[M3devel] fixing try/setjmp in a loop?

Tony Hosking hosking at cs.purdue.edu
Mon Jan 31 18:14:09 CET 2011


Hi Jay,

I've not had a chance to digest this, but I do understand the problem.  We need the Variable to be entered into the outermost scope of the procedure in which the TRY appears so that it will have initialization code (assigning NIL) generated for it on entry to the procedure.  Then your usage of the variable should simply check for NIL and alloca if it is, as you already appear to do here.  It would be possible to have the initialization code perform the alloca but then we would have an alloca for every TRY block in a procedure even if they never execute.  Probably not the best plan.

Antony Hosking | Associate Professor | Computer Science | Purdue University
305 N. University Street | West Lafayette | IN 47907 | USA
Office +1 765 494 6001 | Mobile +1 765 427 5484




On Jan 30, 2011, at 5:45 AM, Jay K wrote:

> I'm trying to fix the inadvertant change I made where
> FOR i := 1 TO 10 DO TRY FINALLY END
> 
> will call alloca 10 times.
> 
> I'm not familiar with the frontend, and it is hard for me to understand.
> It seems like it is probably very well factored, written by someone who really knew what they were doing,
> but it is dense, and not verbosely commented.
> 
> Something like this?? But this doesn't work. What am I missing?
> And, we should go the next step and merge the jmpbuf pointer variable with the jmpbuf field in the EF1, right?
> 
> 
> ? 1.txt
> Index: src/misc/Marker.i3
> ===================================================================
> RCS file: /usr/cvs/cm3/m3-sys/m3front/src/misc/Marker.i3,v
> retrieving revision 1.1.1.1
> diff -u -r1.1.1.1 Marker.i3
> --- src/misc/Marker.i3    14 Jan 2001 13:40:31 -0000    1.1.1.1
> +++ src/misc/Marker.i3    30 Jan 2011 10:41:18 -0000
> @@ -64,9 +64,12 @@
>  PROCEDURE SetLock (acquire: BOOLEAN;  var: CG.Var;  offset: INTEGER);
>  (* generate the call to acquire or release a mutex *)
>  
> -PROCEDURE CaptureState (frame: CG.Var;  handler: CG.Label);
> +PROCEDURE CaptureState (frame: CG.Var;  handler: CG.Label;
> +                        jumpbuf: Variable.T);
>  (* call 'setjmp' on 'frame's jmpbuf and branch to 'handler' on re-returns. *)
>  
>  PROCEDURE Reset ();
>  
> +PROCEDURE NewJumpbuf (): Variable.T;
> +
>  END Marker.
> Index: src/misc/Marker.m3
> ===================================================================
> RCS file: /usr/cvs/cm3/m3-sys/m3front/src/misc/Marker.m3,v
> retrieving revision 1.9
> diff -u -r1.9 Marker.m3
> --- src/misc/Marker.m3    13 Jan 2011 14:58:28 -0000    1.9
> +++ src/misc/Marker.m3    30 Jan 2011 10:41:18 -0000
> @@ -10,7 +10,7 @@
>  MODULE Marker;
>  
>  IMPORT CG, Error, Type, Variable, ProcType, ESet, Expr, AssignStmt;
> -IMPORT M3ID, M3RT, Target, Module, RunTyme, Procedure, Host;
> +IMPORT M3ID, M3RT, Target, Module, RunTyme, Procedure, Host, Addr;
>  
>  TYPE
>    Kind = { zFINALLY, zFINALLYPROC, zLOCK, zEXIT, zTRY, zTRYELSE,
> @@ -231,8 +231,10 @@
>      END;
>    END CallFinallyHandler;
>  
> -PROCEDURE CaptureState (frame: CG.Var;  handler: CG.Label) =
> +PROCEDURE CaptureState (frame: CG.Var;  handler: CG.Label;
> +                        jumpbuf: Variable.T) =
>    VAR new: BOOLEAN;
> +      label := CG.Next_label ();
>    BEGIN
>      (* int setjmp(void* ); *)
