From 1a980555aa7db64af2fb745e696ea595fb142c4a Mon Sep 17 00:00:00 2001 From: Son Ho Date: Wed, 23 Feb 2022 18:28:53 +0100 Subject: Improve the code generation by inlining more let-bindings --- src/PureMicroPasses.ml | 129 ++++++++++++++++++++++++++++++++++--------------- 1 file changed, 91 insertions(+), 38 deletions(-) (limited to 'src/PureMicroPasses.ml') diff --git a/src/PureMicroPasses.ml b/src/PureMicroPasses.ml index dd2401b9..9b9107d1 100644 --- a/src/PureMicroPasses.ml +++ b/src/PureMicroPasses.ml @@ -327,60 +327,108 @@ let remove_meta (def : fun_def) : fun_def = let body = obj#visit_texpression () def.body in { def with body } -(** Inline the useless variable reassignments (a lot of variable assignments - like `let x = y in ...ΓΏ` are introduced through the compilation to MIR - and by the translation, and the variable used on the left is often unnamed. +(** Inline the useless variable (re-)assignments: + + A lot of intermediate variable assignments are introduced through the + compilation to MIR and by the translation itself (and the variable used + on the left is often unnamed). + + Note that many of them are just variable "reassignments": `let x = y in ...`. + Some others come from ?? + + TODO: how do we call that when we introduce intermediate variable assignments + for the arguments of a function call? [inline_named]: if `true`, inline all the assignments of the form `let VAR = VAR in ...`, otherwise inline only the ones where the variable on the left is anonymous. + + [inline_pure]: if `true`, inline all the pure assignments where the variable + on the left is anonymous, but the assignments where the r-expression is + a non-primitive function call (i.e.: inline the binops, ADT constructions, + etc.). + + TODO: we have a smallish issue which is that rvalues should be merged with + expressions... For now, this forces us to substitute whenever we can, but + leave the let-bindings where they are, and eliminated them in a subsequent + pass (if they are useless). *) -let inline_useless_var_reassignments (inline_named : bool) (def : fun_def) : - fun_def = - (* Register a substitution. - When registering that we need to substitute v0 with v1, we check - if v1 is itself substituted by v2, in which case we register: - `v0 --> v2` instead of `v0 --> v1` - *) - let add_subst v0 v1 m = - match VarId.Map.find_opt v1 m with - | None -> VarId.Map.add v0 v1 m - | Some v2 -> VarId.Map.add v0 v2 m - in - +let inline_useless_var_reassignments (inline_named : bool) (inline_pure : bool) + (def : fun_def) : fun_def = let obj = - object + object (self) inherit [_] map_expression as super method! visit_Let env monadic lv re e = (* Check that: * - the let-binding is not monadic * - the left-value is a variable - * - the assigned expression is a value *) - match (monadic, lv.value, re.e) with - | false, LvVar (Var (lv_var, _)), Value (rv, _) -> ( - (* Check that: - * - the left variable is unnamed or that [inline_named] is true - * - the right-value is a variable + *) + match (monadic, lv.value) with + | false, LvVar (Var (lv_var, _)) -> + (* Check that: *) + let filter = false in + (* 1. Either: + * - the left variable is unnamed or [inline_named] is true + * - the right-expression is a variable + *) + let filter = + match (inline_named, lv_var.basename) with + | true, _ | _, None -> is_var re + | _ -> filter + in + (* 2. Or: + * - the left variable is an unnamed variable + * - the right-expression is a value or a primitive function call *) - match ((inline_named, lv_var.basename), rv.value) with - | (true, _ | false, None), RvPlace { var; projection = [] } -> - (* Update the environment and explore the next expression - * (dropping the currrent let) *) - let env = add_subst lv_var.id var env in - super#visit_expression env e.e - | _ -> super#visit_Let env monadic lv re e) + let filter = + if inline_pure then + match re.e with + | Value _ -> true + | Call call -> ( + match call.func with + | Regular _ -> false + | Unop _ | Binop _ -> true) + | _ -> filter + else false + in + + (* Update the environment and continue the exploration *) + let re = self#visit_texpression env re in + (* TODO: once rvalues and expressions are merged, filter the + * let-binding (note that for now we leave it, expect it to + * become useless, and wait for a subsequent pass to filter it) *) + (* let env = add_subst lv_var.id re env in *) + let env = if filter then VarId.Map.add lv_var.id re env else env in + let e = self#visit_texpression env e in + Let (monadic, lv, re, e) | _ -> super#visit_Let env monadic lv re e (** Visit the let-bindings to filter the useless ones (and update the substitution map while doing so *) - method! visit_place env p = + method! visit_Value env v mp = (* Check if we need to substitute *) - match VarId.Map.find_opt p.var env with - | None -> (* No substitution *) p - | Some nv -> - (* Substitute *) - { p with var = nv } + match v.value with + | RvPlace p -> ( + match VarId.Map.find_opt p.var env with + | None -> (* No substitution *) super#visit_Value env v mp + | Some ne -> + (* Substitute - note that we need to reexplore, because + * there may be stacked substitutions, if we have: + * var0 --> var1 + * var1 --> var2. + * + * Also: we can always substitute if we substitute with + * a variable. If we substitute with a value we need to + * check the path is empty (TODO: actually do a projection) *) + if is_var ne then + let var = as_var ne in + let p = { p with var } in + let nv = { v with value = RvPlace p } in + self#visit_Value env nv mp + else if p.projection = [] then self#visit_expression env ne.e + else super#visit_Value env v mp) + | _ -> (* No substitution *) super#visit_Value env v mp (** Visit the places used as rvalues, to substitute them if necessary *) end in @@ -901,7 +949,9 @@ let apply_passes_to_def (config : config) (ctx : trans_ctx) (def : fun_def) : (* TODO: reorder the branches of the matches/switches *) - (* The meta-information is now useless: remove it *) + (* The meta-information is now useless: remove it. + * Rk.: some passes below use the fact that we removed the meta-data + * (otherwise we would have to "unmeta" expressions before matching) *) let def = remove_meta def in log#ldebug (lazy ("remove_meta:\n\n" ^ fun_def_to_string ctx def ^ "\n")); @@ -929,7 +979,10 @@ let apply_passes_to_def (config : config) (ctx : trans_ctx) (def : fun_def) : (* Inline the useless variable reassignments *) let inline_named_vars = true in - let def = inline_useless_var_reassignments inline_named_vars def in + let inline_pure = true in + let def = + inline_useless_var_reassignments inline_named_vars inline_pure def + in log#ldebug (lazy ("inline_useless_var_assignments:\n\n" ^ fun_def_to_string ctx def -- cgit v1.2.3