Inline statically known method errors. (#54972)

This replaces the `Expr(:call, ...)` with a call of a new builtin
`Core.throw_methoderror`

This is useful because it makes very clear if something is a static
method error or a plain dynamic dispatch that always errors.
Tools such as AllocCheck or juliac can notice that this is not a genuine
dynamic dispatch, and prevent it from becoming a false positive
compile-time error.

Dependent on #55705

---------

Co-authored-by: Cody Tapscott <topolarity@tapscott.me>

Author: gbaraldi

base/compiler/abstractinterpretation.jl

@@ -209,8 +209,7 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
         rettype = exctype = Any
         all_effects = Effects()
     else
-        if (matches isa MethodMatches ? (!matches.fullmatch || any_ambig(matches)) :
-            (!all(matches.fullmatches) || any_ambig(matches)))
+        if !fully_covering(matches) || any_ambig(matches)
             # Account for the fact that we may encounter a MethodError with a non-covered or ambiguous signature.
             all_effects = Effects(all_effects; nothrow=false)
             exctype = exctype ⊔ₚ MethodError
@@ -275,21 +274,23 @@ struct MethodMatches
     applicable::Vector{Any}
     info::MethodMatchInfo
     valid_worlds::WorldRange
-    mt::MethodTable
-    fullmatch::Bool
 end
-any_ambig(info::MethodMatchInfo) = info.results.ambig
+any_ambig(result::MethodLookupResult) = result.ambig
+any_ambig(info::MethodMatchInfo) = any_ambig(info.results)
 any_ambig(m::MethodMatches) = any_ambig(m.info)
+fully_covering(info::MethodMatchInfo) = info.fullmatch
+fully_covering(m::MethodMatches) = fully_covering(m.info)
 
 struct UnionSplitMethodMatches
     applicable::Vector{Any}
     applicable_argtypes::Vector{Vector{Any}}
     info::UnionSplitInfo
     valid_worlds::WorldRange
-    mts::Vector{MethodTable}
-    fullmatches::Vector{Bool}
 end
-any_ambig(m::UnionSplitMethodMatches) = any(any_ambig, m.info.matches)
+any_ambig(info::UnionSplitInfo) = any(any_ambig, info.matches)
+any_ambig(m::UnionSplitMethodMatches) = any_ambig(m.info)
+fully_covering(info::UnionSplitInfo) = all(info.fullmatches)
+fully_covering(m::UnionSplitMethodMatches) = fully_covering(m.info)
 
 function find_method_matches(interp::AbstractInterpreter, argtypes::Vector{Any}, @nospecialize(atype);
                              max_union_splitting::Int = InferenceParams(interp).max_union_splitting,
@@ -307,7 +308,7 @@ is_union_split_eligible(𝕃::AbstractLattice, argtypes::Vector{Any}, max_union_
 function find_union_split_method_matches(interp::AbstractInterpreter, argtypes::Vector{Any},
                                          @nospecialize(atype), max_methods::Int)
     split_argtypes = switchtupleunion(typeinf_lattice(interp), argtypes)
-    infos = MethodMatchInfo[]
+    infos = MethodLookupResult[]
     applicable = Any[]
     applicable_argtypes = Vector{Any}[] # arrays like `argtypes`, including constants, for each match
     valid_worlds = WorldRange()
@@ -323,29 +324,29 @@ function find_union_split_method_matches(interp::AbstractInterpreter, argtypes::
         if matches === nothing
             return FailedMethodMatch("For one of the union split cases, too many methods matched")
         end
-        push!(infos, MethodMatchInfo(matches))
+        push!(infos, matches)
         for m in matches
             push!(applicable, m)
             push!(applicable_argtypes, arg_n)
         end
         valid_worlds = intersect(valid_worlds, matches.valid_worlds)
         thisfullmatch = any(match::MethodMatch->match.fully_covers, matches)
-        found = false
+        mt_found = false
         for (i, mt′) in enumerate(mts)
             if mt′ === mt
                 fullmatches[i] &= thisfullmatch
-                found = true
+                mt_found = true
                 break
             end
         end
-        if !found
+        if !mt_found
             push!(mts, mt)
             push!(fullmatches, thisfullmatch)
         end
     end
-    info = UnionSplitInfo(infos)
+    info = UnionSplitInfo(infos, mts, fullmatches)
     return UnionSplitMethodMatches(
-        applicable, applicable_argtypes, info, valid_worlds, mts, fullmatches)
+        applicable, applicable_argtypes, info, valid_worlds)
 end
 
