EXPORT ${project}${suffix} PARENT_SCOPE)
-    set_property(GLOBAL PROPERTY ${project_upper}_HAS_EXPORTS True)
-    return()
-  endif()
+  get_llvm_distribution(${target} in_distribution distribution ${ARGN})
 
-  cmake_parse_arguments(ARG "" UMBRELLA "" ${ARGN})
-  get_property(distribution GLOBAL PROPERTY LLVM_DISTRIBUTION_FOR_${target})
-  if(ARG_UMBRELLA)
-    get_property(umbrella_distribution GLOBAL PROPERTY LLVM_DISTRIBUTION_FOR_${ARG_UMBRELLA})
-    if(distribution AND umbrella_distribution AND NOT distribution STREQUAL umbrella_distribution)
-      message(SEND_ERROR "Target ${target} has different distribution ${distribution} from its"
-                         " umbrella target ${ARG_UMBRELLA} distribution ${umbrella_distribution}")
-    elseif(NOT distribution)
-      set(distribution ${umbrella_distribution})
-    endif()
-  endif()
-  if(distribution)
-    if(distribution STREQUAL "<DEFAULT>")
-      set(${export_arg_var} EXPORT ${project}${suffix} PARENT_SCOPE)
-      set_property(GLOBAL PROPERTY ${project_upper}_HAS_EXPORTS True)
-    else()
-      set(${export_arg_var} EXPORT ${project}${distribution}${suffix} PARENT_SCOPE)
+  if(in_distribution)
+    set(${export_arg_var} EXPORT ${project}${distribution}${suffix} PARENT_SCOPE)
+    if(distribution)
       string(TOUPPER "${distribution}" distribution_upper)
       set_property(GLOBAL PROPERTY ${project_upper}_${distribution_upper}_HAS_EXPORTS True)
     endif()