Python: Clarify pruning code.

Author: markshannon

python/ql/src/semmle/python/Pruning.qll

@@ -423,7 +423,7 @@ module Pruner {
         reachableEdge(_, bb)
     }
 
-    Constraint constraintFromTest(SsaVariable var, UnprunedCfgNode node) {
+    Constraint constraintFromExpr(SsaVariable var, UnprunedCfgNode node) {
         py_ssa_use(node, var) and result = TTruthy(true)
         or
         exists(boolean b |
@@ -435,7 +435,11 @@ module Pruner {
             result = TConstrainedByConstant(op, k)
         )
         or
-        result = constraintFromTest(var, node.(UnprunedNot).getOperand()).invert()
+        result = constraintFromExpr(var, node.(UnprunedNot).getOperand()).invert()
+    }
+
+    Constraint constraintFromTest(SsaVariable var, UnprunedCfgNode node) {
+        result = constraintFromExpr(var, node) and node.isBranch()
     }
 
     predicate none_test(UnprunedCompareNode test, SsaVariable var, boolean is) {
@@ -462,8 +466,6 @@ module Pruner {
             py_ssa_use(right, var) and
             intValue(left.getNode()) = k
         )
-        or
-        int_test(test.(UnprunedNot).getOperand(), var, op.invert(), k)
     }
 
     private predicate constrainingValue(Expr e) {

python/ql/test/library-tests/ControlFlow/pruning/Constraint.expected

@@ -1,10 +1,8 @@
 | 8 | test | test | Truthy | test |
 | 10 | test | test | Truthy | test |
 | 14 | seq | seq | Truthy | test |
-| 16 | seq | seq | Truthy | test |
 | 17 | seq | seq | Truthy | test |
 | 21 | UnaryExpr | t1 | Falsey | test |
-| 21 | t1 | t1 | Truthy | test |
 | 24 | t1 | t1 | Truthy | test |
 | 25 | t1 | t1 | Truthy | test |
 | 26 | t2 | t2 | Truthy | test |
@@ -24,91 +22,43 @@
 | 40 | t6 | t6 | Truthy | test |
 | 43 | t1 | t1 | Truthy | test |
 | 44 | UnaryExpr | t2 | Falsey | test |
-| 44 | t2 | t2 | Truthy | test |
 | 47 | t1 | t1 | Truthy | test |
 | 48 | t2 | t2 | Truthy | test |
 | 49 | t2 | t2 | Truthy | test |
 | 51 | t2 | t2 | Truthy | test |
 | 52 | t2 | t2 | Truthy | test |
 | 55 | seq1 | seq1 | Truthy | test |
 | 57 | UnaryExpr | seq2 | Falsey | test |
-| 57 | seq2 | seq2 | Truthy | test |
 | 60 | seq1 | seq1 | Truthy | test |
-| 62 | seq1 | seq1 | Truthy | test |
 | 63 | seq2 | seq2 | Truthy | test |
-| 65 | seq2 | seq2 | Truthy | test |
 | 66 | seq3 | seq3 | Truthy | test |
 | 68 | UnaryExpr | seq4 | Falsey | test |
-| 68 | seq4 | seq4 | Truthy | test |
-| 71 | seq3 | seq3 | Truthy | test |
-| 73 | var | var | Truthy | test |
-| 74 | seq4 | seq4 | Truthy | test |
-| 76 | var | var | Truthy | test |
 | 78 | seq5 | seq5 | Truthy | test |
-| 80 | seq5 | seq5 | Truthy | test |
-| 81 | seq5 | seq5 | Truthy | test |
-| 83 | var | var | Truthy | test |
 | 88 | UnaryExpr | x | Falsey | test |
-| 88 | x | x | Truthy | test |
-| 89 | Exception | Exception | Truthy | test |
 | 90 | y | y | Truthy | test |
-| 91 | Exception | Exception | Truthy | test |
-| 92 | make_a_call | make_a_call | Truthy | test |
 | 93 | UnaryExpr | x | Falsey | test |
-| 93 | x | x | Truthy | test |
-| 94 | count | count | Truthy | test |
 | 95 | y | y | Truthy | test |
-| 96 | count | count | Truthy | test |
 | 99 | another_module | another_module | Truthy | assign |
-| 101 | make_a_call | make_a_call | Truthy | test |
 | 102 | UnaryExpr | another_module | Falsey | test |
-| 102 | another_module | another_module | Truthy | test |
-| 103 | count | count | Truthy | test |
 | 107 | UnaryExpr | t1 | Falsey | test |
-| 107 | t1 | t1 | Truthy | test |
 | 109 | t2 | t2 | Truthy | test |
 | 111 | t1 | t1 | Truthy | test |
 | 113 | UnaryExpr | t2 | Falsey | test |
-| 113 | t2 | t2 | Truthy | test |
 | 117 | UnaryExpr | test | Falsey | test |
-| 117 | test | test | Truthy | test |
 | 119 | UnaryExpr | test | Falsey | test |
-| 119 | test | test | Truthy | test |
 | 123 | m | m | Truthy | test |
-| 125 | m | m | Truthy | test |
 | 126 | m | m | Truthy | test |
 | 158 | Compare | ps | Is not None | test |
-| 158 | ps | ps | Truthy | test |
-| 159 | ps | ps | Truthy | test |
 | 160 | Compare | ps | Is None | test |
-| 160 | ps | ps | Truthy | test |
-| 171 | __name__ | __name__ | Truthy | test |
-| 172 | None | None | Truthy | test |
 | 172 | escapes | escapes | Is None | assign |
-| 174 | func | func | Truthy | test |
-| 175 | Exception | Exception | Truthy | test |
-| 176 | count | count | Truthy | test |
 | 177 | Compare | escapes | Is None | test |
-| 177 | None | None | Truthy | test |
-| 177 | escapes | escapes | Truthy | test |
-| 178 | count | count | Truthy | test |
-| 180 | count | count | Truthy | test |
-| 188 | true12 | true12 | Truthy | test |
 | 191 | true12 | true12 | == 0 | assign |
 | 195 | Compare | x | < 4 | test |
-| 195 | x | x | Truthy | test |
 | 197 | Compare | x | < 4 | test |
-| 197 | x | x | Truthy | test |
 | 201 | Compare | x | < 4 | test |
-| 201 | x | x | Truthy | test |
-| 203 | Compare | x | >= 4 | test |
 | 203 | UnaryExpr | x | < 4 | test |
-| 203 | x | x | Truthy | test |
 | 207 | Compare | x | < 4 | test |
-| 207 | x | x | Truthy | test |
 | 209 | Compare | x | < 4 | test |
-| 209 | x | x | Truthy | test |
-| 214 | None | None | Truthy | test |
 | 215 | x | x | Truthy | test |
 | 215 | y | y | Truthy | test |
 | 217 | x | x | Truthy | test |