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inference: propagate variable changes to all exception frames #42081

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Sep 3, 2021
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inference: propagate variable changes to all exception frames #42081

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b672e6c
inference: propagate variable changes to all exception frames
vtjnash Sep 1, 2021
ec9f9a5
Update test/compiler/inference.jl
vtjnash Sep 1, 2021
c759eee
Update test/compiler/inference.jl
vtjnash Sep 2, 2021
695f9f8
fixup! inference: propagate variable changes to all exception frames
vtjnash Sep 2, 2021
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43 changes: 20 additions & 23 deletions base/compiler/abstractinterpretation.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1764,18 +1764,16 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
ssavaluetypes = frame.src.ssavaluetypes::Vector{Any}
while frame.pc´´ <= n
# make progress on the active ip set
local pc::Int = frame.pc´´ # current program-counter
local pc::Int = frame.pc´´
while true # inner loop optimizes the common case where it can run straight from pc to pc + 1
#print(pc,": ",s[pc],"\n")
local pc´::Int = pc + 1 # next program-counter (after executing instruction)
if pc == frame.pc´´
# need to update pc´´ to point at the new lowest instruction in W
min_pc = _bits_findnext(W.bits, pc + 1)
frame.pc´´ = min_pc == -1 ? n + 1 : min_pc
# want to update pc´´ to point at the new lowest instruction in W
frame.pc´´ = pc´
end
delete!(W, pc)
frame.currpc = pc
frame.cur_hand = frame.handler_at[pc]
edges = frame.stmt_edges[pc]
edges === nothing || empty!(edges)
frame.stmt_info[pc] = nothing
Expand Down Expand Up @@ -1817,7 +1815,6 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
pc´ = l
else
# general case
frame.handler_at[l] = frame.cur_hand
changes_else = changes
if isa(condt, Conditional)
changes_else = conditional_changes(changes_else, condt.elsetype, condt.var)
Expand Down Expand Up @@ -1877,7 +1874,6 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
elseif hd === :enter
stmt = stmt::Expr
l = stmt.args[1]::Int
frame.cur_hand = Pair{Any,Any}(l, frame.cur_hand)
# propagate type info to exception handler
old = states[l]
newstate_catch = stupdate!(old, changes)
Expand All @@ -1889,12 +1885,7 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
states[l] = newstate_catch
end
typeassert(states[l], VarTable)
frame.handler_at[l] = frame.cur_hand
elseif hd === :leave
stmt = stmt::Expr
for i = 1:((stmt.args[1])::Int)
frame.cur_hand = (frame.cur_hand::Pair{Any,Any}).second
end
else
if hd === :(=)
stmt = stmt::Expr
Expand Down Expand Up @@ -1928,16 +1919,22 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
ssavaluetypes[pc] = t
end
end
if frame.cur_hand !== nothing && isa(changes, StateUpdate)
# propagate new type info to exception handler
# the handling for Expr(:enter) propagates all changes from before the try/catch
# so this only needs to propagate any changes
l = frame.cur_hand.first::Int
if stupdate1!(states[l]::VarTable, changes::StateUpdate) !== false
if l < frame.pc´´
frame.pc´´ = l
if isa(changes, StateUpdate)
let cur_hand = frame.handler_at[pc], l, enter
while cur_hand != 0
enter = frame.src.code[cur_hand]
l = (enter::Expr).args[1]::Int
# propagate new type info to exception handler
# the handling for Expr(:enter) propagates all changes from before the try/catch
# so this only needs to propagate any changes
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if stupdate1!(states[l]::VarTable, changes::StateUpdate) !== false
if l < frame.pc´´
frame.pc´´ = l
end
push!(W, l)
end
Comment on lines +1930 to +1935
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Well, why do we want to propagate changes via :enter ? Can't we propagate changes directly to :leave statements here ?

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The l value here is short for :leave (strictly speaking, it doesn't have to be a :leave, but it normally will be)

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frame.src.code[l] is supposed to be :enter expression always, no ?
My understanding is that the algorithm accumulates all changes within try/catch clauses to :enter expression's states, and then :enter will propagate the changes to :leave.

