Record captured locals per lambda

Author: c42f

src/closure_conversion.jl

@@ -6,7 +6,7 @@ struct ClosureConversionCtx{GraphType} <: AbstractLoweringContext
 end
 
 function add_lambda_local!(ctx::ClosureConversionCtx, id)
-    push!(ctx.lambda_bindings.locals, id)
+    init_lambda_binding(ctx.lambda_bindings, id)
 end
 
 # Convert `ex` to `type` by calling `convert(type, ex)` when necessary.

src/linear_ir.jl

@@ -399,7 +399,7 @@ function compile_conditional(ctx, ex, false_label)
 end
 
 function add_lambda_local!(ctx::LinearIRContext, id)
-    push!(ctx.lambda_bindings.locals, id)
+    init_lambda_binding(ctx.lambda_bindings, id)
 end
 
 # Lowering of exception handling must ensure that
@@ -941,11 +941,14 @@ function compile_lambda(outer_ctx, ex)
         end
     end
     # Sorting the lambda locals is required to remove dependence on Dict iteration order.
-    for id in sort(collect(ex.lambda_bindings.locals))
-        info = lookup_binding(ctx.bindings, id)
-        @assert info.kind == :local
-        push!(slots, Slot(info.name, :local, false))
-        slot_rewrites[id] = length(slots)
+    for (id, lbinfo) in sort(collect(pairs(ex.lambda_bindings.bindings)), by=first)
+        if !lbinfo.is_captured
+            info = lookup_binding(ctx.bindings, id)
+            if info.kind == :local
+                push!(slots, Slot(info.name, :local, false))
+                slot_rewrites[id] = length(slots)
+            end
+        end
     end
     for (i,arg) in enumerate(children(static_parameters))
         @assert kind(arg) == K"BindingId"

src/scope_analysis.jl

@@ -123,19 +123,49 @@ function NameKey(ex::SyntaxTree)
     NameKey(ex.name_val, get(ex, :scope_layer, _lowering_internal_layer))
 end
 
-struct CaptureInfo
+# Metadata about how a binding is used within some enclosing lambda
+struct LambdaBindingInfo
+    is_captured::Bool
     is_read::Bool
     is_assigned::Bool
     is_called::Bool
 end
 
+LambdaBindingInfo() = LambdaBindingInfo(false, false, false, false)
+
+function LambdaBindingInfo(parent::LambdaBindingInfo;
+                           is_captured = nothing,
+                           is_read     = nothing,
+                           is_assigned = nothing,
+                           is_called   = nothing)
+    LambdaBindingInfo(
+        isnothing(is_captured) ? parent.is_captured : is_captured,
+        isnothing(is_read)     ? parent.is_read     : is_read,
+        isnothing(is_assigned) ? parent.is_assigned : is_assigned,
+        isnothing(is_called)   ? parent.is_called   : is_called,
+    )
+end
+
 struct LambdaBindings
-    # Local bindings within the lambda
-    locals::Set{IdTag}
-    captures::Dict{IdTag,CaptureInfo}
+    # Bindings used within the lambda
+    bindings::Dict{IdTag,LambdaBindingInfo}
 end
 
-LambdaBindings() = LambdaBindings(Set{IdTag}(), Dict{IdTag,CaptureInfo}())
+function init_lambda_binding(binds::LambdaBindings, id; kws...)
+    @assert !haskey(binds.bindings, id)
+    binds.bindings[id] = LambdaBindingInfo(LambdaBindingInfo(); kws...)
+end
+
+function update_lambda_binding!(binds::LambdaBindings, id; kws...)
+    binfo = binds.bindings[id]
+    binds.bindings[id] = LambdaBindingInfo(binfo; kws...)
+end
+
+function update_lambda_binding!(ctx::AbstractLoweringContext, id; kws...)
+    update_lambda_binding!(last(ctx.scope_stack).lambda_bindings, id; kws...)
+end
+
+LambdaBindings() = LambdaBindings(Dict{IdTag,LambdaBindings}())
 
 
 struct ScopeInfo
@@ -230,17 +260,19 @@ function add_lambda_args(ctx, var_ids, args, args_kind)
                       "static parameter name not distinct from function argument"
                 throw(LoweringError(arg, msg))
             end
-            var_ids[varkey] = init_binding(ctx, varkey, args_kind;
-                                           is_nospecialize=getmeta(arg, :nospecialize, false))
+            id = init_binding(ctx, varkey, args_kind;
+                              is_nospecialize=getmeta(arg, :nospecialize, false))
+            var_ids[varkey] = id
         elseif ka != K"BindingId" && ka != K"Placeholder"
             throw(LoweringError(arg, "Unexpected lambda arg kind"))
         end
     end
 end
 
