slike bài giảng môn chương trình dịch chương 5 syntax-directed translation

Syntax-Directed Translation
Dr. Nguyen Hua Phung
Falcuty of CSE – HCMUT
2007
Outline
• Review
• Syntax-directed definition
• Attributes
• Top-down translation
• Bottom-up translation
CSE - HCMUT Syntax-directed Translation 2
Compilation Phases
CSE - HCMUT Syntax-directed Translation 3
Source code
Scanner
Parser
Semantic analyzer
Intermediate code
generation
Code optimization
Code generation
Sequence of tokens
AST or Parse tree
front end
Symbol
table
AST tree
Intermediate code
Optimized code
back end
Machine code

Pass
• A pass consists of reading an input file
and writing an output file.
• A pass may include many phases
• One-pass or multi-pass compilation
– internal form
– information dependence
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One-pass Compiler
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BKIT code
Scanner √
Parser
Semantic analyzer
Code generation
Sequence of tokens
Parse tree
Symbol
table
Parse tree
Jasmin code
Multi-pass Compiler
BKIT code
Scanner √
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Parser
Semantic analyzer
Code generation
Sequence of tokens
AST

Symbol
table
AST
Jasmin code
Semantic Analyzer
• enforce semantic requirements:
– is an identifier a scalar, array, struct or a method ?
– is an identifier declared before used?
– is an expression type-consistent?
– is a method called with right number and type of args?
– which declaration of a reference is?
– does the dimension of an array match with the
declaration?
–etc.
These requirement does not enforced by a CFG
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Outline
• Review √
• Syntax-directed definition
• Attributes
• Top-down translation
• Bottom-up translation
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Syntax-directed Definition
• Each grammar symbol associates with it a
set of attributes
• Each grammar production associates with
it a set of semantics rules which evaluate
and refer only to attributes associated with
the symbols in the production.

CSE - HCMUT Syntax-directed Translation 9
Example 1
Production Semantic Rules
L → E $
print(E.val)
E → E
1
+ T
E.val = E
1
.val add T.val
E → T
E.val = T.val
T → T
1
* F
T.val = T
1
.val mul F.val
T → F
T.val = F.val
F → ( E )
F.val = E.val
F → digit
F.val = IntVal(digit.lexeme)
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Example 1 (cont’d)
8 + 5 * 4 $
L→ E $ {print(E.val)}
L

28
E→ E + T {E.val = E
1
.val + T.val}
E
$
E T
+
T F
*
CSE - HCMUT Syntax-directed Translation 11
F
T
F
8 5
4
F.val = 8
T.val = 8
E.val = 8
F.val = 5
F.val = 4
E.val = 28
T.val = 20
E
E T
+
T F
*
F
T

F
8 5
4
F.val = 5
E
E T
+
T F
*
F
T
F
8 5
4
F.val = 5
T→ F {T.val = F.val}
E→ T {E.val = T.val}
F→digit {F.val=IntVal(digit.lexeme)}
T→T + F {T.val = T
1
.val * F.val}
Example 2
• 8 + 5 * 4
E
E T
+
CSE - HCMUT Syntax-directed Translation 12
T F
*
T

F F
8 5
4
Parse Tree
Example 2
8 + 5 * 4
BinExp
LitExp(8)
+
BinExp
LitExp(5)
LitExp(4)
*
Abstract Syntax Tree (AST)
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Example 2
Production Semantic Rules
E → E
1
+ T
E.node = new BinExp(E
1
.node,+, T.node)
E → T
E.node = T.node
T → T
1
* F
T.node = new BinExp(T
1

.node,*, F.node)
T → F
T.node = F.node
F → ( E )
F.node = E.node
F → digit
F.node = new LitExp(digit.lexeme)
F → id
F.node = new VarExp(id.lexeme)
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Example 2
8 + 5 * 4
E.node
T.nodeE.node
+
T.node F.node
*
F.node 4
5
T.node
F.node
8
BinExp
BinExpLitExp(8)
LitExp(4)LitExp(5)
*
+
parser tree
AST
F.node=new LitExp(num)

