[clang][cmake] Fixes for PGO builds when invoking ninja twice

clang/CMakeLists.txt

@@ -849,23 +849,17 @@ if (CLANG_ENABLE_BOOTSTRAP)
     set(CLANG_BOOTSTRAP_TARGETS check-llvm check-clang check-all)
   endif()
   foreach(target ${CLANG_BOOTSTRAP_TARGETS})
-    # Install targets have side effects, so we always want to execute them.
-    # "install" is reserved by CMake and can't be used as a step name for
-    # ExternalProject_Add_Step, so we can match against "^install-" instead of
-    # "^install" to get a tighter match. CMake's installation scripts already
-    # skip up-to-date files, so there's no behavior change if you install to the
-    # same destination multiple times.
-    if(target MATCHES "^install-")
-      set(step_always ON)
-    else()
-      set(step_always OFF)
-    endif()
 
     ExternalProject_Add_Step(${NEXT_CLANG_STAGE} ${target}
       COMMAND ${CMAKE_COMMAND} --build <BINARY_DIR> --target ${target}
       COMMENT "Performing ${target} for '${NEXT_CLANG_STAGE}'"
       DEPENDEES configure
-      ALWAYS ${step_always}
+      # We need to set ALWAYS to ON here, otherwise these targets won't be
+      # built on a second invocation of ninja.  The targets have their own
+      # logic to determine if they should build or not so setting ALWAYS ON
+      # here does not mean the targets will always rebuild it just means that
+      # they will check their dependenices and see if they need to be built.
+      ALWAYS ON
       EXCLUDE_FROM_MAIN ON
       USES_TERMINAL 1
     )

clang/cmake/caches/Release.cmake

@@ -30,7 +30,7 @@ endfunction()
 #
 # cmake -D LLVM_RELEASE_ENABLE_PGO=ON -C Release.cmake
 set(LLVM_RELEASE_ENABLE_LTO THIN CACHE STRING "")
-set(LLVM_RELEASE_ENABLE_PGO OFF CACHE BOOL "")
+set(LLVM_RELEASE_ENABLE_PGO ON CACHE BOOL "")
 set(LLVM_RELEASE_ENABLE_RUNTIMES "compiler-rt;libcxx;libcxxabi;libunwind" CACHE STRING "")
 set(LLVM_RELEASE_ENABLE_PROJECTS "clang;lld;lldb;clang-tools-extra;bolt;polly;mlir;flang" CACHE STRING "")
 # Note we don't need to add install here, since it is one of the pre-defined

clang/utils/perf-training/CMakeLists.txt

@@ -15,7 +15,7 @@ if(LLVM_BUILD_INSTRUMENTED)
   add_lit_testsuite(generate-profraw "Generating clang PGO data"
     ${CMAKE_CURRENT_BINARY_DIR}/pgo-data/
     EXCLUDE_FROM_CHECK_ALL
-    DEPENDS clang clear-profraw ${CLANG_PGO_TRAINING_DEPS}
+    DEPENDS clear-profraw
     )
 
   add_custom_target(clear-profraw
@@ -29,10 +29,21 @@ if(LLVM_BUILD_INSTRUMENTED)
   if(NOT LLVM_PROFDATA)
     message(STATUS "To enable merging PGO data LLVM_PROFDATA has to point to llvm-profdata")
   else()
-    add_custom_target(generate-profdata
+    add_custom_command(
+      OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/clang.profdata
+      # generate-profraw is a custom_target which are always considered stale.
+      # If we add it here to 'DEPENDS', then it will always execute and running
+      # ninja install && ninja check-all will result in the profile data being
+      # generated twice, and cause the ninja check-all build to fail with errors like:
+      # `ld.lld: error: Function Import: link error: linking module flags 'ProfileSummary': IDs have conflicting values in`
+      # Therefor we call the generate-profraw target manually as part of this custom
+      # command, which will only run if clang or ${CLANG_PGO_TRAINING_DEPS} are updated.
+      COMMAND ${CMAKE_COMMAND} --build ${CMAKE_BINARY_DIR} --target generate-profraw
       COMMAND "${Python3_EXECUTABLE}" ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py merge ${LLVM_PROFDATA} ${CMAKE_CURRENT_BINARY_DIR}/clang.profdata ${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_BINARY_DIR}/profiles/
       COMMENT "Merging profdata"
-      DEPENDS generate-profraw)
+      DEPENDS clang ${CLANG_PGO_TRAINING_DEPS}
+    )
+    add_custom_target(generate-profdata DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/clang.profdata)
     if (CLANG_PGO_TRAINING_DATA_SOURCE_DIR)
       llvm_ExternalProject_Add(generate-profraw-external ${CLANG_PGO_TRAINING_DATA_SOURCE_DIR}
               USE_TOOLCHAIN EXLUDE_FROM_ALL NO_INSTALL DEPENDS generate-profraw)