> On Jul 18, 2017, at 10:40 AM, Johannes Weiß <[email protected]> wrote:
>
> Thanks, both suggestions look great. Will work them in tomorrow and will also
> try to add a test for the whole thing.
>
>> On 18 Jul 2017, at 5:53 pm, Michael Gottesman <[email protected]> wrote:
>>
>>>
>>> On Jul 18, 2017, at 8:39 AM, Johannes Weiß <[email protected]> wrote:
>>>
>>> Hi Erik,
>>>
>>>> On 17 Jul 2017, at 10:26 pm, Erik Eckstein <[email protected]> wrote:
>>>>
>>>> Hi Johannes,
>>>>
>>>> great that you want to work on this!
>>>
>>> Thanks for your help, without Michael's and your help I wouldn't have been
>>> able to do anything here really!
>>>
>>>
>>>> Some ideas:
>>>> SideEffectAnalysis currently does not have a notion of “this argument is
>>>> not modified by the callee” if the callee is unknown or does anything
>>>> non-trivial.
>>>> Therefore I think it’s best to put the in_guarantee check directly into
>>>> MemoryBehaviorVisitor::visitApplyInst():
>>>> If the parameter convention is in_guaranteed and the parameter is V, then
>>>> the behavior can be MemBehavior::MayRead
>>>
>>>
>>> Thanks, that actually makes a lot of sense. Here's my diff right now
>>>
>>> diff --git a/lib/SILOptimizer/Analysis/MemoryBehavior.cpp
>>> b/lib/SILOptimizer/Analysis/MemoryBehavior.cpp
>>> index b1fe7fa665..c44cc64f94 100644
>>> --- a/lib/SILOptimizer/Analysis/MemoryBehavior.cpp
>>> +++ b/lib/SILOptimizer/Analysis/MemoryBehavior.cpp
>>> @@ -245,6 +245,23 @@ MemBehavior
>>> MemoryBehaviorVisitor::visitApplyInst(ApplyInst *AI) {
>>> (InspectionMode == RetainObserveKind::ObserveRetains &&
>>> ApplyEffects.mayAllocObjects())) {
>>> Behavior = MemBehavior::MayHaveSideEffects;
You should move your new code out of the if (ApplyEffects.mayReadRC() ...
Otherwise it will not be executed if the called function does not read a
reference count.
Beside that it looks good to me.
>>> +
>>> + unsigned Idx = 0;
>>> + bool AllReadOnly = false;
>>> + for (Operand &operand : AI->getArgumentOperands()) {
>>> + if (operand.get() == V &&
>>> AI->getOrigCalleeType()->getParameters()[Idx].isIndirectInGuaranteed()) {
>>> + AllReadOnly = true;
>>> + } else {
>>> + AllReadOnly = false;
>>> + break;
>>> + }
>>> +
>>> + Idx++;
>>> + }
>>> +
>>> + if (AllReadOnly) {
>>> + Behavior = MemBehavior::MayRead;
>>> + }
>>
>> Suggestion:
>>
>> if (all_of(enumerate(AI->getArgumentOperands()),
>> [&](std::pair<unsigned, SILValue> pair) -> bool {
>> return pair.second.get() == V &&
>> AI->getOrigCalleeType()->getParameters()[Idx].isIndirectInGuaranteed()
>> })) {
>> Behavior = MemBehavior::MayRead;
>> }
>>
>> I may have gotten the order of the pair templates wrong. But something like
>> this is a little cleaner.