So I wonder why we don't want to do:

if isa(changes, StateUpdate)
    while cur_hand != 0
        let l = frame.handler_at[cur_hand + 1]
            # propagate new type info to exception handler
            enter = frame.src.code[l]
            @assert isexpr(enter, :enter)
            leavestate = states[enter.args[1]::Int]::VarTable
            stupdate1!(leavestate, changes::StateUpdate) !== false
        end
        cur_hand = frame.handler_at[cur_hand]
    end
end

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Because l is almost always a :leave expr there

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oh, or was supposed to be, until I rearranged the code, and then it wasn't anymore

cur_hand = frame.handler_at[cur_hand]
end
push!(W, l)
end
end
end
Expand All @@ -1950,7 +1947,6 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
end

pc´ > n && break # can't proceed with the fast-path fall-through
frame.handler_at[pc´] = frame.cur_hand
newstate = stupdate!(states[pc´], changes)
if isa(stmt, GotoNode) && frame.pc´´ < pc´
# if we are processing a goto node anyways,
Expand All @@ -1961,7 +1957,7 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
states[pc´] = newstate
end
push!(W, pc´)
pc = frame.pc´´
break
elseif newstate !== nothing
states[pc´] = newstate
pc = pc´
Expand All @@ -1971,6 +1967,7 @@ function typeinf_local(interp::AbstractInterpreter, frame::InferenceState)
break
end
end
frame.pc´´ = _bits_findnext(W.bits, frame.pc´´)::Int # next program-counter
end
frame.dont_work_on_me = false
nothing
Expand Down
103 changes: 91 additions & 12 deletions base/compiler/inferencestate.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -28,9 +28,7 @@ mutable struct InferenceState
pc´´::LineNum
nstmts::Int
# current exception handler info
cur_hand #::Union{Nothing, Pair{LineNum, prev_handler}}
handler_at::Vector{Any}
n_handlers::Int
handler_at::Vector{LineNum}
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I think "handler_at" naming is actually a bit confusing ? To me "entered_at" sounds more reasonable ("handler" usually mean catch clause ... ?).

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I think it is the same to say it is handled by the try statement. The catch / leave is where we stop handling errors (which is why it is simpler to point to the try statement also, since we have more information there)

# ssavalue sparsity and restart info
ssavalue_uses::Vector{BitSet}
throw_blocks::BitSet
Expand Down Expand Up @@ -86,25 +84,21 @@ mutable struct InferenceState
throw_blocks = find_throw_blocks(code)

# exception handlers
cur_hand = nothing
handler_at = Any[ nothing for i=1:n ]
n_handlers = 0

W = BitSet()
push!(W, 1) #initial pc to visit
ip = BitSet()
handler_at = compute_trycatch(src.code, ip)
push!(ip, 1)

mod = isa(def, Method) ? def.module : def

valid_worlds = WorldRange(src.min_world,
src.max_world == typemax(UInt) ? get_world_counter() : src.max_world)

frame = new(
InferenceParams(interp), result, linfo,
sp, slottypes, mod, 0,
IdSet{InferenceState}(), IdSet{InferenceState}(),
src, get_world_counter(interp), valid_worlds,
nargs, s_types, s_edges, stmt_info,
Union{}, W, 1, n,
cur_hand, handler_at, n_handlers,
Union{}, ip, 1, n, handler_at,
ssavalue_uses, throw_blocks,
Vector{Tuple{InferenceState,LineNum}}(), # cycle_backedges
Vector{InferenceState}(), # callers_in_cycle
Expand All @@ -118,6 +112,91 @@ mutable struct InferenceState
end
end

function compute_trycatch(code::Vector{Any}, ip::BitSet)
# The goal initially is to record the frame like this for the state at exit:
# 1: (enter 3) # == 0
# 3: (expr) # == 1
# 3: (leave 1) # == 1
# 4: (expr) # == 0
# then we can find all trys by walking backwards from :enter statements,
# and all catches by looking at the statement after the :enter
n = length(code)
empty!(ip)
ip.offset = 0 # for _bits_findnext
push!(ip, n + 1)
handler_at = fill(0, n)

