diff -r da483bda6efc .gitignore
--- a/.gitignore	Mon Aug 24 16:17:13 2015 -0400
+++ b/.gitignore	Mon Sep 07 15:09:01 2015 +0300
@@ -6,6 +6,9 @@
 *.pyo
 *.rej
 *~
+*.gc??
+*.profclang?
+*.profraw
 Doc/build/
 Doc/tools/docutils/
 Doc/tools/jinja2/
diff -r da483bda6efc .hgignore
--- a/.hgignore	Mon Aug 24 16:17:13 2015 -0400
+++ b/.hgignore	Mon Sep 07 15:09:01 2015 +0300
@@ -45,6 +45,9 @@
 *.pyd
 *.cover
 *~
+*.gc??
+*.profclang?
+*.profraw
 Lib/distutils/command/*.pdb
 Lib/lib2to3/*.pickle
 Lib/test/data/*
diff -r da483bda6efc Makefile.pre.in
--- a/Makefile.pre.in	Mon Aug 24 16:17:13 2015 -0400
+++ b/Makefile.pre.in	Mon Sep 07 15:09:01 2015 +0300
@@ -42,6 +42,11 @@
 HGVERSION=	@HGVERSION@
 HGTAG=		@HGTAG@
 HGBRANCH=	@HGBRANCH@
+PGO_PROF_GEN_FLAG=@PGO_PROF_GEN_FLAG@
+PGO_PROF_USE_FLAG=@PGO_PROF_USE_FLAG@
+LLVM_PROF_MERGER=@LLVM_PROF_MERGER@
+LLVM_PROF_FILE=@LLVM_PROF_FILE@
+LLVM_PROF_ERR=@LLVM_PROF_ERR@
 
 GNULD=          @GNULD@
 
@@ -204,8 +209,8 @@
 TCLTK_LIBS=	@TCLTK_LIBS@
 
 # The task to run while instrument when building the profile-opt target
-PROFILE_TASK=	$(srcdir)/Tools/pybench/pybench.py -n 2 --with-gc --with-syscheck
-#PROFILE_TASK=	$(srcdir)/Lib/test/regrtest.py
+PROFILE_TASK=-m test.regrtest >/dev/null 2>&1
+PROFILE_TASK_OLD=$(srcdir)/Tools/pybench/pybench.py -n 2 --with-gc --with-syscheck
 
 # === Definitions added by makesetup ===
 
@@ -420,27 +425,47 @@
 all:		build_all
 build_all:	$(BUILDPYTHON) oldsharedmods sharedmods gdbhooks
 
-# Compile a binary with gcc profile guided optimization.
+# Compile a binary with profile guided optimization.
 profile-opt:
+	@if [ $(LLVM_PROF_ERR) == yes ]; then \
+		echo "Error: Cannot perform PGO build because llvm-profdata was not found in PATH" ;\
+		echo "Please add it to PATH and run ./configure again" ;\
+		exit 1;\
+	fi
+	@if [ `uname -m | grep 86` == '' ];then \
+		echo "Warning: the benefits of profile-guided optimization only tested x86 architectures!" ;\
+	fi
 	@echo "Building with support for profile generation:"
 	$(MAKE) clean
+	$(MAKE) profile-removal
 	$(MAKE) build_all_generate_profile
-	@echo "Running benchmark to generate profile data:"
 	$(MAKE) profile-removal
+	@echo "Running code to generate profile data:"
+	@echo "Warning: all output is suppressed. Please wait until the profile is generated."
+	@echo "Code failures will not adversely affect the results!"
 	$(MAKE) run_profile_task
+	$(MAKE) build_all_merge_profile
 	@echo "Rebuilding with profile guided optimizations:"
 	$(MAKE) clean
 	$(MAKE) build_all_use_profile
+	$(MAKE) profile-removal
 
 build_all_generate_profile:
-	$(MAKE) all CFLAGS="$(CFLAGS) -fprofile-generate" LIBS="$(LIBS) -lgcov"
+	$(MAKE) all CFLAGS="$(CFLAGS) $(PGO_PROF_GEN_FLAG)" LDFLAGS="$(LDFLAGS) $(PGO_PROF_GEN_FLAG)" LIBS="$(LIBS)"
 
 run_profile_task:
 	: # FIXME: can't run for a cross build
-	./$(BUILDPYTHON) $(PROFILE_TASK)
+	@if [ `uname -m | grep 86` == '' ];then \
+		$(LLVM_PROF_FILE) ./$(BUILDPYTHON) $(PROFILE_TASK_OLD) || true ;\
+	else \
+		$(LLVM_PROF_FILE) ./$(BUILDPYTHON) $(PROFILE_TASK) || true ;\
+	fi
+
+build_all_merge_profile:
+	$(LLVM_PROF_MERGER)
 
 build_all_use_profile:
-	$(MAKE) all CFLAGS="$(CFLAGS) -fprofile-use"
+	$(MAKE) all CFLAGS="$(CFLAGS) $(PGO_PROF_USE_FLAG)"
 
 coverage:
 	@echo "Building with support for coverage checking:"
@@ -1330,9 +1355,11 @@
 	find build -name 'fficonfig.h' -exec rm -f {} ';' || true
 	find build -name 'fficonfig.py' -exec rm -f {} ';' || true
 	-rm -f Lib/lib2to3/*Grammar*.pickle
+	-rm -rf build
 
