bpo-28015: Support LTO build with clang (GH-9908)

.o generated by clang in LTO mode actually are LLVM bitcode files, which
leads to a few errors during configure/build step:

- add lto flags to the BASECFLAGS instead of CFLAGS, as CFLAGS are used
  to build autoconf test case, and some are not compatible with clang LTO
  (they assume binary in the .o, not bitcode)
- force llvm-ar instead of ar, as ar is not aware of .o files generated
  by clang -flto
(cherry picked from commit 5ad36f9b21a3aa3b2265b1b43d73522cc3322df2)

Co-authored-by: serge-sans-paille <serge.guelton@telecom-bretagne.eu>

4 files changed, 235 insertions, 83 deletions

diff --git a/Misc/NEWS.d/next/Build/2018-10-16-12-22-36.bpo-28015.ylSgFh.rst b/Misc/NEWS.d/next/Build/2018-10-16-12-22-36.bpo-28015.ylSgFh.rst
new file mode 100644
index 0000000000..5a7a43c773
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2018-10-16-12-22-36.bpo-28015.ylSgFh.rst
@@ -0,0 +1 @@
+Have --with-lto works correctly with clang.
diff --git a/aclocal.m4 b/aclocal.m4
index 6a24d8e6b9..32828c24dd 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -13,7 +13,7 @@
 
 m4_ifndef([AC_CONFIG_MACRO_DIRS], [m4_defun([_AM_CONFIG_MACRO_DIRS], [])m4_defun([AC_CONFIG_MACRO_DIRS], [_AM_CONFIG_MACRO_DIRS($@)])])
 dnl pkg.m4 - Macros to locate and utilise pkg-config.   -*- Autoconf -*-
-dnl serial 11 (pkg-config-0.29.1)
+dnl serial 11 (pkg-config-0.29)
 dnl
 dnl Copyright © 2004 Scott James Remnant <scott@netsplit.com>.
 dnl Copyright © 2012-2015 Dan Nicholson <dbn.lists@gmail.com>
@@ -55,7 +55,7 @@ dnl
 dnl See the "Since" comment for each macro you use to see what version
 dnl of the macros you require.
 m4_defun([PKG_PREREQ],
-[m4_define([PKG_MACROS_VERSION], [0.29.1])
+[m4_define([PKG_MACROS_VERSION], [0.29])
 m4_if(m4_version_compare(PKG_MACROS_VERSION, [$1]), -1,
     [m4_fatal([pkg.m4 version $1 or higher is required but ]PKG_MACROS_VERSION[ found])])
 ])dnl PKG_PREREQ
diff --git a/configure b/configure
index 36e117a755..12663996ff 100755
--- a/configure
+++ b/configure
@@ -672,16 +672,18 @@ BASECFLAGS
 CFLAGS_ALIASING
 OPT
 LLVM_PROF_FOUND
-target_os
-target_vendor
-target_cpu
-target
 LLVM_PROFDATA
 LLVM_PROF_ERR
 LLVM_PROF_FILE
 LLVM_PROF_MERGER
 PGO_PROF_USE_FLAG
 PGO_PROF_GEN_FLAG
+LLVM_AR_FOUND
+target_os
+target_vendor
+target_cpu
+target
+LLVM_AR
 DEF_MAKE_RULE
 DEF_MAKE_ALL_RULE
 ABIFLAGS
@@ -6432,6 +6434,26 @@ else
   DEF_MAKE_RULE="all"
 fi
 
