# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1220741240 -7200
# Node ID 4cb6ccaaf758bf4f5eeeaa9b12dc016c7a69b9f6
# Parent  bd6baced90abb0cbce59aa18cb0c569c0283344a
Removed the superfluous temporary storage optimisation since it could never work
as implemented (and would be mostly equivalent to the source storage
optimisation).

diff -r bd6baced90ab -r 4cb6ccaaf758 docs/optimisations.txt
--- a/docs/optimisations.txt	Sun Sep 07 00:35:03 2008 +0200
+++ b/docs/optimisations.txt	Sun Sep 07 00:47:20 2008 +0200
@@ -2,44 +2,38 @@
 ------------                    ------------------------
 
 constant_storage                value instruction references a constant;
-                                storage instruction references a constant;
-                                remove both instructions (currently a single merged instruction)
+(elimination)                   storage instruction references a constant;
+                                remove both instructions (currently a single
+                                merged instruction)
 
 source_storage                  source instruction is a simple input operation;
-                                source instruction is the last instruction;
+(elimination)                   source instruction is the last instruction;
                                 remove the source instruction
 
 known_target                    value instruction references a constant;
-                                target and context are provided (no instructions removed)
+(guidance)                      target and context are provided (no instructions removed)
 
 self_access                     value instruction references "self" in a method;
-                                specified attribute name always has the same position;
+(guidance)                      specified attribute name always has the same position;
                                 appropriate instruction generated
 
 temp_storage                    value instruction is a simple input operation;
-                                value instruction is the last instruction;
-                                remove the value instruction, provide the value
+(elimination)                   value instruction is the last instruction;
+(guidance)                      remove the value instruction, provide the value
                                 instruction in place of a temporary storage
                                 reference
 
 load_operations                 value instruction is a simple input operation;
-                                value instruction is the last instruction;
+(merge)                         value instruction is the last instruction;
                                 current instruction uses simple input;
                                 remove the value instruction, make the value
                                 instruction the input to the current instruction
 
 no_operations                   input to the current instruction loads from the
-                                destination of the current instruction;
+(elimination)                   destination of the current instruction;
                                 omit the current instruction
 
 unused_results                  value instruction is a simple input operation;
-                                value instruction is the final instruction of a
+(elimination)                   value instruction is the final instruction of a
                                 discarded expression;
                                 remove the value instruction
-
-superfluous_temp_operations     source instruction writes to temporary storage;
-                                current instruction reads from the same storage;
-                                source instruction is the last instruction;
-                                remove the source instruction, make the current
-                                instruction use the input of the source
-                                instruction
diff -r bd6baced90ab -r 4cb6ccaaf758 micropython/ast.py
--- a/micropython/ast.py	Sun Sep 07 00:35:03 2008 +0200
+++ b/micropython/ast.py	Sun Sep 07 00:47:20 2008 +0200
@@ -31,8 +31,7 @@
 
     supported_optimisations = [
         "constant_storage", "source_storage", "known_target", "self_access",
-        "temp_storage", "load_operations", "no_operations", "unused_results",
-        "superfluous_temp_operations"
+        "temp_storage", "load_operations", "no_operations", "unused_results"
         ]
 
     def __init__(self, translation, optimisations=None):
@@ -69,9 +68,6 @@
     def should_optimise_away_no_operations(self):
         return "no_operations" in self.optimisations
 
-    def should_optimise_away_superfluous_temp_operations(self):
-        return "superfluous_temp_operations" in self.optimisations
-
     def should_optimise_unused_results(self):
         return "unused_results" in self.optimisations
 
@@ -132,18 +128,6 @@
             isinstance(instruction.input, LoadResult) and isinstance(instruction, StoreResult)
             )
 
-    def is_superfluous_temp_operation(self, instruction):
-
-        """
-        Return whether 'instruction' merely loads its input from a recent
-        temporary storage operation.
-        """
-
-        return (
-            isinstance(instruction.source, LoadTemp) and isinstance(self.translation.active_source, StoreTemp) and
-                instruction.source.attr == self.translation.active_source.attr
-            )
-
     def is_input(self, instruction):
 
         "Return whether 'instruction' provides an input."
@@ -377,20 +361,6 @@
         else:
             return 0
 
-    def optimise_away_superfluous_temp_operations(self, instruction):
-
-        """
-        Optimise away operations which just store temporary values for
-        immediate retrieval.
-        """
-
-        if self.should_optimise_away_superfluous_temp_operations() and \
-            self.is_superfluous_temp_operation(instruction) and \
-            self.translation.active_source == self.translation.active:
-
-            instruction.source = self.translation.active_source.input
-            self.translation.remove_op()
-
     def optimise_unused_results(self):
 
         "Discard results which will not be used."
@@ -701,7 +671,6 @@
         self.optimiser.optimise_load_operations(op)
         if self.optimiser.optimise_away_no_operations(op):
             return
-        self.optimiser.optimise_away_superfluous_temp_operations(op)
 
         self.code.append(op)
         self.active = op