gh-90536: Add support for the BOLT post-link binary optimizer (gh-95908)

* Add support for the BOLT post-link binary optimizer

Using [bolt](https://github.com/llvm/llvm-project/tree/main/bolt)
provides a fairly large speedup without any code or functionality
changes. It provides roughly a 1% speedup on pyperformance, and a
4% improvement on the Pyston web macrobenchmarks.

It is gated behind an `--enable-bolt` configure arg because not all
toolchains and environments are supported. It has been tested on a
Linux x86_64 toolchain, using llvm-bolt built from the LLVM 14.0.6
sources (their binary distribution of this version did not include bolt).

Compared to [a previous attempt](https://github.com/faster-cpython/ideas/issues/224),
this commit uses bolt's preferred "instrumentation" approach, as well as adds some non-PIE
flags which enable much better optimizations from bolt.

The effects of this change are a bit more dependent on CPU microarchitecture
than other changes, since it optimizes i-cache behavior which seems
to be a bit more variable between architectures. The 1%/4% numbers
were collected on an Intel Skylake CPU, and on an AMD Zen 3 CPU I
got a slightly larger speedup (2%/4%), and on a c6i.xlarge EC2 instance
I got a slightly lower speedup (1%/3%).

The low speedup on pyperformance is not entirely unexpected, because
BOLT improves i-cache behavior, and the benchmarks in the pyperformance
suite are small and tend to fit in i-cache.

This change uses the existing pgo profiling task (`python -m test --pgo`),
though I was able to measure about a 1% macrobenchmark improvement by
using the macrobenchmarks as the training task. I personally think that
both the PGO and BOLT tasks should be updated to use macrobenchmarks,
but for the sake of splitting up the work this PR uses the existing pgo task.

* Simplify the build flags

* Add a NEWS entry

* Update Makefile.pre.in

Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

* Update configure.ac

Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

* Add myself to ACKS

* Add docs

* Other review comments

* fix tab/space issue

* Make it more clear that --enable-bolt is experimental

* Add link to bolt's github page

Co-authored-by: Dong-hee Na <donghee.na92@gmail.com>

Doc/using/configure.rst

@@ -191,7 +191,8 @@ Performance options
 -------------------
 
 Configuring Python using ``--enable-optimizations --with-lto`` (PGO + LTO) is
-recommended for best performance.
+recommended for best performance. The experimental ``--enable-bolt`` flag can
+also be used to improve performance.
 
 .. cmdoption:: --enable-optimizations
 
@@ -231,6 +232,24 @@ recommended for best performance.
    .. versionadded:: 3.11
       To use ThinLTO feature, use ``--with-lto=thin`` on Clang.
 
+.. cmdoption:: --enable-bolt
+
+   Enable usage of the `BOLT post-link binary optimizer
+   <https://github.com/llvm/llvm-project/tree/main/bolt>` (disabled by
+   default).
+
+   BOLT is part of the LLVM project but is not always included in their binary
+   distributions. This flag requires that ``llvm-bolt`` and ``merge-fdata``
+   are available.
+
+   BOLT is still a fairly new project so this flag should be considered
+   experimental for now. Because this tool operates on machine code its success
+   is dependent on a combination of the build environment + the other
+   optimization configure args + the CPU architecture, and not all combinations
+   are supported.
+
+   .. versionadded:: 3.12
+
 .. cmdoption:: --with-computed-gotos
 
    Enable computed gotos in evaluation loop (enabled by default on supported

Doc/whatsnew/3.12.rst

@@ -133,6 +133,10 @@ Optimizations
   It reduces object size by 8 or 16 bytes on 64bit platform. (:pep:`623`)
   (Contributed by Inada Naoki in :gh:`92536`.)
 
+* Added experimental support for using the BOLT binary optimizer in the build
+  process, which improves performance by 1-5%.
+  (Contributed by Kevin Modzelewski in :gh:`90536`.)
+
 
 CPython bytecode changes
 ========================

Makefile.pre.in

@@ -640,6 +640,16 @@ profile-opt: profile-run-stamp
 	-rm -f profile-clean-stamp
 	$(MAKE) @DEF_MAKE_RULE@ CFLAGS_NODIST="$(CFLAGS_NODIST) $(PGO_PROF_USE_FLAG)" LDFLAGS_NODIST="$(LDFLAGS_NODIST)"
 