# start from all :enter statements and record the location of the try
for pc = 1:n
stmt = code[pc]
if isexpr(stmt, :enter)
l = stmt.args[1]::Int
handler_at[pc + 1] = pc
push!(ip, pc + 1)
handler_at[l] = pc
push!(ip, l)
end
end

# now forward those marks to all :leave statements
pc´´ = 0
while true
# make progress on the active ip set
pc = _bits_findnext(ip.bits, pc´´)::Int
pc > n && break
while true # inner loop optimizes the common case where it can run straight from pc to pc + 1
pc´ = pc + 1 # next program-counter (after executing instruction)
if pc == pc´´
pc´´ = pc´
end
delete!(ip, pc)
cur_hand = handler_at[pc]
@assert cur_hand != 0 "unbalanced try/catch"
stmt = code[pc]
if isa(stmt, GotoNode)
pc´ = stmt.label
elseif isa(stmt, GotoIfNot)
l = stmt.dest::Int
if handler_at[l] != cur_hand
@assert handler_at[l] == 0 "unbalanced try/catch"
handler_at[l] = cur_hand
if l < pc´´
pc´´ = l
end
push!(ip, l)
end
elseif isa(stmt, ReturnNode)
@assert !isdefined(stmt, :val) "unbalanced try/catch"
break
elseif isa(stmt, Expr)
head = stmt.head
if head === :enter
cur_hand = pc
elseif head === :leave
l = stmt.args[1]::Int
for i = 1:l
cur_hand = handler_at[cur_hand]
end
cur_hand == 0 && break
end
end

pc´ > n && break # can't proceed with the fast-path fall-through
if handler_at[pc´] != cur_hand
@assert handler_at[pc´] == 0 "unbalanced try/catch"
handler_at[pc´] = cur_hand
elseif !in(pc´, ip)
break # already visited
end
pc = pc´
end
end

@assert first(ip) == n + 1
return handler_at
end


"""
Iterate through all callers of the given InferenceState in the abstract
interpretation stack (including the given InferenceState itself), vising
Expand Down
45 changes: 45 additions & 0 deletions test/compiler/inference.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -3428,3 +3428,48 @@ end
f41908(x::Complex{T}) where {String<:T<:String} = 1
g41908() = f41908(Any[1][1])
@test only(Base.return_types(g41908, ())) <: Int

# issue #42022
let x = Tuple{Int,Any}[
#= 1=# (0, Expr(:(=), Core.SlotNumber(3), 1))
#= 2=# (0, Expr(:enter, 18))
#= 3=# (2, Expr(:(=), Core.SlotNumber(3), 2.0))
#= 4=# (2, Expr(:enter, 12))
#= 5=# (4, Expr(:(=), Core.SlotNumber(3), '3'))
#= 6=# (4, Core.GotoIfNot(Core.SlotNumber(2), 9))
#= 7=# (4, Expr(:leave, 2))
#= 8=# (0, Core.ReturnNode(1))
#= 9=# (4, Expr(:call, GlobalRef(Main, :throw)))
#=10=# (4, Expr(:leave, 1))
#=11=# (2, Core.GotoNode(16))
#=12=# (4, Expr(:leave, 1))
#=13=# (2, Expr(:(=), Core.SlotNumber(4), Expr(:the_exception)))
#=14=# (2, Expr(:call, GlobalRef(Main, :rethrow)))
#=15=# (2, Expr(:pop_exception, Core.SSAValue(4)))
#=16=# (2, Expr(:leave, 1))
#=17=# (0, Core.GotoNode(22))
#=18=# (2, Expr(:leave, 1))
#=19=# (0, Expr(:(=), Core.SlotNumber(5), Expr(:the_exception)))
#=20=# (0, nothing)
#=21=# (0, Expr(:pop_exception, Core.SSAValue(2)))
#=22=# (0, Core.ReturnNode(Core.SlotNumber(3)))
]
handler_at = Core.Compiler.compute_trycatch(last.(x), Core.Compiler.BitSet())
@test handler_at == first.(x)
end

@test only(Base.return_types((Bool,)) do y
x = 1
try
x = 2.0
try
x = '3'
y ? (return 1) : throw()
catch ex1
rethrow()
end
catch ex2
nothing
end
return x
end) === Union{Int, Float64, Char}