>>
>> Michael
>>
>>> } else {
>>> auto &GlobalEffects = ApplyEffects.getGlobalEffects();
>>> Behavior = GlobalEffects.getMemBehavior(InspectionMode);
>>>
>>> which indeed turns
>>>
>>> --- SNIP ---
>>> sil @bar : $@convention(thin) (@in Int) -> () {
>>> bb0(%0 : $*Int):
>>> %value_raw = integer_literal $Builtin.Int64, 42
>>> %value = struct $Int (%value_raw : $Builtin.Int64)
>>> store %value to %0 : $*Int
>>>
>>> %f_buz = function_ref @buz : $@convention(thin) (@in_guaranteed Int) -> ()
>>> %r1 = apply %f_buz(%0) : $@convention(thin) (@in_guaranteed Int) -> ()
>>>
>>> %value_again = load %0 : $*Int
>>> %f_test = function_ref @test : $@convention(thin) (Int) -> ()
>>> %r2 = apply %f_test(%value_again) : $@convention(thin) (Int) -> ()
>>>
>>> /*
>>> %f_bad = function_ref @bad : $@convention(thin) (@in_guaranteed Int) -> ()
>>> %r3 = apply %f_bad(%0) : $@convention(thin) (@in_guaranteed Int) -> ()
>>>
>>> %value_again2 = load %0 : $*Int
>>> %r4 = apply %f_test(%value_again2) : $@convention(thin) (Int) -> ()
>>> */
>>>
>>> %9999 = tuple()
>>> return %9999 : $()
>>> }
>>> --- SNAP ---
>>>
>>> into
>>>
>>> --- SNIP ---
>>> bb0(%0 : $*Int):
>>> %1 = integer_literal $Builtin.Int64, 42 // user: %2
>>> %2 = struct $Int (%1 : $Builtin.Int64) // users: %7, %3
>>> store %2 to %0 : $*Int // id: %3
>>> // function_ref buz
>>> %4 = function_ref @buz : $@convention(thin) (@in_guaranteed Int) -> () //
>>> user: %5
>>> %5 = apply %4(%0) : $@convention(thin) (@in_guaranteed Int) -> ()
>>> // function_ref test
>>> %6 = function_ref @test : $@convention(thin) (Int) -> () // user: %7
>>> %7 = apply %6(%2) : $@convention(thin) (Int) -> ()
>>> %8 = tuple () // user: %9
>>> return %8 : $() // id: %9
>>> } // end sil function 'bar'
>>> --- SNAP ---
>>>
>>> so the load has successfully been eliminated. Also taking my initial repro
>>> [1], the retain, the load, and the release are now gone 😃.
>>>
>>> Is that roughly what you were thinking of?
>>>
>>> Many thanks,
>>> Johannes
>>>
>>> [1]: https://bugs.swift.org/secure/attachment/12378/test.swift
>>>
>>>>
>>>> Erik
>>>>
>>>>> On Jul 17, 2017, at 9:23 AM, Johannes Weiß <[email protected]>
>>>>> wrote:
>>>>>
>>>>> Thanks Michael!
>>>>>
>>>>> Erik, I hope what I wrote makes some sense. Any questions or suggestions,
>>>>> please let me know.
>>>>>
>>>>>> On 14 Jul 2017, at 7:30 pm, Michael Gottesman <[email protected]>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>> On Jul 12, 2017, at 9:53 AM, Johannes Weiß <[email protected]>
>>>>>>> wrote:
>>>>>>>
>>>>>>> Hi Michael,
>>>>>>>
>>>>>>>
>>>>>>>> [...]
>>>>>>>>> Long story short, I think the RLE actually works for the test case I
>>>>>>>>> created. It's even clever enough to see through my invalid function
>>>>>>>>> bad() which modified the storage despite its claim that it doesn't. I
>>>>>>>>> might also be misunderstanding something.
>>>>>>>>
>>>>>>>> When something is marked as in_guaranteed, it should be immutable. If
>>>>>>>> the callee violates that, then the SIL is malformed. Perhaps, we can
>>>>>>>> add some sort of verification check.
>>>>>>>
>>>>>>> Right, yes I was aware that that'd be illegal but I added it as a way
>>>>>>> to check whether this optimisation is 'looking into' the called
>>>>>>> function.
>>>>>>>
>>>>>>>
>>>>>>>> That being said, I have a good feeling that there is some sort of
>>>>>>>> analysis occuring here since you provided enough information to the
>>>>>>>> optimizer. The optimization here is regardless of whether or not we
>>>>>>>> can see the body of a function, we know that it is safe to optimize
>>>>>>>> this just based off the @in_guaranteed. This implies using a
>>>>>>>> declaration, not a definition of the bad function.
>>>>>>>
>>>>>>> makes sense, didn't think about just only declaring it...
>>>>>>>
>>>>>>>
>>>>>>>> When I said write the SIL by hand, what I meant was writing the whole
>>>>>>>> program by hand. In general, we prefer SIL programs that do not have
>>>>>>>> extraneous stuff that is added by the compiler (for instance
>>>>>>>> debug_value). Additionally, it is important for SIL files to not have
>>>>>>>> dependencies on the stdlib unless absolutely necessary (i.e. your
>>>>>>>> usage of Int). This prevents the stdlib maintainers from having to
>>>>>>>> update these tests given chances to the stdlib. Below is a cleaned up
>>>>>>>> version that shows the problem. Look at how small it is and how it
>>>>>>>> tests /exactly/ what we are trying to test and via the use of
>>>>>>>> declarations and the like we are able to exclude other optimizations:
>>>>>>>
>>>>>>> That makes a lot of sense, thank you. I wasn't yet that familiar with
>>>>>>> SIL so I thought I start from a program generated by the compiler and
>>>>>>> then replace the guts with handwritten SIL. But your version is clearly
>>>>>>> a lot easier to understand and shows what precisely we want to see!