+bolt-opt: @PREBOLT_RULE@
+	rm -f *.fdata
+	@LLVM_BOLT@ ./$(BUILDPYTHON) -instrument -instrumentation-file-append-pid -instrumentation-file=$(abspath $(BUILDPYTHON).bolt) -o $(BUILDPYTHON).bolt_inst
+	./$(BUILDPYTHON).bolt_inst $(PROFILE_TASK) || true
+	@MERGE_FDATA@ $(BUILDPYTHON).*.fdata > $(BUILDPYTHON).fdata
+	@LLVM_BOLT@ ./$(BUILDPYTHON) -o $(BUILDPYTHON).bolt -data=$(BUILDPYTHON).fdata -update-debug-sections -reorder-blocks=ext-tsp -reorder-functions=hfsort+ -split-functions=3 -icf=1 -inline-all -split-eh -reorder-functions-use-hot-size -peepholes=all -jump-tables=aggressive -inline-ap -indirect-call-promotion=all -dyno-stats -use-gnu-stack -frame-opt=hot
+	rm -f *.fdata
+	rm -f $(BUILDPYTHON).bolt_inst
+	mv $(BUILDPYTHON).bolt $(BUILDPYTHON)
+
 # Compile and run with gcov
 .PHONY=coverage coverage-lcov coverage-report
 coverage:

Misc/ACKS

@@ -1212,6 +1212,7 @@ Gideon Mitchell
 Tim Mitchell
 Zubin Mithra
 Florian Mladitsch
+Kevin Modzelewski
 Doug Moen
 Jakub Molinski
 Juliette Monsel

Misc/NEWS.d/next/Build/2022-08-12-13-06-03.gh-issue-90536.qMpF6p.rst

@@ -0,0 +1,2 @@
+Use the BOLT post-link optimizer to improve performance, particularly on
+medium-to-large applications.

configure

@@ -887,6 +887,9 @@ LLVM_PROF_FILE
 LLVM_PROF_MERGER
 PGO_PROF_USE_FLAG
 PGO_PROF_GEN_FLAG
+MERGE_FDATA
+LLVM_BOLT
+PREBOLT_RULE
 LLVM_AR_FOUND
 LLVM_AR
 PROFILE_TASK
@@ -1049,6 +1052,7 @@ enable_pystats
 with_assertions
 enable_optimizations
 with_lto
+enable_bolt
 with_address_sanitizer
 with_memory_sanitizer
 with_undefined_behavior_sanitizer
@@ -1774,6 +1778,8 @@ Optional Features:
   --enable-pystats        enable internal statistics gathering (default is no)
   --enable-optimizations  enable expensive, stable optimizations (PGO, etc.)
                           (default is no)
+  --enable-bolt           enable usage of the llvm-bolt post-link optimizer
+                          (default is no)
   --enable-loadable-sqlite-extensions
                           support loadable extensions in the sqlite3 module,
                           see Doc/library/sqlite3.rst (default is no)
@@ -7878,6 +7884,261 @@ $as_echo "$as_me: llvm-ar found via xcrun: ${LLVM_AR}" >&6;}
   LDFLAGS_NODIST="$LDFLAGS_NODIST $LTOFLAGS"
 fi
 
