Scoping and Global Symbols

The SUIF system captures the scoping information in the source program by using a nesting of symbol tables. The two SymbolTable fields in the FileSetBlock hold the outermost scope:

• external_symbol_table holds the symbols and types visible to the outside, and
• file_set_symbol_table holds the symbols and types visible to the code in this file set.

The next level in the hierarchy are the symbol_tables belonging to FileBlocks. They contain all the symbols local to a single file. For example, C static symbols will be placed in this symbol table.

Figure 2: Example 1 Output using the Suifprinter Style (a)

************* EXTERNALS *************
External Symbol Table
  type:t0:  bool 32 align:32
  type:t1:  void 0
  type:t2:  int signed:0 32 align:32
  type:t3:  int signed:1 32 align:32
  type:t4:  int signed:1 8 align:8
  type:t5:  int signed:0 8 align:8
  type:t6:  int signed:1 16 align:16
  type:t7:  int signed:0 16 align:16
  type:t8:  float 32 align:32
  type:t9:  float 64 align:32
  type:t10:  float 64 align:64
  type:t11:  qual of @t3:i.32 qualifications:<None>
  var_sym:t12:  "i" with t:@t11:q.(@t3:i.32) addrTaken:0
    <None>
  var_sym:t13:  "l" with t:@t11:q.(@t3:i.32) addrTaken:0
    <None>
  var_sym:t14:  "j" with t:@t11:q.(@t3:i.32) addrTaken:0
    <None>
  type:t15:  array [(@t3:i.32) 0..(@t3:i.32) 2] of @t11:q.(@t3:i.32)
  type:t16:  qual of @t15:a[] qualifications:<None>
  type:t17:  ptr 32 align:32 to @t11:q.(@t3:i.32)
  type:t18:  qual of @t17:p.32 qualifications:<None>
  type:t19:  qual of @t3:i.32 qualifications:const
  type:t20:  Cfunc(@t18:q.(@t17:p.32), @t19:q.(@t3:i.32)) 
                vararg:0 argknwn:1 algn:0 ret:@t3:i.32
  proc_sym:t21:  "proc" with t:@t20:f((@t3:i.32)()) addrTaken:0
    <None>
  type:t22:  ptr 32 align:32 to @t16:q.(@t15:a[])
  type:t23:  array [(@t3:i.32) 0..(@t3:i.32) 0] of @t11:q.(@t3:i.32)
  type:t24:  qual of @t23:a[] qualifications:<None>
  type:t25:  ptr 32 align:32 to @t24:q.(@t23:a[])
************* GLOBALS *************
Global Symbol Table
  <None>

Our sample program declares four variables in different ways. Each of these has a different meaning in C. The first variable, i, is declared extern. The second variable, l, is also externally visible but is not declared extern. These are actually different declarations in C with different semantics. The third variable, j, is given an initial value. All three of these variables are placed in the external symbol table, as they are all visible outside of this SUIF file. The definition of j is found in the definition block in a file block. Finally, the variable a is declared static, and can thus be found in the symbol table for the file block. There are no symbols in the file set symbol table, the table containing objects that are visible across compilation units that have been incorporated into this SUIF file but which are not externally visible. This is because there are no such symbols in C. If one was compiling a module in Ada which contained child modules, then there might be entries in this symbol table.

One more thing needs to be observed about variable declarations. The type of symbol, must be no more deeply nested than the declaration of the variable. For the purposes of this rule, the file set symbol table is considered to be nested inside the external symbol table.

Figure 3: Example 1 Output using the Suifprinter Style (b)

  
  ************* FILE   ex.cpp.cil *************
  Annotes:
    <None>
  Symbol Table:
    var_sym:t26:  "a" with t:@t16:q.(@t15:a[]) addrTaken:1
      <None>
  Definition Block:
    Variable Definitions:
    @t13:(@t11:q.(@t3:i.32)) "l" = 
    @t14:(@t11:q.(@t3:i.32)) "j" = ExprVal: (@t3:i.32) 0
    @t26:(@t16:q.(@t15:a[])) "a" = 
  Procedure Definitions:
     
    PROC  @t21:"proc"
      <None>
    Proc Symbol Table:
      param_sym:t27:  "k" with t:@t18:q.(@t17:p.32) addrTaken:0
        <None>
      param_sym:t28:  "i" with t:@t19:q.(@t3:i.32) addrTaken:0
        <None>
    Definitions:
      Variable Definitions:
        <None>
      Procedure Definitions:
        <None>
      Annotes:
        <None>
    Args:
      @t27:(@t18:q.(@t17:p.32)) "k"
      @t28:(@t19:q.(@t3:i.32)) "i"
    Body:
      STR <dst> = <src>
        <dst>:   (@t17:p.32) array <base> [ <idx> ]
            <base>:  (@t25:p.32) convert <exp>
            <None>
              <exp>:  (@t22:p.32) SYMADDR @t26:(@t16:q.(@t15:a[])) "a"
              <None>
            <idx>:  (@t3:i.32) @t28:(@t19:q.(@t3:i.32)) "i" 
        <src>:  (@t3:i.32) <e1> add <e2>
          <None>
            <e1>:  (@t3:i.32) LOADEXP <addr>
              <addr>:  (@t17:p.32) @t27:(@t18:q.(@t17:p.32)) "k"
            <e2>:  (@t3:i.32) @t14:(@t11:q.(@t3:i.32)) "j"
      RET <retval>
        <retval>:  (@t3:i.32) @t14:(@t11:q.(@t3:i.32)) "j"
    PROC END   @t21:"proc"
  Annotes:
     <None>