Is it possible to merge them?
> On Dec 21, 2017, at 11:07 AM, Raj Barik via swift-dev <swift-dev@swift.org>
> wrote:
>
> Hi,
>
> Thanks.
>
>
> Are you implementing it as a separate pass, or is it part of function
> signature specialization?
>
>
> I am currently implementing this as a separate pass. There is some code
> overlap between the two (FunctionSignatureOpt and ProtocolDevirtualizerOpt)
> in terms of checking which functions can be optimized. Barring that, the code
> is quite different even though they follow the same pattern (thunk and a
> separate function).
>
> --Raj
>
>
>
> Slava
>
>>
>> @inline(never) internal func wrap_inc_optional(a:SumProtocol?, val:Int) ->
>> Int?{
>> return a?.increment(i:val)
>> }
>>
>> The generated SIL looks something like this:
>>
>> sil hidden [noinline]
>> @_T04main21wrap_inc_optionalSiSgAA11SumProtocol_pSg1a_Si3valtF :
>> $@convention(thin) (@owned Optional<SumProtocol>, Int) -> Optional<Int> {
>> // %0 // users: %11, %4, %7, %2
>> // %1 // users: %10, %3
>> bb0(%0 : $Optional<SumProtocol>, %1 : $Int):
>> debug_value %0 : $Optional<SumProtocol>, let, name "a", argno 1 // id: %2
>> debug_value %1 : $Int, let, name "val", argno 2 // id: %3
>> switch_enum %0 : $Optional<SumProtocol>, case #Optional.some!enumelt.1:
>> bb2, case #Optional.none!enumelt: bb1 // id: %4
>>
>> bb1: // Preds: bb0
>> %5 = enum $Optional<Int>, #Optional.none!enumelt // user: %6
>> br bb3(%5 : $Optional<Int>) // id: %6
>>
>> bb2: // Preds: bb0
>> %7 = unchecked_enum_data %0 : $Optional<SumProtocol>,
>> #Optional.some!enumelt.1 // user: %8
>> %8 = open_existential_ref %7 : $SumProtocol to
>> $@opened("F0395A0A-E5DE-11E7-A06A-420039484801") SumProtocol // users: %10,
>> %10, %9
>> %9 = witness_method $@opened("F0395A0A-E5DE-11E7-A06A-420039484801")
>> SumProtocol, #SumProtocol.increment!1 : <Self where Self : SumProtocol>
>> (Self) -> (Int) -> Int, %8 :
>> $@opened("F0395A0A-E5DE-11E7-A06A-420039484801") SumProtocol :
>> $@convention(witness_method) <τ_0_0 where τ_0_0 : SumProtocol> (Int,
>> @guaranteed τ_0_0) -> Int // type-defs: %8; user: %10
>> %10 = apply %9<@opened("F0395A0A-E5DE-11E7-A06A-420039484801")
>> SumProtocol>(%1, %8) : $@convention(witness_method) <τ_0_0 where τ_0_0 :
>> SumProtocol> (Int, @guaranteed τ_0_0) -> Int // type-defs: %8; user: %12
>> release_value %0 : $Optional<SumProtocol> // id: %11
>> %12 = enum $Optional<Int>, #Optional.some!enumelt.1, %10 : $Int // user:
>> %13
>> br bb3(%12 : $Optional<Int>) // id: %13
>>
>> // %14 // user: %15
>> bb3(%14 : $Optional<Int>): // Preds: bb1 bb2
>> return %14 : $Optional<Int> // id: %15
>>
>>
>> The above branching code (in red) in the SIL makes it non-trivial to
>> abstract out the non-nil path to a generic outlined method while keeping the
>> branching code in the thunk and also its not clear if the SILCombiner
>> peephole optimizer will actually come into affect for this scenario (because
>> of the branching code getting inlined in the caller). It also gets more
>> complicated if there are more than one optional types as parameter to
>> wrap_inc_optional. Any clue on how one can handle optional types for
>> devirtualization or if there are any existing transformations in Swift
>> compiler that can help implement this easily? Thanks.
