1. 7.4 Boolean Expression and Control Flow Statements
Two goals of Boolean expression
Calculate logic value c = (a > b) && a > 1
Conditional expression in control flow
if (a > b && a > 1) then …
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2. 7.4 Boolean Expression and Control Flow Statements
Two ways of calculation：
if ( 1 or i++ > 3) then
Non short-circuit
E1 or E2
Short-circuit
E1 or E => if E1 then true else E2
E1 and E2 => if E1 then E2 else false

3. 7.4 Boolean Expression and Control Flow Statements
7.4.1 Translation for Boolean Expressions
E  E or E | E and E | not E | ( E )
| id relop id | true | false
a < b
100: if a < b goto 103
101: t := 0
102: goto 104
103: t := 1
104:
>, >=, <, <=, <>, ==
对于a<b的翻译而言，由于三地址代码中不包括形如t=a<b的格式，故此使用if x relop y goto L 来实现。

4. 7.4 Boolean Expression and Control Flow Statements
E  E1 or E2 {E.place := newtemp;
emit (E.place, ‘:=’, E1.place, ‘or’ E2.place) }
E  id1 relop id2
{E.place := newtemp;
emit (‘if’, id1.place, relop.op, id2.place, ‘goto’, nextstat+3 );
emit (E.place, ‘:=’, ‘0’ );
emit (‘goto’, nextstat + 2 );
emit (E.place, ‘:=’, ‘1’ ) }
a < b的翻译
100: if a < b goto 103
101: t := 0
102: goto 104
103: t := 1
104:

5. 7.4 Boolean Expression and Control Flow Statements
7.4.2 Translation of control flow statements
S  if E then S1
| if E then S1 else S2
| while E do S1
| S1; S2
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6. 7.4 Boolean Expression and Control Flow Statements
To E.true
To E.true
E.code
To E.false
E.code
To E.false
E.true:
E.true:
S1.code
S1.code
. . .
S1.next:
goto S.next (S1.next)
E.false:
S2.code
E s1
(a) if--then
. . .
E s1 s2
(b) if-then-else
E.code
S1.code
E.true:
. . .
To E.true
To E.false
goto S.begin
S.begin:
(c) while-do
S1.code
S2.code
S1.next:
. . .
(d) S1; S2
E s1

7. 7.4 Boolean Expression and Control Flow Statements
E.code
S1.code
E.true:
. . .
To E.true
To E.false
(a) if-then
S  if E then S1
{E.true := newlabel;
E.false := S.next;
S1.next := S.next;
S.code := E.code || gen(E.true, ‘:’) || S1.code }

8. 7.4 Boolean Expression and Control Flow Statements
E.code
S1.code
E.true:
. . .
To E.true
To E.false
E.false:
goto S.next
S2.code
(b) if-then-else
S  if E then S1 else S2
{E.true := newlabel;
E.false := newlabel;
S1.next := S.next;
S2.next := S.next;
S.code := E.code || gen(E.true, ‘:’) || S1.code ||
gen(‘goto’, S.next) || gen(E.false, ‘:’) ||
S2.code}

9. 7.4 Boolean Expression and Control Flow Statements
S  while E do S1
{S.begin:= newlabel;
E.true := newlabel;
E.false := S.next;
S1.next := S.begin;
S.code := gen(S.begin, ‘:’) || E.code ||
gen(E.true, ‘:’) || S1.code || gen(‘goto’, S.begin) }
E.code
S1.code
E.true:
. . .
To E.true
To E.false
goto S.begin
S.begin:
(c) while-do

10. 7.4 Boolean Expression and Control Flow Statements
S  S1; S2
{S.code := S1.code || gen(S1.next, ‘:’) || S2.code }
S1.code
S2.code
S1.next:
. . .
(d) S1; S2
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11. 7.4 Boolean Expression and Control Flow Statements
7.4.3 Translation for Boolean Expression based Control Flow
If E of a < b format,
The corresponding code is:
if a < b goto E.true
goto E.false

12. 7.4 Boolean Expression and Control Flow Statements
The code for
a < b or c < d and e < f
is:
if a < b goto Ltrue
goto L1
L1: if c < d goto L2
goto Lfalse
L2: if e < f goto Ltrue