 profile-removal:
 	find . -name '*.gc??' -exec rm -f {} ';'
+	find . -name '*.profclang?' -exec rm -f {} ';'
 
 clobber: clean profile-removal
 	-rm -f $(BUILDPYTHON) $(PGEN) $(LIBRARY) $(LDLIBRARY) $(DLLLIBRARY) \
diff -r da483bda6efc configure
--- a/configure	Mon Aug 24 16:17:13 2015 -0400
+++ b/configure	Mon Sep 07 15:09:01 2015 +0300
@@ -661,6 +661,12 @@
 SO
 LIBTOOL_CRUFT
 OTHER_LIBTOOL_OPT
+LLVM_PROF_FOUND
+LLVM_PROF_ERR
+LLVM_PROF_FILE
+LLVM_PROF_MERGER
+PGO_PROF_USE_FLAG
+PGO_PROF_GEN_FLAG
 UNIVERSAL_ARCH_FLAGS
 BASECFLAGS
 OPT
@@ -6326,6 +6332,82 @@
   CFLAGS=$save_CFLAGS
 fi
 
+
+# Enable PGO flags.
+# Extract the first word of "llvm-profdata", so it can be a program name with args.
+set dummy llvm-profdata; 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_prog_LLVM_PROF_FOUND+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  if test -n "$LLVM_PROF_FOUND"; then
+  ac_cv_prog_LLVM_PROF_FOUND="$LLVM_PROF_FOUND" # Let the user override the test.
+else
+as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$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_prog_LLVM_PROF_FOUND="found"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
+  done
+IFS=$as_save_IFS
+
+  test -z "$ac_cv_prog_LLVM_PROF_FOUND" && ac_cv_prog_LLVM_PROF_FOUND="not-found"
+fi
+fi
+LLVM_PROF_FOUND=$ac_cv_prog_LLVM_PROF_FOUND
+if test -n "$LLVM_PROF_FOUND"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $LLVM_PROF_FOUND" >&5
+$as_echo "$LLVM_PROF_FOUND" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+LLVM_PROF_ERR=no
+case $CC in
+  *clang*)
+    # Any changes made here should be reflected in the GCC+Darwin case below
+    PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
+    PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd"
+    LLVM_PROF_MERGER="llvm-profdata merge -output=code.profclangd *.profclangr"
+    LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
+    if test $LLVM_PROF_FOUND = not-found
+    then
+      LLVM_PROF_ERR=yes
+    fi
+    ;;
+  *gcc*)
+    case $ac_sys_system in
+      Darwin*)
+        PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
+        PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd"
+        LLVM_PROF_MERGER="llvm-profdata merge -output=code.profclangd *.profclangr"
+        LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
+        if test $LLVM_PROF_FOUND = not-found
+        then
+          LLVM_PROF_ERR=yes
+        fi
+        ;;
+      *)
+        PGO_PROF_GEN_FLAG="-fprofile-generate"
+        PGO_PROF_USE_FLAG="-fprofile-use -fprofile-correction"
+        LLVM_PROF_MERGER="true"
+        LLVM_PROF_FILE=""
+        ;;
+    esac
+    ;;
+esac
+
+
 # On some compilers, pthreads are available without further options
 # (e.g. MacOS X). On some of these systems, the compiler will not
 # complain if unaccepted options are passed (e.g. gcc on Mac OS X).
diff -r da483bda6efc configure.ac
--- a/configure.ac	Mon Aug 24 16:17:13 2015 -0400
+++ b/configure.ac	Mon Sep 07 15:09:01 2015 +0300
@@ -1352,6 +1352,51 @@
   CFLAGS=$save_CFLAGS
 fi
 
+
+# Enable PGO flags.
+AC_SUBST(PGO_PROF_GEN_FLAG)
+AC_SUBST(PGO_PROF_USE_FLAG)
+AC_SUBST(LLVM_PROF_MERGER)
+AC_SUBST(LLVM_PROF_FILE)
+AC_SUBST(LLVM_PROF_ERR)
+AC_SUBST(LLVM_PROF_FOUND)
+AC_CHECK_PROG(LLVM_PROF_FOUND, llvm-profdata, found, not-found)
+LLVM_PROF_ERR=no
+case $CC in
+  *clang*)
+    # Any changes made here should be reflected in the GCC+Darwin case below
+    PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
+    PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd"
+    LLVM_PROF_MERGER="llvm-profdata merge -output=code.profclangd *.profclangr"
+    LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
+    if test $LLVM_PROF_FOUND = not-found
+    then
+      LLVM_PROF_ERR=yes
+    fi
+    ;;
+  *gcc*)
+    case $ac_sys_system in
+      Darwin*)
+        PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
+        PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd"
+        LLVM_PROF_MERGER="llvm-profdata merge -output=code.profclangd *.profclangr"
+        LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
+        if test $LLVM_PROF_FOUND = not-found
+        then
+          LLVM_PROF_ERR=yes
+        fi
+        ;;
+      *)
+        PGO_PROF_GEN_FLAG="-fprofile-generate"
+        PGO_PROF_USE_FLAG="-fprofile-use -fprofile-correction"
+        LLVM_PROF_MERGER="true"
+        LLVM_PROF_FILE=""
+        ;;
+    esac
+    ;;
+esac
+
+
 # On some compilers, pthreads are available without further options
 # (e.g. MacOS X). On some of these systems, the compiler will not
 # complain if unaccepted options are passed (e.g. gcc on Mac OS X).