>>
>> -R
>>
>>
>>
>> On Wed, Dec 13, 2017 at 3:28 PM, Arnold Schwaighofer
>> <aschwaigho...@apple.com> wrote:
>> You don’t need a second open_existential_ref in the _wrap_inc<T:
>> SumProtocol> function. It should look something like this:
>>
>> sil @_wrap_inc : $@convention(thin) <T where T : SumProtocol> (@owned T,
>> Int) -> Int {
>> bb0(%0 : $T, %1 : $Int):
>> %5 = witness_method $T, #SumProtocol.inc!1 : <Self where Self :
>> SumProtocol> (Self) -> (Int) -> Int : $@convention(witness_method:
>> SumProtocol) <τ_0_0 where τ_0_0 : SumProtocol> (Int, @guaranteed τ_0_0) ->
>> Int
>> %6 = apply %5<T>(%1, %0) : $@convention(witness_method: SumProtocol)
>> <τ_0_0 where τ_0_0 : SumProtocol> (Int, @guaranteed τ_0_0) -> Int
>> destroy_value %0 : $T
>> return %6 : $Int
>> }
>>
>> In the other function it looks like you need to apply the proper
>> substitution list to the apply instruction:
>>
>> sil hidden [thunk] [always_inline]
>> @_T04main8wrap_incSiAA11SumProtocol_p1a_Si3valtF : $@convention(thin)
>> (@owned SumProtocol, Int) -> Int {
>> bb0(%0 : $SumProtocol, %1 : $Int):
>> // function_ref specialized wrap_inc(a:val:)
>> %2 = function_ref @_T04main8wrap_incSiAA11SumProtocol_p1a_Si3valtFTf4nn_n
>> %3 = open_existential_ref %0 : $SumProtocol to
>> $@opened("E6196082-DF72-11E7-8C84-420039484801") SumProtocol
>> %4 = apply %2<τ_0_0>(%3, %1) : $@convention(thin) <τ_0_0 where τ_0_0 :
>> SumProtocol> (@owned τ_0_0, Int) -> Int // user: %5
>>
>> τ_0_0 should have been substituted by the opened type:
>> $@opened("E6196082-DF72-11E7-8C84-420039484801”) SumProtocol.
>>
>> %3 = open_existential_ref %0 : $SumProtocol to
>> $@opened("E6196082-DF72-11E7-8C84-420039484801") SumProtocol
>> %4 = apply %2<@opened("E6196082-DF72-11E7-8C84-420039484801”)
>> SumProtocol>(%3, %1) : $@convention(thin) <τ_0_0 where τ_0_0 : SumProtocol>
>> (@owned τ_0_0, Int) -> Int
>>
>>
>> Probably, you have to pass the right SubstitutionList to the createApplyInst
>> call.
>>
>>
>> The peephole that propagates types from an init existential Slava referred
>> to is here:
>>
>>
>> https://github.com/apple/swift/blob/master/lib/SILOptimizer/SILCombiner/SILCombinerApplyVisitors.cpp#L974
>> (SILCombiner::propagateConcreteTypeOfInitExistential)
>>
>> Here is a test case that shows how the type from the init existential is
>> propagated (instead of a generic type ’T’ as in the test case, in your case
>> it would be the class type SumClass):
>>
>>
>> https://github.com/apple/swift/blob/master/test/SILOptimizer/sil_combine.sil#L2569
>>
>> > On Dec 13, 2017, at 11:39 AM, Raj Barik via swift-dev
>> > <swift-dev@swift.org> wrote:
>> >
>> > Slava,
>> >
>> > I have two (clarification) questions in your proposed implementation:
>> >
>> > Original Function:
>> > @inline(never) internal func wrap_inc(a:SumProtocol, val:Int) -> Int{
>> > return a.increment(i:val)
>> > }
>> > Transformed code:
>> > @inline(always) internal func wrap_inc(a: SumProtocol, val: Int) -> Int {
>> > // opening an existential cannot be expressed in Swift, but it can in
>> > SIL…
>> > let _a = a open as T
>> >
>> > return _wrap_inc(_a, val)
>> > }
>> >
>> > @inline(never) internal func _wrap_inc<T : SumProtocol>(_a:T, val:Int) ->
>> > Int{
>> > return _a.increment(i:val)
>> > }
>> > ****************************************************************************************
>> > In the above code sequence, did you mean that "let _a = a open as T" opens
>> > "a:SumProtocol" using open_existential_ref instruction as "SumClass"
>> > which is the concrete type of a or it is opened as the "$@opened
>> > SumProtocol". In both cases, the open_existential_ref in the original
>> > function is still there and giving rise to opening the existential twice.
