Propagate iteration info to optimizer (#36684)

This supersedes #36169. Rather than re-implementing the iteration
analysis as done there, this uses the new stmtinfo infrastrcture
to propagate all the analysis done during inference all the way
to inlining. As a result, it applies not only to splats of
singletons, but also to splats of any other short iterable
that inference can analyze. E.g.:

```
f(x) = (x...,)
@code_typed f(1=>2)
@benchmark f(1=>2)
```

Before:
```
julia> @code_typed f(1=>2)
CodeInfo(
1 ─ %1 = Core._apply_iterate(Base.iterate, Core.tuple, x)::Tuple{Int64,Int64}
└──      return %1
) => Tuple{Int64,Int64}

julia> @benchmark f(1=>2)
BenchmarkTools.Trial:
  memory estimate:  96 bytes
  allocs estimate:  3
  --------------
  minimum time:     242.659 ns (0.00% GC)
  median time:      246.904 ns (0.00% GC)
  mean time:        255.390 ns (1.08% GC)
  maximum time:     4.415 μs (93.94% GC)
  --------------
  samples:          10000
  evals/sample:     405
```

After:
```
julia> @code_typed f(1=>2)
CodeInfo(
1 ─ %1 = Base.getfield(x, 1)::Int64
│   %2 = Base.getfield(x, 2)::Int64
│   %3 = Core.tuple(%1, %2)::Tuple{Int64,Int64}
└──      return %3
) => Tuple{Int64,Int64}

julia> @benchmark f(1=>2)
BenchmarkTools.Trial:
  memory estimate:  0 bytes
  allocs estimate:  0
  --------------
  minimum time:     1.701 ns (0.00% GC)
  median time:      1.925 ns (0.00% GC)
  mean time:        1.904 ns (0.00% GC)
  maximum time:     6.941 ns (0.00% GC)
  --------------
  samples:          10000
  evals/sample:     1000
```

I also implemented the TODO, I had left in #36169 to inline
the iterate calls themselves, which gives another 3x
improvement over the solution in that PR:

```
julia> @code_typed f(1)
CodeInfo(
1 ─ %1 = Core.tuple(x)::Tuple{Int64}
└──      return %1
) => Tuple{Int64}

julia> @benchmark f(1)
BenchmarkTools.Trial:
  memory estimate:  0 bytes
  allocs estimate:  0
  --------------
  minimum time:     1.696 ns (0.00% GC)
  median time:      1.699 ns (0.00% GC)
  mean time:        1.702 ns (0.00% GC)
  maximum time:     5.389 ns (0.00% GC)
  --------------
  samples:          10000
  evals/sample:     1000
```

Fixes #36087
Fixes #29114

base/compiler/abstractinterpretation.jl

@@ -78,7 +78,7 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
                 push!(fullmatch, thisfullmatch)
             end
         end
-        info = UnionSplitInfo(splitsigs, infos)
+        info = UnionSplitInfo(infos)
     else
         mt = ccall(:jl_method_table_for, Any, (Any,), atype)
         if mt === nothing
@@ -505,13 +505,13 @@ end
 # returns an array of types
 function precise_container_type(interp::AbstractInterpreter, @nospecialize(itft), @nospecialize(typ), vtypes::VarTable, sv::InferenceState)
     if isa(typ, PartialStruct) && typ.typ.name === Tuple.name
-        return typ.fields
+        return typ.fields, nothing
     end
 
     if isa(typ, Const)
         val = typ.val
         if isa(val, SimpleVector) || isa(val, Tuple)
-            return Any[ Const(val[i]) for i in 1:length(val) ] # avoid making a tuple Generator here!
+            return Any[ Const(val[i]) for i in 1:length(val) ], nothing # avoid making a tuple Generator here!
         end
     end
 
