[v4,00/10] Add an option to use LTO for DPDK build

  This patch series adds an option to make use of link time optimization
(if compiler has support for it).  It is split as follows:
- 1st patch (build) is the enablement
- remaining patches are fixes for the warnings produced by the compiler
  and they are split by directory/subsystem so their maintainers can
  easily find and verify the changes - please note that there are two
  groups:
  * errors (or possible errors) - with title "fix possible use ..."
  * false positives - warnings that _I_ think are not valid and the
    changes are made only to silence the compiler.

v4 Changes:
-----------
- merge nested conditionals in config/meson.build into one

v3 Changes:
-----------
- removed support for clang (only gcc and icc remain):
  - it turned out that 'fat-lto-objects' is not really supported - it is
    accepted as a flag but ignored e.g. clang v6.0:
      clang: error: optimization flag '-ffat-lto-objects' is not supported
      [-Werror,-Wignored-optimization-argument]
    this was probably masked previously by playing around with meson and
    testing for the availability of this flag and dropping LTO if not
    supported.
- improved commit messages:
  - added 'Fixes' tags where appropriate
  - included snippets of compiler warnings
- changed commit names for the commits cleaning up 'false positive'
  compiler warnings - these are not really 'fixes' for the code, just
  workarounds for compiler shortcomings and check-git-log.sh was
  complaining about missing 'Fixes' tag.

v2 Changes:
-----------
- fixed building of shared libraries:
  - gcc does not scan top level assembler statements so it missed that
    function implementations for specific versions were being used and
    was removing them
- fixed meson.build config files:
  - moved from 'enable_lto' project option to built-in 'b_lto'
  - documented that 'default_library' should be 'shared':
    with 'default_library=static' (the default) the meson build with LTO
    is broken - this is because, SHARED_LIB is fixed in rte_config.h
    used by meson which leads to no alias for default version in
    generated static libraries (MAP_STATIC_SYMBOL() is empty)
- app/test: added log for failed bonding "config get"

Andrzej Ostruszka (10):
  build: add an option to enable LTO build
  eventdev: fix possible use of uninitialized var
  app/eventdev: clean LTO build warnings (maybe-uninitialized)
  event/octeontx2: clean LTO build warnings (maybe-uninitialized)
  app/test: clean LTO build warnings (maybe-uninitialized)
  net/dpaa2: fix possible use of uninitialized vars
  net/e1000: clean LTO build warnings (maybe-uninitialized)
  net/i40e: clean LTO build warnings (maybe-uninitialized)
  net/ifc: clean LTO build warnings (maybe-uninitialized)
  net/qede: clean LTO build warnings (maybe-uninitialized)

 .travis.yml                                   |  7 ++++
 app/test-eventdev/test_perf_common.c          |  2 +-
 app/test-eventdev/test_pipeline_common.c      |  4 +--
 app/test/test_hash_readwrite.c                |  2 +-
 app/test/test_link_bonding_mode4.c            | 10 ++++--
 app/test/test_memzone.c                       |  3 +-
 config/common_base                            |  5 +++
 config/meson.build                            | 13 +++++++
 doc/guides/prog_guide/lto.rst                 | 36 +++++++++++++++++++
 doc/guides/rel_notes/release_19_11.rst        |  8 +++++
 drivers/event/octeontx2/otx2_tim_worker.h     |  2 +-
 drivers/net/dpaa2/base/dpaa2_hw_dpni.c        |  1 +
 drivers/net/dpaa2/mc/dpkg.c                   |  2 +-
 drivers/net/dpaa2/mc/dpni.c                   |  9 +++--
 drivers/net/e1000/base/e1000_82543.c          |  2 +-
 drivers/net/e1000/base/e1000_ich8lan.c        |  2 +-
 drivers/net/e1000/base/e1000_phy.c            |  2 +-
 drivers/net/i40e/i40e_ethdev.c                |  2 +-
 drivers/net/ifc/ifcvf_vdpa.c                  | 14 +++++---
 drivers/net/qede/base/ecore_mcp.c             | 13 +++----
 lib/librte_distributor/rte_distributor.c      | 18 +++++-----
 lib/librte_distributor/rte_distributor_v20.c  | 18 +++++-----
 lib/librte_eventdev/rte_event_timer_adapter.c |  8 ++---
 lib/librte_lpm/rte_lpm.c                      | 28 +++++++--------
 lib/librte_lpm/rte_lpm6.c                     | 16 ++++-----
 lib/librte_timer/rte_timer.c                  | 20 +++++------
 mk/toolchain/gcc/rte.toolchain-compat.mk      |  4 +++
 mk/toolchain/gcc/rte.vars.mk                  | 12 +++++++
 mk/toolchain/icc/rte.vars.mk                  |  8 +++++
 29 files changed, 190 insertions(+), 81 deletions(-)
 create mode 100644 doc/guides/prog_guide/lto.rst