[PPT] - Advanced Code Generation Parameter Passing Short-circuit boolean PowerPoint Presentation

SLIDE 1

Advanced Code Generation

Parameter Passing
Short-circuit boolean evaluation
Arrays
Classes

SLIDE 2

Advanced Code Generation

Parameter Passing
Short-circuit boolean evaluation
Arrays
Classes
I’m away this coming Thursday (lecture) and Friday (lab hours).
Will have substitutes for both
Instruction Scheduling (look ahead in slides/notes)
Will be on quiz and/or final
I’m going to a research conference, ACM SIGCSE
Special Interest Group on Computer Science Education
Presenting a paper there with Beth Simon and a student
n Ubiquitous Presenter
I’m away this coming Thursday (lecture) and Friday (lab hours).
Will have substitutes for both
Instruction Scheduling (look ahead in slides/notes)
Will be on quiz and/or final
I’m going to a research conference, ACM SIGCSE
Special Interest Group on Computer Science Education
Presenting a paper there with Beth Simon and a student
n Ubiquitous Presenter

SLIDE 3

Parameter Passing

For call, need to put args at right place

n the stack, without using ‘new’ FP

w := qsort(A, lo+mid, hi) Let’s take model-driven approach (Remember, I’m not doing SPARC)

mid (locals & temps)

ther registers

(state)

ld sp
ld fp

return pc high low A

return value

sp sp

fp

fp

hi

lo A mid (locals & temps)

ther registers

(state)

ld sp
ld fp

return pc

return value

sp sp

fp

fp

SLIDE 4

Parameter Passing

Des ::= Des ‘(‘ A ‘)’ A ::= A ‘,’ E | E <T1 = lo + mid> ; E ld &A, r1 ; A:E st r1, [sp + -4] ; A:E ld T1, r1 ; A:E “load” st r1, [sp + -8] ; A:E “store” ld hi, r1 ; A:E st r1, [sp + -12] ; A:E call qsort ; Des:Des(A) ld [sp + -16], r1 ; Des:Des(A) st r1, T2 ; Des:Des(A) ld T2, r1 ; S : R := E /E st r1, w ; S : R := E /R :=

String r1 = Machine.getReg() foreach a := STO in argument list, p := STO in parameter list do Machine.emitLoad(a, r1); Machine.emitStoreArg(r1, p); end String r1 = Machine.getReg() foreach a := STO in argument list, p := STO in parameter list do Machine.emitLoad(a, r1); Machine.emitStoreArg(r1, p); end

What to do for retrieving

return val?

What to do for args passed

in regs, like SPARC?

What to do for retrieving

return val?

What to do for args passed

in regs, like SPARC?

w := qsort(A, lo+mid, hi)

SLIDE 5

Short-Circuit Boolean Evaluation

Some nice ‘syntactic sugar’ for programmer:

if (x != 0 && y/x > 2) (* when 1st fails, don't test 2nd *) S1 if (y == 0 || x/y < 0) (* when 1st succeeds, don't test 2nd *) S2

Instead of:

if (x != 0) if (y/x > 2) S1 if (y == 0) S2 else if (x/y < 0) S2

How about compiling directly with if/else like this?

SLIDE 6

Short-Circuit Boolean Evaluation

Some nice ‘syntactic sugar’ for programmer:

if (x != 0 && y/x > 2) (* when 1st fails, don't test 2nd *) S1 if (y == 0 || x/y < 0) (* when 1st succeeds, don't test 2nd *) S2

Instead of:

if (x != 0) if (y/x > 2) S1 if (y == 0) S2 else if (x/y < 0) S2

How about compiling directly with if/else like this?

1. Replicate S2 - sounds complicated (e.g., whether to dup

code is an inherited attribute, need a code buffer).

2. Since generating assembly, have both pieces of code

jump to the same single piece of code?

3. Short-circuit booleans are expressions, not statements,

so produce a value, not control flow. We abandoned our model-driven approach!

1. Replicate S2 - sounds complicated (e.g., whether to dup

code is an inherited attribute, need a code buffer).

2. Since generating assembly, have both pieces of code

jump to the same single piece of code?

3. Short-circuit booleans are expressions, not statements,

so produce a value, not control flow. We abandoned our model-driven approach!

SLIDE 7

Mode-Driven Short-Circuit Evaluation

E ::= E T_AND E | E T_OR E Target code: < T1 := y = 0 > ; E : E = E ld T1, r1 ; E OR {} E if r1 goto L1 < T2 := x/y < 0> ; E : E < E ld T2, r2 ; E OR E {} if r2 goto L1 st 0, T3 ; 0 FALSE goto L2 L1: st 1, T3 ; 1 TRUE L2: ... if (y == 0 || x/y < 0) S2 if (y == 0 || x/y < 0) S2

SLIDE 8

Mode-Driven Short-Circuit Evaluation

E ::= E T_AND E | E T_OR E Target code: < T1 := y = 0 > ; E : E = E ld T1, r1 ; E OR {} E if r1 goto L1 < T2 := x/y < 0> ; E : E < E ld T2, r2 ; E OR E {} if r2 goto L1 st 0, T3 ; 0 represents FALSE goto L2 L1: st 1, T3 ; 1 represents TRUE L2: ...

E ::= E:e1 T_OR {: orTrueStack.push(Machine.newLabel());

rFalseStack.push(Machine.newLabel());

RESULT = new ExprSTO(TypeValues.bool); Machine.emitCond(e1, orTrueStack.top()); // if true, jump to set true :} E:e2 {: Machine.emitCond(e2, orTrueStack.top()); // if true, jump, to set true Machine.emitSetFalse(RESULT); // fall through to set false Machine.emitGoto(orFalseStack.top()); Machine.emitLabel(orTrueStack.top()); Machine.emitSetTrue(RESULT); Machine.emitLabel(orFalseStack.pop()); Machine.emitLabel(orTrueStack.pop()); :} E ::= E:e1 T_OR {: orTrueStack.push(Machine.newLabel());

rFalseStack.push(Machine.newLabel());

RESULT = new ExprSTO(TypeValues.bool); Machine.emitCond(e1, orTrueStack.top()); // if true, jump to set true :} E:e2 {: Machine.emitCond(e2, orTrueStack.top()); // if true, jump, to set true Machine.emitSetFalse(RESULT); // fall through to set false Machine.emitGoto(orFalseStack.top()); Machine.emitLabel(orTrueStack.top()); Machine.emitSetTrue(RESULT); Machine.emitLabel(orFalseStack.pop()); Machine.emitLabel(orTrueStack.pop()); :}