@@ -529,27 +529,27 @@ function precise_container_type(interp::AbstractInterpreter, @nospecialize(itft)
     if isa(tti, Union)
         utis = uniontypes(tti)
         if _any(t -> !isa(t, DataType) || !(t <: Tuple) || !isknownlength(t), utis)
-            return Any[Vararg{Any}]
+            return Any[Vararg{Any}], nothing
         end
         result = Any[rewrap_unionall(p, tti0) for p in utis[1].parameters]
         for t in utis[2:end]
             if length(t.parameters) != length(result)
-                return Any[Vararg{Any}]
+                return Any[Vararg{Any}], nothing
             end
             for j in 1:length(t.parameters)
                 result[j] = tmerge(result[j], rewrap_unionall(t.parameters[j], tti0))
             end
         end
-        return result
+        return result, nothing
     elseif tti0 <: Tuple
         if isa(tti0, DataType)
             if isvatuple(tti0) && length(tti0.parameters) == 1
-                return Any[Vararg{unwrapva(tti0.parameters[1])}]
+                return Any[Vararg{unwrapva(tti0.parameters[1])}], nothing
             else
-                return Any[ p for p in tti0.parameters ]
+                return Any[ p for p in tti0.parameters ], nothing
             end
         elseif !isa(tti, DataType)
-            return Any[Vararg{Any}]
+            return Any[Vararg{Any}], nothing
         else
             len = length(tti.parameters)
             last = tti.parameters[len]
@@ -558,12 +558,12 @@ function precise_container_type(interp::AbstractInterpreter, @nospecialize(itft)
             if va
                 elts[len] = Vararg{elts[len]}
             end
-            return elts
+            return elts, nothing
         end
     elseif tti0 === SimpleVector || tti0 === Any
-        return Any[Vararg{Any}]
+        return Any[Vararg{Any}], nothing
     elseif tti0 <: Array
-        return Any[Vararg{eltype(tti0)}]
+        return Any[Vararg{eltype(tti0)}], nothing
     else
         return abstract_iteration(interp, itft, typ, vtypes, sv)
     end
@@ -572,30 +572,34 @@ end
 # simulate iteration protocol on container type up to fixpoint
 function abstract_iteration(interp::AbstractInterpreter, @nospecialize(itft), @nospecialize(itertype), vtypes::VarTable, sv::InferenceState)
     if !isdefined(Main, :Base) || !isdefined(Main.Base, :iterate) || !isconst(Main.Base, :iterate)
-        return Any[Vararg{Any}]
+        return Any[Vararg{Any}], nothing
     end
     if itft === nothing
         iteratef = getfield(Main.Base, :iterate)
         itft = Const(iteratef)
     elseif isa(itft, Const)
         iteratef = itft.val
     else
-        return Any[Vararg{Any}]
+        return Any[Vararg{Any}], nothing
     end
     @assert !isvarargtype(itertype)
-    stateordonet = abstract_call_known(interp, iteratef, nothing, Any[itft, itertype], vtypes, sv).rt
+    call = abstract_call_known(interp, iteratef, nothing, Any[itft, itertype], vtypes, sv)
+    stateordonet = call.rt
+    info = call.info
     # Return Bottom if this is not an iterator.
     # WARNING: Changes to the iteration protocol must be reflected here,
     # this is not just an optimization.
-    stateordonet === Bottom && return Any[Bottom]
+    stateordonet === Bottom && return Any[Bottom], AbstractIterationInfo(CallMeta[CallMeta(Bottom, info)])
     valtype = statetype = Bottom
     ret = Any[]
+    calls = CallMeta[call]
+
     # Try to unroll the iteration up to MAX_TUPLE_SPLAT, which covers any finite
     # length iterators, or interesting prefix
     while true
         stateordonet_widened = widenconst(stateordonet)
         if stateordonet_widened === Nothing
-            return ret
+            return ret, AbstractIterationInfo(calls)
         end
         if Nothing <: stateordonet_widened || length(ret) >= InferenceParams(interp).MAX_TUPLE_SPLAT
             break
@@ -607,12 +611,14 @@ function abstract_iteration(interp::AbstractInterpreter, @nospecialize(itft), @n
         # If there's no new information in this statetype, don't bother continuing,
         # the iterator won't be finite.
         if nstatetype ⊑ statetype
-            return Any[Bottom]
+            return Any[Bottom], nothing
         end
         valtype = getfield_tfunc(stateordonet, Const(1))
         push!(ret, valtype)
         statetype = nstatetype
-        stateordonet = abstract_call_known(interp, iteratef, nothing, Any[Const(iteratef), itertype, statetype], vtypes, sv).rt
+        call = abstract_call_known(interp, iteratef, nothing, Any[Const(iteratef), itertype, statetype], vtypes, sv)
+        stateordonet = call.rt
+        push!(calls, call)
     end
     # From here on, we start asking for results on the widened types, rather than
     # the precise (potentially const) state type
@@ -629,15 +635,15 @@ function abstract_iteration(interp::AbstractInterpreter, @nospecialize(itft), @n
         if nounion.parameters[1] <: valtype && nounion.parameters[2] <: statetype
             if typeintersect(stateordonet, Nothing) === Union{}
                 # Reached a fixpoint, but Nothing is not possible => iterator is infinite or failing
-                return Any[Bottom]
+                return Any[Bottom], nothing
             end
             break
         end
         valtype = tmerge(valtype, nounion.parameters[1])
         statetype = tmerge(statetype, nounion.parameters[2])
     end
     push!(ret, Vararg{valtype})
-    return ret
+    return ret, nothing
 end
 