-# Analyze identifier usage within a scope, adding all newly discovered
-# identifiers to ctx.bindings and returning a lookup table from identifier
-# names to their variable IDs
+# Analyze identifier usage within a scope
+# * Allocate a new binding for each identifier which the scope introduces.
+# * Record the identifier=>binding mapping in a lookup table
+# * Return a `ScopeInfo` with the mapping plus additional scope metadata
 function analyze_scope(ctx, ex, scope_type, is_toplevel_global_scope=false,
                        lambda_args=nothing, lambda_static_parameters=nothing)
     parentscope = isempty(ctx.scope_stack) ? nothing : ctx.scope_stack[end]
@@ -251,8 +283,13 @@ function analyze_scope(ctx, ex, scope_type, is_toplevel_global_scope=false,
     assignments, locals, destructured_args, globals,
         used, used_bindings, alias_bindings = find_scope_vars(ex)
 
-    # Create new lookup table for variables in this scope which differ from the
-    # parent scope.
+    # Construct a mapping from identifiers to bindings
+    #
+    # This will contain a binding ID for each variable which is introduced by
+    # the scope, including
+    # * Explicit locals
+    # * Explicit globals
+    # * Implicit locals created by assignment
     var_ids = Dict{NameKey,IdTag}()
 
     if !isnothing(lambda_args)
@@ -272,8 +309,9 @@ function analyze_scope(ctx, ex, scope_type, is_toplevel_global_scope=false,
             end
         elseif var_kind(ctx, varkey) === :static_parameter
             throw(LoweringError(e, "local variable name `$(varkey.name)` conflicts with a static parameter"))
+        else
+            var_ids[varkey] = init_binding(ctx, varkey, :local)
         end
-        var_ids[varkey] = init_binding(ctx, varkey, :local)
     end
 
     # Add explicit globals
@@ -353,24 +391,67 @@ function analyze_scope(ctx, ex, scope_type, is_toplevel_global_scope=false,
         end
     end
 
-    for varkey in used
-        if lookup_var(ctx, varkey) === nothing
-            # Add other newly discovered identifiers as globals
-            init_binding(ctx, varkey, :global)
-        end
-    end
-
+    #--------------------------------------------------
+    # At this point we've discovered all the bindings defined in this scope and
+    # added them to `var_ids`.
+    #
+    # Next we record information about how the new bindings relate to the
+    # enclosing lambda
+    # * All non-globals are recorded (kind :local and :argument will later be turned into slots)
+    # * Captured variables are detected and recorded
     lambda_bindings = is_outer_lambda_scope ? LambdaBindings() : parentscope.lambda_bindings
+
     for id in values(var_ids)
-        vk = var_kind(ctx, id)
-        if vk === :local
-            push!(lambda_bindings.locals, id)
+        binfo = lookup_binding(ctx, id)
+        if !binfo.is_ssa && binfo.kind !== :global
+            init_lambda_binding(lambda_bindings, id)
         end
     end
+
+    # FIXME: This assumes used bindings are internal to the lambda and cannot
+    # be from the environment, and also assumes they are assigned. That's
+    # correct for now but in general we should go by the same code path that
+    # identifiers do.
     for id in used_bindings
-        info = lookup_binding(ctx, id)
-        if !info.is_ssa && info.kind == :local
-            push!(lambda_bindings.locals, id)
+        binfo = lookup_binding(ctx, id)
+        if !binfo.is_ssa && binfo.kind !== :global
+            if !haskey(lambda_bindings.bindings, id)
+                init_lambda_binding(lambda_bindings, id, is_read=true, is_assigned=true)
+            end
+        end
+    end
+
+    for varkey in used
+        id = haskey(var_ids, varkey) ? var_ids[varkey] : lookup_var(ctx, varkey)
+        if id === nothing
+            # Identifiers which are used but not defined in some scope are
+            # newly discovered global bindings
+            init_binding(ctx, varkey, :global)
+        elseif !in_toplevel_thunk
+            binfo = lookup_binding(ctx, id)
+            if binfo.kind !== :global
+                if !haskey(lambda_bindings.bindings, id)
+                    # Used vars from a scope *outside* the current lambda are captured
+                    init_lambda_binding(lambda_bindings, id, is_captured=true, is_read=true)
+                else
+                    update_lambda_binding!(lambda_bindings, id, is_read=true)
+                end
+            end
+        end
+    end
+
+    if !in_toplevel_thunk
+        for (varkey,_) in assignments
+            id = haskey(var_ids, varkey) ? var_ids[varkey] : lookup_var(ctx, varkey)
+            binfo = lookup_binding(ctx, id)
+            if binfo.kind !== :global
+                if !haskey(lambda_bindings.bindings, id)
+                    # Assigned vars from a scope *outside* the current lambda are captured
+                    init_lambda_binding(lambda_bindings, id, is_captured=true, is_assigned=true)
+                else
+                    update_lambda_binding!(lambda_bindings, id, is_assigned=true)
+                end
+            end
         end
     end
 
@@ -410,6 +491,14 @@ function maybe_update_bindings!(ctx, ex)
             throw(LoweringError(ex, "unsupported `const` declaration on local variable"))
         end
         update_binding!(ctx, id; is_const=true)
+    elseif k == K"call"
+        name = ex[1]
+        if kind(name) == K"BindingId"
+            id = name.var_id
+            if haskey(last(ctx.scope_stack).lambda_bindings.bindings, id)
+                update_lambda_binding!(ctx, id, is_called=true)
+            end
+        end
     end
     nothing
 end