optimizer: fully support inlining of union-split, partially constant-prop' callsite

Makes full use of constant-propagation, by addressing this [TODO](https://github.com/JuliaLang/julia/blob/00734c5fd045316a00d287ca2c0ec1a2eef6e4d1/base/compiler/ssair/inlining.jl#L1212).
Here is a performance improvement from #43287:
```julia
ulia> using BenchmarkTools

julia> X = rand(ComplexF32, 64, 64);

julia> dst = reinterpret(reshape, Float32, X);

julia> src = copy(dst);

julia> @Btime copyto!($dst, $src);
  50.819 μs (1 allocation: 32 bytes) # v1.6.4
  41.081 μs (0 allocations: 0 bytes) # this commit
```

fixes #43287

Author: aviatesk

base/compiler/abstractinterpretation.jl

@@ -139,6 +139,7 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
     # by constant analysis, but let's create `ConstCallInfo` if there has been any successful
     # constant propagation happened since other consumers may be interested in this
     if any_const_result && seen == napplicable
+        @assert napplicable == nmatches(info) == length(const_results)
         info = ConstCallInfo(info, const_results)
     end
 

base/compiler/ssair/inlining.jl

@@ -672,19 +672,16 @@ function rewrite_apply_exprargs!(
                 new_sig = with_atype(call_sig(ir, new_stmt)::Signature)
                 new_info = call.info
                 if isa(new_info, ConstCallInfo)
-                    maybe_handle_const_call!(
+                    handle_const_call!(
                         ir, state1.id, new_stmt, new_info, flag,
-                        new_sig, istate, todo) && @goto analyzed
-                    new_info = new_info.call # cascade to the non-constant handling
-                end
-                if isa(new_info, MethodMatchInfo) || isa(new_info, UnionSplitInfo)
+                        new_sig, istate, todo)
+                elseif isa(new_info, MethodMatchInfo) || isa(new_info, UnionSplitInfo)
                     new_infos = isa(new_info, MethodMatchInfo) ? MethodMatchInfo[new_info] : new_info.matches
                     # See if we can inline this call to `iterate`
                     analyze_single_call!(
                         ir, state1.id, new_stmt, new_infos, flag,
                         new_sig, istate, todo)
                 end
-                @label analyzed
                 if i != length(thisarginfo.each)
                     valT = getfield_tfunc(call.rt, Const(1))
                     val_extracted = insert_node!(ir, idx, NewInstruction(
@@ -1126,139 +1123,150 @@ function process_simple!(ir::IRCode, idx::Int, state::InliningState, todo::Vecto
     return stmt, sig
 end
 
-# TODO inline non-`isdispatchtuple`, union-split callsites
+# TODO inline non-`isdispatchtuple`, union-split callsites?
 function analyze_single_call!(
     ir::IRCode, idx::Int, stmt::Expr, infos::Vector{MethodMatchInfo}, flag::UInt8,
     sig::Signature, state::InliningState, todo::Vector{Pair{Int, Any}})
     (; argtypes, atype) = sig
     cases = InliningCase[]
     local signature_union = Bottom
     local only_method = nothing  # keep track of whether there is one matching method
-    local meth
+    local meth::MethodLookupResult
     local fully_covered = true
     for i in 1:length(infos)
-        info = infos[i]
-        meth = info.results
+        meth = infos[i].results
         if meth.ambig
             # Too many applicable methods
             # Or there is a (partial?) ambiguity
-            return
+            return nothing
         elseif length(meth) == 0
             # No applicable methods; try next union split
             continue
-        elseif length(meth) == 1 && only_method !== false
-            if only_method === nothing
-                only_method = meth[1].method
-            elseif only_method !== meth[1].method
+        else
+            if length(meth) == 1 && only_method !== false
+                if only_method === nothing
+                    only_method = meth[1].method
+                elseif only_method !== meth[1].method
+                    only_method = false
+                end
+            else
                 only_method = false
             end
-        else
-            only_method = false
         end
         for match in meth
-            spec_types = match.spec_types
-            signature_union = Union{signature_union, spec_types}
-            if !isdispatchtuple(spec_types)
-                fully_covered = false
-                continue
-            end
-            item = analyze_method!(match, argtypes, flag, state)
-            if item === nothing
-                fully_covered = false
-                continue
-            elseif _any(case->case.sig === spec_types, cases)
-                continue
-            end
-            push!(cases, InliningCase(spec_types, item))
+            signature_union = Union{signature_union, match.spec_types}
+            fully_covered &= handle_match!(match, argtypes, flag, state, cases)
         end
     end
 
