Stop setting force_noinline for function of union arguments (#27057)

The original motivation for setting force_noinline for functions
with union arguments seems to have been bugs in type intersection.
However, the type system has improved quite a bit and at least in
the test suites we don't seem to run into any issues. Thus, we can
stop setting force_noinline. Nevertheless, it still make since
to penalize functions with union arguments. Doing so encourages
union splits to happen at the call site, rather than having multiple
redundant union splits inside the function. However, for simple functions
of intrinsics and builtins it can make a lot of sense to inline
the union split signature.

base/compiler/optimize.jl

@@ -125,7 +125,7 @@ function add_backedge!(li::CodeInstance, caller::OptimizationState)
     nothing
 end
 
-function isinlineable(m::Method, me::OptimizationState, params::OptimizationParams, bonus::Int=0)
+function isinlineable(m::Method, me::OptimizationState, params::OptimizationParams, union_penalties::Bool, bonus::Int=0)
     # compute the cost (size) of inlining this code
     inlineable = false
     cost_threshold = params.inline_cost_threshold
@@ -143,7 +143,7 @@ function isinlineable(m::Method, me::OptimizationState, params::OptimizationPara
         end
     end
     if !inlineable
-        inlineable = inline_worthy(me.src.code, me.src, me.sptypes, me.slottypes, params, cost_threshold + bonus)
+        inlineable = inline_worthy(me.src.code, me.src, me.sptypes, me.slottypes, params, union_penalties, cost_threshold + bonus)
     end
     return inlineable
 end
@@ -219,15 +219,14 @@ function optimize(opt::OptimizationState, params::OptimizationParams, @nospecial
     replace_code_newstyle!(opt.src, ir, nargs)
 
     # determine and cache inlineability
+    union_penalties = false
     if !force_noinline
-        # don't keep ASTs for functions specialized on a Union argument
-        # TODO: this helps avoid a type-system bug mis-computing sparams during intersection
         sig = unwrap_unionall(opt.linfo.specTypes)
         if isa(sig, DataType) && sig.name === Tuple.name
             for P in sig.parameters
                 P = unwrap_unionall(P)
                 if isa(P, Union)
-                    force_noinline = true
+                    union_penalties = true
                     break
                 end
             end
@@ -252,7 +251,7 @@ function optimize(opt::OptimizationState, params::OptimizationParams, @nospecial
                 # For functions declared @inline, increase the cost threshold 20x
                 bonus += params.inline_cost_threshold*19
             end
-            opt.src.inlineable = isinlineable(def, opt, params, bonus)
+            opt.src.inlineable = isinlineable(def, opt, params, union_penalties, bonus)
         end
     end
     nothing
@@ -281,7 +280,9 @@ plus_saturate(x::Int, y::Int) = max(x, y, x+y)
 # known return type
 isknowntype(@nospecialize T) = (T === Union{}) || isa(T, Const) || isconcretetype(widenconst(T))
 
-function statement_cost(ex::Expr, line::Int, src::CodeInfo, sptypes::Vector{Any}, slottypes::Vector{Any}, params::OptimizationParams, error_path::Bool = false)
+function statement_cost(ex::Expr, line::Int, src::CodeInfo, sptypes::Vector{Any},
+                        slottypes::Vector{Any}, union_penalties::Bool,
+                        params::OptimizationParams, error_path::Bool = false)
     head = ex.head
     if is_meta_expr_head(head)
         return 0
@@ -314,6 +315,13 @@ function statement_cost(ex::Expr, line::Int, src::CodeInfo, sptypes::Vector{Any}
                 # tuple iteration/destructuring makes that impossible
                 # return plus_saturate(argcost, isknowntype(extyp) ? 1 : params.inline_nonleaf_penalty)
                 return 0
+            elseif f === Main.Core.isa
+                # If we're in a union context, we penalize type computations
+                # on union types. In such cases, it is usually better to perform
+                # union splitting on the outside.
+                if union_penalties && isa(argextype(ex.args[2],  src, sptypes, slottypes), Union)
+                    return params.inline_nonleaf_penalty
+                end
             elseif (f === Main.Core.arrayref || f === Main.Core.const_arrayref) && length(ex.args) >= 3
                 atyp = argextype(ex.args[3], src, sptypes, slottypes)
                 return isknowntype(atyp) ? 4 : error_path ? params.inline_error_path_cost : params.inline_nonleaf_penalty
@@ -362,10 +370,12 @@ function statement_cost(ex::Expr, line::Int, src::CodeInfo, sptypes::Vector{Any}
     return 0
 end
 
