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HashCons: Make some functionality apparent.

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The user knows that an expression functionally determines its
hashCons value, and that an expression functionally determines
its number of children, but this is not provable from the
definitions, and so not usable by the optimiser. By storing
the result of those known-functional calls in a variable,
rather than repeating the call, we enable better join orders.
This commit is contained in:
Pavel Avgustinov
2019-09-18 12:53:52 +01:00
parent 03502863cf
commit eca31908ab
1 changed files with 9 additions and 6 deletions
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15
cpp/ql/src/semmle/code/cpp/valuenumbering/HashCons.qll
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@@ -766,11 +766,13 @@ private predicate mk_ClassAggregateLiteral(Class c, HC_Fields hcf, ClassAggregat
analyzableClassAggregateLiteral(cal) and
c = cal.getUnspecifiedType() and
(
exists(HC_Fields tail, Expr e, Field f |
exists(HC_Fields tail, Expr e, Field f, int numChildren, HashCons eCons |
f.getInitializationOrder() = cal.getNumChild() - 1 and
e = cal.getFieldExpr(f).getFullyConverted() and
hcf = HC_FieldCons(c, cal.getNumChild() - 1, f, hashCons(e), tail) and
mk_FieldCons(c, cal.getNumChild() - 1, f, hashCons(e), tail, cal)
eCons = hashCons(e) and
numChildren = cal.getNumChild() and
hcf = HC_FieldCons(c, numChildren - 1, f, eCons, tail) and
mk_FieldCons(c, numChildren - 1, f, eCons, tail, cal)
)
or
cal.getNumChild() = 0 and
@@ -801,9 +803,10 @@ private predicate mk_ArrayCons(Type t, int i, HashCons hc, HC_Array hca, ArrayAg
private predicate mk_ArrayAggregateLiteral(Type t, HC_Array hca, ArrayAggregateLiteral aal) {
t = aal.getUnspecifiedType() and
(
exists(HashCons head, HC_Array tail |
hca = HC_ArrayCons(t, aal.getNumChild() - 1, head, tail) and
mk_ArrayCons(t, aal.getNumChild() - 1, head, tail, aal)
exists(HashCons head, HC_Array tail, int numElements |
numElements = aal.getNumChild() and
hca = HC_ArrayCons(t, numElements - 1, head, tail) and
mk_ArrayCons(t, numElements - 1, head, tail, aal)
)
or
aal.getNumChild() = 0 and