 # do apply(af, fargs...), where af is a function value
@@ -656,13 +662,15 @@ function abstract_apply(interp::AbstractInterpreter, @nospecialize(itft), @nospe
     nargs = length(aargtypes)
     splitunions = 1 < countunionsplit(aargtypes) <= InferenceParams(interp).MAX_APPLY_UNION_ENUM
     ctypes = Any[Any[aft]]
+    infos = [Union{Nothing, AbstractIterationInfo}[]]
     for i = 1:nargs
         ctypes´ = []
+        infos′ = []
         for ti in (splitunions ? uniontypes(aargtypes[i]) : Any[aargtypes[i]])
             if !isvarargtype(ti)
-                cti = precise_container_type(interp, itft, ti, vtypes, sv)
+                cti, info = precise_container_type(interp, itft, ti, vtypes, sv)
             else
-                cti = precise_container_type(interp, itft, unwrapva(ti), vtypes, sv)
+                cti, info = precise_container_type(interp, itft, unwrapva(ti), vtypes, sv)
                 # We can't represent a repeating sequence of the same types,
                 # so tmerge everything together to get one type that represents
                 # everything.
@@ -678,19 +686,29 @@ function abstract_apply(interp::AbstractInterpreter, @nospecialize(itft), @nospe
             if _any(t -> t === Bottom, cti)
                 continue
             end
-            for ct in ctypes
+            for j = 1:length(ctypes)
+                ct = ctypes[j]
                 if isvarargtype(ct[end])
+                    # This is vararg, we're not gonna be able to do any inling,
+                    # drop the info
+                    info = nothing
+
                     tail = tuple_tail_elem(unwrapva(ct[end]), cti)
                     push!(ctypes´, push!(ct[1:(end - 1)], tail))
                 else
                     push!(ctypes´, append!(ct[:], cti))
                 end
+                push!(infos′, push!(copy(infos[j]), info))
             end
         end
         ctypes = ctypes´
+        infos = infos′
     end
-    local info = nothing
-    for ct in ctypes
+    retinfos = ApplyCallInfo[]
+    retinfo = UnionSplitApplyCallInfo(retinfos)
+    for i = 1:length(ctypes)
+        ct = ctypes[i]
+        arginfo = infos[i]
         lct = length(ct)
         # truncate argument list at the first Vararg
         for i = 1:lct-1
@@ -701,15 +719,17 @@ function abstract_apply(interp::AbstractInterpreter, @nospecialize(itft), @nospe
             end
         end
         call = abstract_call(interp, nothing, ct, vtypes, sv, max_methods)
-        info = call.info
+        push!(retinfos, ApplyCallInfo(call.info, arginfo))
         res = tmerge(res, call.rt)
         if res === Any
+            # No point carrying forward the info, we're not gonna inline it anyway
+            retinfo = nothing
             break
         end
     end
     # TODO: Add a special info type to capture all the iteration info.
     # For now, only propagate info if we don't also union-split the iteration
-    return CallMeta(res, length(ctypes) == 1 ? info : false)
+    return CallMeta(res, retinfo)
 end
 
 function is_method_pure(method::Method, @nospecialize(sig), sparams::SimpleVector)
@@ -779,7 +799,7 @@ function abstract_call_builtin(interp::AbstractInterpreter, f::Builtin, fargs::U
     end
     rt = builtin_tfunction(interp, f, argtypes[2:end], sv)
     if f === getfield && isa(fargs, Vector{Any}) && la == 3 && isa(argtypes[3], Const) && isa(argtypes[3].val, Int) && argtypes[2] ⊑ Tuple
-        cti = precise_container_type(interp, nothing, argtypes[2], vtypes, sv)
+        cti, _ = precise_container_type(interp, nothing, argtypes[2], vtypes, sv)
         idx = argtypes[3].val
         if 1 <= idx <= length(cti)
             rt = unwrapva(cti[idx])