>> > Did you also intended that the _wrap_inc function is rewritten to
>> > eliminate the open_existential_ref as well (this is more complicated if
>> > the protocol is passed down a call chain)? So, I do not really understand
>> > what the "let _a = a open as T" is suggesting. The other part of the
>> > confusion is about the peephole optimization which optimizes the code
>> > sequence consisting of the creation of object for SumClass and then the
>> > init_existential_ref and followed by the open_existential_ref. Can you
>> > clarify?
>> >
>> > Thanks.
>> >
>> >
>> > On Wed, Nov 29, 2017 at 1:43 PM, Slava Pestov <spes...@apple.com> wrote:
>> > Hi Raj,
>> >
>> > The way I would approach this problem is first, turn a function taking a
>> > protocol value into one taking a protocol-constrained generic parameter. So
>> >
>> > @inline(never) internal func wrap_inc(a:SumProtocol, val:Int) -> Int{
>> > return a.increment(i:val)
>> > }
>> >
>> > Would become
>> >
>> > @inline(always) internal func wrap_inc(a: SumProtocol, val: Int) -> Int {
>> > // opening an existential cannot be expressed in Swift, but it can in
>> > SIL…
>> > let _a = a open as T
>> >
>> > return _wrap_inc(_a, val)
>> > }
>> >
>> > @inline(never) internal func _wrap_inc<T : SumProtocol>(_a:T, val:Int) ->
>> > Int{
>> > let a: SomeProtocol = _a
>> > return a.increment(i:val)
>> > }
>> >
>> > (Note that the existing function signature specialization pass performs a
>> > similar transformation where it creates a new function with the same body
>> > as the old function but a different signature, and replaces the old
>> > function with a short thunk that transforms arguments and results and
>> > calls the new function.)
>> >
>> > At this point, the existing “initialize existential with concrete type”
>> > peephole in the SILCombiner should eliminate the existential (but the
>> > peephole doesn’t work in 100% of cases yet):
>> >
>> > @inline(always) internal func wrap_inc(a: SumProtocol, val: Int) -> Int {
>> > // opening an existential cannot be expressed in Swift, but it can in
>> > SIL…
>> > let _a = a open as T
>> >
>> > return _wrap_inc(_a, val)
>> > }
>> >
>> > @inline(never) internal func _wrap_inc<T : SumProtocol>(_a:T, val:Int) ->
>> > Int{
>> > return _a.increment(i:val)
>> > }
>> >
>> > Now, if I have a call to wrap_inc somewhere,
>> >
>> > internal let magic:SumProtocol = SumClass(base:10)
>> > _ = wrap_inc(magic)
>> >
>> > Then the optimizer will inline the thunk, giving you a call to _wrap_inc.
>> > The existential value built from the SumClass instance is immediately
>> > opened so it will be peepholed away. At this point you have a call of a
>> > generic function _wrap_inc with a concrete type SumClass, and the generic
>> > specializer can produce a specialization of it.
>> >
>> > Notice how this approach combines several existing optimizations and only
>> > requires adding a relatively simple new transformation, and possibly
>> > improving some of the existing optimizations to cover more cases.
