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Re: [Qemu-devel] [PATCH v3 00/26] tcg: rework liveness analysis and regi
From: |
Richard Henderson |
Subject: |
Re: [Qemu-devel] [PATCH v3 00/26] tcg: rework liveness analysis and register allocator |
Date: |
Mon, 22 Oct 2012 06:35:06 +1000 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121016 Thunderbird/16.0.1 |
On 2012-10-20 07:38, Aurelien Jarno wrote:
> 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
Reviewed-by: Richard Henderson <address@hidden>
It all looks good.
r~
>
> 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(-)
>
- [Qemu-devel] [PATCH v3 19/26] target-microblaze: rename helper flags, (continued)
- [Qemu-devel] [PATCH v3 19/26] target-microblaze: rename helper flags, Aurelien Jarno, 2012/10/19
- [Qemu-devel] [PATCH v3 14/26] tcg: rework TCG helper flags, Aurelien Jarno, 2012/10/19
- [Qemu-devel] [PATCH v3 04/26] tcg: sync output arguments on liveness request, Aurelien Jarno, 2012/10/19
- [Qemu-devel] [PATCH v3 03/26] tcg: add temp_sync(), Aurelien Jarno, 2012/10/19
- [Qemu-devel] [PATCH v3 08/26] tcg: always mark dead input arguments as dead, Aurelien Jarno, 2012/10/19
- [Qemu-devel] [PATCH v3 12/26] tcg: forbid ld/st function to modify globals, Aurelien Jarno, 2012/10/19
- [Qemu-devel] [PATCH v3 13/26] tcg: synchronize globals for ops with side effects, Aurelien Jarno, 2012/10/19
- [Qemu-devel] [PATCH v3 10/26] tcg: don't explicitly save globals and temps, Aurelien Jarno, 2012/10/19
- [Qemu-devel] [PATCH v3 16/26] target-arm: rename helper flags, Aurelien Jarno, 2012/10/19
- [Qemu-devel] [PATCH v3 22/26] target-s390x: rename helper flags, Aurelien Jarno, 2012/10/19
- Re: [Qemu-devel] [PATCH v3 00/26] tcg: rework liveness analysis and register allocator,
Richard Henderson <=