[PATCH] D132975: [clang][BOLT] Add clangbolt target (WIP)

[Amir Ayupov via Phabricator via cfe-commits]

Amir created this revision.
Amir added a reviewer: bolt.
Herald added subscribers: treapster, wenlei, mgorny.
Herald added a project: All.
Amir requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

This patch adds `CLANG_BOLT_INSTRUMENT` option that applies BOLT instrumentation
to Clang, performs a bootstrap build with the resulting Clang, merges resulting
fdata files into a single profile file, and uses it to perform BOLT optimization
on the original Clang binary.

The intended use of the functionality is through BOLT CMake cache file, similar
to PGO 2-stage build:

  cmake <llvm-project>/llvm -C <llvm-project>/clang/cmake/caches/BOLT.cmake
  ninja clang-bolt


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D132975

Files:
  clang/CMakeLists.txt
  clang/cmake/caches/BOLT.cmake


Index: clang/cmake/caches/BOLT.cmake
===================================================================
--- /dev/null
+++ clang/cmake/caches/BOLT.cmake
@@ -0,0 +1,12 @@
+set(CMAKE_BUILD_TYPE Release CACHE STRING "")
+set(CLANG_BOLT_INSTRUMENT ON CACHE BOOL "")
+set(CMAKE_EXE_LINKER_FLAGS "-Wl,--emit-relocs,-znow" CACHE STRING "")
+
+set(LLVM_ENABLE_PROJECTS "bolt;clang;lld" CACHE STRING "")
+set(LLVM_TARGETS_TO_BUILD Native CACHE STRING "")
+
+# Disable function splitting enabled by default in GCC8+
+if("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fno-reorder-blocks-and-partition")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-reorder-blocks-and-partition")
+endif()
Index: clang/CMakeLists.txt
===================================================================
--- clang/CMakeLists.txt
+++ clang/CMakeLists.txt
@@ -878,6 +878,57 @@
   endforeach()
 endif()
 
+if (CLANG_BOLT_INSTRUMENT)
+  find_program(LLVM_BOLT llvm-bolt)
+  find_program(MERGE_FDATA merge-fdata)
+
+  # Instrument clang with BOLT
+  add_custom_target(clang-instrumented
+    DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/bin/clang.bolt.inst
+  )
+  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/bin/clang.bolt.inst
+    DEPENDS clang
+    COMMAND ${LLVM_BOLT} ${CMAKE_BINARY_DIR}/bin/clang -o
+      ${CMAKE_CURRENT_BINARY_DIR}/bin/clang.bolt.inst
+      -instrument --instrumentation-file-append-pid
+      --instrumentation-file=${CMAKE_CURRENT_BINARY_DIR}/bin/prof.fdata
+    COMMENT "Instrumenting clang binary with BOLT"
+    )
+  # Make a symlink from clang.bolt.inst to clang++.bolt.inst
+  add_clang_symlink(${CMAKE_CURRENT_BINARY_DIR}/bin/clang++.bolt.inst
+                    ${CMAKE_CURRENT_BINARY_DIR}/bin/clang.bolt.inst)
+
+  # Configure and build Clang with instrumented Clang to collect the profile
+  include(ExternalProject)
+  ExternalProject_Add(bolt-instrumentation-profile
+    DEPENDS clang
+    PREFIX bolt-instrumentation-profile
+    SOURCE_DIR ${CMAKE_SOURCE_DIR}
+    CMAKE_ARGS
+                # We shouldn't need to set this here, but INSTALL_DIR doesn't
+                # seem to work, so instead I'm passing this through
+                -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
+                -DCMAKE_CXX_COMPILER=${CMAKE_CURRENT_BINARY_DIR}/bin/clang++.bolt.inst
+                -DCMAKE_C_COMPILER=${CMAKE_CURRENT_BINARY_DIR}/bin/clang.bolt.inst
+    STEP_TARGETS configure build install
+  )
+  # Merge profiles into one using merge-fdata
+  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/bin/prof.fdata
+    COMMAND ${MERGE_FDATA} ${CMAKE_CURRENT_BINARY_DIR}/bin/prof.fdata.*
+      -o ${CMAKE_CURRENT_BINARY_DIR}/bin/prof.fdata
+  )
+  # Optimize original (pre-bolt) Clang using the collected profile
+  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/bin/clang.bolt
+    DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/bin/prof.fdata clang
+    COMMAND ${CMAKE_BINARY_DIR}/bin/llvm-bolt ${CMAKE_BINARY_DIR}/bin/clang
+    -o ${CMAKE_BINARY_DIR}/bin/clang.bolt -fdata
+    ${CMAKE_CURRENT_BINARY_DIR}/bin/prof.fdata
+  )
+  add_custom_target(clang-bolt
+    DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/bin/clang.bolt
+    )
+endif()
+
 if (LLVM_ADD_NATIVE_VISUALIZERS_TO_SOLUTION)
   add_subdirectory(utils/ClangVisualizers)
 endif()


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