1. Compiler Construction
Sohail Aslam
Lecture 33
compiler: Bottom-up Parsing

2. Implementing Ad-Hoc Scheme
Parser needs a mechanism to pass values of attributes from definitions in one snippet to uses in another
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compiler: Bottom-up Parsing

3. Implementing Ad-Hoc Scheme
We will adopt notation used by YACC for snippets and passing values
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compiler: Bottom-up Parsing

4. Implementing Ad-Hoc Scheme
Recall that the skeleton LR(1) parser stored two values on the stack symbol,state
We can replace this with triples value,symbol,state
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compiler: Bottom-up Parsing

5. Implementing Ad-Hoc Scheme
Recall that the skeleton LR(1) parser stored two values on the stack symbol,state
We can replace this with triples value,symbol,state
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compiler: Bottom-up Parsing

6. Implementing Ad-Hoc Scheme
On a reduction by A → b, the parser pops 3|b| items from the stack rather than 2|b|
It pushes value along with the symbol
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compiler: Bottom-up Parsing

7. Implementing Ad-Hoc Scheme
On a reduction by A → b, the parser pops 3|b| items from the stack rather than 2|b|
It pushes value along with the symbol
This is a note
compiler: Bottom-up Parsing

8. YACC file for a calculator
%token NUMBER LPAREN RPAREN
%token PLUS MINUS TIMES DIVIDE %%
expr : expr PLUS expr
| expr MINUS expr
| expr TIMES expr
| expr DIVIDE expr
| LPAREN expr RPAREN
| MINUS expr
| NUMBER ;
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compiler: Bottom-up Parsing

9. #include <iostream> %} %union {int val;} %{
#include <iostream> %}
%union {int val;}
%token NUMBER LPAREN RPAREN EQUAL
%token PLUS MINUS TIMES DIVIDE
/* associativity and precedence:
in order of increasing precedence */
%nonassoc EQUAL
%left PLUS MINUS
%left TIMES DIVIDE
%left UMINUS /* dummy token to use as
precedence marker */
%type <val> NUMBER expr %%
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compiler: Bottom-up Parsing

10. struct and union
struct rec { int x; // 4 bytes double y; // 8 bytes char c; // 1 byte } v, w;
sizeof v: 13 bytes, sizeof w: 13 bytes
v.x = 10; v.y = 0.345; v.c = ‘#’; w.x = 20; w.y = 24.05; w.c = ‘$’;
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compiler: Bottom-up Parsing

11. struct and union
struct rec { int x; // 4 bytes double y; // 8 bytes char c; // 1 byte } v, w;
sizeof v: 13 bytes, sizeof w: 13 bytes
v.x = 10; v.y = 0.345; v.c = ‘#’; w.x = 20; w.y = 24.05; w.c = ‘$’;
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compiler: Bottom-up Parsing

12. struct and union
struct rec { int x; // 4 bytes double y; // 8 bytes char c; // 1 byte } v, w;
sizeof v: 13 bytes, sizeof w: 13 bytes
v.x = 10; v.y = 0.345; v.c = ‘#’; w.x = 20; w.y = 24.05; w.c = ‘$’;
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compiler: Bottom-up Parsing

13. struct and union
union urec { int x; // 4 bytes double y; // 8 bytes char c; // 1 byte } v, w;
sizeof v: 8 bytes, sizeof w: 8 bytes
assign to one of the 3 fields v.x, v.y, or v.c
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compiler: Bottom-up Parsing

14. struct and union
union urec { int x; // 4 bytes double y; // 8 bytes char c; // 1 byte } v, w;
sizeof v: 8 bytes, sizeof w: 8 bytes
assign to one of the 3 fields v.x, v.y, or v.c
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compiler: Bottom-up Parsing

15. struct and union
union urec { int x; // 4 bytes double y; // 8 bytes char c; // 1 byte } v, w;
sizeof v: 8 bytes, sizeof w: 8 bytes
assign to one of the 3 fields v.x, v.y, or v.c
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compiler: Bottom-up Parsing

16. struct v struct rec { int x; double y; char c; } v; x (4 bytes)
y (8 bytes)
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c (1 byte)
compiler: Bottom-up Parsing

17. union v union urec { int x; double y; char c; } v; c (1 byte)
8 bytes
x (4 bytes)
y (8 bytes)
c (1 byte)
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compiler: Bottom-up Parsing

18. struct and union
union urec { int x; // 4 bytes double y; // 8 bytes char c; // 1 byte } v;
short int whichOne;
v.x = 10; whichOne = 1; v.y = 25.4; whichOne = 2; v.c = ‘a’; whichOne = 3;
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compiler: Bottom-up Parsing