>>>>>>>
>>>>>>> Today, I looked into why this is happening more precisely.
>>>>>>>
>>>>>>> So we don't get the RLE because in this code
>>>>>>>
>>>>>>> if (isComputeAvailValue(Kind) || isPerformingRLE(Kind)) {
>>>>>>> for (unsigned i = 0; i < Locs.size(); ++i) {
>>>>>>> if (isTrackingLocation(ForwardSetIn, Ctx.getLocationBit(Locs[i])))
>>>>>>> continue;
>>>>>>> updateForwardSetAndValForRead(Ctx, Ctx.getLocationBit(Locs[i]),
>>>>>>> Ctx.getValueBit(Vals[i]));
>>>>>>> // We can not perform the forwarding as we are at least missing
>>>>>>> // some pieces of the read location.
>>>>>>> CanForward = false;
>>>>>>>
>>>>>>> (https://github.com/apple/swift/blob/86620aaa7ebd32d33f4cdf61add5c63a72d3f02a/lib/SILOptimizer/Transforms/RedundantLoadElimination.cpp#L917)
>>>>>>>
>>>>>>> we're not taking the `continue` for the call to `buz()`. The reason why
>>>>>>> is that here
>>>>>>>
>>>>>>> if (!AA->mayWriteToMemory(I, R.getBase()))
>>>>>>> continue;
>>>>>>> // MayAlias.
>>>>>>> stopTrackingLocation(ForwardSetIn, i);
>>>>>>> stopTrackingValue(ForwardValIn, i);
>>>>>>>
>>>>>>> (https://github.com/apple/swift/blob/86620aaa7ebd32d33f4cdf61add5c63a72d3f02a/lib/SILOptimizer/Transforms/RedundantLoadElimination.cpp#L972)
>>>>>>>
>>>>>>> we're not taking the `continue`, ie. `AA->mayWriteToMemory(I,
>>>>>>> R.getBase())` is true. The reason for that is that the `SILFunction`
>>>>>>> for `buz` has
>>>>>>>
>>>>>>> EffectsKindAttr = Unspecified
>>>>>>>
>>>>>>> which equates to `MayHaveSideEffects`, that's also what
>>>>>>> `-debug-only=sil-redundant-load-elim,sil-membehavior` outputs:
>>>>>>>
>>>>>>> GET MEMORY BEHAVIOR FOR:
>>>>>>> %5 = apply %4(%0) : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>> %0 = argument of bb0 : $*Int // users: %6, %5, %3
>>>>>>> Found apply, returning MayHaveSideEffects
>>>>>>>
>>>>>>>
>>>>>>> So where I'm stuck today is that I'm not sure how `EffectsKindAttr` is
>>>>>>> actually defined. Sure, `$@convention(thin) (@in_guaranteed Int) -> ()`
>>>>>>> doesn't actually write to the `@in_guaranteed Int` (as that'd be
>>>>>>> illegal) but it may have other side effects. So I'm not sure if we can
>>>>>>> just create the function differently if we find only "read-only" kind
>>>>>>> of parameters. That'd be I think in
>>>>>>>
>>>>>>>
>>>>>>> auto *fn = SILMod.createFunction(SILLinkage::Private, Name.str(), Ty,
>>>>>>> nullptr, loc, IsNotBare,
>>>>>>> IsNotTransparent, IsNotSerialized);
>>>>>>>
>>>>>>> (https://github.com/apple/swift/blob/ec6fc4d54db95f78ae72dab29734533f709ea2d7/lib/Parse/ParseSIL.cpp#L508
>>>>>>> ->
>>>>>>> https://github.com/apple/swift/blob/157db57506b813837481b574a9d38e806bf954b6/lib/SIL/SILModule.cpp#L249)
>>>>>>>
>>>>>>> which doesn't specify any EffectsAttrKind and therefore it defaults to
>>>>>>> `Unspecified`.
>>>>>>>
>>>>>>>
>>>>>>> Just as a test, I did put a `[readonly]` in `sil @buz :
>>>>>>> $@convention(thin) (@in_guaranteed Int) -> ()` and as expected
>>>>>>> everything propagates through correctly and we get a successful RLE.
>>>>>>>
>>>>>>> So yes, maybe you have some pointers on where to best educate the
>>>>>>> compiler that the `buz` function won't write to that bit of memory.
>>>>>>
>>>>>> I have a few ideas of where to put it, but really the person to bring in
>>>>>> here is Erik. He is the one who wrote the side-effect part of the
>>>>>> optimizer. Keep in mind he is on vacation right now until next week. So
>>>>>> I wouldn't expect a response until then.
