[clang][cmake] Apply bolt optimizations as part of the clang target (llvm#119896)

tstellar · aaupov · petrhosek · web-flow · commit 1a53d4baeb02 · 2025-01-25T03:59:45.000-08:00
This change removes the need to call the clang-bolt target in order to
apply bolt optimizations to clang. Now running `ninja clang` will build
a clang with bolt optimizations, and `ninja check-clang` and `ninja
install-clang` will test and install bolt optimized clang too.

The clang-bolt target has been kept for compatibilty reasons, but it is
now just an alias to the clang target.

Also, this new design for applying the bolt optimizations to clang will
be easier to generalize and use to optimize other binaries/libraries in
the project.

---------

Co-authored-by: Amir Ayupov &lt;fads93@gmail.com&gt;
Co-authored-by: Petr Hosek &lt;phosek@google.com&gt;
diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
@@ -872,58 +872,6 @@ if (CLANG_ENABLE_BOOTSTRAP)
   endforeach()
 endif()
 
-set(CLANG_BOLT OFF CACHE STRING "Apply BOLT optimization to Clang. \
-  May be specified as Instrument or Perf or LBR to use a particular profiling \
-  mechanism.")
-string(TOUPPER "${CLANG_BOLT}" CLANG_BOLT)
-
-if (CLANG_BOLT AND NOT LLVM_BUILD_INSTRUMENTED)
-  set(CLANG_PATH ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang)
-  set(CLANG_INSTRUMENTED ${LLVM_RUNTIME_OUTPUT_INTDIR}/${CLANG_BOLT_INSTRUMENTED})
-  set(BOLT_FDATA ${CMAKE_CURRENT_BINARY_DIR}/utils/perf-training/prof.fdata)
-
-  # Pass extra flag in no-LBR mode
-  if (CLANG_BOLT STREQUAL "PERF")
-    set(BOLT_NO_LBR "-nl")
-  endif()
-
-  if (CLANG_BOLT STREQUAL "INSTRUMENT")
-    # Instrument clang with BOLT
-    add_custom_target(clang-instrumented
-      DEPENDS ${CLANG_INSTRUMENTED}
-    )
-    add_custom_command(OUTPUT ${CLANG_INSTRUMENTED}
-      DEPENDS clang llvm-bolt
-      COMMAND llvm-bolt ${CLANG_PATH} -o ${CLANG_INSTRUMENTED}
-        -instrument --instrumentation-file-append-pid
-        --instrumentation-file=${BOLT_FDATA}
-      COMMENT "Instrumenting clang binary with BOLT"
-      USES_TERMINAL
-      VERBATIM
-    )
-    add_custom_target(clang-bolt-training-deps DEPENDS clang-instrumented)
-  else() # perf or LBR
-    add_custom_target(clang-bolt-training-deps DEPENDS clang)
-  endif()
-
-  # Optimize original (pre-bolt) Clang using the collected profile
-  add_custom_target(clang-bolt
-    DEPENDS clang-bolt-profile
-    COMMAND ${CMAKE_COMMAND} -E rename $<TARGET_FILE:clang> ${CLANG_PATH}-prebolt
-    COMMAND ${CMAKE_COMMAND} -E create_symlink ${CLANG_PATH}-prebolt ${CLANG_PATH}++-prebolt
-    COMMAND llvm-bolt ${CLANG_PATH}-prebolt
-      -o $<TARGET_FILE:clang>
-      -data ${BOLT_FDATA}
-      -reorder-blocks=ext-tsp -reorder-functions=cdsort -split-functions
-      -split-all-cold -split-eh -dyno-stats -use-gnu-stack
-      -update-debug-sections
-      ${BOLT_NO_LBR}
-    COMMENT "Optimizing Clang with BOLT"
-    USES_TERMINAL
-    VERBATIM
-  )
-endif()
-
 if (LLVM_ADD_NATIVE_VISUALIZERS_TO_SOLUTION)
   add_subdirectory(utils/ClangVisualizers)
 endif()
diff --git a/clang/tools/driver/CMakeLists.txt b/clang/tools/driver/CMakeLists.txt
@@ -23,6 +23,18 @@ if(CLANG_PLUGIN_SUPPORT)
   set(support_plugins SUPPORT_PLUGINS)
 endif()
 