+# Make llvm-relatec checks work on systems where llvm tools are not installed with their
+# normal names in the default $PATH (ie: Ubuntu).  They exist under the
+# non-suffixed name in their versioned llvm directory.
+
+llvm_bin_dir=''
+llvm_path="${PATH}"
+if test "${CC}" = "clang"
+then
+  clang_bin=`which clang`
+  # Some systems install clang elsewhere as a symlink to the real path
+  # which is where the related llvm tools are located.
+  if test -L "${clang_bin}"
+  then
+    clang_dir=`dirname "${clang_bin}"`
+    clang_bin=`readlink "${clang_bin}"`
+    llvm_bin_dir="${clang_dir}/"`dirname "${clang_bin}"`
+    llvm_path="${llvm_path}${PATH_SEPARATOR}${llvm_bin_dir}"
+  fi
+fi
+
 # Enable LTO flags
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for --with-lto" >&5
 $as_echo_n "checking for --with-lto... " >&6; }
@@ -6457,65 +6479,8 @@ fi
 if test "$Py_LTO" = 'true' ; then
   case $CC in
     *clang*)
-      case $ac_sys_system in
-        Darwin*)
-          # Any changes made here should be reflected in the GCC+Darwin case below
-          LTOFLAGS="-flto -Wl,-export_dynamic"
-          ;;
-        *)
-          LTOFLAGS="-flto"
-          ;;
-      esac
-      ;;
-    *gcc*)
-      case $ac_sys_system in
-        Darwin*)
-          LTOFLAGS="-flto -Wl,-export_dynamic"
-          ;;
-        *)
-          LTOFLAGS="-flto -fuse-linker-plugin -ffat-lto-objects -flto-partition=none"
-          ;;
-      esac
-      ;;
-  esac
 