-    # if the signature is fully or mostly covered and there is only one applicable method,
+    # if the signature is fully covered and there is only one applicable method,
     # we can try to inline it even if the signature is not a dispatch tuple
     if length(cases) == 0 && only_method isa Method
         if length(infos) > 1
             (metharg, methsp) = ccall(:jl_type_intersection_with_env, Any, (Any, Any),
                 atype, only_method.sig)::SimpleVector
             match = MethodMatch(metharg, methsp::SimpleVector, only_method, true)
         else
-            meth = meth::MethodLookupResult
             @assert length(meth) == 1
             match = meth[1]
         end
         item = analyze_method!(match, argtypes, flag, state)
-        item === nothing && return
+        item === nothing && return nothing
         push!(cases, InliningCase(match.spec_types, item))
         fully_covered = match.fully_covers
     else
         fully_covered &= atype <: signature_union
     end
 
-    # If we only have one case and that case is fully covered, we may either
-    # be able to do the inlining now (for constant cases), or push it directly
-    # onto the todo list
-    if fully_covered && length(cases) == 1
-        handle_single_case!(ir, idx, stmt, cases[1].item, todo)
-    elseif length(cases) > 0
-        push!(todo, idx=>UnionSplit(fully_covered, atype, cases))
-    end
-    return nothing
+    handle_cases!(ir, idx, stmt, sig, cases, fully_covered, todo)
 end
 
-# try to create `InliningCase`s using constant-prop'ed results
-# currently it works only when constant-prop' succeeded for all (union-split) signatures
-# TODO use any of constant-prop'ed results, and leave the other unhandled cases to later
-# TODO this function contains a lot of duplications with `analyze_single_call!`, factor them out
-function maybe_handle_const_call!(
-    ir::IRCode, idx::Int, stmt::Expr, info::ConstCallInfo, flag::UInt8,
+# similar to `analyze_single_call!`, but with constant results
+function handle_const_call!(
+    ir::IRCode, idx::Int, stmt::Expr, cinfo::ConstCallInfo, flag::UInt8,
     sig::Signature, state::InliningState, todo::Vector{Pair{Int, Any}})
     (; argtypes, atype) = sig
-    results = info.results
-    cases = InliningCase[] # TODO avoid this allocation for single cases ?
+    (; call, results) = cinfo
+    infos = isa(call, MethodMatchInfo) ? MethodMatchInfo[call] : call.matches
+    cases = InliningCase[]
     local fully_covered = true
     local signature_union = Bottom
-    for result in results
-        isa(result, InferenceResult) || return false
-        (; mi) = item = InliningTodo(result, argtypes)
-        spec_types = mi.specTypes
-        signature_union = Union{signature_union, spec_types}
-        if !isdispatchtuple(spec_types)
-            fully_covered = false
-            continue
-        end
-        if !validate_sparams(mi.sparam_vals)
-            fully_covered = false
+    local j = 0
+    for i in 1:length(infos)
+        meth = infos[i].results
+        if meth.ambig
+            # Too many applicable methods
+            # Or there is a (partial?) ambiguity
+            return nothing
+        elseif length(meth) == 0
+            # No applicable methods; try next union split
             continue
         end
-        state.mi_cache !== nothing && (item = resolve_todo(item, state, flag))
-        if item === nothing
-            fully_covered = false
-            continue
+        for match in meth
+            j += 1
+            result = results[j]
+            if result === nothing
+                signature_union = Union{signature_union, match.spec_types}
+                fully_covered &= handle_match!(match, argtypes, flag, state, cases)
+            else
+                signature_union = Union{signature_union, result.linfo.specTypes}
+                fully_covered &= handle_const_result!(result, argtypes, flag, state, cases)
+            end
         end
-        push!(cases, InliningCase(spec_types, item))
     end
 
     # if the signature is fully covered and there is only one applicable method,
     # we can try to inline it even if the signature is not a dispatch tuple
     if length(cases) == 0 && length(results) == 1
         (; mi) = item = InliningTodo(results[1]::InferenceResult, argtypes)
         state.mi_cache !== nothing && (item = resolve_todo(item, state, flag))
-        validate_sparams(mi.sparam_vals) || return true
-        item === nothing && return true
+        validate_sparams(mi.sparam_vals) || return nothing
+        item === nothing && return nothing
         push!(cases, InliningCase(mi.specTypes, item))
         fully_covered = atype <: mi.specTypes
     else
         fully_covered &= atype <: signature_union
     end
 
+    handle_cases!(ir, idx, stmt, sig, cases, fully_covered, todo)
+end
+
+function handle_match!(
+    match::MethodMatch, argtypes::Vector{Any}, flag::UInt8, state::InliningState,
+    cases::Vector{InliningCase})
+    spec_types = match.spec_types
+    isdispatchtuple(spec_types) || return false
+    item = analyze_method!(match, argtypes, flag, state)
+    item === nothing && return false
+    _any(case->case.sig === spec_types, cases) && return true
+    push!(cases, InliningCase(spec_types, item))
+    return true
+end
+
+function handle_const_result!(
+    result::InferenceResult, argtypes::Vector{Any}, flag::UInt8, state::InliningState,
+    cases::Vector{InliningCase})
+    (; mi) = item = InliningTodo(result, argtypes)
+    spec_types = mi.specTypes
+    isdispatchtuple(spec_types) || return false
+    validate_sparams(mi.sparam_vals) || return false
+    state.mi_cache !== nothing && (item = resolve_todo(item, state, flag))
+    item === nothing && return false
+    push!(cases, InliningCase(spec_types, item))
+    return true
+end
+
+function handle_cases!(ir::IRCode, idx::Int, stmt::Expr, sig::Signature,
+    cases::Vector{InliningCase}, fully_covered::Bool, todo::Vector{Pair{Int, Any}})
     # If we only have one case and that case is fully covered, we may either
     # be able to do the inlining now (for constant cases), or push it directly
     # onto the todo list
     if fully_covered && length(cases) == 1
         handle_single_case!(ir, idx, stmt, cases[1].item, todo)
     elseif length(cases) > 0
-        push!(todo, idx=>UnionSplit(fully_covered, atype, cases))
+        push!(todo, idx=>UnionSplit(fully_covered, sig.atype, cases))
     end
-    return true
+    return nothing
 end
 
 function handle_const_opaque_closure_call!(
@@ -1324,10 +1332,10 @@ function assemble_inline_todo!(ir::IRCode, state::InliningState)
         # if inference arrived here with constant-prop'ed result(s),
         # we can perform a specialized analysis for just this case
         if isa(info, ConstCallInfo)
-            maybe_handle_const_call!(
+            handle_const_call!(
                 ir, idx, stmt, info, flag,
-                sig, state, todo) && continue
-            info = info.call # cascade to the non-constant handling
+                sig, state, todo)
+            continue
         end
 
         # Ok, now figure out what method to call

base/compiler/stmtinfo.jl

@@ -38,6 +38,27 @@ struct UnionSplitInfo
     matches::Vector{MethodMatchInfo}
 end
 
+nmatches(info::MethodMatchInfo) = length(info.results)
+function nmatches(info::UnionSplitInfo)
+    n = 0
+    for mminfo in info.matches
+        n += nmatches(mminfo)
+    end
+    return n
+end
+
+"""
+    info::ConstCallInfo
+
+The precision of this call was improved using constant information.
+In addition to the original call information `info.call`, this info also keeps
+the inference results with constant information `info.results::Vector{Union{Nothing,InferenceResult}}`.
+"""
+struct ConstCallInfo
+    call::Union{MethodMatchInfo,UnionSplitInfo}
+    results::Vector{Union{Nothing,InferenceResult}}
+end
+
 """
     info::MethodResultPure
 
@@ -92,18 +113,6 @@ struct UnionSplitApplyCallInfo
     infos::Vector{ApplyCallInfo}
 end
 
-"""
-    info::ConstCallInfo
-
-The precision of this call was improved using constant information.
-In addition to the original call information `info.call`, this info also keeps
-the inference results with constant information `info.results::Vector{Union{Nothing,InferenceResult}}`.
-"""
-struct ConstCallInfo
-    call::Union{MethodMatchInfo,UnionSplitInfo}
-    results::Vector{Union{Nothing,InferenceResult}}
-end
-
 """
     info::InvokeCallInfo
 

test/compiler/inline.jl

@@ -758,13 +758,18 @@ end
 import Base: @constprop
 
 # test union-split callsite with successful and unsuccessful constant-prop' results
-@constprop :aggressive @inline f42840(xs, a::Int) = xs[a]             # should be successful, and inlined
-@constprop :none @noinline f42840(xs::AbstractVector, a::Int) = xs[a] # should be unsuccessful, but still statically resolved
+# (also for https://github.com/JuliaLang/julia/issues/43287)
+@constprop :aggressive @inline f42840(cond::Bool, xs::Tuple, a::Int) =  # should be successful, and inlined with constant prop' result
+    cond ? xs[a] : @noinline(length(xs))
+@constprop :none @noinline f42840(::Bool, xs::AbstractVector, a::Int) = # should be unsuccessful, but still statically resolved
+    xs[a]
 let src = code_typed((Union{Tuple{Int,Int,Int}, Vector{Int}},)) do xs
-             f42840(xs, 2)
+             f42840(true, xs, 2)
          end |> only |> first
-    # `(xs::Tuple{Int,Int,Int})[a::Const(2)]` => `getfield(xs, 2)`
+    # `f43287(true, xs::Tuple{Int,Int,Int}, 2)` => `getfield(xs, 2)`
+    # `f43287(true, xs::Vector{Int}, 2)` => `:invoke f43287(true, xs, 2)`
     @test count(iscall((src, getfield)), src.code) == 1
+    @test count(isinvoke(:length), src.code) == 0
     @test count(isinvoke(:f42840), src.code) == 1
 end
 # a bit weird, but should handle this kind of case as well