-function statement_or_branch_cost(@nospecialize(stmt), line::Int, src::CodeInfo, sptypes::Vector{Any}, slottypes::Vector{Any}, params::OptimizationParams, throw_blocks::Union{Nothing,BitSet})
+function statement_or_branch_cost(@nospecialize(stmt), line::Int, src::CodeInfo, sptypes::Vector{Any},
+                                  slottypes::Vector{Any}, union_penalties::Bool, params::OptimizationParams,
+                                  throw_blocks::Union{Nothing,BitSet})
     thiscost = 0
     if stmt isa Expr
-        thiscost = statement_cost(stmt, line, src, sptypes, slottypes, params,
+        thiscost = statement_cost(stmt, line, src, sptypes, slottypes, union_penalties, params,
                                   params.unoptimize_throw_blocks && line in throw_blocks)::Int
     elseif stmt isa GotoNode
         # loops are generally always expensive
@@ -379,24 +389,24 @@ function statement_or_branch_cost(@nospecialize(stmt), line::Int, src::CodeInfo,
 end
 
 function inline_worthy(body::Array{Any,1}, src::CodeInfo, sptypes::Vector{Any}, slottypes::Vector{Any},
-                       params::OptimizationParams, cost_threshold::Integer=params.inline_cost_threshold)
+                       params::OptimizationParams, union_penalties::Bool=false, cost_threshold::Integer=params.inline_cost_threshold)
     bodycost::Int = 0
     throw_blocks = params.unoptimize_throw_blocks ? find_throw_blocks(body) : nothing
     for line = 1:length(body)
         stmt = body[line]
-        thiscost = statement_or_branch_cost(stmt, line, src, sptypes, slottypes, params, throw_blocks)
+        thiscost = statement_or_branch_cost(stmt, line, src, sptypes, slottypes, union_penalties, params, throw_blocks)
         bodycost = plus_saturate(bodycost, thiscost)
         bodycost > cost_threshold && return false
     end
     return true
 end
 
-function statement_costs!(cost::Vector{Int}, body::Vector{Any}, src::CodeInfo, sptypes::Vector{Any}, params::OptimizationParams)
+function statement_costs!(cost::Vector{Int}, body::Vector{Any}, src::CodeInfo, sptypes::Vector{Any}, unionpenalties::Bool, params::OptimizationParams)
     throw_blocks = params.unoptimize_throw_blocks ? find_throw_blocks(body) : nothing
     maxcost = 0
     for line = 1:length(body)
         stmt = body[line]
-        thiscost = statement_or_branch_cost(stmt, line, src, sptypes, src.slottypes, params, throw_blocks)
+        thiscost = statement_or_branch_cost(stmt, line, src, sptypes, src.slottypes, unionpenalties, params, throw_blocks)
         cost[line] = thiscost
         if thiscost > maxcost
             maxcost = thiscost

base/reflection.jl

@@ -1161,7 +1161,7 @@ function print_statement_costs(io::IO, @nospecialize(tt::Type);
         code === nothing && error("inference not successful") # inference disabled?
         empty!(cst)
         resize!(cst, length(code.code))
-        maxcost = Core.Compiler.statement_costs!(cst, code.code, code, Any[match.sparams...], params)
+        maxcost = Core.Compiler.statement_costs!(cst, code.code, code, Any[match.sparams...], false, params)
         nd = ndigits(maxcost)
         println(io, meth)
         IRShow.show_ir(io, code, (io, linestart, idx) -> (print(io, idx > 0 ? lpad(cst[idx], nd+1) : " "^(nd+1), " "); return ""))