IR verification error during testing of Parsers.jl

[maleadt]

As seen during testing of Parsers.jl with -g2:

Block 18 successors (Array{Int64, 1}(dims=(2,), mem=Memory{Int64}(2, 0x7f51dfec7410)[20, 19])), does not match fall-through terminator %69 (Expr(:throw_undef_if_not, Symbol("##getfield##"), SSAValue(57)))::Nothing
    1 ──       nothing::Nothing
362 2 ── %2  = %new(Base.CodeUnits{UInt8, String}, _3)::Base.CodeUnits{UInt8, String}
    3 ── %3  = Parsers._xparse2::typeof(Parsers._xparse2)
    │    %4  = invoke %3($(QuoteNode(Parsers.DefaultConf{String}()))::Parsers.DefaultConf{String}, %2::Base.CodeUnits{UInt8, String}, _5::Int64, _6::Int64, _4::Parsers.Options, PosLen::Type{PosLen})::Parsers.Result{PosLen}
    │    %5  = Base.getfield(%4, :code)::Int16
    │    %6  = Base.getfield(%4, :val)::PosLen
    │    %7  = Parsers.SUCCESS::Int16
    │    %8  = Base.slt_int(%5, %7)::Bool
    │    %9  = Base.not_int(%8)::Bool
    └───       goto #12 if not %9
    4 ── %11 = Parsers.SENTINEL::Int16
    │    %12 = Base.and_int(%5, %11)::Int16
    │    %13 = Parsers.SENTINEL::Int16
    │    %14 = (%12 === %13)::Bool
    │    %15 = Base.not_int(%14)::Bool
    └───       goto #12 if not %15
    5 ──       goto #6
    6 ──       goto #7
    7 ── %19 = Parsers.getfield(_4, :e)::UInt8
    └───       goto #8
    8 ── %21 = Base.bitcast(Parsers.Int64, %6)::Int64
    │    %22 = Parsers.ESCAPE_BIT::Int64
    │    %23 = Base.and_int(%21, %22)::Int64
    │    %24 = Parsers.ESCAPE_BIT::Int64
    │    %25 = (%23 === %24)::Bool
    └───       goto #10 if not %25
    9 ── %27 = invoke Parsers.unescape(%2::Base.CodeUnits{UInt8, String}, %6::PosLen, %19::UInt8)::String
    └───       goto #11
    10 ─ %29 = Base.bitcast(Parsers.Int64, %6)::Int64
    │    %30 = Base.and_int(%29, 4611686018426339328)::Int64
    │    %31 = Base.sle_int(0, 20)::Bool
    │    %32 = Base.bitcast(UInt64, 20)::UInt64
    │    %33 = Base.ashr_int(%30, %32)::Int64
    │    %34 = Base.neg_int(20)::Int64
    │    %35 = Base.bitcast(UInt64, %34)::UInt64
    │    %36 = Base.shl_int(%30, %35)::Int64
    │    %37 = Core.ifelse(%31, %33, %36)::Int64
    │    %38 = $(Expr(:foreigncall, :(:jl_string_ptr), Ptr{UInt8}, svec(Any), 0, :(:ccall), Core.Argument(3)))::Ptr{UInt8}
    │    %39 = Base.sub_int(%37, 1)::Int64
    │    %40 = Base.mul_int(%39, 1)::Int64
    │    %41 = Core.bitcast(Core.UInt, %38)::UInt64
    │    %42 = Base.bitcast(UInt64, %40)::UInt64
    │    %43 = Base.add_ptr(%41, %42)::UInt64
    │    %44 = Core.bitcast(Ptr{UInt8}, %43)::Ptr{UInt8}
    │    %45 = Base.bitcast(Parsers.Int64, %6)::Int64
    │    %46 = Base.and_int(%45, 1048575)::Int64
    │    %47 = $(Expr(:foreigncall, :(:jl_pchar_to_string), Ref{String}, svec(Ptr{UInt8}, Int64), 0, :(:ccall), :(%44), :(%46), :(%46), :(%44)))::String
    └───       goto #11
    11 ┄ %49 = φ (#9 => %27, #10 => %47)::String
    │    %50 = %new(Main.CustomType, %49)::CustomType
    │    %51 = Base.getfield(%4, :tlen)::Int64
    └───       goto #13
    12 ┄ %53 = Base.getfield(%4, :tlen)::Int64
    └───       goto #13
    13 ┄ %55 = φ (#11 => %51, #12 => %53)::Int64
    │    %56 = φ (#11 => %50, #12 => #undef)::CustomType
    │    %57 = φ (#11 => true, #12 => false)::Bool
    └───       goto #14
    14 ─       goto #15
    15 ─       nothing::Nothing
365 16 ─ %61 = Base.sub_int(_6, _5)::Int64
    │    %62 = Base.add_int(%61, 1)::Int64
    └─── %63 = (%55 === %62)::Bool
366 17 ─ %64 = Base.and_int(%5, -32767)::Int16
    │    %65 = Parsers.OK::Int16
    │    %66 = (%64 === %65)::Bool
    └───       goto #20 if not %66
    18 ─       goto #20 if not %63
    └───       $(Expr(:throw_undef_if_not, Symbol("##getfield##"), :(%57)))::Nothing
    19 ─       return %56
    20 ┄ %71 = Parsers.Error(_3, CustomType, %5, _5, %55)::Any
    │          Parsers.throw(%71)::Union{}
    └───       unreachable

Reduced to:

struct Result
    val
    Result(Int16) = new()
end
function foo(f)
    if whatever
        f.e
    else
        Result(code)
    end
end
parse(Type, f) = foo(identity).val
struct CustomType end
parse(CustomType, identity)

Terminator 7 in bb 3 is not the last statement in the block
1 1 ─ %1 = Main.identity::Core.Const(identity)
  │   %2 = Main.whatever::Any
  └──      goto #3 if not %2
  2 ─      Base.getfield(%1, :e)::Union{}
  └──      unreachable
  3 ─      Main.code::Any
  │        goto #4
  └──      $(Expr(:throw_undef_if_not, Symbol("##getfield##"), false))::Nothing
  4 ─      return nothing

The verification error here is different, however, it looks related to me because of the throw_undef_if_not, and more importantly because both bisect to the same PR: #52338; cc @Keno @aviatesk

[maleadt]

Actually, here's the MWE slightly tweaked so that it retains the original verification error:

struct Result
    val
    Result(x) = new()
end
function foo(f)
    if whatever
        f.e
    else
        Result(code)
    end
end
function parse(Type, f)
    res = foo(sizeof)
    fin ? res.val : nothing
end
struct CustomType end
parse(CustomType, identity)

Block 4 successors (Array{Int64, 1}(dims=(2,), mem=Memory{Int64}(2, 0x7f52cd1d7c80)[6, 5])), does not match fall-through terminator %10 (Expr(:throw_undef_if_not, :var"##getfield##", false))::Nothing
2 1 ─ %1 = Main.sizeof::Core.Const(sizeof)
  │   %2 = Main.whatever::Any
  └──      goto #3 if not %2
  2 ─      Base.getfield(%1, :e)::Union{}
  └──      unreachable
  3 ─      Main.code::Any
  └──      goto #4
3 4 ─ %8 = Main.fin::Any
  │        goto #6 if not %8
  └──      $(Expr(:throw_undef_if_not, Symbol("##getfield##"), false))::Nothing
  5 ─      return nothing
  6 ─      return Main.nothing