Before:
```
Tuple counts for Essa::EssaEdgeRefinement::getInput#dispred#f0820431#ff/2@b84afc77 after 20.3s:
873421 ~0% {3} r1 = JOIN Essa::TEssaEdgeDefinition#24e22a14#ffff_31#join_rhs WITH Essa::TEssaEdgeDefinition#24e22a14#ffff_30#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.0 'this'
181627951 ~0% {3} r2 = JOIN r1 WITH Essa::EssaDefinition::getSourceVariable#dispred#f0820431#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1 'result', Lhs.1, Lhs.2 'this'
873418 ~0% {2} r3 = JOIN r2 WITH Essa::EssaDefinition::reachesEndOfBlock#dispred#f0820431#ff ON FIRST 2 OUTPUT Lhs.2 'this', Lhs.0 'result'
return r3
```
It's perhaps not immediately obvious what's going on here (because of
the `...join_rhs` indirection), but basically we're joining together
`this` and `def` and their `getSourceVariable`, and only then actually
relating `this` and `def` through `reachesEndOfBlock`.
By unbinding `var`, we prevent this early join, which now encourages the
`reachesEndOfBlock` join to happen earlier:
```
Tuple counts for Essa::EssaEdgeRefinement::getInput#dispred#f0820431#ff/2@2d63e5lb after 2s
873421 ~0% {2} r1 = SCAN Essa::TEssaEdgeDefinition#24e22a14#ffff OUTPUT In.3 'this', In.1
873421 ~0% {3} r2 = JOIN r1 WITH Essa::TEssaEdgeDefinition#24e22a14#ffff_30#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.0 'this'
873421 ~0% {3} r3 = JOIN r2 WITH Definitions::SsaSourceVariable#class#486534ab#f ON FIRST 1 OUTPUT Lhs.1, Lhs.2 'this', Lhs.0
8758877 ~0% {3} r4 = JOIN r3 WITH Essa::EssaDefinition::reachesEndOfBlock#dispred#f0820431#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1 'result', Lhs.2, Lhs.1 'this'
873418 ~0% {2} r5 = JOIN r4 WITH Essa::EssaDefinition::getSourceVariable#dispred#f0820431#ff ON FIRST 2 OUTPUT Lhs.2 'this', Lhs.0 'result'
return r5
```
On certain databases, the evaluation of this predicate was running out
of memory due to the way the `count` aggregate was being used. Here's
an example of the tuple counts involved:
```
Tuple counts for PointsToContext::syntactic_call_count#cf3039a0#ff#antijoin_rhs/1@d2199bb8 after 1m27s:
595518502 ~521250% {1} r1 = JOIN PointsToContext::syntactic_call_count#cf3039a0#ff#shared#3 WITH Flow::CallNode::getFunction#dispred#f0820431#ff_1#join_rhs ON FIRST 1 OUTPUT Lhs.1 'arg0'
26518709 ~111513% {1} r2 = JOIN PointsToContext::syntactic_call_count#cf3039a0#ff#shared#2 WITH Flow::CallNode::getFunction#dispred#f0820431#ff_1#join_rhs ON FIRST 1 OUTPUT Lhs.1 'arg0'
622037211 ~498045% {1} r3 = r1 UNION r2
return r3
```
and a timing report that looked like this:
```
time | evals | max @ iter | predicate
------|-------|--------------|----------
5m8s | | | PointsToContext::syntactic_call_count#cf3039a0#ff#shared#2@6d98d1nd
4m38s | | | PointsToContext::syntactic_call_count#cf3039a0#ff#count_range@f5df1do4
3m51s | | | PointsToContext::syntactic_call_count#cf3039a0#ff#shared#3@da3b4abf
1m58s | 7613 | 37ms @ 4609 | MRO::ClassListList::removedClassParts#f0820431#fffff#reorder_2_3_4_0_1@8155axyi
1m37s | 7613 | 33ms @ 3904 | MRO::ClassListList::bestMergeCandidate#f0820431#2#fff@8155a83w
1m27s | | | PointsToContext::syntactic_call_count#cf3039a0#ff#antijoin_rhs@d2199bb8
1m8s | 1825 | 63ms @ 404 | PointsTo::Expressions::equalityEvaluatesTo#741b54e2#fffff@8155aw7w
37.6s | | | PointsToContext::syntactic_call_count#cf3039a0#ff#join_rhs@e348fc1p
...
