+/* This file contains the code required to manage the operands cache of the
+ SSA optimizer. For every stmt, we maintain an operand cache in the stmt
+ annotation. This cache contains operands that will be of interest to
+ optimizers and other passes wishing to manipulate the IL.
+
+ The operand type are broken up into REAL and VIRTUAL operands. The real
+ operands are represented as pointers into the stmt's operand tree. Thus
+ any manipulation of the real operands will be reflected in the actual tree.
+ Virtual operands are represented solely in the cache, although the base
+ variable for the SSA_NAME may, or may not occur in the stmt's tree.
+ Manipulation of the virtual operands will not be reflected in the stmt tree.
+
+ The routines in this file are concerned with creating this operand cache
+ from a stmt tree.
+
+ The operand tree is the parsed by the various get_* routines which look
+ through the stmt tree for the occurrence of operands which may be of
+ interest, and calls are made to the append_* routines whenever one is
+ found. There are 5 of these routines, each representing one of the
+ 5 types of operands. Defs, Uses, Virtual Uses, Virtual May Defs, and
+ Virtual Must Defs.
+
+ The append_* routines check for duplication, and simply keep a list of
+ unique objects for each operand type in the build_* extendable vectors.
+
+ Once the stmt tree is completely parsed, the finalize_ssa_operands()
+ routine is called, which proceeds to perform the finalization routine
+ on each of the 5 operand vectors which have been built up.
+
+ If the stmt had a previous operand cache, the finalization routines
+ attempt to match up the new operands with the old ones. If it's a perfect
+ match, the old vector is simply reused. If it isn't a perfect match, then
+ a new vector is created and the new operands are placed there. For
+ virtual operands, if the previous cache had SSA_NAME version of a
+ variable, and that same variable occurs in the same operands cache, then
+ the new cache vector will also get the same SSA_NAME.
+
+ i.e., if a stmt had a VUSE of 'a_5', and 'a' occurs in the new operand
+ vector for VUSE, then the new vector will also be modified such that
+ it contains 'a_5' rather than 'a'.
+
+*/
+
+
+/* Flags to describe operand properties in helpers. */