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.
v1 -> v2
--------
- patch 3: changed TEMP_VAL_CONST to fallthrough into TEMP_VAL_REG
- patch 7: fixed ts->mem_coherent = 1 in const case
factorized ots->fixed_reg & ts->val_type == TEMP_VAL_CONST
case in the first if block
changed comments for the first block
- patch 10: move wrong hunk to patch 7
- patch 12: new patch
- patch 14: should be considered as a new patch
- patches 15-26: new patches
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 | 453 +++++++++++++++++++++++++++-----------------
tcg/tcg.h | 29 ++-
17 files changed, 597 insertions(+), 471 deletions(-)
--
1.7.10.4
