[cfe-dev] Recursive Descent Parser

[Raghavan]

Hi,

I just wanted to see how the recursive descent parser functions get activated. This is more for showing students how a recursive descent parser works in a production compiler rather than checking correctness.

I had done a similar thing for the 'cc1' in gcc by compiling 'cc1' using the '-finstrument-functions' option. This gives me control each time a function gets called or exits. Using that I was able to generate something like this.



# The input C source file 
$ cat -n test3.c 
     1	int var1,var2;

# The output from my instrumented 'cc1' compiler when I compile the above file.

{ enter c_parser_translation_unit 
   { enter c_parser_external_declaration 
      { enter c_parser_declaration_or_fndef 
         { enter c_parser_declspecs 
            { enter c_parser_consume_token 
               Token No:1 Lexeme:'int' Type:CPP_NAME 
            } exit c_parser_consume_token 
         } exit c_parser_declspecs 
         { enter c_parser_declarator 
            { enter c_parser_direct_declarator 
               { enter c_parser_consume_token 
                  Token No:2 Lexeme:'var1' Type:CPP_NAME 
               } exit c_parser_consume_token 
               { enter c_parser_direct_declarator_inner 
               } exit c_parser_direct_declarator_inner 
            } exit c_parser_direct_declarator 
         } exit c_parser_declarator 
         { enter c_parser_consume_token 
            Token No:3 Lexeme:',' Type:CPP_COMMA 
         } exit c_parser_consume_token 
         { enter c_parser_declarator 
            { enter c_parser_direct_declarator 
               { enter c_parser_consume_token 
                  Token No:4 Lexeme:'var2' Type:CPP_NAME 
               } exit c_parser_consume_token 
               { enter c_parser_direct_declarator_inner 
               } exit c_parser_direct_declarator_inner 
            } exit c_parser_direct_declarator 
         } exit c_parser_declarator 
         { enter c_parser_consume_token 
            Token No:5 Lexeme:';' Type:CPP_SEMICOLO 
         } exit c_parser_consume_token 
      } exit c_parser_declaration_or_fndef 
   } exit c_parser_external_declaration 
} exit c_parser_translation_unit 

It maps closely with the following productions from the standard at
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf. The section numbers given in the Table 3 1 correspond to the sections in the same document.



translation-unit	:	external-declaration	6.9.1 
external-declaration	:	declaration	6.9.1
external-declaration	:	function-definition	6.9.1
declaration	:	declaration-specifiers init-declarator-listopt ;    	6.7.1
declaration-specifiers	:	type-specifier declaration-specifiersopt   	6.7.1
type-specifier	:	int	6.7.2 
init-declarator-list	:	init-declarator	6.7.1
	:	init-declarator-list , init-declarator	6.7.1 
init-declarator 	:	declarator	6.7.1
declarator                 	:	pointeropt direct-declarator	6.7.6 
direct-declarator	:	identifier	6.7.6



Thanks.

Bye,
Raghavan V



From: Nikola Smiljanic [mailto:popizdeh at gmail.com] 
Sent: Thursday, September 25, 2014 3:33 AM
To: Daniel Dilts
Cc: Raghavan; cfe-dev Developers
Subject: Re: [cfe-dev] Recursive Descent Parser

I'm not sure what Raghvan is trying to achieve but I don't think the graph would be very helpful. Grammar productions are available in Annex A of the standard (if that's all he's after) but AFAIK clang's parser doesn't map 1:1 to them.

On Thu, Sep 25, 2014 at 7:47 AM, Daniel Dilts <diltsman at gmail.com> wrote:
I suppose that someone could write a utility using Clang to dump the call graph starting at the base rule.


On Wed, Sep 24, 2014 at 2:31 PM, Nikola Smiljanic <popizdeh at gmail.com> wrote:
I don't think there is. Have a look at clang::ParseAST. it keeps track of the callstack in case of crash. It also keeps track of some statistics but I think that's all there is.

On Sun, Sep 21, 2014 at 9:55 AM, Raghavan <raghavan97 at yahoo.co.in> wrote:
Hi,
 
I am a newbie to clang and LLVM.
 
I realize that the clang uses Recursive descent parsing for compiling a c file.
 
I was wondering, if there is any way to print the production rules or any kind of parser related details during the parsing of a C file by clang.
 
 
Thanks.
 
Bye,
Raghavan V
 

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