[swift-dev] High-level SIL Optimization: How do I get a FuncRef from the stdlib?
Ben Ng
me at benng.me
Tue Nov 29 02:10:12 CST 2016
Hi Slava,
The use of the unsubstituted function type turned out to be the issue. The
verifier was satisfied after I fixed that, and my proof of concept worked.
For context, I'm working on an addition to the ArrayValuePropagation pass
that makes code like this:
foo += [5]
Equivalent to this code:
foo.append(5)
Which is 6x faster.
I do not understand what the danger of using the lowered AST type over the
"unlowered" AST type is. An example would help here. Additionally, I am not
sure how to get the unlowered AST type. This code is in an optimization
pass, so I don't see how I can reach back into the original AST to get the
unlowered type. Does it involve SilInstruction::getLoc()?
I also do not understand why constructing the ArrayRef<Substitution> by
hand is discouraged. I will refactor it tomorrow to start with a
substitution map instead. I've looked at the methods on GenericEnvironment,
and it's still not clear to me how I would use them to turn the map into an
array. Can you give me a hint here?
Thanks,
Ben
On Sun, Nov 27, 2016 at 10:17 PM Slava Pestov <spestov at apple.com> wrote:
> One more thing:
>
>
> auto subTy = V->getType();
>
>
> This is a SILType.
>
> auto &ValLowering = Builder.getModule().getTypeLowering(subTy);
> auto copiedVal = ValLowering.emitCopyValue(Builder,
> SemanticsCall->getLoc(), V);
> auto allocStackInst = Builder.createAllocStack(SemanticsCall->getLoc(),
> subTy);
> Builder.createStore(SemanticsCall->getLoc(), copiedVal, allocStackInst,
> StoreOwnershipQualifier::Unqualified);
> ArrayRef<Substitution> subs{Substitution(subTy.getSwiftType(),
> conformances)};
>
>
> ‘subTy.getSwiftType()’ is a “lowered AST type”. The replacement type in a
> substitution should be the “unlowered” AST type that came from the original
> Expr that you’re emitting into SIL.
>
> Slava
>
> SILValue args[] = {allocStackInst, ArrRef};
> Builder.createApply(SemanticsCall->getLoc(), fnRef, fnTy,
> fnTy.castTo<SILFunctionType>()->getSILResult(),
> subs, args, false);
> Builder.createDeallocStack(SemanticsCall->getLoc(), allocStackInst);
>
>
> Here is Builder.createApply’s signature for convenience:
>
> ApplyInst *createApply(SILLocation Loc, SILValue Fn, SILType SubstFnTy,
> SILType Result, ArrayRef<Substitution> Subs,
> ArrayRef<SILValue> Args, bool isNonThrowing)
>
>
> On Nov 27, 2016, at 3:22 PM, Ben Ng <me at benng.me> wrote:
>
> Slava gave me a hint: create a SubstitutionMap and then use the methods on
> GenericEnvironment to turn it into ArrayRef<Substitution>. I'll try that
> out tonight and see how far I get.
> On Sun, Nov 27, 2016 at 2:12 PM Michael Gottesman <mgottesman at apple.com>
> wrote:
>
> +CC Slava.
>
> He has been messing around with this area in the past bit since many of us
> have looked at this. He is the person you want.
>
> Michael
>
> > On Nov 25, 2016, at 8:42 PM, Ben Ng <me at benng.me> wrote:
> >
> > Hi everyone,
> >
> > I’ve made good progress with the information in this thread but I can’t
> figure out how to create the proper set of substitutions for the method
> that I’m calling.
> >
> > The error I’m getting, as expected, is "SIL verification failed: callee
> of apply without substitutions must not be polymorphic:
> !fnTy->isPolymorphic()"
> >
> > I was hoping that there would be a way to delay specialization of the
> function that I’m replacing so that I can simply reuse those substitutions,
> but it doesn’t seem like that’s possible.
> >
> > At a high level I assumed that I’d simply be able to substitute a type
> like `Int` for `τ_0_0`, but it looks like I have to use a
> ProtocolConformanceRef, which I don’t understand.
> >
> > I looked into iterating through
> `getLoweredFunctionType()->getGenericSignature()->getGenericParams()`, but
> I don’t see how I can turn the information there into
> ProtocolConformanceRef.
> >
> > Thanks for the help as always,
> >
> > Ben
> >
> >> On Nov 16, 2016, at 10:47 PM, Ben Ng <me at benng.me> wrote:
> >>
> >>> On Nov 16, 2016, at 7:11 PM, Arnold Schwaighofer <
> aschwaighofer at apple.com> wrote:
> >>>
> >>>
> >>>> On Nov 16, 2016, at 2:58 PM, Ben Ng <me at benng.me> wrote:
> >>>>
> >>>> Correct, that is what I am trying to do.