-  if test "$ac_cv_prog_cc_g" = "yes"
-  then
-      # bpo-30345: Add -g to LDFLAGS when compiling with LTO
-      # to get debug symbols.
-      LTOFLAGS="$LTOFLAGS -g"
-  fi
-
-  CFLAGS="$CFLAGS $LTOFLAGS"
-  LDFLAGS="$LDFLAGS $LTOFLAGS"
-fi
-
-# Enable PGO flags.
-
-
-
-
-
-# Make this work on systems where llvm tools are not installed with their
-# normal names in the default $PATH (ie: Ubuntu).  They exist under the
-# non-suffixed name in their versioned llvm directory.
-llvm_bin_dir=''
-llvm_path="${PATH}"
-if test "${CC}" = "clang"
-then
-  clang_bin=`which clang`
-  # Some systems install clang elsewhere as a symlink to the real path
-  # which is where the related llvm tools are located.
-  if test -L "${clang_bin}"
-  then
-    clang_dir=`dirname "${clang_bin}"`
-    clang_bin=`readlink "${clang_bin}"`
-    llvm_bin_dir="${clang_dir}/"`dirname "${clang_bin}"`
-    llvm_path="${llvm_path}${PATH_SEPARATOR}${llvm_bin_dir}"
-  fi
-fi
-
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking target system type" >&5
+      { $as_echo "$as_me:${as_lineno-$LINENO}: checking target system type" >&5
 $as_echo_n "checking target system type... " >&6; }
 if ${ac_cv_target+:} false; then :
   $as_echo_n "(cached) " >&6
@@ -6554,6 +6519,163 @@ test -n "$target_alias" &&
   test "$program_prefix$program_suffix$program_transform_name" = \
     NONENONEs,x,x, &&
   program_prefix=${target_alias}-
+# Extract the first word of "$target_alias-llvm-ar", so it can be a program name with args.
+set dummy $target_alias-llvm-ar; 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_AR+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  case $LLVM_AR in
+  [\\/]* | ?:[\\/]*)
+  ac_cv_path_LLVM_AR="$LLVM_AR" # 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_AR="$as_dir/$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_AR=$ac_cv_path_LLVM_AR
+if test -n "$LLVM_AR"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $LLVM_AR" >&5
+$as_echo "$LLVM_AR" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+
+if test -z "$ac_cv_path_LLVM_AR"; then
+  if test "$build" = "$target"; then
+    ac_pt_LLVM_AR=$LLVM_AR
+    # Extract the first word of "llvm-ar", so it can be a program name with args.
+set dummy llvm-ar; 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_AR+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  case $ac_pt_LLVM_AR in
+  [\\/]* | ?:[\\/]*)
+  ac_cv_path_ac_pt_LLVM_AR="$ac_pt_LLVM_AR" # 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_AR="$as_dir/$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
+
+  test -z "$ac_cv_path_ac_pt_LLVM_AR" && ac_cv_path_ac_pt_LLVM_AR="''"
+  ;;
+esac
+fi
+ac_pt_LLVM_AR=$ac_cv_path_ac_pt_LLVM_AR
+if test -n "$ac_pt_LLVM_AR"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_pt_LLVM_AR" >&5
+$as_echo "$ac_pt_LLVM_AR" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
+fi
+
+    LLVM_AR=$ac_pt_LLVM_AR
+  else
+    LLVM_AR="''"
+  fi
+else
+  LLVM_AR="$ac_cv_path_LLVM_AR"
+fi
+
+
+      if test -n "${LLVM_AR}" -a -x "${LLVM_AR}"
+      then
+        LLVM_AR_FOUND="found"
+      else
+        LLVM_AR_FOUND="not-found"
+      fi
+      if test "$ac_sys_system" = "Darwin" -a "${LLVM_AR_FOUND}" = "not-found"
+      then
+        found_llvm_ar=`/usr/bin/xcrun -find llvm-ar 2>/dev/null`
+        if test -n "${found_llvm_ar}"
+        then
+          LLVM_AR='/usr/bin/xcrun llvm-ar'
+          LLVM_AR_FOUND=found
+          { $as_echo "$as_me:${as_lineno-$LINENO}: llvm-ar found via xcrun: ${LLVM_AR}" >&5
+$as_echo "$as_me: llvm-ar found via xcrun: ${LLVM_AR}" >&6;}
+        fi
+      fi
+      if test $LLVM_AR_FOUND = not-found
+      then
+        LLVM_PROFR_ERR=yes
+        as_fn_error $? "llvm-ar is required for a --with-lto build with clang but could not be found." "$LINENO" 5
+      else
+        LLVM_AR_ERR=no
+      fi
+      AR="${LLVM_AR}"
+      case $ac_sys_system in
+        Darwin*)
+          # Any changes made here should be reflected in the GCC+Darwin case below
+          LTOFLAGS="-flto -Wl,-export_dynamic"
+          ;;
+        *)
+          LTOFLAGS="-flto"
+          ;;
+      esac
+      ;;
+    *gcc*)
+      case $ac_sys_system in
+        Darwin*)
+          LTOFLAGS="-flto -Wl,-export_dynamic"
+          ;;
+        *)
+          LTOFLAGS="-flto -fuse-linker-plugin -ffat-lto-objects -flto-partition=none"
+          ;;
+      esac
+      ;;
+  esac
+
+  if test "$ac_cv_prog_cc_g" = "yes"
+  then
+      # bpo-30345: Add -g to LDFLAGS when compiling with LTO
+      # to get debug symbols.
+      LTOFLAGS="$LTOFLAGS -g"
+  fi
+
+  BASECFLAGS="$BASECFLAGS $LTOFLAGS"
+  LDFLAGS="$LDFLAGS $LTOFLAGS"
+fi
+
+# Enable PGO flags.
+
+
+
+
+
+
 # Extract the first word of "$target_alias-llvm-profdata", so it can be a program name with args.
 set dummy $target_alias-llvm-profdata; ac_word=$2
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
diff --git a/configure.ac b/configure.ac
index 620b48a6e7..e322d0ae6c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1302,6 +1302,26 @@ else
   DEF_MAKE_RULE="all"
 fi
 