 function find_simple_method_matches(interp::AbstractInterpreter, @nospecialize(atype), max_methods::Int)
@@ -360,10 +361,9 @@ function find_simple_method_matches(interp::AbstractInterpreter, @nospecialize(a
         # (assume this will always be true, so we don't compute / update valid age in this case)
         return FailedMethodMatch("Too many methods matched")
     end
-    info = MethodMatchInfo(matches)
     fullmatch = any(match::MethodMatch->match.fully_covers, matches)
-    return MethodMatches(
-        matches.matches, info, matches.valid_worlds, mt, fullmatch)
+    info = MethodMatchInfo(matches, mt, fullmatch)
+    return MethodMatches(matches.matches, info, matches.valid_worlds)
 end
 
 """
@@ -584,9 +584,10 @@ function add_call_backedges!(interp::AbstractInterpreter, @nospecialize(rettype)
     # also need an edge to the method table in case something gets
     # added that did not intersect with any existing method
     if isa(matches, MethodMatches)
-        matches.fullmatch || add_mt_backedge!(sv, matches.mt, atype)
+        fully_covering(matches) || add_mt_backedge!(sv, matches.info.mt, atype)
     else
-        for (thisfullmatch, mt) in zip(matches.fullmatches, matches.mts)
+        matches::UnionSplitMethodMatches
+        for (thisfullmatch, mt) in zip(matches.info.fullmatches, matches.info.mts)
             thisfullmatch || add_mt_backedge!(sv, mt, atype)
         end
     end

base/compiler/ssair/inlining.jl

@@ -50,12 +50,13 @@ struct InliningCase
 end
 
 struct UnionSplit
-    fully_covered::Bool
+    handled_all_cases::Bool # All possible dispatches are included in the cases
+    fully_covered::Bool # All handled cases are fully covering
     atype::DataType
     cases::Vector{InliningCase}
     bbs::Vector{Int}
-    UnionSplit(fully_covered::Bool, atype::DataType, cases::Vector{InliningCase}) =
-        new(fully_covered, atype, cases, Int[])
+    UnionSplit(handled_all_cases::Bool, fully_covered::Bool, atype::DataType, cases::Vector{InliningCase}) =
+        new(handled_all_cases, fully_covered, atype, cases, Int[])
 end
 