> >>>>
> >>>>> On Nov 16, 2016, at 12:22 PM, Arnold Schwaighofer <
> aschwaighofer at apple.com> wrote:
> >>>>>
> >>>>> // Really, by the time you look at this in array value prop
> >>>>> // this call should have been inline and you would see a call
> >>>>> // to:
> >>>>> // a.append(contentsOf: [1])
> >>>>
> >>>> I do not understand this comment; I thought that inlining of stdlib
> functions happened after high-level SIL optimizations are run. Is my
> understanding incorrect?
> >>>
> >>>
> >>> Inlining of functions with @_semantics is delayed until after
> high-level SIL optimizations are run. Other functions are inlined.
> >>>
> >>>
> https://github.com/apple/swift/blob/master/lib/SILOptimizer/PassManager/Passes.cpp#L221
> >>>
> https://github.com/apple/swift/blob/master/lib/SILOptimizer/Transforms/PerformanceInliner.cpp#L722
> >>>
> >>>
> >>> I recommend looking at the SIL function dump in
> ArrayElementValuePropagation of an example function after adding
> @semantics(“array.mutate_unknown”) to “append(contentsOf:)”.
> >>>
> >>>
> >>> $ git diff HEAD~
> >>> diff --git
> a/lib/SILOptimizer/Transforms/ArrayElementValuePropagation.cpp
> b/lib/SILOptimizer/Transforms/ArrayElementValuePropagation.cpp
> >>> index 76328a6..cb976f7 100644
> >>> --- a/lib/SILOptimizer/Transforms/ArrayElementValuePropagation.cpp
> >>> +++ b/lib/SILOptimizer/Transforms/ArrayElementValuePropagation.cpp
> >>> @@ -259,6 +259,8 @@ public:
> >>> void run() override {
> >>> auto &Fn = *getFunction();
> >>>
> >>> + Fn.dump();
> >>> +
> >>> bool Changed = false;
> >>>
> >>> // Propagate the elements an of array value to its users.
> >>> diff --git a/stdlib/public/core/Arrays.swift.gyb
> b/stdlib/public/core/Arrays.swift.gyb
> >>> index f00cc23..2acfd06 100644
> >>> --- a/stdlib/public/core/Arrays.swift.gyb
> >>> +++ b/stdlib/public/core/Arrays.swift.gyb
> >>> @@ -1344,6 +1344,7 @@ extension ${Self} : RangeReplaceableCollection,
> _ArrayProtocol {
> >>> /// - Parameter newElements: The elements to append to the array.
> >>> ///
> >>> /// - Complexity: O(*n*), where *n* is the length of the resulting
> array.
> >>> + @_semantics("array.mutate_unknown")
> >>> public mutating func append<C : Collection>(contentsOf newElements: C)
> >>> where C.Iterator.Element == Element {
> >>>
> >>>
> >>> # Rebuild the compiler and stdlib (without stdlib assertions).
> >>> $ swift/utils/build-script -r --assertions
> --no-swift-stdlib-assertions
> >>>
> >>>
> >>> $ cat TestArray.swift
> >>> @inline(never)
> >>> public func test() {
> >>> var a = [1, 2, 3]
> >>> a += [1]
> >>> print(a)
> >>> }
> >>>
> >>> $ bin/swiftc -O 2>&1 | less
> >>> ...
> >>> sil shared [_semantics "array.mutate_unknown"]
> @_TTSg5Si_GSaSi_GSaSi_s10Collections___TFSa6appenduRd__s10CollectionxzWd__8Iterator7Element_rfT10contentsOfqd___T_
> : $@convention(method) (@owned Array<I
> >>> nt>, @inout Array<Int>) -> () {
> >>>
> >>> …
> >>> // testArray() -> ()
> >>> sil [noinline] @_TF9TestArray9testArrayFT_T_ : $@convention(thin) ()
> -> () {
> >>> bb0:
> >>> %0 = alloc_stack $Array<Int>, var, name "a", loc
> "TestArray.swift":3:7, scope 2 // users: %54, %32, %60, %23, %43
> >>> %1 = integer_literal $Builtin.Word, 3, loc "TestArray.swift":3:12,
> scope 2 // user: %4
> >>> %2 = integer_literal $Builtin.Int64, 3, scope 5 // user: %3
> >>> %3 = struct $Int (%2 : $Builtin.Int64), scope 5 // users: %22, %7
> >>> %4 = alloc_ref [tail_elems $Int * %1 : $Builtin.Word]
> $_ContiguousArrayStorage<Int>, scope 5 // user: %7
> >>> %5 = metatype $@thin Array<Int>.Type, scope 5 // users: %25, %7
> >>> // function_ref specialized static
> Array._adoptStorage(_ContiguousArrayStorage<A>, count : Int) -> ([A],