+# Enable bolt flags
+Py_BOLT='false'
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for --enable-bolt" >&5
+$as_echo_n "checking for --enable-bolt... " >&6; }
+# Check whether --enable-bolt was given.
+if test "${enable_bolt+set}" = set; then :
+  enableval=$enable_bolt;
+if test "$enableval" != no
+then
+  Py_BOLT='true'
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+$as_echo "yes" >&6; };
+else
+  Py_BOLT='false'
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; };
+fi
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+
+if test "$Py_BOLT" = 'true' ; then
+  PREBOLT_RULE="${DEF_MAKE_ALL_RULE}"
+  DEF_MAKE_ALL_RULE="bolt-opt"
+  DEF_MAKE_RULE="build_all"
+
+  # These flags are required for bolt to work:
+  CFLAGS_NODIST="$CFLAGS_NODIST -fno-reorder-blocks-and-partition"
+  LDFLAGS_NODIST="$LDFLAGS_NODIST -Wl,--emit-relocs"
+
+  # These flags are required to get good performance from bolt:
+  CFLAGS_NODIST="$CFLAGS_NODIST -fno-pie"
+  # We want to add these no-pie flags to linking executables but not shared libraries:
+  LINKCC="$LINKCC -fno-pie -no-pie"
+  # Designate the DWARF version into 4 since the LLVM-BOLT does not support DWARF5 yet.
+  CFLAGS="$CFLAGS -gdwarf-4"
+  LDFLAGS="$LDFLAGS -gdwarf-4"
+
+  if test -n "$ac_tool_prefix"; then
+  # Extract the first word of "${ac_tool_prefix}llvm-bolt", so it can be a program name with args.
+set dummy ${ac_tool_prefix}llvm-bolt; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_path_LLVM_BOLT+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  case $LLVM_BOLT in
+  [\\/]* | ?:[\\/]*)
+  ac_cv_path_LLVM_BOLT="$LLVM_BOLT" # Let the user override the test with a path.
+  ;;
+  *)
+  as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in ${llvm_path}
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_path_LLVM_BOLT="$as_dir/$ac_word$ac_exec_ext"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+  ;;
+esac
+fi
+LLVM_BOLT=$ac_cv_path_LLVM_BOLT
+if test -n "$LLVM_BOLT"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $LLVM_BOLT" >&5
+$as_echo "$LLVM_BOLT" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+fi
+if test -z "$ac_cv_path_LLVM_BOLT"; then
+  ac_pt_LLVM_BOLT=$LLVM_BOLT
+  # Extract the first word of "llvm-bolt", so it can be a program name with args.
+set dummy llvm-bolt; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_path_ac_pt_LLVM_BOLT+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  case $ac_pt_LLVM_BOLT in
+  [\\/]* | ?:[\\/]*)
+  ac_cv_path_ac_pt_LLVM_BOLT="$ac_pt_LLVM_BOLT" # Let the user override the test with a path.
+  ;;
+  *)
+  as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in ${llvm_path}
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_path_ac_pt_LLVM_BOLT="$as_dir/$ac_word$ac_exec_ext"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+  ;;
+esac
+fi
+ac_pt_LLVM_BOLT=$ac_cv_path_ac_pt_LLVM_BOLT
+if test -n "$ac_pt_LLVM_BOLT"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_pt_LLVM_BOLT" >&5
+$as_echo "$ac_pt_LLVM_BOLT" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+  if test "x$ac_pt_LLVM_BOLT" = x; then
+    LLVM_BOLT="''"
+  else
+    case $cross_compiling:$ac_tool_warned in
+yes:)
+{ $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: using cross tools not prefixed with host triplet" >&5
+$as_echo "$as_me: WARNING: using cross tools not prefixed with host triplet" >&2;}
+ac_tool_warned=yes ;;
+esac
+    LLVM_BOLT=$ac_pt_LLVM_BOLT
+  fi
+else
+  LLVM_BOLT="$ac_cv_path_LLVM_BOLT"
+fi
+
+  if test -n "${LLVM_BOLT}" -a -x "${LLVM_BOLT}"
+  then
+    { $as_echo "$as_me:${as_lineno-$LINENO}: result: \"Found llvm-bolt\"" >&5
+$as_echo "\"Found llvm-bolt\"" >&6; }
+  else
+    as_fn_error $? "llvm-bolt is required for a --enable-bolt build but could not be found." "$LINENO" 5
+  fi
+
+
+  if test -n "$ac_tool_prefix"; then
+  # Extract the first word of "${ac_tool_prefix}merge-fdata", so it can be a program name with args.
+set dummy ${ac_tool_prefix}merge-fdata; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_path_MERGE_FDATA+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  case $MERGE_FDATA in
+  [\\/]* | ?:[\\/]*)
+  ac_cv_path_MERGE_FDATA="$MERGE_FDATA" # Let the user override the test with a path.
+  ;;
+  *)
+  as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in ${llvm_path}
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_path_MERGE_FDATA="$as_dir/$ac_word$ac_exec_ext"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+  ;;
+esac
+fi
+MERGE_FDATA=$ac_cv_path_MERGE_FDATA
+if test -n "$MERGE_FDATA"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $MERGE_FDATA" >&5
+$as_echo "$MERGE_FDATA" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+fi
+if test -z "$ac_cv_path_MERGE_FDATA"; then
+  ac_pt_MERGE_FDATA=$MERGE_FDATA
+  # Extract the first word of "merge-fdata", so it can be a program name with args.
+set dummy merge-fdata; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_path_ac_pt_MERGE_FDATA+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  case $ac_pt_MERGE_FDATA in
+  [\\/]* | ?:[\\/]*)
+  ac_cv_path_ac_pt_MERGE_FDATA="$ac_pt_MERGE_FDATA" # Let the user override the test with a path.
+  ;;
+  *)
+  as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in ${llvm_path}
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_path_ac_pt_MERGE_FDATA="$as_dir/$ac_word$ac_exec_ext"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+  ;;
+esac
+fi
+ac_pt_MERGE_FDATA=$ac_cv_path_ac_pt_MERGE_FDATA
+if test -n "$ac_pt_MERGE_FDATA"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_pt_MERGE_FDATA" >&5
+$as_echo "$ac_pt_MERGE_FDATA" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+  if test "x$ac_pt_MERGE_FDATA" = x; then
+    MERGE_FDATA="''"
+  else
+    case $cross_compiling:$ac_tool_warned in
+yes:)
+{ $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: using cross tools not prefixed with host triplet" >&5
+$as_echo "$as_me: WARNING: using cross tools not prefixed with host triplet" >&2;}
+ac_tool_warned=yes ;;
+esac
+    MERGE_FDATA=$ac_pt_MERGE_FDATA
+  fi
+else
+  MERGE_FDATA="$ac_cv_path_MERGE_FDATA"
+fi
+
+  if test -n "${MERGE_FDATA}" -a -x "${MERGE_FDATA}"
+  then
+    { $as_echo "$as_me:${as_lineno-$LINENO}: result: \"Found merge-fdata\"" >&5
+$as_echo "\"Found merge-fdata\"" >&6; }
+  else
+    as_fn_error $? "merge-fdata is required for a --enable-bolt build but could not be found." "$LINENO" 5
+  fi
+fi
+
 # Enable PGO flags.
 