>      IF (setjmp = NIL) THEN
> @@ -262,13 +264,33 @@
>                                          Target.Word.size, Target.Word.align,
>                                          Target.Word.cg_type, 0);
>      END;
> -    
> -    (* frame.jmpbuf = alloca(Csetjmp__Jumpbuf_size); *)
> +
> +    (* IF jumpuf # NIL THEN    
> +     *   frame.jmpbuf = alloca(Csetjmp__Jumpbuf_size);
> +     * END
> +     *)
> +
> +    CG.Load_nil ();
> +    Variable.Load (jumpbuf);
> +    CG.If_compare (CG.Type.Addr, CG.Cmp.NE, label, CG.Maybe);
> +
>      CG.Start_call_direct (alloca, 0, Target.Address.cg_type);
>      CG.Load_int (Target.Word.cg_type, Jumpbuf_size);
>      CG.Pop_param (Target.Word.cg_type);
>      CG.Call_direct (alloca, Target.Address.cg_type);
> +
> +    (* FUTURE: We should actually have a Variable
> +     * for the entire EF1, including initializing the jumpbuf
> +     * in it. That would save us this extra load/store,
> +     * and save a local variable.
> +     *)
> +    Variable.LoadLValue (jumpbuf);
> +    CG.Swap ();
> +    CG.Store_indirect (CG.Type.Addr, 0, Target.Address.size);
> +    Variable.Load (jumpbuf);
> +
>      CG.Store_addr (frame, M3RT.EF1_jmpbuf);
> +    CG.Set_label (label);
>  
>      (* setmp(frame.jmpbuf) *)
>      CG.Start_call_direct (setjmp, 0, Target.Integer.cg_type);
> @@ -806,5 +828,15 @@
>      tos          := 0;
>    END Reset;
>  
> +PROCEDURE NewJumpbuf (): Variable.T =
> +  VAR jumpbuf: Variable.T;
> +  BEGIN
> +   jumpbuf := Variable.New (M3ID.NoID, TRUE);
> +   Variable.BindType (jumpbuf, Addr.T, indirect := FALSE,
> +                      readonly := FALSE, open_array_ok := FALSE,
> +                      needs_init := TRUE);
> +   RETURN jumpbuf;
> +  END NewJumpbuf;
> +
>  BEGIN
>  END Marker.
> Index: src/stmts/TryFinStmt.m3
> ===================================================================
> RCS file: /usr/cvs/cm3/m3-sys/m3front/src/stmts/TryFinStmt.m3,v
> retrieving revision 1.6
> diff -u -r1.6 TryFinStmt.m3
> --- src/stmts/TryFinStmt.m3    5 Jan 2011 14:34:54 -0000    1.6
> +++ src/stmts/TryFinStmt.m3    30 Jan 2011 10:41:18 -0000
> @@ -10,6 +10,7 @@
>  
>  IMPORT M3ID, CG, Token, Scanner, Stmt, StmtRep, Marker, Target, Type, Addr;
>  IMPORT RunTyme, Procedure, ProcBody, M3RT, Scope, Fmt, Host, TryStmt, Module;
> +IMPORT Variable;
>  FROM Stmt IMPORT Outcome;
>  
>  TYPE
> @@ -20,6 +21,7 @@
>          viaProc  : BOOLEAN;
>          scope    : Scope.T;
>          handler  : HandlerProc;
> +        jumpbuf  : Variable.T := NIL;
>        OVERRIDES
>          check       := Check;
>          compile     := Compile;
> @@ -63,6 +65,11 @@
>      RETURN p;
>    END Parse;
>  
> +PROCEDURE UsesSetjmp (p: P): BOOLEAN =
> +  BEGIN
> +    RETURN NOT (Target.Has_stack_walker OR p.viaProc);
> +  END UsesSetjmp;
> +
>  PROCEDURE Check (p: P;  VAR cs: Stmt.CheckState) =
>    VAR zz: Scope.T;  oc: Stmt.Outcomes;  name: INTEGER;
>    BEGIN
> @@ -95,6 +102,9 @@
>        END;
>      END;
>      TryStmt.PopHandler ();
> +    IF UsesSetjmp (p) THEN
> +     p.jumpbuf := Marker.NewJumpbuf ();
> +    END;
>    END Check;
>  
>  PROCEDURE HandlerName (uid: INTEGER): TEXT =
> @@ -106,11 +116,16 @@
>    END HandlerName;
>  
>  PROCEDURE Compile (p: P): Stmt.Outcomes =
> +  VAR usesSetjmp := FALSE;
> +      result: Stmt.Outcomes;
>    BEGIN
> -    IF Target.Has_stack_walker THEN RETURN Compile1 (p);
