Merge pull request #17 from catseye/inconsistent-initialization

Drop check for inconsistent initialization

HISTORY.md

@@ -4,6 +4,9 @@ History of SixtyPical
 0.18
 ----
 
+*   The "consistent initialization" check inside `if` blocks has
+    been dropped.  If a location is initialized inside one block
+    but not the other, it is treated as uninitialized afterwards.
 *   Syntactically, `goto` may only appear at the end of a block.
     It need no longer be the final instruction in a routine,
     as long as the type context is consistent at every exit.

TODO.md

@@ -44,15 +44,6 @@ buffer; and the ones you establish must be disjoint.
 An alternative would be `static` pointers, which are currently not possible because
 pointers must be zero-page, thus `@`, thus uninitialized.
 
-### Question "consistent initialization"
-
-Question the value of the "consistent initialization" principle for `if` statement analysis.
-
-Part of this is the trashes at the end; I think what it should be is that the trashes
-after the `if` is the union of the trashes in each of the branches; this would obviate the
-need to `trash` values explicitly, but if you tried to access them afterwards, it would still
-error.
-
 ### Tail-call optimization
 
 If a block ends in a `call` can that be converted to end in a `goto`?  Why not?  I think it can,

eg/c64/demo-game/demo-game.60p

@@ -311,14 +311,6 @@ define player_logic logic_routine
             ld a, 1
             st a, player_died
         }
-
-        // FIXME these trashes, strictly speaking, probably shouldn't be needed,
-        // but currently the compiler cares a little too much about values that are
-        // initialized in one branch of an `if`, but not the other, but are trashed
-        // at the end of the routine anyway.
-        trash ptr
-        trash y
-        trash v
     }
 }
 
@@ -355,13 +347,6 @@ define enemy_logic logic_routine
             add ptr, pos
             copy 82, [ptr] + y
         }
-
-        // FIXME these trashes, strictly speaking, probably shouldn't be needed,
-        // but currently the compiler cares too much about values that are
-        // initialized in one branch of an `if`, but not the other, but trashed
-        // at the end of the routine anyway.
-        trash ptr
-        trash y
     } else {
         copy delta, compare_target
         st on, c

src/sixtypical/analyzer.py

@@ -411,6 +411,8 @@ class Analyzer(object):
 
         self.analyze_block(routine.block, context)
 
+        trashed = set(context.each_touched()) - set(context.each_meaningful())
+
         if self.debug:
             print("at end of routine `{}`:".format(routine.name))
             print(context)
@@ -438,8 +440,6 @@ class Analyzer(object):
                     raise InconsistentExitError("Exit contexts are not consistent")
             context.update_from(exit_context)
 
-        trashed = set(context.each_touched()) - set(context.each_meaningful())
-
         # these all apply whether we encountered goto(s) in this routine, or not...:
 
         # can't trash an output.
@@ -801,24 +801,6 @@ class Analyzer(object):
         outgoing_meaningful = set(context1.each_meaningful()) & set(context2.each_meaningful())
         outgoing_trashes = incoming_meaningful - outgoing_meaningful
 
-        # TODO may we need to deal with touched separately here too?
-        # probably not; if it wasn't meaningful in the first place, it
-        # doesn't really matter if you modified it or not, coming out.
-        for ref in context1.each_meaningful():
-            if ref in outgoing_trashes:
-                continue
-            context2.assert_meaningful(
-                ref, exception_class=InconsistentInitializationError,
-                message='initialized in block 1 but not in block 2 of `if {}`'.format(instr.src)
-            )
-        for ref in context2.each_meaningful():
-            if ref in outgoing_trashes:
-                continue
-            context1.assert_meaningful(
-                ref, exception_class=InconsistentInitializationError,
-                message='initialized in block 2 but not in block 1 of `if {}`'.format(instr.src)
-            )
-
         # merge the contexts.
 
         # first, the easy case: if one of the contexts has terminated, just use the other one.

tests/SixtyPical Analysis.md

@@ -1629,7 +1629,9 @@ Both blocks of an `if` are analyzed.
     | }
     = ok
 
-If a location is initialized in one block, is must be initialized in the other as well.
+If a location is initialized in one block, it must be initialized in the other as well
+in order to be considered to be initialized after the block.  If it is not consistent,
+it will be considered uninitialized.
 
     | define foo routine
     |   inputs a
@@ -1643,7 +1645,7 @@ If a location is initialized in one block, is must be initialized in the other a
     |         ld a, 23
     |     }
     | }
-    ? InconsistentInitializationError: x
+    ? UnmeaningfulOutputError: x
 
     | define foo routine
     |   inputs a
@@ -1657,7 +1659,7 @@ If a location is initialized in one block, is must be initialized in the other a
     |         ld x, 7
     |     }
     | }
-    ? InconsistentInitializationError: x
+    ? UnmeaningfulOutputError: x
 
     | define foo routine
     |   inputs a
@@ -1671,7 +1673,53 @@ If a location is initialized in one block, is must be initialized in the other a
     |         ld x, 7
     |     }
     | }
-    ? InconsistentInitializationError: x
+    ? UnmeaningfulOutputError: x
+
+    | define foo routine
+    |   inputs a
+    |   trashes a, x, z, n, c
+    | {
+    |     cmp a, 42
+    |     if not z {
+    |         ld a, 6
+    |     } else {
+    |         ld x, 7
+    |     }
+    |     ld a, x
+    | }
+    ? UnmeaningfulReadError: x
+
+If we don't care if it's uninitialized after the `if`, that's okay then.
+
+    | define foo routine
+    |   inputs a
+    |   trashes a, x, z, n, c
+    | {
+    |     cmp a, 42
+    |     if not z {
+    |         ld a, 6
+    |     } else {
+    |         ld x, 7
+    |     }
+    | }
+    = ok
+
+Or, if it does get initialized on both branches, that's okay then.
+
+    | define foo routine
+    |   inputs a
+    |   outputs x
+    |   trashes a, z, n, c
+    | {
+    |     cmp a, 42
+    |     if not z {
+    |         ld x, 0
+    |         ld a, 6
+    |     } else {
+    |         ld x, 7
+    |     }
+    | }
+    = ok
 
 However, this only pertains to initialization.  If a value is already
 initialized, either because it was set previous to the `if`, or is an
@@ -1720,7 +1768,7 @@ An `if` with a single block is analyzed as if it had an empty `else` block.
     |         ld x, 7
     |     }
     | }
-    ? InconsistentInitializationError: x
+    ? UnmeaningfulOutputError: x
 
     | define foo routine
     |   inputs a