> UnsafeMutablePointer<A>)
> >>> %6 = function_ref
> @_TTSg5Si___TZFSa13_adoptStoragefTGCs23_ContiguousArrayStoragex_5countSi_TGSax_GSpx__
> : $@convention(method) (@owned _ContiguousArrayStorage<Int>, Int, @thin
> Array<Int>.Type) -> (@
> >>> owned Array<Int>, UnsafeMutablePointer<Int>), scope 5 // users: %25, %7
> >>> %7 = apply %6(%4, %3, %5) : $@convention(method) (@owned
> _ContiguousArrayStorage<Int>, Int, @thin Array<Int>.Type) -> (@owned
> Array<Int>, UnsafeMutablePointer<Int>), scope 5 // users: %9, %8
> >>> %8 = tuple_extract %7 : $(Array<Int>, UnsafeMutablePointer<Int>), 0,
> scope 5 // user: %23
> >>> %9 = tuple_extract %7 : $(Array<Int>, UnsafeMutablePointer<Int>), 1,
> scope 5 // user: %10
> >>> %10 = struct_extract %9 : $UnsafeMutablePointer<Int>,
> #UnsafeMutablePointer._rawValue, scope 5 // user: %11
> >>> %11 = pointer_to_address %10 : $Builtin.RawPointer to [strict] $*Int,
> loc "TestArray.swift":3:12, scope 2 // users: %14, %21, %16
> >>> %12 = integer_literal $Builtin.Int64, 1, loc "TestArray.swift":3:12,
> scope 2 // user: %13
> >>> %13 = struct $Int (%12 : $Builtin.Int64), loc "TestArray.swift":3:12,
> scope 2 // users: %37, %30, %25, %14
> >>> store %13 to %11 : $*Int, loc "TestArray.swift":3:12, scope 2 // id:
> %14
> >>> %15 = integer_literal $Builtin.Word, 1, loc "TestArray.swift":3:15,
> scope 2 // users: %34, %24, %16
> >>> %16 = index_addr %11 : $*Int, %15 : $Builtin.Word, loc
> "TestArray.swift":3:15, scope 2 // user: %19
> >>> %17 = integer_literal $Builtin.Int64, 2, loc "TestArray.swift":3:15,
> scope 2 // user: %18
> >>> %18 = struct $Int (%17 : $Builtin.Int64), loc "TestArray.swift":3:15,
> scope 2 // user: %19
> >>> store %18 to %16 : $*Int, loc "TestArray.swift":3:15, scope 2 // id:
> %19
> >>> %20 = integer_literal $Builtin.Word, 2, loc "TestArray.swift":3:18,
> scope 2 // user: %21
> >>> %21 = index_addr %11 : $*Int, %20 : $Builtin.Word, loc
> "TestArray.swift":3:18, scope 2 // user: %22
> >>> store %3 to %21 : $*Int, loc "TestArray.swift":3:18, scope 2 // id: %22
> >>> store %8 to %0 : $*Array<Int>, loc "TestArray.swift":3:18, scope 2 //
> id: %23
> >>> %24 = alloc_ref [tail_elems $Int * %15 : $Builtin.Word]
> $_ContiguousArrayStorage<Int>, scope 7 // user: %25
> >>> %25 = apply %6(%24, %13, %5) : $@convention(method) (@owned
> _ContiguousArrayStorage<Int>, Int, @thin Array<Int>.Type) -> (@owned
> Array<Int>, UnsafeMutablePointer<Int>), scope 7 // users: %27, %26
> >>> %26 = tuple_extract %25 : $(Array<Int>, UnsafeMutablePointer<Int>), 0,
> scope 7 // user: %32
> >>> %27 = tuple_extract %25 : $(Array<Int>, UnsafeMutablePointer<Int>), 1,
> scope 7 // user: %28
> >>> %28 = struct_extract %27 : $UnsafeMutablePointer<Int>,
> #UnsafeMutablePointer._rawValue, scope 7 // user: %29
> >>> %29 = pointer_to_address %28 : $Builtin.RawPointer to [strict] $*Int,
> loc "TestArray.swift":4:9, scope 2 // user: %30
> >>> store %13 to %29 : $*Int, loc "TestArray.swift":4:9, scope 2 // id: %30
> >>> // function_ref specialized Array.append<A where ...> (contentsOf :
> A1) -> ()
> >>> %31 = function_ref
> @_TTSg5Si_GSaSi_GSaSi_s10Collections___TFSa6appenduRd__s10CollectionxzWd__8Iterator7Element_rfT10contentsOfqd___T_
> : $@convention(method) (@owned Array<Int>, @inout Array<Int>) -> (), scope
> 10 // user: %32
> >>> %32 = apply %31(%26, %0) : $@convention(method) (@owned Array<Int>,
> @inout Array<Int>) -> (), scope 10
> >>
> >> Ah, I do remember seeing something about how the semantic attribute
> stops some functions from being inlined early. Thanks for saving me a bunch
> of head-scratching!
> >>
> >>
> >
>
>
>
>
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