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Use path-based control-flow analysis (#88)
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This uses a more sophisticated approach to analyzing control flow,
asking which paths include execution of the required statements and
ensuring we mark those statements that affect critical branching.

Fixes #87
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@timholy
timholy authored Dec 30, 2023
1 parent b167804 commit dde32b1
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Showing 2 changed files with 115 additions and 34 deletions.
101 changes: 78 additions & 23 deletions src/codeedges.jl
View file
Original file line number Diff line number Diff line change
Expand Up @@ -609,6 +609,7 @@ function lines_required!(isrequired::AbstractVector{Bool}, objs, src::CodeInfo,

# Compute basic blocks, which we'll use to make sure we mark necessary control-flow
cfg = Core.Compiler.compute_basic_blocks(src.code) # needed for control-flow analysis
paths = enumerate_paths(cfg)

# We'll mostly use generic graph traversal to discover all the lines we need,
# but structs are in a bit of a different category (especially on Julia 1.5+).
Expand All @@ -627,7 +628,8 @@ function lines_required!(isrequired::AbstractVector{Bool}, objs, src::CodeInfo,
changed |= add_named_dependencies!(isrequired, edges, objs, norequire)

# Add control-flow
changed |= add_control_flow!(isrequired, cfg, norequire)
changed |= add_loops!(isrequired, cfg)
changed |= add_control_flow!(isrequired, cfg, paths)

# So far, everything is generic graph traversal. Now we add some domain-specific information
changed |= add_typedefs!(isrequired, src, edges, typedefs, norequire)
Expand Down Expand Up @@ -701,40 +703,93 @@ function add_obj!(isrequired, objs, obj, edges::CodeEdges, norequire)
return chngd
end

# Add control-flow. For any basic block with an evaluated statement inside it,
# check to see if the block has any successors, and if so mark that block's exit statement.
# Likewise, any preceding blocks should have *their* exit statement marked.
function add_control_flow!(isrequired, cfg, norequire)
## Add control-flow

struct Path
path::Vector{Int}
visited::BitSet
end
Path() = Path(Int[], BitSet())
Path(i::Int) = Path([i], BitSet([i]))
Path(path::Path) = copy(path)
Base.copy(path::Path) = Path(copy(path.path), copy(path.visited))
Base.in(node::Int, path::Path) = node ∈ path.visited
Base.push!(path::Path, node::Int) = (push!(path.path, node); push!(path.visited, node); return path)

# Mark loops that contain evaluated statements
function add_loops!(isrequired, cfg)
changed = false
for (ibb, bb) in enumerate(cfg.blocks)
needed = false
for ibbp in bb.preds
# Is there a backwards-pointing predecessor, and if so are there any required statements between the two?
ibbp > ibb || continue # not a loop-block predecessor
r, rp = rng(bb), rng(cfg.blocks[ibbp])
r = first(r):first(rp)-1
needed |= any(view(isrequired, r))
end
if needed
# Mark the final statement of all predecessors
for ibbp in bb.preds
rp = rng(cfg.blocks[ibbp])
changed |= !isrequired[last(rp)]
isrequired[last(rp)] = true
end
end
end
return changed
end

enumerate_paths(cfg) = enumerate_paths!(Path[], cfg, Path(1))
function enumerate_paths!(paths, cfg, path)
bb = cfg.blocks[path.path[end]]
if isempty(bb.succs)
push!(paths, copy(path))
return paths
end
for ibbs in bb.succs
if ibbs ∈ path
push!(paths, push!(copy(path), ibbs)) # close the loop
continue
end
enumerate_paths!(paths, cfg, push!(copy(path), ibbs))
end
return paths
end

