1 Name usage types: as parameters, as base classes, as callables. This potentially restricts
2 attribute usage effects because names mentioned as base classes are not propagated and
3 made freely available for use in attribute accesses.
4
5 Low-Level Instructions and Macro Instructions
6 =============================================
7
8 Have contexts and values stored separately in memory. This involves eliminating DataValue
9 and storing attributes using two words.
10
11 Migrate macro instructions such as the *Index instructions to library code implemented
12 using low-level instructions.
13
14 Consider introducing classic machine level instructions (word addition, subtraction, and
15 so on) in order to implement all current RSVP instructions.
16
17 Move common code sequences to a library routine, such as the context checking that occurs
18 in functions and methods.
19
20 Dataflow Optimisations
21 ======================
22
23 Assignments, particularly now that no result register exists, may cause StoreTemp/LoadTemp
24 instruction pairs to be produced and these could be eliminated.
25
26 Class and Module Attribute Assignment
27 =====================================
28
29 Allow unrestricted class and module assignment (but not new external binding of
30 attributes), eliminating run-time checks on object types in instructions like
31 StoreAttrIndex. This may involve less specific objects being identified during inspection.
32
33 Potentially re-evaluate class bases in order to see if they are non-constant.
34
35 Verify that the context information is correctly set, particularly for the unoptimised
36 cases.
37
38 Update docs/assignment.txt.
39
40 Prevent assignments within classes, such as method aliasing, from causing the source of an
41 assignment from being automatically generated. Instead, only external references should be
42 registered.
43
44 Prevent "from <module> import ..." statements from registering references to such local
45 aliases such that they cause the source of each alias to be automatically generated.
46
47 Consider attribute assignment observations, along with the possibility of class and module
48 attribute assignment.
49
50 (Note direct assignments as usual, indirect assignments via the attribute usage
51 mechanism. During attribute collection and inference, add assigned values to all
52 inferred targets.)
53
54 (Since class attributes can be assigned, StoreAttrIndex would no longer need to reject
55 static attributes, although this might still be necessary where attribute usage analysis
56 has not been performed.)
57
58 Potentially consider changing static attribute details to use object-relative offsets in
59 order to simplify the instruction implementations. This might allow us to eliminate the
60 static attribute flag for attributes in the object table, at least at run-time.
61
62 Dynamic Attribute Access
63 ========================
64
65 Consider explicit accessor initialisation:
66
67 attr = accessor("attr")
68 getattr(C, attr)
69
70 Attribute Usage
71 ===============
72
73 To consider: is it useful to distinguish between attribute name sets when the same names
74 are mentioned, but where one path through the code sets different values on attributes
75 than another? The _attrtypes collapses observations in order to make a list of object
76 types for a name, and the final set of names leading to such type deductions might be a
77 useful annotation to be added alongside _attrcombined.
78
79 (Update the reports to group identical sets of attribute names.)
80
81 Attribute usage on attributes might be possible if one can show that the expression of an
82 attribute access is constant and that the attribute target is also constant or only refers
83 to a single type. For example, in the sys module:
84
85 stderr = file()
86
87 If no work is done to associate the result of the invocation with the stderr name, then
88 one could instead at least attempt to determine whether stderr is assigned only once. If
89 so, it might be possible to record attribute usage on references to the name. For example:
90
91 sys.stderr.write(...) # sys.stderr supports write -> {file, ...}
92
93 Interface/Type Generalisation
94 -----------------------------
95
96 Consolidate interface observations by taking all cached table accesses and determining
97 which usage patterns lead to the same types. For example, if full usage of {a, b} and
98 {a, b, c} leads to A and B in both cases, either {a, b} can be considered as partial usage
99 of the complete interface {a, b, c}, or the latter can be considered as an
100 overspecification of the former.
101
102 Consider type deduction and its consequences where types belong to the same hierarchy
103 and where a guard could be generated for the most general type.
104
105 Consider permitting multiple class alternatives where the attributes are all identical.
106
107 Support class attribute positioning similar to instance attribute positioning, potentially
108 (for both) based on usage observations. For example, if __iter__ is used on two classes,
109 the class attribute could be exposed at a similar relative position to the class (and
110 potentially accessible using a LoadAttr-style instruction).
111
112 **** Constant attribute users need not maintain usage since they are already resolved. ****
113
114 Self-Related Usage
115 ------------------
116
117 Perform attribute usage on attributes of self as names, potentially combining observations
118 across methods.
119
120 Additional Guards
121 -----------------
122
123 Consider handling branches of values within namespaces in order to support more precise value usage.
124
125 Loop entry points and other places where usage becomes more specific might be used as
126 places to impose guards. See tests/attribute_access_type_restriction_loop_list.py for an
127 example. (Such information is already shown in the reports.)
