Merge pull request github#1823 from markshannon/python-dont-prune-in-ql

Python: removing pruning in QL.

Author: pavgust

python/ql/src/semmle/python/Flow.qll

@@ -1,7 +1,6 @@
 import python
 import semmle.python.flow.NameNode
 private import semmle.python.pointsto.PointsTo
-private import semmle.python.Pruning
 
 /* Note about matching parent and child nodes and CFG splitting:
  *
@@ -33,10 +32,6 @@ private AstNode toAst(ControlFlowNode n) {
 */
 class ControlFlowNode extends @py_flow_node {
 
-    cached ControlFlowNode() {
-        Pruner::reachable(this)
-    }
-
     /** Whether this control flow node is a load (including those in augmented assignments) */
     predicate isLoad() {
         exists(Expr e | e = toAst(this) | py_expr_contexts(_, 3, e) and not augstore(_, this))
@@ -180,8 +175,7 @@ class ControlFlowNode extends @py_flow_node {
 
     /** Gets a successor of this flow node */
     ControlFlowNode getASuccessor() {
-        py_successors(this, result) and
-        not Pruner::unreachableEdge(this, result)
+        py_successors(this, result)
     }
 
     /** Gets the immediate dominator of this flow node */
@@ -973,91 +967,21 @@ predicate defined_by(NameNode def, Variable v) {
     exists(NameNode p | defined_by(p, v) and p.getASuccessor() = def and not p.defines(v))
 }
 
-/* Combine extractor-generated basic block after pruning */
-
-private class BasicBlockPart extends @py_flow_node {
-
-    string toString() { result = "Basic block part" }
-
-    BasicBlockPart() {
-        py_flow_bb_node(_, _, this, _) and
-        Pruner::reachable(this)
-    }
-
-    predicate isHead() {
-        count(this.(ControlFlowNode).getAPredecessor()) != 1
-        or
-        exists(ControlFlowNode pred | pred = this.(ControlFlowNode).getAPredecessor() | strictcount(pred.getASuccessor()) > 1)
-    }
-
-    private BasicBlockPart previous() {
-        not this.isHead() and
-        py_flow_bb_node(this.(ControlFlowNode).getAPredecessor(), _, result, _)
-    }
-
-    BasicBlockPart getHead() {
-        this.isHead() and result = this
-        or
-        result = this.previous().getHead()
-    }
-
-    predicate isLast() {
-        not exists(BasicBlockPart part | part.previous() = this)
-    }
-
-    int length() {
-        result = max(int j | py_flow_bb_node(_, _, this, j)) + 1
-    }
-
-    int startIndex() {
-        this.isHead() and result = 0
-        or
-        exists(BasicBlockPart prev |
-            prev = this.previous() and
-            result = prev.startIndex() + prev.length()
-        )
-    }
-
-    predicate contains(ControlFlowNode node) {
-        py_flow_bb_node(node, _, this, _)
-    }
-
-    int indexOf(ControlFlowNode node) {
-        py_flow_bb_node(node, _, this, result)
-    }
-
-    ControlFlowNode lastNode() {
-        this.indexOf(result) = max(this.indexOf(_))
-    }
-
-    BasicBlockPart getImmediateDominator() {
-        result.contains(this.(ControlFlowNode).getImmediateDominator())
-    }
-
-}
-
 /** A basic block (ignoring exceptional flow edges to scope exit) */
 class BasicBlock extends @py_flow_node {
 
     BasicBlock() {
-        this.(BasicBlockPart).isHead()
-    }
-
-    private BasicBlockPart getAPart() {
-        result.getHead() = this
+        py_flow_bb_node(_, _, this, _)
     }
 
     /** Whether this basic block contains the specified node */
     predicate contains(ControlFlowNode node) {
-        this.getAPart().contains(node)
+        py_flow_bb_node(node, _, this, _)
     }
 
     /** Gets the nth node in this basic block */
     ControlFlowNode getNode(int n) {
-        exists(BasicBlockPart part |
-            part = this.getAPart() and
-            n = part.startIndex() + part.indexOf(result)
-        )
+        py_flow_bb_node(result, _, this, n)
     }
 
     string toString() {
@@ -1077,7 +1001,7 @@ class BasicBlock extends @py_flow_node {
     }
 
     cached BasicBlock getImmediateDominator() {
-        this.getAPart().getImmediateDominator() = result.getAPart()
+        this.firstNode().getImmediateDominator().getBasicBlock() = result
     }
 
     /** Dominance frontier of a node x is the set of all nodes `other` such that `this` dominates a predecessor
@@ -1093,10 +1017,9 @@ class BasicBlock extends @py_flow_node {
 
     /** Gets the last node in this basic block */
     ControlFlowNode getLastNode() {
-        exists(BasicBlockPart part |
-            part = this.getAPart() and
-            part.isLast() and
-            result = part.lastNode()
+        exists(int i |
+            this.getNode(i) = result and
+            i = max(int j | py_flow_bb_node(_, _, this, j))
         )
     }