# Mark exits of blocks that bifurcate execution paths in ways that matter for required statements
function add_control_flow!(isrequired, cfg, paths::AbstractVector{Path})
withnode, withoutnode, shared = BitSet(), BitSet(), BitSet()
changed, _changed = false, true
blocks = cfg.blocks
nblocks = length(blocks)
_changed = true
while _changed
_changed = false
for (ibb, bb) in enumerate(blocks)
r = rng(bb)
if any(view(isrequired, r))
if ibb != nblocks
# Check if the exit of this block is a GotoNode
if length(bb.succs) == 1
idxlast = r[end]
idxlast ∈ norequire && continue
_changed |= !isrequired[idxlast]
isrequired[idxlast] = true
end
for ibbp in bb.preds
ibbp > 0 || continue # see Core.Compiler.compute_basic_blocks, near comment re :enter
rpred = rng(blocks[ibbp])
idxlast = rpred[end]
idxlast ∈ norequire && continue
_changed |= !isrequired[idxlast]
isrequired[idxlast] = true
empty!(withnode)
empty!(withoutnode)
for path in paths
union!(ibb ∈ path ? withnode : withoutnode, path.visited)
end
for ibbs in bb.succs
ibbs == nblocks && continue
rpred = rng(blocks[ibbs])
idxlast = rpred[end]
idxlast ∈ norequire && continue
_changed |= !isrequired[idxlast]
isrequired[idxlast] = true
empty!(shared)
union!(shared, withnode)
intersect!(shared, withoutnode)
for icfbb in shared
cfbb = blocks[icfbb]
if any(∉(shared), cfbb.succs)
rcfbb = rng(blocks[icfbb])
idxlast = rcfbb[end]
_changed |= !isrequired[idxlast]
isrequired[idxlast] = true
end
end
end
end
Expand Down Expand Up @@ -850,7 +905,7 @@ function selective_eval!(@nospecialize(recurse), frame::Frame, isrequired::Abstr
pcexec = (pcexec === nothing ? pclast : pcexec)::Int
frame.pc = pcexec
node = pc_expr(frame)
is_return(node) && return lookup_return(frame, node)
is_return(node) && return isrequired[pcexec] ? lookup_return(frame, node) : nothing
isassigned(frame.framedata.ssavalues, pcexec) && return frame.framedata.ssavalues[pcexec]
return nothing
end
Expand Down
48 changes: 37 additions & 11 deletions test/codeedges.jl
View file
Original file line number Diff line number Diff line change
Expand Up @@ -65,7 +65,7 @@ module ModSelective end
# Check that the result of direct evaluation agrees with selective evaluation
Core.eval(ModEval, ex)
isrequired = lines_required(:x, src, edges)
@test sum(isrequired) == 1 + isdefined(Core, :get_binding_type) * 3 # get_binding_type + convert + typeassert
# theere is too much diversity in lowering across Julia versions to make it useful to test `sum(isrequired)`
selective_eval_fromstart!(frame, isrequired)
@test ModSelective.x === ModEval.x
@test allmissing(ModSelective, (:y, :z, :a, :b, :k))
Expand Down Expand Up @@ -128,6 +128,23 @@ module ModSelective end
Core.eval(ModEval, ex)
@test ModSelective.a3 === ModEval.a3 == 2
@test allmissing(ModSelective, (:z3, :x3, :y3))
# ensure we mark all needed control-flow for loops and conditionals,
# and don't fall-through incorrectly
ex = quote
valcf = 0
for i = 1:5
global valcf
if valcf < 4
valcf += 1
end
end
end
frame = Frame(ModSelective, ex)
src = frame.framecode.src
edges = CodeEdges(src)
isrequired = lines_required(:valcf, src, edges)
selective_eval_fromstart!(frame, isrequired)
@test ModSelective.valcf == 4

