xpcom/analysis/mayreturn.js

   1 /* May-return analysis.
   2  * This makes sense only for functions that return a value. The analysis
   3  * determines the set of variables that may transitively reach the return
   4  * statement. */
   5
   6 function MayReturnAnalysis() {
   7   BackwardAnalysis.apply(this, arguments);
   8   // May-return variables. We collect them all here.
   9   this.vbls = create_decl_set();
  10   // The return value variable itself
  11   this.retvar = undefined;
  12 }
  13
  14 MayReturnAnalysis.prototype = new BackwardAnalysis;
  15
  16 MayReturnAnalysis.prototype.flowState = function(isn, state) {
  17   if (TREE_CODE(isn) == RETURN_EXPR) {
  18     let gms = TREE_OPERAND(isn, 0);
  19     if (gms) {
  20       // gms is usually a GIMPLE_MODIFY_STMT but can be a RESULT_DECL
  21       if (TREE_CODE(gms) == GIMPLE_MODIFY_STMT) {
  22         let v = GIMPLE_STMT_OPERAND(gms, 1);
  23         this.vbls.add(v);
  24         state.add(v);
  25         this.retvar = v;
  26       } else if (TREE_CODE(gms) == RESULT_DECL) {
  27         throw new Error("Weird case hit");
  28       }
  29     }
  30   } else if (TREE_CODE(isn) == GIMPLE_MODIFY_STMT) {
  31     let lhs = GIMPLE_STMT_OPERAND(isn, 0);
  32     let rhs = GIMPLE_STMT_OPERAND(isn, 1);
  33     if (DECL_P(rhs) && DECL_P(lhs) && state.has(lhs)) {
  34       this.vbls.add(rhs);
  35       state.add(rhs);
  36     }
  37
  38     for (let e in isn_defs(isn, 'strong')) {
  39       if (DECL_P(e)) {
  40         state.remove(e);
  41       }
  42     }
  43   }
  44 };