optimizer: fix #42840, the performance regression introduced by #42766 (

#42841)

base/compiler/ssair/inlining.jl

@@ -1392,7 +1392,7 @@ function assemble_inline_todo!(ir::IRCode, state::InliningState)
                     ir, idx, stmt, info, sig,
                     state, sig.f === Core.invoke, todo) && continue
             end
-            info = info.call
+            info = info.call # cascade to the non-constant handling
         end
 
         if isa(info, OpaqueClosureCallInfo)

test/compiler/inline.jl

@@ -393,18 +393,26 @@ let f(x) = (x...,)
     @test code_typed(f, Tuple{Union{Int64, CartesianIndex{1}, CartesianIndex{3}}})[1][2] == Tuple{Int64}
 end
 
-# check if `x` is a statically-resolved call of a function whose name is `sym`
-isinvoke(@nospecialize(x), sym::Symbol) = isinvoke(x, mi->mi.def.name===sym)
-function isinvoke(@nospecialize(x), pred)
-    if Meta.isexpr(x, :invoke)
-        return pred(x.args[1]::Core.MethodInstance)
+import Core.Compiler: argextype, singleton_type
+const EMPTY_SPTYPES = Core.Compiler.EMPTY_SLOTTYPES
+
+code_typed1(args...; kwargs...) = first(only(code_typed(args...; kwargs...)))::Core.CodeInfo
+get_code(args...; kwargs...) = code_typed1(args...; kwargs...).code
+
+# check if `x` is a dynamic call of a given function
+function iscall((src, f)::Tuple{Core.CodeInfo,Function}, @nospecialize(x))
+    return iscall(x) do @nospecialize x
+        singleton_type(argextype(x, src, EMPTY_SPTYPES)) === f
     end
-    return false
 end
-code_typed1(args...; kwargs...) = (first(only(code_typed(args...; kwargs...)))::Core.CodeInfo).code
+iscall(pred, @nospecialize(x)) = Meta.isexpr(x, :call) && pred(x.args[1])
+
+# check if `x` is a statically-resolved call of a function whose name is `sym`
+isinvoke(sym::Symbol, @nospecialize(x)) = isinvoke(mi->mi.def.name===sym, x)
+isinvoke(pred, @nospecialize(x)) = Meta.isexpr(x, :invoke) && pred(x.args[1]::Core.MethodInstance)
 
 # https://github.com/JuliaLang/julia/issues/42754
-# inline union-split constant-prop'ed sources
+# inline union-split constant-prop'ed results
 mutable struct X42754
     # NOTE in order to confuse `fieldtype_tfunc`, we need to have at least two fields with different types
     a::Union{Nothing, Int}
@@ -430,6 +438,33 @@ 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
+let src = code_typed((Union{Tuple{Int,Int,Int}, Vector{Int}},)) do xs
+             f42840(xs, 2)
+         end |> only |> first
+    @test count(src.code) do @nospecialize x
+        iscall((src, getfield), x) # `(xs::Tuple{Int,Int,Int})[a::Const(2)]` => `getfield(xs, 2)`
+    end == 1
+    @test count(src.code) do @nospecialize x
+        isinvoke(:f42840, x)
+    end == 1
+end
+# a bit weird, but should handle this kind of case as well
+@constprop :aggressive @noinline g42840(xs, a::Int) = xs[a]         # should be successful, but only statically resolved
+@constprop :none @inline g42840(xs::AbstractVector, a::Int) = xs[a] # should be unsuccessful, still inlined
+let src = code_typed((Union{Tuple{Int,Int,Int}, Vector{Int}},)) do xs
+        g42840(xs, 2)
+    end |> only |> first
+    @test count(src.code) do @nospecialize x
+        iscall((src, Base.arrayref), x) # `(xs::Vector{Int})[a::Const(2)]` => `Base.arrayref(true, xs, 2)`
+    end == 1
+    @test count(src.code) do @nospecialize x
+        isinvoke(:g42840, x)
+    end == 1
+end
+
 # test single, non-dispatchtuple callsite inlining
 
 @constprop :none @inline test_single_nondispatchtuple(@nospecialize(t)) =