T.node=F.node
E.node=T.node
F.node=new LitExp(num)
T.node=new BinExp(T1.node,*,F.node)E.node=new BinExp(E1.node,+,T.node)
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Outline
• Review √
• Syntax-directed definition √
• Attributes
• Top-down translation
• Bottom-up translation
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Attribute
• An attribute can represent
– a string,
– a number,
– a type,
– a memory location,
– a code fragment,
–etc.
• An attribute has its name and value
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Synthesized Attribute
• An attribute of a grammar symbol in LHS is synthesized
if its value is computed from the values of the attributes
of the grammar symbols in RHS
• A syntax-directed definition that consists of only
synthesized attributes is called a S-attributed definition
8 + 5 * 4 $
L

E
$
E T
+
T F
*
F
T
F
8 5
4
F.val = 8
T.val = 8
E.val = 8
F.val = 5
F.val = 4
E.val = 28
T.val = 20
28
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Inherited Attribute
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• An attribute of a grammar symbol in RHS is inherited if its
value is computed from the values of the attributes of the
grammar symbols in LHS and/or RHS
E → E + T | T
T → T * F | F
F → digit | (E)
⇒
E → T E’

E’ → + T E’ | ∈
T → F T’
T’ → * F T’ | ∈
F → digit | (E)
E
T
E’
T
+
T’
F
*
F
T’
F
8
5
4
E’
T’
8 + 5 * 4
Example
Production Semantic Rules
L → E $
print(E.val)
E → T E’
E’.in = T.val; E.val = E’.val
E’ → + T E’
1
E’

1
.in = E’.in add T.val; E.val = E’
1
.val
E’ →∈
E’.val = E’.in
T → F T’
T’.in = F.val; T.val = T’.val
T’ → * F T’
1
T’
1
.in = T’.in mul F.val; T’.val = T’
1
.val
T’ →∈
T’.val = T’.in
F → ( E )
F.val = E.val
F → digit
F.val = IntVal(digit.lexeme)
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Example
E.val = E’.val = 17
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E
T
E’
T
+

E’
T
F
T’
F
8
5
E’
T’
8 + 5 + 4
+
F
T’
4
T’.in = 5
T.val = 5
T’.val =T’.in
E’.in =T.val = 8
E
1
’.in =E’.in add T.val = 13
T.val = 4
T’.in = 4
E
1
’.in =E’.in add T.val = 17
T’.in = F.val = 8
T.val =T’.val
T’.val =T’.in
T’.val = 4

E’.val = E
1
’.val = 17
E’.val = E
1
’.val=17
E’.val =E’.in
L-attributed Definitions
• A syntax-directed definition is L-attributed
if each inherited attribute of X
j
, 1≤j≤n, on
RHS of A → X
1
X
2
…X
n
, depends only on
– the attributes of X
1
,X
2
,…X
j-1
– the inherited attributes of A
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Example
Production Semantic Rules
L → E $

print(E.val)
E → T E’
E’.in = T.val; E.val = E’.val
E’ → + T E’
1
E’
1
.in = E’.in add T.val; E.val = E’
1
.val
E’ →∈
E’.val = E’.in
T → F T’
T’.in = F.val; T.val = T’.val
T’ → * F T’
1
T’
1
.in = T’.in mul F.val; T’.val = T’
1
.val
T’ →∈
T’.val = T’.in
F → ( E )
F.val = E.val
F → digit
F.val = IntVal(digit.lexeme)
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Outline
• Review √

• Syntax-directed definition √
• Attributes √
• Top-down translation
• Bottom-up translation
CSE - HCMUT Syntax-directed Translation 24
Implementation
• Graph-based methods:
– create a dependence graph
– topological sort
– calculate all attibutes
– many passes
• Rule-based methods:
– the order in which the attributes are evaluated
is predetermined
– one-pass evaluation
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