```
To make optimising this easier for the compiler, I moved the bodies of
the `count` aggregate into their own helper predicates (with size
linear in the number of `CallNode`s), and also factored out the many
calls to `f.getName()`.
The astute reader will notice that in writing this as a sum of `count`s
rather than a count of a disjunction, the intersection (if it exists)
will be counted twice, and so the semantics may be different. However,
since `method_call` and `function_call` require `AttrNode` and
`NameNode` functions respectively, and as these two types are disjoint,
there is no intersection, and so the semantics should be preserved.
After the change, the evaluation of `syntactic_call_count` now looks as
follows:
```
Tuple counts for PointsToContext::syntactic_call_count#cf3039a0#ff/2@662dd8s0 after 216ms:
23960 ~0% {1} r1 = @py_scope#f AND NOT py_Functions_0#antijoin_rhs(Lhs.0 's')
23960 ~0% {2} r2 = SCAN r1 OUTPUT In.0 's', 0
276309 ~7% {2} r3 = SCAN @py_scope#f OUTPUT In.0 's', "__init__"
11763 ~0% {2} r4 = JOIN r3 WITH Scope::Scope::getName#dispred#f0820431#fb ON FIRST 2 OUTPUT Lhs.0 's', 1
35723 ~0% {2} r5 = r2 UNION r4
252349 ~0% {2} r6 = JOIN @py_scope#f WITH Function::Function::getName#dispred#f0820431#ff ON FIRST 1 OUTPUT Lhs.0 's', Rhs.1
240586 ~0% {2} r7 = SELECT r6 ON In.1 != "__init__"
131727 ~4% {2} r8 = r7 AND NOT project#PointsToContext::method_call#cf3039a0#ff(Lhs.1)
131727 ~0% {3} r9 = SCAN r8 OUTPUT In.1, In.0 's', 0
240586 ~0% {2} r10 = SCAN r7 OUTPUT In.1, In.0 's'
108859 ~0% {3} r11 = JOIN r10 WITH PointsToContext::syntactic_call_count#cf3039a0#ff#join_rhs ON FIRST 1 OUTPUT Lhs.0, Lhs.1 's', Rhs.1
240586 ~0% {3} r12 = r9 UNION r11
24100 ~0% {2} r13 = JOIN r12 WITH PointsToContext::syntactic_call_count#cf3039a0#ff#join_rhs#1 ON FIRST 1 OUTPUT Lhs.1 's', (Rhs.1 + Lhs.2)
240586 ~0% {2} r14 = SELECT r6 ON In.1 != "__init__"
131727 ~4% {2} r15 = r14 AND NOT project#PointsToContext::method_call#cf3039a0#ff(Lhs.1)
131727 ~0% {3} r16 = SCAN r15 OUTPUT In.0 's', In.1, 0
108859 ~4% {3} r17 = JOIN r10 WITH PointsToContext::syntactic_call_count#cf3039a0#ff#join_rhs ON FIRST 1 OUTPUT Lhs.1 's', Lhs.0, Rhs.1
240586 ~4% {3} r18 = r16 UNION r17
216486 ~2% {3} r19 = r18 AND NOT project#PointsToContext::function_call#cf3039a0#ff(Lhs.1)
216486 ~0% {2} r20 = SCAN r19 OUTPUT In.0 's', (0 + In.2)
240586 ~0% {2} r21 = r13 UNION r20
276309 ~0% {2} r22 = r5 UNION r21
return r22
```