+set(CLANG_BOLT OFF CACHE STRING "Apply BOLT optimization to Clang. \
+  May be specified as Instrument or Perf or LBR to use a particular profiling \
+  mechanism.")
+string(TOUPPER "${CLANG_BOLT}" CLANG_BOLT)
+
+if (CLANG_BOLT AND NOT LLVM_BUILD_INSTRUMENTED)
+  set(CLANG_BOLT_DEPS clear-bolt-fdata llvm-bolt llvm-readobj)
+  if (NOT CLANG_BOLT STREQUAL "INSTRUMENT")
+    list(APPEND CLANG_BOLT_DEPS clear-perf-data)
+  endif()
+endif()
+
 add_clang_tool(clang
   driver.cpp
   cc1_main.cpp
@@ -35,6 +47,7 @@ add_clang_tool(clang
   ARMTargetParserTableGen
   AArch64TargetParserTableGen
   ${support_plugins}
+  ${CLANG_BOLT_DEPS}
   GENERATE_DRIVER
   )
 
@@ -134,3 +147,42 @@ if(CLANG_ORDER_FILE AND
     set_target_properties(clang PROPERTIES LINK_DEPENDS ${CLANG_ORDER_FILE})
   endif()
 endif()
+
+if (CLANG_BOLT AND NOT LLVM_BUILD_INSTRUMENTED)
+  # Add a clang-bolt target for backwards compatibility.
+  add_custom_target(clang-bolt DEPENDS clang)
+
+  set(CLANG_BOLT_INSTRUMENTED "clang-bolt.inst" CACHE STRING
+    "Name of BOLT-instrumented Clang binary")
+  set(CLANG_INSTRUMENTED ${LLVM_RUNTIME_OUTPUT_INTDIR}/${CLANG_BOLT_INSTRUMENTED})
+  set(PERF_TRAINING_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR}/../../utils/perf-training)
+  set(BOLT_FDATA ${PERF_TRAINING_BINARY_DIR}/prof.fdata)
+  get_llvm_lit_path(
+    lit_base_dir
+    lit_file_name
+    ALLOW_EXTERNAL
+  )
+  set(LIT_COMMAND "${lit_base_dir}/${lit_file_name}")
+
+  # This POST_BUILD command is executed unconditionally even if the clang target
+  # is already built.  We need to wrap the whole bolt optimization process in
+  # a single python wrapper, so that we can first check if the binary has
+  # already been optimized and then exit early with a 0 status if it has.
+  add_custom_command(
+    TARGET clang POST_BUILD
+    COMMAND  "${Python3_EXECUTABLE}" ${CMAKE_CURRENT_SOURCE_DIR}/../../utils/perf-training/perf-helper.py
+             bolt-optimize
+	     --method ${CLANG_BOLT}
+	     --input $<TARGET_FILE:clang>
+	     --instrumented-output ${CLANG_INSTRUMENTED}
+	     --fdata ${BOLT_FDATA}
+	     --perf-training-binary-dir ${PERF_TRAINING_BINARY_DIR}
+	     --readelf $<TARGET_FILE:llvm-readobj>
+	     --bolt $<TARGET_FILE:llvm-bolt>
+	     --lit "${LIT_COMMAND}"
+	     --merge-fdata $<TARGET_FILE:merge-fdata>
+    COMMENT "Optimizing Clang with BOLT"
+    USES_TERMINAL
+    VERBATIM
+  )
+endif()
diff --git a/clang/utils/perf-training/CMakeLists.txt b/clang/utils/perf-training/CMakeLists.txt
@@ -83,8 +83,6 @@ if(APPLE AND DTRACE AND NOT LLVM_TOOL_LLVM_DRIVER_BUILD)
 endif()
 
 if(CLANG_BOLT AND NOT LLVM_BUILD_INSTRUMENTED)
-  set(CLANG_BOLT_INSTRUMENTED "clang-bolt.inst" CACHE STRING
-    "Name of BOLT-instrumented Clang binary")
   configure_lit_site_cfg(
     ${CMAKE_CURRENT_SOURCE_DIR}/bolt.lit.site.cfg.in
     ${CMAKE_CURRENT_BINARY_DIR}/bolt-fdata/lit.site.cfg
@@ -93,7 +91,7 @@ if(CLANG_BOLT AND NOT LLVM_BUILD_INSTRUMENTED)
   add_lit_testsuite(generate-bolt-fdata "Generating BOLT profile for Clang"
     ${CMAKE_CURRENT_BINARY_DIR}/bolt-fdata/
     EXCLUDE_FROM_CHECK_ALL
-    DEPENDS clang-bolt-training-deps clear-bolt-fdata clear-perf-data
+    DEPENDS clear-bolt-fdata clear-perf-data
     )
 
   add_custom_target(clear-bolt-fdata
@@ -104,26 +102,4 @@ if(CLANG_BOLT AND NOT LLVM_BUILD_INSTRUMENTED)
     COMMAND "${Python3_EXECUTABLE}" ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py clean ${CMAKE_CURRENT_BINARY_DIR} perf.data
     COMMENT "Clearing old perf data")
 
-  string(TOUPPER "${CLANG_BOLT}" CLANG_BOLT)
-  if (CLANG_BOLT STREQUAL "LBR")
-    set(BOLT_LBR "--lbr")
-  endif()
-
-  add_custom_target(merge-fdata-deps)
-  if (CLANG_BOLT STREQUAL "INSTRUMENT")
-    add_dependencies(merge-fdata-deps generate-bolt-fdata)
-  else()
-    # Convert perf profiles into fdata
-    add_custom_target(convert-perf-fdata
-      COMMAND "${Python3_EXECUTABLE}" ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py perf2bolt $<TARGET_FILE:llvm-bolt> ${CMAKE_CURRENT_BINARY_DIR} $<TARGET_FILE:clang> ${BOLT_LBR}
-      COMMENT "Converting perf files to BOLT fdata"
-      DEPENDS llvm-bolt generate-bolt-fdata)
-    add_dependencies(merge-fdata-deps convert-perf-fdata)
-  endif()
-
-  # Merge profiles into one using merge-fdata
-  add_custom_target(clang-bolt-profile
-    COMMAND "${Python3_EXECUTABLE}" ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py merge-fdata $<TARGET_FILE:merge-fdata> ${CMAKE_CURRENT_BINARY_DIR}/prof.fdata ${CMAKE_CURRENT_BINARY_DIR}
-    COMMENT "Merging BOLT fdata"
-    DEPENDS merge-fdata merge-fdata-deps)
 endif()
diff --git a/clang/utils/perf-training/perf-helper.py b/clang/utils/perf-training/perf-helper.py
@@ -16,6 +16,8 @@
 import bisect
 import shlex
 import tempfile
+import re
+import shutil
 
 test_env = {"PATH": os.environ["PATH"]}
 
@@ -558,7 +560,103 @@ def genOrderFile(args):
     return 0
 
 
+def bolt_optimize(args):
+    parser = argparse.ArgumentParser("%prog  [options] ")
+    parser.add_argument("--method", choices=["INSTRUMENT", "PERF", "LBR"])
+    parser.add_argument("--input")
+    parser.add_argument("--instrumented-output")
+    parser.add_argument("--fdata")
+    parser.add_argument("--perf-training-binary-dir")
+    parser.add_argument("--readelf")
+    parser.add_argument("--bolt")
+    parser.add_argument("--lit")
+    parser.add_argument("--merge-fdata")
+
+    opts = parser.parse_args(args)
+
+    output = subprocess.check_output(
+        [opts.readelf, "-WS", opts.input], universal_newlines=True
+    )
+
+    # This binary has already been bolt-optimized, so skip further processing.
+    if re.search("\\.bolt\\.org\\.text", output, re.MULTILINE):
+        return 0
+
+    if opts.method == "INSTRUMENT":
+        process = subprocess.run(
+            [
+                opts.bolt,
+                opts.input,
+                "-o",
+                opts.instrumented_output,
+                "-instrument",
+                "--instrumentation-file-append-pid",
+                f"--instrumentation-file={opts.fdata}",
+            ],
+            stdout=subprocess.PIPE,
+            stderr=subprocess.STDOUT,
+            text=True,
+        )
+
+        print(process.args)
+        for line in process.stdout:
+            sys.stdout.write(line)
+        process.check_returncode()
+
+    process = subprocess.run(
+        [
+            sys.executable,
+            opts.lit,
+            os.path.join(opts.perf_training_binary_dir, "bolt-fdata"),
+        ],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+        text=True,
+    )
+
+    print(process.args)
+    for line in process.stdout:
+        sys.stdout.write(line)
+    process.check_returncode()
+
+    if opts.method in ["PERF", "LBR"]:
+        perf2bolt([opts.bolt, opts.perf_training_binary_dir, opts.input])
+
+    merge_fdata([opts.merge_fdata, opts.fdata, opts.perf_training_binary_dir])
+
+    shutil.copy(opts.input, f"{opts.input}-prebolt")
+
+    process = subprocess.run(
+        [
+            opts.bolt,
+            f"{opts.input}-prebolt",
+            "-o",
+            opts.input,
+            "-data",
+            opts.fdata,
+            "-reorder-blocks=ext-tsp",
+            "-reorder-functions=cdsort",
+            "-split-functions",
+            "-split-all-cold",
+            "-split-eh",
+            "-dyno-stats",
+            "-use-gnu-stack",
+            "-update-debug-sections",
+            "-nl" if opts.method == "PERF" else "",
+        ],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT,
+        text=True,
+    )
+
+    print(process.args)
+    for line in process.stdout:
+        sys.stdout.write(line)
+    process.check_returncode()
+
+
 commands = {
+    "bolt-optimize": bolt_optimize,
     "clean": clean,
     "merge": merge,
     "dtrace": dtrace,
