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Merge pull request #1582 from goblint/refactor-loopUnroll
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Refactor loopUnrolling autotuner
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@karoliineh
karoliineh authored Sep 30, 2024
2 parents 815336e + 3e9f3cd commit 1f2bb69
Showing 1 changed file with 74 additions and 72 deletions.
146 changes: 74 additions & 72 deletions src/util/loopUnrolling.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -210,89 +210,91 @@ let constBefore var loop f =
in
fst @@ lastAssignmentToVarBeforeLoop (Some Z.zero) f.sbody.bstmts (*the top level call should never return false*)

let rec loopIterations start diff comp =
let flip = function
| Lt -> Gt
| Gt -> Lt
| Ge -> Le
| Le -> Ge
| s -> s
in let loopIterations' goal shouldBeExact =
let range = Z.sub goal start in
if Z.equal diff Z.zero || Z.equal range Z.zero || (Z.gt diff Z.zero && Z.lt range Z.zero) || (Z.lt diff Z.zero && Z.gt range Z.zero) then
None (*unfitting parameters*)
else (
let roundedDown = Z.div range diff in
let isExact = Z.equal (Z.mul roundedDown diff) range in
if isExact then
Some roundedDown
else if shouldBeExact then
None
else
Some (Z.succ roundedDown)
)
in
match comp with
| BinOp (op, (Const _ as c), var, t) -> loopIterations start diff (BinOp (flip op, var, c, t))
| BinOp (Lt, _, (Const (CInt (cint,_,_) )), _) -> if Z.lt diff Z.zero then None else loopIterations' cint false
| BinOp (Gt, _, (Const (CInt (cint,_,_) )), _) -> if Z.gt diff Z.zero then None else loopIterations' cint false
| BinOp (Le, _, (Const (CInt (cint,_,_) )), _) -> if Z.lt diff Z.zero then None else loopIterations' (Z.succ cint) false
| BinOp (Ge, _, (Const (CInt (cint,_,_) )), _) -> if Z.gt diff Z.zero then None else loopIterations' (Z.pred cint) false
| BinOp (Ne, _, (Const (CInt (cint,_,_) )), _) -> loopIterations' cint true
(*find a single break in the else branch of a toplevel if*)
let findBreakComparison loopStatement =
try
let compOption = ref None in
let visitor = new findBreakVisitor (compOption) in
ignore @@ visitCilBlock visitor (loopBody loopStatement);
!compOption
with WrongOrMultiple ->
None

let getLoopVar = function
| BinOp (op, (Const (CInt (goal, _, _) )), Lval ((Var varinfo), NoOffset), (TInt _)) when isCompare op && not varinfo.vglob ->
(* TODO: define isCompare and flip in cilfacade and refactor to use instead of the many separately defined similar functions *)
let flip = function | Lt -> Gt | Gt -> Lt | Ge -> Le | Le -> Ge | s -> s in
Some (flip op, varinfo, goal)
| BinOp (op, Lval ((Var varinfo), NoOffset), (Const (CInt (goal, _, _) )), (TInt _)) when isCompare op && not varinfo.vglob ->
Some (op, varinfo, goal)
| _ -> None

let getsPointedAt var func =
try
let visitor = new isPointedAtVisitor (var) in
ignore @@ visitCilFunction visitor func;
false
with Found ->
true

let assignmentDifference loop var =
try
let diff = ref None in
let visitor = new findAssignmentConstDiff (diff, var) in
ignore @@ visitCilBlock visitor loop;
!diff
with WrongOrMultiple ->
None

let adjustGoal diff goal op =
match op with
| Lt -> if Z.lt diff Z.zero then None else Some goal
| Gt -> if Z.gt diff Z.zero then None else Some goal
| Le -> if Z.lt diff Z.zero then None else Some (Z.succ goal)
| Ge -> if Z.gt diff Z.zero then None else Some (Z.pred goal)
| Ne -> Some goal
| _ -> failwith "unexpected comparison in loopIterations"

let ( >>= ) = Option.bind
let fixedLoopSize loopStatement func =
let findBreakComparison = try (*find a single break in the else branch of a toplevel if*)
let compOption = ref None in
let visitor = new findBreakVisitor(compOption) in
ignore @@ visitCilBlock visitor (loopBody loopStatement);
!compOption
with | WrongOrMultiple -> None
in let getLoopVar = function
| BinOp (op, (Const (CInt _ )), Lval ((Var info), NoOffset), (TInt _))
| BinOp (op, Lval ((Var info), NoOffset), (Const (CInt _ )), (TInt _)) when isCompare op && not info.vglob->
Some info
| _ -> None
in let getsPointedAt var = try
let visitor = new isPointedAtVisitor(var) in
ignore @@ visitCilFunction visitor func;
false
with | Found -> true
in let assignmentDifference loop var = try
let diff = ref None in
let visitor = new findAssignmentConstDiff(diff, var) in
ignore @@ visitCilBlock visitor loop;
!diff
with | WrongOrMultiple -> None
in
let loopIterations start diff goal shouldBeExact =
let range = Z.sub goal start in
if Z.equal diff Z.zero || Z.equal range Z.zero || (Z.gt diff Z.zero && Z.lt range Z.zero) || (Z.lt diff Z.zero && Z.gt range Z.zero) then
None (*unfitting parameters*)
else (
let roundedDown = Z.div range diff in
let isExact = Z.equal (Z.mul roundedDown diff) range in
if isExact then
Some roundedDown
else if shouldBeExact then
None
else
Some (Z.succ roundedDown)
)

findBreakComparison >>= fun comparison ->
getLoopVar comparison >>= fun var ->
if getsPointedAt var then
let fixedLoopSize loopStatement func =
let open GobOption.Syntax in
let* comparison = findBreakComparison loopStatement in
let* op, var, goal = getLoopVar comparison in
if getsPointedAt var func then
None
else
constBefore var loopStatement func >>= fun start ->
assignmentDifference (loopBody loopStatement) var >>= fun diff ->
Logs.debug "comparison: ";
Pretty.fprint stderr (dn_exp () comparison) ~width:max_int;
Logs.debug "";
Logs.debug "variable: ";
Logs.debug "%s" var.vname;
Logs.debug "start:";
Logs.debug "%s" @@ Z.to_string start;
Logs.debug "diff:";
Logs.debug "%s" @@ Z.to_string diff;
let iterations = loopIterations start diff comparison in
let* start = constBefore var loopStatement func in
let* diff = assignmentDifference (loopBody loopStatement) var in
let* goal = adjustGoal diff goal op in
let iterations = loopIterations start diff goal (op=Ne) in
Logs.debug "comparison: %a" CilType.Exp.pretty comparison;
Logs.debug "variable: %s" var.vname;
Logs.debug "start: %a" GobZ.pretty start;
Logs.debug "diff: %a" GobZ.pretty diff;
match iterations with
| None -> Logs.debug "iterations failed"; None
| Some s ->
try
let s' = Z.to_int s in
Logs.debug "iterations:";
Logs.debug "%d" s';
Logs.debug "iterations: %d" s';
Some s'
with Z.Overflow -> Logs.debug "iterations too big for integer"; None
with Z.Overflow ->
Logs.debug "iterations too big for integer";
None


class arrayVisitor = object
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