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 >> >> > > > _______________________________________________ > swift-dev mailing list > swift-dev@swift.org > https://lists.swift.org/mailman/listinfo/swift-dev
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