C++: add isReachableFromFunctionEntry

cpp/ql/src/semmle/code/cpp/controlflow/IRGuards.qll

@@ -310,7 +310,7 @@ class IRGuardCondition extends Instruction {
             succ.dominates(controlled) and
             forall(IRBlock pred
             | pred.getASuccessor() = succ
-            | pred = thisblock or succ.dominates(pred)))) // removed reachability condition - is that OK?
+            | pred = thisblock or succ.dominates(pred) or not pred.isReachableFromFunctionEntry())))
     }
 }
 

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IRBlock.qll

@@ -89,4 +89,12 @@ class IRBlock extends TIRBlock {
     dominates(result.getAPredecessor()) and
     not strictlyDominates(result)
   }
+  
+  /**
+   * Holds if this block is reachable from the entry point of its function
+   */
+  final predicate isReachableFromFunctionEntry() {
+    this = getFunctionIR().getEntryBlock() or
+    getAPredecessor().isReachableFromFunctionEntry()
+  }
 }

cpp/ql/src/semmle/code/cpp/ir/implementation/raw/IRBlock.qll

@@ -89,4 +89,12 @@ class IRBlock extends TIRBlock {
     dominates(result.getAPredecessor()) and
     not strictlyDominates(result)
   }
+  
+  /**
+   * Holds if this block is reachable from the entry point of its function
+   */
+  final predicate isReachableFromFunctionEntry() {
+    this = getFunctionIR().getEntryBlock() or
+    getAPredecessor().isReachableFromFunctionEntry()
+  }
 }

cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/IRBlock.qll

@@ -89,4 +89,12 @@ class IRBlock extends TIRBlock {
     dominates(result.getAPredecessor()) and
     not strictlyDominates(result)
   }
+  
+  /**
+   * Holds if this block is reachable from the entry point of its function
+   */
+  final predicate isReachableFromFunctionEntry() {
+    this = getFunctionIR().getEntryBlock() or
+    getAPredecessor().isReachableFromFunctionEntry()
+  }
 }

cpp/ql/test/library-tests/controlflow/guards-ir/ASTGuardsControl.expected

@@ -87,4 +87,5 @@
 | test.cpp:31:7:31:13 | ... == ... | false | 34 | 34 |
 | test.cpp:31:7:31:13 | ... == ... | true | 30 | 30 |
 | test.cpp:31:7:31:13 | ... == ... | true | 31 | 32 |
+| test.cpp:42:13:42:20 | call to getABool | false | 53 | 53 |
 | test.cpp:42:13:42:20 | call to getABool | true | 43 | 45 |

cpp/ql/test/library-tests/controlflow/guards-ir/IRGuardsControl.expected

@@ -82,4 +82,5 @@
 | test.cpp:31:7:31:13 | ... == ... | false | 34 | 34 |
 | test.cpp:31:7:31:13 | ... == ... | true | 30 | 30 |
 | test.cpp:31:7:31:13 | ... == ... | true | 32 | 32 |
+| test.cpp:42:13:42:20 | call to getABool | false | 53 | 53 |
 | test.cpp:42:13:42:20 | call to getABool | true | 44 | 44 |