ex = quote
if Sys.iswindows()
Expand All @@ -143,7 +160,7 @@ module ModSelective end
src = frame.framecode.src
edges = CodeEdges(src)
isrequired = lines_required(:c_os, src, edges)
@test sum(isrequired) >= length(isrequired) - 2
@test sum(isrequired) >= length(isrequired) - 3
selective_eval_fromstart!(frame, isrequired)
Core.eval(ModEval, ex)
@test ModSelective.c_os === ModEval.c_os == Sys.iswindows()
Expand Down Expand Up @@ -359,9 +376,12 @@ module ModSelective end
str = String(take!(io))
@test occursin(r"slot 1:\n preds: ssas: \[\d+, \d+\], slots: ∅, names: ∅;\n succs: ssas: \[\d+, \d+, \d+\], slots: ∅, names: ∅;\n assign @: \[\d+, \d+\]", str)
@test occursin(r"succs: ssas: ∅, slots: \[\d+\], names: ∅;", str)
@test occursin(r"s:\n preds: ssas: \[\d+\], slots: ∅, names: ∅;\n succs: ssas: \[\d+, \d+, \d+\], slots: ∅, names: ∅;\n assign @: \[\d, \d+\]", str) ||
occursin(r"s:\n preds: ssas: \[\d+, \d+\], slots: ∅, names: ∅;\n succs: ssas: \[\d+, \d+, \d+\], slots: ∅, names: ∅;\n assign @: \[\d, \d+\]", str) # with global var inference
if Base.VERSION < v"1.8" # changed by global var inference
# Some of these differ due to changes by Julia version in global var inference
if Base.VERSION < v"1.10"
@test occursin(r"s:\n preds: ssas: \[\d+\], slots: ∅, names: ∅;\n succs: ssas: \[\d+, \d+, \d+\], slots: ∅, names: ∅;\n assign @: \[\d, \d+\]", str) ||
occursin(r"s:\n preds: ssas: \[\d+, \d+\], slots: ∅, names: ∅;\n succs: ssas: \[\d+, \d+, \d+\], slots: ∅, names: ∅;\n assign @: \[\d, \d+\]", str) # with global var inference
end
if Base.VERSION < v"1.8"
@test occursin(r"\d+ preds: ssas: \[\d+\], slots: ∅, names: \[:s\];\n\d+ succs: ssas: ∅, slots: ∅, names: \[:s\];", str)
end
LoweredCodeUtils.print_with_code(io, src, cl)
Expand All @@ -380,17 +400,21 @@ module ModSelective end
edges = CodeEdges(src)
show(io, edges)
str = String(take!(io))
@test occursin(r"s: assigned on \[\d, \d+\], depends on \[\d+\], and used by \[\d+, \d+, \d+\]", str) ||
occursin(r"s: assigned on \[\d, \d+\], depends on \[\d+, \d+\], and used by \[\d+, \d+, \d+\]", str) # global var inference
if Base.VERSION < v"1.10"
@test occursin(r"s: assigned on \[\d, \d+\], depends on \[\d+\], and used by \[\d+, \d+, \d+\]", str) ||
occursin(r"s: assigned on \[\d, \d+\], depends on \[\d+, \d+\], and used by \[\d+, \d+, \d+\]", str) # global var inference
end
if Base.VERSION < v"1.9"
@test (count(occursin("statement $i depends on [1, $(i-1), $(i+1)] and is used by [1, $(i+1)]", str) for i = 1:length(src.code)) == 1) ||
(count(occursin("statement $i depends on [4, $(i-1), $(i+4)] and is used by [$(i+2)]", str) for i = 1:length(src.code)) == 1)
end
LoweredCodeUtils.print_with_code(io, src, edges)
str = String(take!(io))
if isdefined(Base.IRShow, :show_ir_stmt)
@test occursin(r"s: assigned on \[\d, \d+\], depends on \[\d+\], and used by \[\d+, \d+, \d+\]", str) ||
occursin(r"s: assigned on \[\d, \d+\], depends on \[\d+, \d+\], and used by \[\d+, \d+, \d+\]", str)
if Base.VERSION < v"1.10"
@test occursin(r"s: assigned on \[\d, \d+\], depends on \[\d+\], and used by \[\d+, \d+, \d+\]", str) ||
occursin(r"s: assigned on \[\d, \d+\], depends on \[\d+, \d+\], and used by \[\d+, \d+, \d+\]", str)
end
if Base.VERSION < v"1.9"
@test (count(occursin("preds: [1, $(i-1), $(i+1)], succs: [1, $(i+1)]", str) for i = 1:length(src.code)) == 1) ||
(count(occursin("preds: [4, $(i-1), $(i+4)], succs: [$(i+2)]", str) for i = 1:length(src.code)) == 1) # global var inference
Expand All @@ -404,8 +428,10 @@ module ModSelective end
LoweredCodeUtils.print_with_code(io, frame, edges)
str = String(take!(io))
if isdefined(Base.IRShow, :show_ir_stmt)
@test occursin(r"s: assigned on \[\d, \d+\], depends on \[\d+\], and used by \[\d+, \d+, \d+\]", str) ||
occursin(r"s: assigned on \[\d, \d+\], depends on \[\d, \d+\], and used by \[\d+, \d+, \d+\]", str) # global var inference
if Base.VERSION < v"1.10"
@test occursin(r"s: assigned on \[\d, \d+\], depends on \[\d+\], and used by \[\d+, \d+, \d+\]", str) ||
occursin(r"s: assigned on \[\d, \d+\], depends on \[\d, \d+\], and used by \[\d+, \d+, \d+\]", str) # global var inference
end
if Base.VERSION < v"1.9"
@test (count(occursin("preds: [1, $(i-1), $(i+1)], succs: [1, $(i+1)]", str) for i = 1:length(src.code)) == 1) ||
(count(occursin("preds: [4, $(i-1), $(i+4)], succs: [$(i+2)]", str) for i = 1:length(src.code)) == 1) # global var inference
Expand Down

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