[PATCH][MIPS] Enable load-load/store-store bonding

[sameera]

Hi!

Sorry for delay in sending this patch for review.
Please find attached updated patch.

In P5600, 2 consecutive loads/stores of same type which access contiguous memory locations are bonded together by instruction issue unit to dispatch 
single load/store instruction which accesses both locations. This allows 2X improvement in memory intensive code. This optimization can be performed 
for LH, SH, LW, SW, LWC, SWC, LDC, SDC instructions.

This patch adds peephole2 patterns to identify such loads/stores, and put them in parallel, so that the scheduler will not split it - thereby 
guaranteeing h/w level load/store bonding.

The patch is tested with dejagnu for correctness, and tested on hardware for performance.
Ok for trunk?

Changelog:
gcc/
         * config/mips/mips.md (JOIN_MODE): New mode iterator.
	(join2_load_Store<JOIN_MODE:mode>): New pattern.
	(join2_loadhi): Likewise.
	(define_peehole2): Add peephole2 patterns to join 2 HI/SI/SF/DF-mode
	load-load and store-stores.
	* config/mips/mips.opt (mload-store-pairs): New option.
	(TARGET_LOAD_STORE_PAIRS): New macro.
	*config/mips/mips.h (ENABLE_LD_ST_PAIRS): Likewise.
	*config/mips/mips-protos.h (mips_load_store_bonding_p): New prototype.
	*config/mips/mips.c(mips_load_store_bonding_p): New function.

- Thanks and regards,
   Sameera D.

On Tuesday 24 June 2014 04:12 PM, Sameera Deshpande wrote:
> Hi Richard,
>
> Thanks for the review.
> Please find attached updated patch after your review comments.
>
> Changelog:
> gcc/
> 	* config/mips/mips.md (JOIN_MODE): New mode iterator.
> 	(join2_load_Store<JOIN_MODE:mode>): New pattern.
> 	(join2_loadhi): Likewise.
> 	(define_peehole2): Add peephole2 patterns to join 2 HI/SI/SF/DF-mode
> 	load-load and store-stores.
> 	* config/mips/mips.opt (mload-store-pairs): New option.
> 	(TARGET_LOAD_STORE_PAIRS): New macro.
> 	*config/mips/mips.h (ENABLE_P5600_LD_ST_PAIRS): Likewise.
> 	*config/mips/mips-protos.h (mips_load_store_bonding_p): New prototype.
> 	*config/mips/mips.c(mips_load_store_bonding_p): New function.
>
> The change is tested with dejagnu with additional options -mload-store-pairs and -mtune=p5600.
> The perf measurement is yet to finish.
>
>>> We had offline discussion based on your comment. There is additional
>>> view on the same.
>>> Only ISAs mips32r2, mips32r3 and mips32r5 support P5600. Remaining
>>> ISAs do not support P5600.
>>> For mips32r2 (24K) and mips32r3 (micromips), load-store pairing is
>>> implemented separately, and hence, as you suggested, P5600 Ld-ST
>>> bonding optimization should not be enabled for them.
>>> So, is it fine if I emit error for any ISAs other than mips32r2,
>>> mips32r3 and mips32r5 when P5600 is enabled, or the compilation should
>>> continue by emitting warning and disabling P5600?
>>
>> No, the point is that we have two separate concepts: ISA and optimisation
>> target.  -mipsN and -march=N control the ISA (which instructions are
>> available) and -mtune=M controls optimisation decisions within the
>> constraints of that N, such as scheduling and the cost of things like
>> multiplication and division.
>>
>> E.g. you could have -mips2 -mtune=p5600 -mfix-24k: generate MIPS II-
>> compatible code, optimise it for p5600, but make sure that 24k workarounds
>> are used.  The code would run correctly on any MIPS II-compatible processor
>> without known errata and also on the 24k.
> Ok, disabled the peephole pattern for fix-24k and micromips - to allow specific patterns to be matched.
>
>>> +
>>> +mld-st-pairing
>>> +Target Report Var(TARGET_ENABLE_LD_ST_PAIRING) Enable load/store
>>> +pairing
>>
>> Other options are just "TARGET_" + the captialised form of the option name,
>> so I'd prefer TARGET_LD_ST_PAIRING instead.  Although "ld" might be
>> misleading since it's an abbreviation for "load" rather than the LD instruction.
>> Maybe -mload-store-pairs, since plurals are more common than "-ing"?
>> Not sure that's a great suggestion though.
> Renamed the option and corresponding macro as suggested.
>
>>> Performance testing for this patch is not yet done.
>>> If the patch proves beneficial in most of the testcases (which we
>>> believe will do on P5600) we will enable this optimization by default
>>> for P5600 - in which case this option can be removed.
>>
>> OK.  Sending the patch for comments before performance testing is fine, but
>> I think it'd be better to commit the patch only after the testing is done, since
>> otherwise the patch might need to be tweaked.
>>
>> I don't see any problem with keeping the option in case people want to
>> experiment with it.  I just think the patch should only go in once it can be
>> enabled by default for p5600.  I.e. the option would exist to turn off the
>> pairing.
>>
>> Not having the option is fine too of course.
> Yes, after perf analysis, I will share the results across, and then depending upon the impact, the decision can be made - whether to make the option as default or not, and then the patch will be submitted.
>
>> We should allow pairing even without -mtune=p5600.
> The load-store pairing is currently attribute of P5600, so I have not enabled the pairing without mtune=5600. If need be, can enable that without mtune=p5600.
>
>>
>> (define_mode_iterator JOIN_MODE [
>>    SI
>>    (DI "TARGET_64BIT")
>>    (SF "TARGET_HARD_FLOAT")
>>    (DF "TARGET_HARD_FLOAT && TARGET_DOUBLE_FLOAT")])
>>
> Done this change.
>
>> and then extend:
>>
>>> @@ -883,6 +884,8 @@
>>>   (define_mode_attr loadx [(SF "lwxc1") (DF "ldxc1") (V2SF "ldxc1")])
>>> (define_mode_attr storex [(SF "swxc1") (DF "sdxc1") (V2SF "sdxc1")])
>>>
>>> +(define_mode_attr insn_type [(SI "") (SF "fp") (DF "fp")])
>>> +
>>>   ;; The unextended ranges of the MIPS16 addiu and daddiu instructions
>>> ;; are different.  Some forms of unextended addiu have an 8-bit
>>> immediate  ;; field but the equivalent daddiu has only a 5-bit field.
>>
>> this accordingly.
> In order to allow d/f for both register classes, the pattern join2_load_store<mode> was altered a bit which eliminated this mode iterator.
>
>>
>> Outer (parallel ...)s are redundant in a define_insn.
> Removed.
>
>>
>> It would be better to add the mips_load_store_insns for each operand
>> rather than multiplying one of them by 2.  Or see the next bit for an
>> alternative.
> Using the alternative method as you suggested, so this change is not needed.
>
>> Please instead add HI to the define_mode_iterator so that we can use the
>> same peephole and define_insn.
> Added HI in the mode iterator to eliminate join2_storehi pattern and corresponding peephole2.
> As arithmetic operations on HImode is not supported, we generate zero or sign extended loads in such cases.
> To handle that case, join2_loadhi pattern is kept.
>
> - Thanks and regards,
>     Sameera D.
>
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