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 Frame Optimisations
150 ===================
151
152 Stack frame replacement where a local frame is unused after a call, such as in a tail call
153 situation.
154
155 Local assignment detection plus frame re-use. Example: slice.__init__ calls
156 xrange.__init__ with the same arguments which are unchanged in xrange.__init__. There is
157 therefore no need to build a new frame for this call, although in some cases the locals
158 frame might need expanding.
159
160 Reference tracking where objects associated with names are assigned to attributes of other
161 objects may assist in allocation optimisations. Recording whether an object referenced by
162 a name is assigned to an attribute, propagated to another name and assigned to an
163 attribute, or passed to another function or method might, if such observations were
164 combined, allow frame-based or temporary allocation to occur.
165
166 Instantiation Deduction
167 =======================
168
169 Consider handling Const, List and Tuple in micropython.inspect in order to produce
170 instances of specific classes. Then, consider adding support for guard
171 removal/verification where known instances are involved. For example:
172
173 l = []
174 l.append(123) # type deductions are filtered using instantiation knowledge
175
176 Currently, this is done only for Const values in the context of attribute accesses during
177 inspection.
178
179 Handling CallFunc in a similar way is more challenging. Consider the definitions in the sys module:
180
181 stderr = file()
182
183 It must first be established that file only ever refers to the built-in file class, and
184 only then can the assumption be made that stderr in this case refers to instances of file.
185 If file can also refer to other objects, potential filtering operations are more severely
186 limited.
187
188 Invocation-Related Deduction
189 ============================
190
191 Where an attribute access (either in conjunction with usage observations or independently)
192 could refer to a number of different targets, but where the resulting attribute is then
193 used in an invocation, filtering of the targets could be done to eliminate any targets
194 that are not callable. Guards would need introducing to prevent inappropriate operations
195 from occurring at run-time.
196
197 Inlining
198 ========
199
200 Where a function or method call can always be determined, the body of the target could be
201 inlined - copied into place - within the caller. If the target is only ever called by a
202 single caller it could be moved into place. This could enhance deductions based on
203 attribute usage since observations from the inlined function would be merged into the
204 caller.
205
206 Function Specialisation
207 =======================
208
209 Specialisation of certain functions, such as isinstance(x, cls) where cls is a known
210 constant.
211
212 Structure and Object Table Optimisations
213 ========================================
214
215 Fix object table entries for attributes not provided by any known object, or provide an
216 error, potentially overridden by options. For example, the augmented assignment methods
217 are not supported by the built-in objects and thus the operator module functions cause
218 the compilation to fail. Alternatively, just supply the methods since something has to do
219 so in the builtins.
220
221 Consider attribute merging where many attributes are just aliases for the same underlying
222 definition.
223
224 Consider references to defaults as occurring only within the context of a particular
225 function, thus eliminating default value classes if such functions are not themselves
226 invoked.
227
228 Scope Handling
229 ==============
230
231 Consider merging the InspectedModule.store tests with the scope conflict handling.
232
233 Consider labelling _scope on assignments and dealing with the assignment of removed
234 attributes, possibly removing the entire assignment, and distinguishing between such cases
235 and unknown names.
236
237 Check name origin where multiple branches could yield multiple scope interpretations:
238
239 try:
240 set # built-in name
241 except NameError:
242 from sets import Set as set # local definition of name
243
244 set # could be confused by the local definition at run-time
245
246 Object Coverage
247 ===============
248
249 Support __init__ traversal (and other implicit names) more effectively.
250
251 Importing Modules
252 =================
253
254 Consider supporting relative imports, even though this is arguably a misfeature.
255
256 Other
257 =====
258
259 Consider a separate annotation phase where deductions are added to the AST for the
260 benefit of both the reporting and code generation phases.
261
262 Check context_value initialisation (avoiding or handling None effectively).
263
264 Consider better "macro" support where new expressions need to be generated and processed.
265
266 Detect TestIdentity results involving constants, potentially optimising status-affected
267 instructions:
268
269 TestIdentity(x, y) # where x is always y
270 JumpIfFalse(...) # would be removed (never false)
271 JumpIfTrue(...) # changed to Jump(...)
272
273 Status-affected blocks could be optimised away for such constant-related results.