Bison derivation problems with code generation

Hello I'm using bison for a compiler for study purposes, i got the next code:

if :
if2
|
if1;

if2: 
SE expressao {$1 = (struct lbs *) newlblrec(); $1->for_jmp_false = reserve_loc(); $1->label = label; label+=2;} ENTAO 
comandos
SENAO  {$1->for_goto = reserve_loc(); back_patch($1->for_jmp_false, JMP_FALSE, $1->label);}
comandos
FIMSE  {back_patch($1->for_goto, GOTO, $1->label开发者_如何学JAVA+1);}
| 
SE expressao error {yyerrok; errors++; yyerror("Entao nao encontrado no se");}
comandos
SENAO 
comandos
FIMSE ;

if1: 
SE expressao {$1 = (struct lbs *) newlblrec(); $1->for_jmp_false = reserve_loc(); $1->label = label++;} ENTAO 
comandos 
FIMSE {back_patch($1->for_jmp_false, JMP_FALSE, $1->label); gen_code(LABEL,$1->label);}
|
SE expressao  error {yyerrok; errors++; yyerror("Entao nao encontrado no se");}
comandos 
FIMSE;

This code only generates the rule 'if2', when it found the "FIMSE" (this indicates that the command is a simple if) before the "SENAO" (in this case is a if else command) it's raises an error, this only happen when i put the C code to generate the intermediate code. My question is: Why? How can i fix this?

---

When the parser receives SE and expressao, in your augmented form, it then immediately needs to make a choice which action to perform (because you asked that the action happens at that point. Without the annotation, it can first push ENTAO and commandos, and then make a decision to reduce.

In essence, an action inside the RHS is translated into one that has the action at the end, with another non-terminal. So

 foo: bar { action1 } foobar
 foo: bar { action2 } baz

is translated into

 foo: helper1 foobar
 foo: helper2 baz
 helper1: bar { action1 }
 helper2: bar { action2 }

As a consequence, these actions produce a reduce-reduce conflict in your grammar.

There are two approaches:

1. put the action at the end.
2. refactor the grammar so that the action is actually the same one in both alternatives.