 struct InliningEdgeTracker
@@ -215,7 +216,7 @@ end
 
 function cfg_inline_unionsplit!(ir::IRCode, idx::Int, union_split::UnionSplit,
                                 state::CFGInliningState, params::OptimizationParams)
-    (; fully_covered, #=atype,=# cases, bbs) = union_split
+    (; handled_all_cases, fully_covered, #=atype,=# cases, bbs) = union_split
     inline_into_block!(state, block_for_inst(ir, idx))
     from_bbs = Int[]
     delete!(state.split_targets, length(state.new_cfg_blocks))
@@ -235,7 +236,7 @@ function cfg_inline_unionsplit!(ir::IRCode, idx::Int, union_split::UnionSplit,
             end
         end
         push!(from_bbs, length(state.new_cfg_blocks))
-        if !(i == length(cases) && fully_covered)
+        if !(i == length(cases) && (handled_all_cases && fully_covered))
             # This block will have the next condition or the final else case
             push!(state.new_cfg_blocks, BasicBlock(StmtRange(idx, idx)))
             push!(state.new_cfg_blocks[cond_bb].succs, length(state.new_cfg_blocks))
@@ -244,7 +245,10 @@ function cfg_inline_unionsplit!(ir::IRCode, idx::Int, union_split::UnionSplit,
         end
     end
     # The edge from the fallback block.
-    fully_covered || push!(from_bbs, length(state.new_cfg_blocks))
+    # NOTE This edge is only required for `!handled_all_cases` and not `!fully_covered`,
+    #      since in the latter case we inline `Core.throw_methoderror` into the fallback
+    #      block, which is must-throw, making the subsequent code path unreachable.
+    !handled_all_cases && push!(from_bbs, length(state.new_cfg_blocks))
     # This block will be the block everyone returns to
     push!(state.new_cfg_blocks, BasicBlock(StmtRange(idx, idx), from_bbs, orig_succs))
     join_bb = length(state.new_cfg_blocks)
@@ -523,7 +527,7 @@ assuming their order stays the same post-discovery in `ml_matches`.
 function ir_inline_unionsplit!(compact::IncrementalCompact, idx::Int, argexprs::Vector{Any},
                                union_split::UnionSplit, boundscheck::Symbol,
                                todo_bbs::Vector{Tuple{Int,Int}}, interp::AbstractInterpreter)
-    (; fully_covered, atype, cases, bbs) = union_split
+    (; handled_all_cases, fully_covered, atype, cases, bbs) = union_split
     stmt, typ, line = compact.result[idx][:stmt], compact.result[idx][:type], compact.result[idx][:line]
     join_bb = bbs[end]
     pn = PhiNode()
@@ -538,7 +542,7 @@ function ir_inline_unionsplit!(compact::IncrementalCompact, idx::Int, argexprs::
         cond = true
         nparams = fieldcount(atype)
         @assert nparams == fieldcount(mtype)
-        if !(i == ncases && fully_covered)
+        if !(i == ncases && fully_covered && handled_all_cases)
             for i = 1:nparams
                 aft, mft = fieldtype(atype, i), fieldtype(mtype, i)
                 # If this is always true, we don't need to check for it
@@ -597,14 +601,18 @@ function ir_inline_unionsplit!(compact::IncrementalCompact, idx::Int, argexprs::
     end
     bb += 1
     # We're now in the fall through block, decide what to do
-    if !fully_covered
+    if !handled_all_cases
         ssa = insert_node_here!(compact, NewInstruction(stmt, typ, line))
         push!(pn.edges, bb)
         push!(pn.values, ssa)
         insert_node_here!(compact, NewInstruction(GotoNode(join_bb), Any, line))
         finish_current_bb!(compact, 0)
+    elseif !fully_covered
+        insert_node_here!(compact, NewInstruction(Expr(:call, GlobalRef(Core, :throw_methoderror), argexprs...), Union{}, line))
+        insert_node_here!(compact, NewInstruction(ReturnNode(), Union{}, line))
+        finish_current_bb!(compact, 0)
+        ncases == 0 && return insert_node_here!(compact, NewInstruction(nothing, Any, line))
     end
-
     # We're now in the join block.
     return insert_node_here!(compact, NewInstruction(pn, typ, line))
 end
@@ -1348,10 +1356,6 @@ function compute_inlining_cases(@nospecialize(info::CallInfo), flag::UInt32, sig
             # Too many applicable methods
             # Or there is a (partial?) ambiguity
             return nothing
-        elseif length(meth) == 0
-            # No applicable methods; try next union split
-            handled_all_cases = false
-            continue
         end
         local split_fully_covered = false
         for (j, match) in enumerate(meth)
@@ -1392,22 +1396,26 @@ function compute_inlining_cases(@nospecialize(info::CallInfo), flag::UInt32, sig
             handled_all_cases &= handle_any_const_result!(cases,
                 result, match, argtypes, info, flag, state; allow_typevars=true)
         end
+        if !fully_covered
+            atype = argtypes_to_type(sig.argtypes)
+            # We will emit an inline MethodError so we need a backedge to the MethodTable
+            add_uncovered_edges!(state.edges, info, atype)
+        end
     elseif !isempty(cases)
         # if we've not seen all candidates, union split is valid only for dispatch tuples
         filter!(case::InliningCase->isdispatchtuple(case.sig), cases)
     end
-
-    return cases, (handled_all_cases & fully_covered), joint_effects
+    return cases, handled_all_cases, fully_covered, joint_effects
 end
 
 function handle_call!(todo::Vector{Pair{Int,Any}},
     ir::IRCode, idx::Int, stmt::Expr, @nospecialize(info::CallInfo), flag::UInt32, sig::Signature,
     state::InliningState)
     cases = compute_inlining_cases(info, flag, sig, state)
     cases === nothing && return nothing
-    cases, all_covered, joint_effects = cases
+    cases, handled_all_cases, fully_covered, joint_effects = cases
     atype = argtypes_to_type(sig.argtypes)
-    handle_cases!(todo, ir, idx, stmt, atype, cases, all_covered, joint_effects)
+    handle_cases!(todo, ir, idx, stmt, atype, cases, handled_all_cases, fully_covered, joint_effects)
 end
 