>>>>>>
>>>>>> Michael
>>>>>>
>>>>>>>
>>>>>>> Many thanks,
>>>>>>> Johannes
>>>>>>>
>>>>>>>>
>>>>>>>> ----
>>>>>>>> sil_stage canonical
>>>>>>>>
>>>>>>>> import Builtin
>>>>>>>>
>>>>>>>> struct Int {
>>>>>>>> var _value : Builtin.Int64
>>>>>>>> }
>>>>>>>>
>>>>>>>> sil @test : $@convention(thin) (Int) -> ()
>>>>>>>> sil @buz : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>>> sil @bad : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>>>
>>>>>>>> sil @bar : $@convention(thin) (@in Int) -> () {
>>>>>>>> bb0(%0 : $*Int):
>>>>>>>> %value_raw = integer_literal $Builtin.Int64, 42
>>>>>>>> %value = struct $Int (%value_raw : $Builtin.Int64)
>>>>>>>> store %value to %0 : $*Int
>>>>>>>>
>>>>>>>> %f_buz = function_ref @buz : $@convention(thin) (@in_guaranteed Int)
>>>>>>>> -> ()
>>>>>>>> %r1 = apply %f_buz(%0) : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>>>
>>>>>>>> %value_again = load %0 : $*Int
>>>>>>>> %f_test = function_ref @test : $@convention(thin) (Int) -> ()
>>>>>>>> %r2 = apply %f_test(%value_again) : $@convention(thin) (Int) -> ()
>>>>>>>>
>>>>>>>> %f_bad = function_ref @bad : $@convention(thin) (@in_guaranteed Int)
>>>>>>>> -> ()
>>>>>>>> %r3 = apply %f_bad(%0) : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>>>
>>>>>>>> %value_again2 = load %0 : $*Int
>>>>>>>> %r4 = apply %f_test(%value_again2) : $@convention(thin) (Int) -> ()
>>>>>>>>
>>>>>>>> %9999 = tuple()
>>>>>>>> return %9999 : $()
>>>>>>>> }
>>>>>>>> ----
>>>>>>>>
>>>>>>>> When I run this test file through rle, I get:
>>>>>>>>
>>>>>>>> ----
>>>>>>>> sil_stage canonical
>>>>>>>>
>>>>>>>> import Builtin
>>>>>>>> import Swift
>>>>>>>> import SwiftShims
>>>>>>>>
>>>>>>>> struct Int {
>>>>>>>> @sil_stored var _value: Builtin.Int64
>>>>>>>> init(_value: Builtin.Int64)
>>>>>>>> }
>>>>>>>>
>>>>>>>> // test
>>>>>>>> sil @test : $@convention(thin) (Int) -> ()
>>>>>>>>
>>>>>>>> // buz
>>>>>>>> sil @buz : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>>>
>>>>>>>> // bad
>>>>>>>> sil @bad : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>>>
>>>>>>>> // bar
>>>>>>>> sil @bar : $@convention(thin) (@in Int) -> () {
>>>>>>>> // %0 // users: %11, %10,
>>>>>>>> %6, %5, %3
>>>>>>>> bb0(%0 : $*Int):
>>>>>>>> %1 = integer_literal $Builtin.Int64, 42 // user: %2
>>>>>>>> %2 = struct $Int (%1 : $Builtin.Int64) // user: %3
>>>>>>>> store %2 to %0 : $*Int // id: %3
>>>>>>>> // function_ref buz
>>>>>>>> %4 = function_ref @buz : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>>> // user: %5
>>>>>>>> %5 = apply %4(%0) : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>>> %6 = load %0 : $*Int // user: %8
>>>>>>>> // function_ref test
>>>>>>>> %7 = function_ref @test : $@convention(thin) (Int) -> () // users:
>>>>>>>> %12, %8
>>>>>>>> %8 = apply %7(%6) : $@convention(thin) (Int) -> ()
>>>>>>>> // function_ref bad
>>>>>>>> %9 = function_ref @bad : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>>> // user: %10
>>>>>>>> %10 = apply %9(%0) : $@convention(thin) (@in_guaranteed Int) -> ()
>>>>>>>> %11 = load %0 : $*Int // user: %12
>>>>>>>> %12 = apply %7(%11) : $@convention(thin) (Int) -> ()
>>>>>>>> %13 = tuple () // user: %14
>>>>>>>> return %13 : $() // id: %14
>>>>>>>> } // end sil function 'bar'
>>>>>>>> ----
>>>>>>>>
>>>>>>>> Michael
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Does that all make sense?
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>> Johannes
>>>>>>>>> <test-load-forwarding.sil><test-load-forwarding.sil-opt>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Thanks,
>>>>>>>>>>> Johannes
>>>>>>>>>>>
>>>>>>>>>>> [1]: https://bugs.swift.org/browse/SR-5403
>
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