>> >
>> > Slava
>> >
>> >> On Nov 29, 2017, at 11:30 AM, Raj Barik via swift-dev
>> >> <swift-dev@swift.org> wrote:
>> >>
>> >> Hi,
>> >>
>> >> I am thinking about writing a Protocol Devirtualizer Pass that
>> >> specializes functions that take Protocols as arguments to transform them
>> >> with concrete types instead of protocol types when the concrete types can
>> >> be determined statically by some compiler analysis. This is the first
>> >> step of the transformation that I am proposing. My goal is to extend this
>> >> to eliminate the original function implementation and also to remove the
>> >> corresponding protocol type (by deleting it from the witness table), if
>> >> possible. For simple cases, where the protocol is only used for mocking
>> >> for example and that there is just one class that conforms to it, we
>> >> should be able to eliminate the protocol altogether. This is the second
>> >> and final step of the transformation. Does anyone see any issues with
>> >> both these steps? Arnold from Apple pointed out that there might be
>> >> demangling issues when the protocol is eliminated. Any ideas on how to
>> >> fix the demangling issues? Moreover, would such a pass be helpful to
>> >> Swift folks?
>> >>
>> >> Original code:
>> >>
>> >>
>> >> protocol SumProtocol: class {
>> >> func increment(i:Int) -> Int
>> >> }
>> >>
>> >> internal class SumClass: SumProtocol {
>> >> var a:Int
>> >> init(base:Int) {
>> >> self.a = base
>> >> }
>> >> func increment(i:Int) -> Int {
>> >> self.a += i
>> >> return self.a
>> >> }
>> >> }
>> >>
>> >> @inline(never) internal func wrap_inc(a:SumProtocol, val:Int) -> Int{
>> >> return a.increment(i:val)
>> >> }
>> >>
>> >> internal let magic:SumProtocol = SumClass(base:10)
>> >> print("c=\(wrap_inc(a:magic,val:10))")
>> >>
>> >>
>> >> After Step 1:
>> >>
>> >>
>> >> protocol SumProtocol: class {
>> >> func increment(i:Int) -> Int
>> >> }
>> >>
>> >> internal class SumClass: SumProtocol {
>> >> var a:Int
>> >> init(base:Int) {
>> >> self.a = base
>> >> }
>> >> func increment(i:Int) -> Int {
>> >> self.a += i
>> >> return self.a
>> >> }
>> >> }
>> >>
>> >> @inline(never) internal func wrap_inc(a:SumProtocol, val:Int) -> Int{
>> >> return a.increment(i:val)
>> >> }
>> >>
>> >> @inline(never) internal func wrap_inc_1(a:SumClass, val:Int) -> Int{
>> >> return a.increment(i:val)
>> >> }
>> >>
>> >> internal let magic:SumClass = SumClass(base:10)
>> >> print("c=\(wrap_inc_1(a:magic,val:10))")
>> >>
>> >>
>> >> After Step 2:
>> >>
>> >> internal class SumClass {
>> >> var a:Int
>> >> init(base:Int) {
>> >> self.a = base
>> >> }
>> >> func increment(i:Int) -> Int {
>> >> self.a += i
>> >> return self.a
>> >> }
>> >> }
>> >>
>> >> @inline(never) internal func wrap_inc(a:SumClass, val:Int) -> Int{
>> >> return a.increment(i:val)
>> >> }
>> >>
>> >> internal let magic:SumClass = SumClass(base:10)
>> >> print("c=\(wrap_inc(a:magic,val:10))")
>> >>
>> >> Any comments/thought on this transformation?
>> >>
>> >> Best,
>> >> Raj
>> >> _______________________________________________
>> >> swift-dev mailing list
>> >> swift-dev@swift.org
>> >> https://lists.swift.org/mailman/listinfo/swift-dev
>> >
>> >
>> > _______________________________________________
>> > swift-dev mailing list
>> > swift-dev@swift.org
>> > https://lists.swift.org/mailman/listinfo/swift-dev
>>
>>
>
>
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