glsl2: Add module to suss out loop control variables from loop analysis data

This is the next step on the road to loop unrolling

src/glsl/loop_analysis.h

@@ -36,6 +36,26 @@ extern class loop_state *
 analyze_loop_variables(exec_list *instructions);
 
 
+/**
+ * Fill in loop control fields
+ *
+ * Based on analysis of loop variables, this function tries to remove sequences
+ * in the loop of the form
+ *
+ *  (if (expression bool ...) (break))
+ *
+ * and fill in the \c ir_loop::from, \c ir_loop::to, and \c ir_loop::counter
+ * fields of the \c ir_loop.
+ *
+ * In this process, some conditional break-statements may be eliminated
+ * altogether.  For example, if it is provable that one loop exit condition will
+ * always be satisfied before another, the unnecessary exit condition will be
+ * removed.
+ */
+extern bool
+set_loop_controls(exec_list *instructions, loop_state *ls);
+
+
 /**
  * Tracking for all variables used in a loop
  */