> -    ELSIF p.viaProc            THEN RETURN Compile2 (p);
> -    ELSE                            RETURN Compile3 (p);
> +    IF Target.Has_stack_walker THEN result := Compile1 (p);
> +    ELSIF p.viaProc            THEN result := Compile2 (p);
> +    ELSE                            usesSetjmp := TRUE;
> +                                    result := Compile3 (p);
>      END;
> +    <* ASSERT usesSetjmp = UsesSetjmp (p) *>
> +    RETURN result;
>    END Compile;
>  
>  PROCEDURE Compile1 (p: P): Stmt.Outcomes =
> @@ -302,7 +317,9 @@
>      l := CG.Next_label (3);
>      CG.Set_label (l, barrier := TRUE);
>      Marker.PushFrame (frame, M3RT.HandlerClass.Finally);
> -    Marker.CaptureState (frame, l+1);
> +    <* ASSERT UsesSetjmp (p) *>
> +    <* ASSERT p.jumpbuf # NIL *>
> +    Marker.CaptureState (frame, l+1, p.jumpbuf);
>  
>      (* compile the body *)
>      Marker.PushFinally (l, l+1, frame);
> Index: src/stmts/TryStmt.m3
> ===================================================================
> RCS file: /usr/cvs/cm3/m3-sys/m3front/src/stmts/TryStmt.m3,v
> retrieving revision 1.3
> diff -u -r1.3 TryStmt.m3
> --- src/stmts/TryStmt.m3    5 Jan 2011 14:34:54 -0000    1.3
> +++ src/stmts/TryStmt.m3    30 Jan 2011 10:41:18 -0000
> @@ -22,6 +22,7 @@
>          hasElse   : BOOLEAN;
>          elseBody  : Stmt.T;
>          handled   : ESet.T;
> +        jumpbuf   : Variable.T := NIL;
>        OVERRIDES
>          check       := Check;
>          compile     := Compile;
> @@ -153,6 +154,14 @@
>      p.handles := h3;
>    END ReverseHandlers;
>  
> +PROCEDURE UsesSetjmp (p: P): BOOLEAN =
> +  BEGIN
> +    IF (p.handles = NIL) AND (NOT p.hasElse) THEN
> +      RETURN FALSE;
> +    END;
> +    RETURN NOT Target.Has_stack_walker;
> +  END UsesSetjmp;
> +
>  PROCEDURE Check (p: P;  VAR cs: Stmt.CheckState) =
>    VAR h: Handler;  handled: ESet.T;
>    BEGIN
> @@ -182,6 +191,10 @@
>        WHILE (h # NIL) DO CheckHandler (h, cs); h := h.next; END;
>        Stmt.TypeCheck (p.elseBody, cs);
>      PopHandler ();
> +
> +    IF UsesSetjmp (p) THEN
> +      p.jumpbuf := Marker.NewJumpbuf ();
> +    END;
>    END Check;
>  
>  PROCEDURE CheckLabels (h: Handler;  scope: Scope.T;  VAR cs: Stmt.CheckState) =
> @@ -245,14 +258,19 @@
>    END CheckHandler;
>  
>  PROCEDURE Compile (p: P): Stmt.Outcomes =
> +  VAR usesSetjmp := FALSE;
> +      result: Stmt.Outcomes;
>    BEGIN
>      IF (p.handles = NIL) AND (NOT p.hasElse) THEN
> -      RETURN Stmt.Compile (p.body);
> -    END;
> -    IF Target.Has_stack_walker
> -      THEN RETURN Compile1 (p);
> -      ELSE RETURN Compile2 (p);
> +      result := Stmt.Compile (p.body);
> +    ELSIF Target.Has_stack_walker THEN
> +      result := Compile1 (p);
> +    ELSE
> +      usesSetjmp := TRUE;
> +      result := Compile2 (p);
>      END;
> +    <* ASSERT usesSetjmp = UsesSetjmp (p) *>
> +    RETURN result;
>    END Compile;
>  
>  PROCEDURE Compile1 (p: P): Stmt.Outcomes =
> @@ -423,7 +441,9 @@
>      END;
>  
>      (* capture the machine state *)
> -    Marker.CaptureState (frame, l+1);
> +    <* ASSERT UsesSetjmp (p) *>
> +    <* ASSERT p.jumpbuf # NIL *>
> +    Marker.CaptureState (frame, l+1, p.jumpbuf);
>  
>      (* compile the body *)
>      oc := Stmt.Compile (p.body);
> 
> Thanks,
>  - Jay

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