1 / 21

Parameter Passing

Parameter Passing. COP 3402 Software Systems Spring 2014. Parameter Passing. Passing parameter to procedures (instead of using variables) simplifies some types of programs, i.e., recursive procedures. int a, b; procedure sum; int c; begin c := a + b; write c; end; begin a = 2;

louise
Télécharger la présentation

Parameter Passing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Parameter Passing COP 3402 Software Systems Spring 2014

  2. Parameter Passing • Passing parameter to procedures (instead of using variables) simplifies some types of programs, i.e., recursive procedures. int a, b; procedure sum; int c; begin c := a + b; write c; end; begin a = 2; b = 3; call sum; end. procedure sum(a,b); int c; begin c := a + b; write c; end; begin call sum(2,3); end.

  3. Parameter Passing • To implement parameter passing we must modify: • Grammar • Activation Record • Parsing • Code generation

  4. GRAMMAR Changes

  5. Grammar Changes program ::= block "." . block ::= const-declaration var-declaration procedure-declaration statement. const-declaration ::= ["const"ident "=" number {"," ident "=" number} ";"]. var-declaration ::= [ "int "ident {"," ident} “;"]. procedure-declaration ::= { "procedure" ident ";" block ";" } statement ::= [ ident ":=" expression | "call" ident | "begin" statement { ";" statement } "end" | "if" condition "then" statement ["else" statement] | "while" condition "do" statement | "read" ident | "write" expression | e ] . ...

  6. Grammar Changes program ::= block "." . block ::= const-declaration var-declaration procedure-declaration statement. const-declaration ::= ["const"ident "=" number {"," ident "=" number} ";"]. var-declaration ::= [ "int "ident {"," ident} “;"]. procedure-declaration ::= { "procedure" identparam-block ";" block ";" }. param-block ::= "(" [ ident { "," ident} ] ")". param-list ::= "(" [ expression { "," expression} ] ")". statement ::= [ ident ":=" expression | "call" identparam-list | "begin" statement { ";" statement } "end" | "if" condition "then" statement ["else" statement] | "while" condition "do" statement | "read" ident | "write" expression | e ]. ...

  7. Activation Record Changes • The AR must be expanded to include the Parameter Slots. Return Value Return Value Static Link Static Link Dynamic Link Dynamic Link Return Address Return Address Int Slots Param Slots … … Int Slots …

  8. Parsing Changes

  9. PROC-DECL Procedure procedure-declaration ::= { "procedure" ident ";" block ";" }. procedure PROC-DECL (level); begin while TOKEN = "procedure" do begin GET_TOKEN(); if TOKEN <> IDENT then ERROR (missing procedure declaration); ENTER(procedure, ident); GET_TOKEN(); if TOKEN <> ";" then ERROR (procedure declaration must end with ;); GET_TOKEN(); BLOCK(level+1); if TOKEN <> ";" then ERROR (no ; at the end of block); GET_TOKEN(); end; end;

  10. PROC-DECL Procedure procedure-declaration ::= { "procedure" identparam-block ";" block ";" }. procedure PROC-DECL (level); begin while TOKEN = "procedure" do begin GET_TOKEN(); if TOKEN <> IDENT then ERROR (missing procedure declaration); GET_TOKEN(); num_params = PARAM-BLOCK(level); ENTER(procedure, ident, num_params); if TOKEN <> ";" then ERROR (procedure declaration must end with ;); GET_TOKEN(); BLOCK(level+1, num_params); if TOKEN <> ";" then ERROR (no ; at the end of block); GET_TOKEN(); end; end;

  11. PARAM-BLOCK Procedure param-block ::= "(" [ ident { "," ident} ] ")". • procedure PARAM-BLOCK(level); • begin • intparams = 0; • if TOKEN <> "(" then ERROR(); • GET_TOKEN(); • if TOKEN == IDENT then begin • params++; • param_addr = 4 + params; • ENTER(int, ident, param_addr); • GET_TOKEN(); • while TOKEN == "," do begin • GET_TOKEN(); • if TOKEN <> IDENT then ERROR(); • params++; • param_addr = 4 + params; • ENTER(int, ident, param_addr); • GET_TOKEN(); • end • end • if TOKEN <> ")" then ERROR(); • GET_TOKEN(); • return params; • end

  12. STATEMENT Procedure statement ::= … | "call" ident | … procedure STATEMENT(level); … else if TOKEN == "call" then begin GET_TOKEN(); IF TOKEN <> IDENT then ERROR(); GET_TOKEN(); end …

