[Qemu-devel] [PATCH v3 00/26] tcg: rework liveness analysis and register allocator

[Aurelien Jarno]

This patch series rework the liveness analysis and register allocator
in order to generate more optimized code, by avoiding a lot of move
instructions. I have measured a 9% performance improvement in user mode
and 4% in system mode.

The idea behind this patch series is to free registers as soon as the
temps are not used anymore instead of waiting for a basic block end or
an op with side effects. In addition temps are copied to memory as soon
as they are not going to be written anymore, this way even globals can
be marked as "dead", avoiding moves to a new register when inputs and
outputs are aliased. Finally qemu_ld/st operations do not save back
globals to memory, but only copy them there. In case of an exception
the globals have the correct values, and otherwise they do not have
to be reloaded.

Overall this greatly reduces the number of moves emitted, and spread
them all over the TBs, increasing the performances on in-order CPUs.
This also reduces register spilling, especially on CPUs with few
registers.

In practice it means the liveness analysis is providing more
information to the register allocator, and especially when to the memory
version of a temp with the content of the associated register. This
means that the two are now quite linked, and that for some functions the
code exist in two versions, one used when the liveness analysis is
enabled which only does some checks with assert(), the other when it is
disabled. It might be possible to keep only one version, but it implies
de-optimizing the liveness analysis disabled case. In any case the
checks with assert() should be kept, as they are quite useful to make
sure nothing subtly breaks.


Changes v2 -> v3:
 - rebased against master
 - patch 7: fixed indentation
 - patch 14 and later: renamed TCG_CALL_NO_RG into TCG_CALL_NO_RWG
                       renamed TCG_CALL_NO_WGSE into TCG_CALL_NO_WG_SE
                       renamed TCG_CALL_NO_RGSE TCG_CALL_NO_RWG_SE

Aurelien Jarno (26):
  tcg: add temp_dead()
  tcg: add tcg_reg_sync()
  tcg: add temp_sync()
  tcg: sync output arguments on liveness request
  tcg: rework liveness analysis
  tcg: improve tcg_reg_alloc_movi()
  tcg: rewrite tcg_reg_alloc_mov()
  tcg: always mark dead input arguments as dead
  tcg: start with local temps in TEMP_VAL_MEM state
  tcg: don't explicitly save globals and temps
  tcg: fix some op flags
  tcg: forbid ld/st function to modify globals
  tcg: synchronize globals for ops with side effects
  tcg: rework TCG helper flags
  target-alpha: rename helper flags
  target-arm: rename helper flags
  target-cris: rename helper flags
  target-i386: rename helper flags
  target-microblaze: rename helper flags
  target-mips: rename helper flags
  target-ppc: rename helper flags
  target-s390x: rename helper flags
  target-sh4: rename helper flags
  target-sparc: rename helper flags
  target-xtensa: rename helper flags
  tcg: remove compatiblity call flags

 target-alpha/helper.h      |  176 ++++++++---------
 target-arm/helper.h        |   18 +-
 target-cris/helper.h       |   18 +-
 target-i386/helper.h       |    4 +-
 target-microblaze/helper.h |    6 +-
 target-mips/helper.h       |  106 +++++------
 target-ppc/helper.h        |   38 ++--
 target-s390x/helper.h      |   76 ++++----
 target-sh4/helper.h        |    6 +-
 target-sparc/helper.h      |   50 ++---
 target-xtensa/helper.h     |   16 +-
 tcg/README                 |   22 ++-
 tcg/optimize.c             |    3 +-
 tcg/tcg-op.h               |   18 +-
 tcg/tcg-opc.h              |   29 ++-
 tcg/tcg.c                  |  449 +++++++++++++++++++++++++++-----------------
 tcg/tcg.h                  |   29 ++-
 17 files changed, 595 insertions(+), 469 deletions(-)

-- 
1.7.10.4