+# Make llvm-relatec checks work on systems where llvm tools are not installed with their
+# normal names in the default $PATH (ie: Ubuntu).  They exist under the
+# non-suffixed name in their versioned llvm directory.
+
+llvm_bin_dir=''
+llvm_path="${PATH}"
+if test "${CC}" = "clang"
+then
+  clang_bin=`which clang`
+  # Some systems install clang elsewhere as a symlink to the real path
+  # which is where the related llvm tools are located.
+  if test -L "${clang_bin}"
+  then
+    clang_dir=`dirname "${clang_bin}"`
+    clang_bin=`readlink "${clang_bin}"`
+    llvm_bin_dir="${clang_dir}/"`dirname "${clang_bin}"`
+    llvm_path="${llvm_path}${PATH_SEPARATOR}${llvm_bin_dir}"
+  fi
+fi
+
 # Enable LTO flags
 AC_MSG_CHECKING(for --with-lto)
 AC_ARG_WITH(lto, AS_HELP_STRING([--with-lto], [Enable Link Time Optimization in any build. Disabled by default.]),
@@ -1318,6 +1338,33 @@ fi],
 if test "$Py_LTO" = 'true' ; then
   case $CC in
     *clang*)
+      AC_SUBST(LLVM_AR)
+      AC_PATH_TARGET_TOOL(LLVM_AR, llvm-ar, '', ${llvm_path})
+      AC_SUBST(LLVM_AR_FOUND)
+      if test -n "${LLVM_AR}" -a -x "${LLVM_AR}"
+      then
+        LLVM_AR_FOUND="found"
+      else
+        LLVM_AR_FOUND="not-found"
+      fi
+      if test "$ac_sys_system" = "Darwin" -a "${LLVM_AR_FOUND}" = "not-found"
+      then
+        found_llvm_ar=`/usr/bin/xcrun -find llvm-ar 2>/dev/null`
+        if test -n "${found_llvm_ar}"
+        then
+          LLVM_AR='/usr/bin/xcrun llvm-ar'
+          LLVM_AR_FOUND=found
+          AC_MSG_NOTICE([llvm-ar found via xcrun: ${LLVM_AR}])
+        fi
+      fi
+      if test $LLVM_AR_FOUND = not-found
+      then
+        LLVM_PROFR_ERR=yes
+        AC_MSG_ERROR([llvm-ar is required for a --with-lto build with clang but could not be found.])
+      else
+        LLVM_AR_ERR=no
+      fi
+      AR="${LLVM_AR}"
       case $ac_sys_system in
         Darwin*)
           # Any changes made here should be reflected in the GCC+Darwin case below
@@ -1347,7 +1394,7 @@ if test "$Py_LTO" = 'true' ; then
       LTOFLAGS="$LTOFLAGS -g"
   fi
 
-  CFLAGS="$CFLAGS $LTOFLAGS"
+  BASECFLAGS="$BASECFLAGS $LTOFLAGS"
   LDFLAGS="$LDFLAGS $LTOFLAGS"
 fi
 
@@ -1357,24 +1404,6 @@ AC_SUBST(PGO_PROF_USE_FLAG)
 AC_SUBST(LLVM_PROF_MERGER)
 AC_SUBST(LLVM_PROF_FILE)
 AC_SUBST(LLVM_PROF_ERR)
-# Make this work on systems where llvm tools are not installed with their
-# normal names in the default $PATH (ie: Ubuntu).  They exist under the
-# non-suffixed name in their versioned llvm directory.
-llvm_bin_dir=''
-llvm_path="${PATH}"
-if test "${CC}" = "clang"
-then
-  clang_bin=`which clang`
-  # Some systems install clang elsewhere as a symlink to the real path
-  # which is where the related llvm tools are located.
-  if test -L "${clang_bin}"
-  then
-    clang_dir=`dirname "${clang_bin}"`
-    clang_bin=`readlink "${clang_bin}"`
-    llvm_bin_dir="${clang_dir}/"`dirname "${clang_bin}"`
-    llvm_path="${llvm_path}${PATH_SEPARATOR}${llvm_bin_dir}"
-  fi
-fi
 AC_SUBST(LLVM_PROFDATA)
 AC_PATH_TARGET_TOOL(LLVM_PROFDATA, llvm-profdata, '', ${llvm_path})
 AC_SUBST(LLVM_PROF_FOUND)