  13. STATEMENT Procedure statement ::= … | "call" identparam-list | … procedure STATEMENT(level, ar_size); … else if TOKEN == "call" then begin GET_TOKEN(); IF TOKEN <> IDENT then ERROR(); GET_TOKEN(); PARAM-LIST(level, ar_size); end …

  14. PARAM-LIST Procedure param-list ::= "(" [ expression { "," expression} ] ")". • procedure PARAM-LIST(level, ar_size); • begin • if TOKEN <> "(" then ERROR(); • GET_TOKEN(); • if TOKEN <> ")" then begin • EXPRESSION(); • while TOKEN == "," do begin • GET_TOKEN(); • EXPRESSION(); • end • end • if TOKEN <> ")" then ERROR(); • GET_TOKEN(); • end

  15. CODE GENERATION Changes

  16. BLOCK Procedure procedure BLOCK(level, num_params); begin ar_size = 4 + num_params; jmpaddr = gen(JMP, 0, 0); if TOKEN = “const” then CONST-DECL(level); if TOKEN = “var” then VAR-DECL(level, &ar_size); if TOKEN = “procedure” then PROC-DECL(level); code[jmpaddr].addr = NEXT_CODE_ADDR; gen(INC, 0, ar_size); STATEMENT(level, ar_size); gen(OPR, 0, 0); end;

  17. PARAM-LIST Procedure procedure PARAM-LIST(level, ar_size); Begin intparam_count = 0; if TOKEN <> "(" then ERROR(); GET_TOKEN(); if TOKEN <> ")" then begin EXPRESSION(); param_count++; gen(STO, curreg, 0, ar_size+4+param_count); curreg--; while TOKEN == "," do begin GET_TOKEN(); EXPRESSION(); param_count++; gen(STO, curreg, 0, ar_size+4+param_count); curreg--; end end if TOKEN <> ")" then ERROR(); GET_TOKEN(); return param_count; end PARAM-LIST must initialize the parameters before we call the procedure. EXPRESSION() gets the value for the parameter… …and here we store the value in the parameter.

  18. PARAM-LIST Procedure procedure PARAM-LIST(level, ar_size); Begin intparam_count = 0; if TOKEN <> "(" then ERROR(); GET_TOKEN(); if TOKEN <> ")" then begin EXPRESSION(); param_count++; gen(STO, curreg, 0, ar_size+4+param_count); curreg--; while TOKEN == "," do begin GET_TOKEN(); EXPRESSION(); param_count++; gen(STO, curreg, 0, ar_size+4+param_count); curreg--; end end if TOKEN <> ")" then ERROR(); GET_TOKEN(); return param_count; end Why???

  19. PARAM-LIST Procedure procedure PARAM-LIST(level, ar_size); Begin intparam_count = 0; if TOKEN <> "(" then ERROR(); GET_TOKEN(); if TOKEN <> ")" then begin EXPRESSION(); param_count++; gen(STO, curreg, 0, ar_size+4+param_count); curreg--; while TOKEN == "," do begin GET_TOKEN(); EXPRESSION(); param_count++; gen(STO, curreg, 0, ar_size+4+param_count); curreg--; end end if TOKEN <> ")" then ERROR(); GET_TOKEN(); return param_count; end Return Value Return Value Current AR Static Link Static Link Dynamic Link Dynamic Link Return Address Return Address Param Slots Param Slots … … Next AR (not created yet!) Int Slots Int Slots … …

  20. Call Code Generation • procedure STATEMENT(level, ar_size); • begin • … • else if TOKEN = "call" then begin • GET_TOKEN(); • if TOKEN <> IDENT then ERROR (missing identifier); • i = find(TOKEN); • if i == 0 then ERROR (); • if symboltype(i) <> PROCEDURE then ERROR(); • param_count = PARAM-LIST(level, ar_size); • if param_count <> symbolparams(i) then ERROR(); • gen(CAL, 0, 0, symboladdr(i)); • GET_TOKEN(); • end • …

  21. Call Code Generation • procedure STATEMENT(level, ar_size); • begin • … • else if TOKEN = "call" then begin • GET_TOKEN(); • if TOKEN <> IDENT then ERROR (missing identifier); • i = find(TOKEN); • if i == 0 then ERROR (); • if symboltype(i) <> PROCEDURE then ERROR(); • param_count = PARAM-LIST(level, ar_size); • if param_count <> symbolparams(i) then ERROR(); • gen(CAL, 0, 0, symboladdr(i)); • GET_TOKEN(); • end • … We must verify that the amount of parameters is exactly the same amount that the procedure declared.

More Related