 function handle_match!(cases::Vector{InliningCase},
@@ -1496,19 +1504,19 @@ function concrete_result_item(result::ConcreteResult, @nospecialize(info::CallIn
 end
 
 function handle_cases!(todo::Vector{Pair{Int,Any}}, ir::IRCode, idx::Int, stmt::Expr,
-    @nospecialize(atype), cases::Vector{InliningCase}, all_covered::Bool,
+    @nospecialize(atype), cases::Vector{InliningCase}, handled_all_cases::Bool, fully_covered::Bool,
     joint_effects::Effects)
     # 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 all_covered && length(cases) == 1
+    if fully_covered && handled_all_cases && length(cases) == 1
         handle_single_case!(todo, ir, idx, stmt, cases[1].item)
-    elseif length(cases) > 0
+    elseif length(cases) > 0 || handled_all_cases
         isa(atype, DataType) || return nothing
         for case in cases
             isa(case.sig, DataType) || return nothing
         end
-        push!(todo, idx=>UnionSplit(all_covered, atype, cases))
+        push!(todo, idx=>UnionSplit(handled_all_cases, fully_covered, atype, cases))
     else
         add_flag!(ir[SSAValue(idx)], flags_for_effects(joint_effects))
     end

base/compiler/stmtinfo.jl

@@ -33,10 +33,13 @@ not a call to a generic function.
 """
 struct MethodMatchInfo <: CallInfo
     results::MethodLookupResult
+    mt::MethodTable
+    fullmatch::Bool
 end
 nsplit_impl(info::MethodMatchInfo) = 1
 getsplit_impl(info::MethodMatchInfo, idx::Int) = (@assert idx == 1; info.results)
 getresult_impl(::MethodMatchInfo, ::Int) = nothing
+add_uncovered_edges_impl(edges::Vector{Any}, info::MethodMatchInfo, @nospecialize(atype)) = (!info.fullmatch && push!(edges, info.mt, atype); )
 
 """
     info::UnionSplitInfo <: CallInfo
@@ -48,20 +51,27 @@ each partition (`info.matches::Vector{MethodMatchInfo}`).
 This info is illegal on any statement that is not a call to a generic function.
 """
 struct UnionSplitInfo <: CallInfo
-    matches::Vector{MethodMatchInfo}
+    matches::Vector{MethodLookupResult}
+    mts::Vector{MethodTable}
+    fullmatches::Vector{Bool}
 end
 
 nmatches(info::MethodMatchInfo) = length(info.results)
 function nmatches(info::UnionSplitInfo)
     n = 0
     for mminfo in info.matches
-        n += nmatches(mminfo)
+        n += length(mminfo)
     end
     return n
 end
 nsplit_impl(info::UnionSplitInfo) = length(info.matches)
-getsplit_impl(info::UnionSplitInfo, idx::Int) = getsplit_impl(info.matches[idx], 1)
+getsplit_impl(info::UnionSplitInfo, idx::Int) = info.matches[idx]
 getresult_impl(::UnionSplitInfo, ::Int) = nothing
+function add_uncovered_edges_impl(edges::Vector{Any}, info::UnionSplitInfo, @nospecialize(atype))
+    for (mt, fullmatch) in zip(info.mts, info.fullmatches)
+        !fullmatch && push!(edges, mt, atype)
+    end
+end
 
 abstract type ConstResult end
 
@@ -105,6 +115,7 @@ end
 nsplit_impl(info::ConstCallInfo) = nsplit(info.call)
 getsplit_impl(info::ConstCallInfo, idx::Int) = getsplit(info.call, idx)
 getresult_impl(info::ConstCallInfo, idx::Int) = info.results[idx]
+add_uncovered_edges_impl(edges::Vector{Any}, info::ConstCallInfo, @nospecialize(atype)) = add_uncovered_edges!(edges, info.call, atype)
 
 """
     info::MethodResultPure <: CallInfo

base/compiler/tfuncs.jl

@@ -2983,9 +2983,9 @@ function abstract_applicable(interp::AbstractInterpreter, argtypes::Vector{Any},
         # also need an edge to the method table in case something gets
         # added that did not intersect with any existing method
         if isa(matches, MethodMatches)
-            matches.fullmatch || add_mt_backedge!(sv, matches.mt, atype)
+            fully_covering(matches) || add_mt_backedge!(sv, matches.info.mt, atype)
         else
-            for (thisfullmatch, mt) in zip(matches.fullmatches, matches.mts)
+            for (thisfullmatch, mt) in zip(matches.info.fullmatches, matches.info.mts)
                 thisfullmatch || add_mt_backedge!(sv, mt, atype)
             end
         end
@@ -3001,8 +3001,7 @@ function abstract_applicable(interp::AbstractInterpreter, argtypes::Vector{Any},
                 add_backedge!(sv, edge)
             end
 
-            if isa(matches, MethodMatches) ? (!matches.fullmatch || any_ambig(matches)) :
-                    (!all(matches.fullmatches) || any_ambig(matches))
+            if !fully_covering(matches) || any_ambig(matches)
                 # Account for the fact that we may encounter a MethodError with a non-covered or ambiguous signature.
                 rt = Bool
             end

base/compiler/types.jl

@@ -450,10 +450,16 @@ abstract type CallInfo end
 
 nsplit(info::CallInfo) = nsplit_impl(info)::Union{Nothing,Int}
 getsplit(info::CallInfo, idx::Int) = getsplit_impl(info, idx)::MethodLookupResult
+add_uncovered_edges!(edges::Vector{Any}, info::CallInfo, @nospecialize(atype)) = add_uncovered_edges_impl(edges, info, atype)
+
 getresult(info::CallInfo, idx::Int) = getresult_impl(info, idx)
 
+# must implement `nsplit`, `getsplit`, and `add_uncovered_edges!` to opt in to inlining
 nsplit_impl(::CallInfo) = nothing
 getsplit_impl(::CallInfo, ::Int) = error("unexpected call into `getsplit`")
+add_uncovered_edges_impl(edges::Vector{Any}, info::CallInfo, @nospecialize(atype)) = error("unexpected call into `add_uncovered_edges!`")
+
+# must implement `getresult` to opt in to extended lattice return information
 getresult_impl(::CallInfo, ::Int) = nothing
 
 @specialize

test/compiler/AbstractInterpreter.jl

@@ -409,6 +409,7 @@ end
 CC.nsplit_impl(info::NoinlineCallInfo) = CC.nsplit(info.info)
 CC.getsplit_impl(info::NoinlineCallInfo, idx::Int) = CC.getsplit(info.info, idx)
 CC.getresult_impl(info::NoinlineCallInfo, idx::Int) = CC.getresult(info.info, idx)
+CC.add_uncovered_edges_impl(edges::Vector{Any}, info::NoinlineCallInfo, @nospecialize(atype)) = CC.add_uncovered_edges!(edges, info.info, atype)
 
 function CC.abstract_call(interp::NoinlineInterpreter,
     arginfo::CC.ArgInfo, si::CC.StmtInfo, sv::CC.InferenceState, max_methods::Int)
@@ -431,6 +432,8 @@ end
 @inline function inlined_usually(x, y, z)
     return x * y + z
 end
+foo_split(x::Float64) = 1
+foo_split(x::Int) = 2
 
 # check if the inlining algorithm works as expected
 let src = code_typed1((Float64,Float64,Float64)) do x, y, z
@@ -444,6 +447,7 @@ let NoinlineModule = Module()
     main_func(x, y, z) = inlined_usually(x, y, z)
     @eval NoinlineModule noinline_func(x, y, z) = $inlined_usually(x, y, z)
     @eval OtherModule other_func(x, y, z) = $inlined_usually(x, y, z)
+    @eval NoinlineModule bar_split_error() = $foo_split(Core.compilerbarrier(:type, nothing))
 
     interp = NoinlineInterpreter(Set((NoinlineModule,)))
 
@@ -473,6 +477,11 @@ let NoinlineModule = Module()
         @test count(isinvoke(:inlined_usually), src.code) == 0
         @test count(iscall((src, inlined_usually)), src.code) == 0
     end
+
+    let src = code_typed1(NoinlineModule.bar_split_error)
+        @test count(iscall((src, foo_split)), src.code) == 0
+        @test count(iscall((src, Core.throw_methoderror)), src.code) > 0
+    end
 end
 
 # Make sure that Core.Compiler has enough NamedTuple infrastructure