[tarantool-patches] [PATCH 2/3] Add LTO support

[AKhatskevich]

This commit introduces LTO support.

Changes:
  - update submodules (fix lto-related warnings)
  - add `TARANTOOL_LTO` cmake option (by default it is `False`)

LTO speeds up cpu-intensive workloads by up to 20%.

Requirements for LTO enabling:
  - cmake >= 3.9
  - linker
    - ld >= 2.31 (or latest 2.30)
    - gold >= 1.15 (binutils 2.30)
    - mac xcode >= 8 (earlier versions are not tested)
This small patch required fixing bug in GNU ld linker.
(link gcc.gnu.org/bugzilla/show_bug.cgi?id=84901)
`ld` was not exporting symbols from dynamic list when LTO enabled.

Closes #3117
---
 CMakeLists.txt      |  1 +
 cmake/lto.cmake     | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/lib/msgpuck     |  2 +-
 src/lib/small       |  2 +-
 third_party/libyaml |  2 +-
 5 files changed, 59 insertions(+), 3 deletions(-)
 create mode 100644 cmake/lto.cmake

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d0cae0f01..432d2a6fb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -63,6 +63,7 @@ include(cmake/pod2man.cmake)
 include(cmake/arch.cmake)
 include(cmake/os.cmake)
 include(cmake/compiler.cmake)
+include(cmake/lto.cmake NO_POLICY_SCOPE)
 include(cmake/simd.cmake)
 include(cmake/atomic.cmake)
 include(cmake/profile.cmake)
diff --git a/cmake/lto.cmake b/cmake/lto.cmake
new file mode 100644
index 000000000..96129ebfd
--- /dev/null
+++ b/cmake/lto.cmake
@@ -0,0 +1,55 @@
+##
+## Manage LTO (Link-Time-Optimization) and IPO (Inter-Procedural-Optimization)
+##
+
+# Tarantool uses both dynamic-list and lto link options, which works only
+# since binutils:
+#  - 2.30 for linking with gold (gold version is 1.15)
+#  - last 2.30 or 2.31 in case of ld (bfd)
+
+if (NOT DEFINED TARANTOOL_LTO)
+    set(TARANTOOL_LTO FALSE)
+endif()
+
+if(NOT CMAKE_VERSION VERSION_LESS 3.9)
+    cmake_policy(SET CMP0069 NEW)
+    include(CheckIPOSupported)
+    check_ipo_supported(RESULT CMAKE_IPO_AVAILABLE)
+else()
+    set(CMAKE_IPO_AVAILABLE FALSE)
+endif()
+
+# Ensure that default value is false
+set(CMAKE_INTERPROCEDURAL_OPTIMIZATION FALSE)
+if (TARANTOOL_LTO AND CMAKE_IPO_AVAILABLE AND NOT TARGET_OS_DARWIN)
+    execute_process(COMMAND ld -v OUTPUT_VARIABLE linker_v)
+	message(STATUS "LTO linker_v ${linker_v}")
+
+    # e.g. GNU ld (GNU Binutils) 2.29
+    string(REGEX MATCH "^GNU ld [^)]+[)] ([0-9.]+).*$" linker_valid ${linker_v})
+
+    if (NOT linker_valid)
+        message(FATAL_ERROR "Unsuported linker (ld expected)")
+    endif()
+
+    set(linker_version ${CMAKE_MATCH_1})
+    message(STATUS "Found linker ld VERSION ${linker_version}")
+
+    if (NOT linker_version VERSION_LESS "2.31")
+        set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+    elseif(NOT linker_version VERSION_LESS "2.30")
+        # Use gold if LTO+dynamic-list is available in gold & not in ld
+        find_program(gold_available "ld.gold")
+        if (gold_available)
+            message(WARNING "Use gold linker (to enable LTO)")
+            SET(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=gold")
+            set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+        endif()
+    endif()
+endif()
+
+if (TARANTOOL_LTO AND CMAKE_IPO_AVAILABLE AND TARGET_OS_DARWIN)
+    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+endif()
+
+message(STATUS "LTO enabled ${CMAKE_INTERPROCEDURAL_OPTIMIZATION}")
diff --git a/src/lib/msgpuck b/src/lib/msgpuck
index 3b8f3e59b..1eb56a447 160000
--- a/src/lib/msgpuck
+++ b/src/lib/msgpuck
@@ -1 +1 @@
-Subproject commit 3b8f3e59b62d74f0198e01cbec0beb9c6a3082fb
+Subproject commit 1eb56a447ea35f9c403dbc8aa98a25336303c1cb
diff --git a/src/lib/small b/src/lib/small
index 22d1bad18..0627a7f98 160000
--- a/src/lib/small
+++ b/src/lib/small
@@ -1 +1 @@
-Subproject commit 22d1bad1873edcb9b1383a273e70c4cf881d5349
+Subproject commit 0627a7f986ff91701bd741908818749fef5e2266
diff --git a/third_party/libyaml b/third_party/libyaml
index 6bd4be1a7..e554afad0 160000
--- a/third_party/libyaml
+++ b/third_party/libyaml
@@ -1 +1 @@
-Subproject commit 6bd4be1a7751d6022a413864666880bef8a87c3c
+Subproject commit e554afad015b2c7df76f9d5213d883e931246fad
-- 
2.14.1