13. 7.4 Boolean Expression and Control Flow Statements
To E1.true
E1.code
To E1.false
E1.true:
E  E1 and E2
{E1.true := newlabel;
E1.false := E.false;
E2.true := E.true;
E2.false := E.false;
E.code := E1.code || gen(E1.true, ‘:’) || E2.code }
E2.code
. . .
E1 and E2

14. 7.4 Boolean Expression and Control Flow Statements
E  E1 and E2
{E1.true := newlabel;
E1.false := E.false;
E2.true := E.true;
E2.false := E.false;
E.code := E1.code || gen(E1.true, ‘:’) || E2.code }
E  (E1 )
{E1.true := E.true;
E.code := E1.code }

15. 7.4 Boolean Expression and Control Flow Statements
E  E1 or E2
{E1.true := E.true;
E1.false := newlabel;
E2.true := E.true;
E2.false := E.false;
E.code := E1.code || gen(E1.false, ‘:’) || E2.code }
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16. 7.4 Boolean Expression and Control Flow Statements
E  E1 or E2
{E1.true := E.true;
E1.false := newlabel;
E2.true := E.true;
E2.false := E.false;
E.code := E1.code || gen(E1.false, ‘:’) || E2.code }
E  not E1
{E1.true := E.false;
E1.false := E.true;
E.code := E1.code }

17. 7.4 Boolean Expression and Control Flow Statements
E:a < b，
The code is:
if a < b goto E.true
goto E.false
E  id1 relop id2
{E.code := gen(‘if’, id1.place, relop.op, id2.place,
‘goto’, E.true) ||
gen(‘goto’, E.false) }
E  true
{E.code := gen(‘goto’, E.true)}
E  false
{E.code := gen(‘goto’, E.false)}

18. 7.4 Boolean Expression and Control Flow Statements
7.4.4 Translation for Switch Statement
switch E
begin
case V1: S1
case V2: S2
. . .
case Vn - 1: Sn – 1
default: Sn
end

19. 7.4 Boolean Expression and Control Flow Statements
Small number of cases:
t := E’s code
if t  V1 goto L1
S1’s code
goto next
L1: if t  V2 goto L2
S2’s code
L2: . . .
. . .
Ln-2: if t  Vn-1 goto Ln-1
Sn -1’s code
| goto next
Ln-1: Sn’s code
next:

20. 7.4 Boolean Expression and Control Flow Statements
Large number of cases, put the test code for the cases together
t := E's code | Ln: Sn's code
goto test | goto next
L1: S1's code |test: if t = V1 goto L1
goto next | if t = V2 goto L2
L2: S2's code |
goto next | if t = Vn-1 goto Ln-1
| goto Ln
Ln-1: Sn -1's code | next:
goto next
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21. 7.4 Boolean Expression and Control Flow Statements
In IR, add a special case, to facilitate the special processing for it
test: case V1 L1
case V2 L2
. . .
case Vn-1 Ln-1
case t Ln
next:

22. 7.4 Boolean Expression and Control Flow Statements
7.4.5 Translation for procedure calls
S  call id (Elist)
Elist  Elist, E
Elist  E

23. 7.4 Boolean Expression and Control Flow Statements
The IR structure of calling id(E1, E2, …, En)
E1.place := E1's code
E2.place := E2's code
. . .
En.place := En's code
param E1.place
param E2.place
param En.place
call id.place, n

24. 7.4 Boolean Expression and Control Flow Statements
S  call id (Elist)
{For each E.place in the queue,
emit(‘param’, E.place);
emit(‘call’, id.plase, n) }
Elist  Elist, E
{Push E.place to the end of queue}
Elist  E
{Initialize the queue, make it contain only E.place}
E1.place | E2.place | E3.place | E4.place …..

25. Revision Types of IRs, and the transformation between them
Structure of the symbol table, and the storage of the scope information
Two ways of realization for Boolean expressions
IR structures for assignment/control flow statements, and their translation schemes
IR structures for procedure call, and the translation schemes
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