128
129 Strict Interfaces/Types
130 -----------------------
131
132 Make the gathering of usage parameterisable according to the optimisation level so that a
133 choice can be made between control-flow-dependent observations and the simple collection
134 of all attributes used with a name (producing a more static interface observation).
135
136 AttributeError
137 --------------
138
139 Consider attribute usage observations being suspended or optional inside blocks where
140 AttributeError may be caught (although this doesn't anticipate such exceptions being
141 caught outside a function altogether). For example:
142
143 y = a.y
144 try:
145 z = a.z # z is an optional attribute
146 except AttributeError:
147 z = None
148
149 Instantiation Deduction
150 -----------------------
151
152 Consider handling Const in micropython.inspect in order to produce instances of specific
153 classes. Then, consider adding support for guard removal/verification where known
154 instances are involved. For example:
155
156 l = []
157 l.append(123) # type deductions are filtered using instantiation knowledge
158
159 Handling CallFunc in a similar way is more challenging. Consider the definitions in the sys module:
160
161 stderr = file()
162
163 It must first be established that file only ever refers to the built-in file class, and
164 only then can the assumption be made that stderr in this case refers to instances of file.
165 If file can also refer to other objects, potential filtering operations are more severely
166 limited.
167
168 Frame Optimisations
169 ===================
170
171 Stack frame replacement where a local frame is unused after a call, such as in a tail call
172 situation.
173
174 Local assignment detection plus frame re-use. Example: slice.__init__ calls
175 xrange.__init__ with the same arguments which are unchanged in xrange.__init__. There is
176 therefore no need to build a new frame for this call, although in some cases the locals
177 frame might need expanding.
178
179 Reference tracking where objects associated with names are assigned to attributes of other
180 objects may assist in allocation optimisations. Recording whether an object referenced by
181 a name is assigned to an attribute, propagated to another name and assigned to an
182 attribute, or passed to another function or method might, if such observations were
183 combined, allow frame-based or temporary allocation to occur.
184
185 Instantiation
186 =============
187
188 Specific instances could be produced, providing type information and acting somewhat like
189 classes during inspection.
190
191 Inlining
192 ========
193
194 Where a function or method call can always be determined, the body of the target could be
195 inlined - copied into place - within the caller. If the target is only ever called by a
196 single caller it could be moved into place. This could enhance deductions based on
197 attribute usage since observations from the inlined function would be merged into the
198 caller.
199
200 Function Specialisation
201 =======================
202
203 Specialisation of certain functions, such as isinstance(x, cls) where cls is a known
204 constant.
205
206 Structure and Object Table Optimisations
207 ========================================
208
209 Fix object table entries for attributes not provided by any known object, or provide an
210 error, potentially overridden by options. For example, the augmented assignment methods
211 are not supported by the built-in objects and thus the operator module functions cause
212 the compilation to fail. Alternatively, just supply the methods since something has to do
213 so in the builtins.
214
215 Consider attribute merging where many attributes are just aliases for the same underlying
216 definition.
217
218 Consider references to defaults as occurring only within the context of a particular
219 function, thus eliminating default value classes if such functions are not themselves
220 invoked.
221
222 Scope Handling
223 ==============
224
225 Consider merging the InspectedModule.store tests with the scope conflict handling.
226
227 Consider labelling _scope on assignments and dealing with the assignment of removed
228 attributes, possibly removing the entire assignment, and distinguishing between such cases
229 and unknown names.
230
231 Check name origin where multiple branches could yield multiple scope interpretations:
232
233 try:
234 set # built-in name
235 except NameError:
236 from sets import Set as set # local definition of name
237
238 set # could be confused by the local definition at run-time
239
240 Object Coverage
241 ===============
242
243 Support __init__ traversal (and other implicit names) more effectively.
244
245 Importing Modules
246 =================
247
248 Consider supporting relative imports, even though this is arguably a misfeature.
249
250 Other
251 =====
252
253 Consider a separate annotation phase where deductions are added to the AST for the
254 benefit of both the reporting and code generation phases.
255
256 Check context_value initialisation (avoiding or handling None effectively).
257
258 Consider better "macro" support where new expressions need to be generated and processed.
259
260 Detect TestIdentity results involving constants, potentially optimising status-affected
261 instructions:
262
263 TestIdentity(x, y) # where x is always y
264 JumpIfFalse(...) # would be removed (never false)
265 JumpIfTrue(...) # changed to Jump(...)
266
267 Status-affected blocks could be optimised away for such constant-related results.