 

configure.ac

@@ -1917,6 +1917,59 @@ if test "$Py_LTO" = 'true' ; then
   LDFLAGS_NODIST="$LDFLAGS_NODIST $LTOFLAGS"
 fi
 
+# Enable bolt flags
+Py_BOLT='false'
+AC_MSG_CHECKING(for --enable-bolt)
+AC_ARG_ENABLE(bolt, AS_HELP_STRING(
+                [--enable-bolt],
+                [enable usage of the llvm-bolt post-link optimizer (default is no)]),
+[
+if test "$enableval" != no
+then
+  Py_BOLT='true'
+  AC_MSG_RESULT(yes);
+else
+  Py_BOLT='false'
+  AC_MSG_RESULT(no);
+fi],
+[AC_MSG_RESULT(no)])
+
+AC_SUBST(PREBOLT_RULE)
+if test "$Py_BOLT" = 'true' ; then
+  PREBOLT_RULE="${DEF_MAKE_ALL_RULE}"
+  DEF_MAKE_ALL_RULE="bolt-opt"
+  DEF_MAKE_RULE="build_all"
+
+  # These flags are required for bolt to work:
+  CFLAGS_NODIST="$CFLAGS_NODIST -fno-reorder-blocks-and-partition"
+  LDFLAGS_NODIST="$LDFLAGS_NODIST -Wl,--emit-relocs"
+
+  # These flags are required to get good performance from bolt:
+  CFLAGS_NODIST="$CFLAGS_NODIST -fno-pie"
+  # We want to add these no-pie flags to linking executables but not shared libraries:
+  LINKCC="$LINKCC -fno-pie -no-pie"
+  # Designate the DWARF version into 4 since the LLVM-BOLT does not support DWARF5 yet.
+  CFLAGS="$CFLAGS -gdwarf-4"
+  LDFLAGS="$LDFLAGS -gdwarf-4"
+  AC_SUBST(LLVM_BOLT)
+  AC_PATH_TOOL(LLVM_BOLT, llvm-bolt, '', ${llvm_path})
+  if test -n "${LLVM_BOLT}" -a -x "${LLVM_BOLT}"
+  then
+    AC_MSG_RESULT("Found llvm-bolt")
+  else
+    AC_MSG_ERROR([llvm-bolt is required for a --enable-bolt build but could not be found.])
+  fi
+
+  AC_SUBST(MERGE_FDATA)
+  AC_PATH_TOOL(MERGE_FDATA, merge-fdata, '', ${llvm_path})
+  if test -n "${MERGE_FDATA}" -a -x "${MERGE_FDATA}"
+  then
+    AC_MSG_RESULT("Found merge-fdata")
+  else
+    AC_MSG_ERROR([merge-fdata is required for a --enable-bolt build but could not be found.])
+  fi
+fi
+
 # Enable PGO flags.
 AC_SUBST(PGO_PROF_GEN_FLAG)
 AC_SUBST(PGO_PROF_USE_FLAG)