C++: Add ''isLiveAtEndOfBlock' predicate to 'Definition'.

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaImpl.qll

@@ -940,6 +940,11 @@ module SsaCached {
     SsaImpl::phiHasInputFromBlock(phi, inp, bb)
   }
 
+  cached
+  predicate ssaDefReachesEndOfBlock(IRBlock bb, Definition def) {
+    SsaImpl::ssaDefReachesEndOfBlock(bb, def, _)
+  }
+
   predicate variableRead = SsaInput::variableRead/4;
 
   predicate variableWrite = SsaInput::variableWrite/4;
@@ -1176,6 +1181,14 @@ class Definition extends SsaImpl::Definition {
     SsaImpl::uncertainWriteDefinitionInput(this, result)
   }
 
+  /**
+   * Holds if this SSA definition is live at the end of basic block `bb`.
+   * That is, this definition reaches the end of basic block `bb`, at which
+   * point it is still live, without crossing another SSA definition of the
+   * same source variable.
+   */
+  predicate isLiveAtEndOfBlock(IRBlock bb) { ssaDefReachesEndOfBlock(bb, this) }
+
   /**
    * Gets a definition that ultimately defines this SSA definition and is
    * not itself a phi node.