# HG changeset patch
# User Manuele Conti <conti.ma@alice.it>
# Date 1356690122 -3600
# Node ID 577547327f6725f65e891cdaf093acd7cbaac39e
# Parent  9fbdf8a7430e25c0a5bd3f4c20d0375dc3d68268
Add note about How Constant Folding class is extended with a implementation constant propagation algorithm
by Mario de Sousa.

diff -r 9fbdf8a7430e -r 577547327f67 stage3/constant_folding.cc
--- a/stage3/constant_folding.cc	Thu Dec 27 00:17:08 2012 +0100
+++ b/stage3/constant_folding.cc	Fri Dec 28 11:22:02 2012 +0100
@@ -117,13 +117,24 @@
  * NOTE 2 
  *    This file does not print out any error messages!
  *    We cannot really print out error messages when we find an overflow. Since each operation
- *    (symbol in the absract syntax tree for that operation) will have up to 4 constant results,
+ *    (symbol in the abstract syntax tree for that operation) will have up to 4 constant results,
  *    it may happen that some of them overflow, while other do not.
  *    We must wait for data type checking to determine the exact data type of each expression
  *    before we can decide whether or not we should print out an overflow error message.
  *
  *    For this reason, this visitor merely annotates the abstract syntax tree, and leaves the
- *    actuall printing of errors for the print_datatype_errors_c class!
+ *    actually printing of errors for the print_datatype_errors_c class!
+ *
+ * NOTE 3
+ *    Constant Folding class is extended with a implementation constant propagation algorithm
+ *    by Mario de Sousa.
+ *    Main idea is not to implement a general constant propagation algorithm but to reinterpret it
+ *    for visitor classes.
+ *    We declared a hash map, it contains a variables list linked with current constant values.
+ *    During expression evaluation we can retrieve a constant value to symbolic variables getting it from the map.
+ *    Also at join source points we use a meet semilattice rules to merge current values between a block
+ *    and adjacent block.
+ *
  */
 
 #include "constant_folding.hh"
diff -r 9fbdf8a7430e -r 577547327f67 stage3/constant_folding.hh
--- a/stage3/constant_folding.hh	Thu Dec 27 00:17:08 2012 +0100
+++ b/stage3/constant_folding.hh	Fri Dec 28 11:22:02 2012 +0100
@@ -30,7 +30,7 @@
  *
  */
 
-/* Determine the data type of an constant expression.
+/* Determine the value of an constant expression.
  * A reference to the relevant type definition is returned.
  *
  * For example: