C++: IR data flow through inheritance conversions

This makes IR data flow behave more like AST data flow, and it makes IR
virtual dispatch work without further changes.

Author: jbj

cpp/ql/src/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll

@@ -205,7 +205,8 @@ private predicate simpleInstructionLocalFlowStep(Instruction iFrom, Instruction
   iTo.(CopyInstruction).getSourceValue() = iFrom or
   iTo.(PhiInstruction).getAnOperand().getDef() = iFrom or
   // Treat all conversions as flow, even conversions between different numeric types.
-  iTo.(ConvertInstruction).getUnary() = iFrom
+  iTo.(ConvertInstruction).getUnary() = iFrom or
+  iTo.(InheritanceConversionInstruction).getUnary() = iFrom
 }
 
 /**

cpp/ql/test/library-tests/dataflow/dataflow-tests/dispatch.cpp

@@ -28,17 +28,17 @@ struct Bottom : Middle {
 void VirtualDispatch(Bottom *bottomPtr, Bottom &bottomRef) {
   Top *topPtr = bottomPtr, &topRef = bottomRef;
 
-  sink(topPtr->isSource1()); // flow [NOT DETECTED]
+  sink(topPtr->isSource1()); // flow [NOT DETECTED by AST]
   sink(topPtr->isSource2()); // flow [NOT DETECTED by AST]
-  topPtr->isSink(source()); // flow [NOT DETECTED]
+  topPtr->isSink(source()); // flow [NOT DETECTED by AST]
 
   sink(topPtr->notSource1()); // no flow [FALSE POSITIVE]
   sink(topPtr->notSource2()); // no flow [FALSE POSITIVE]
   topPtr->notSink(source()); // no flow [FALSE POSITIVE]
 
-  sink(topRef.isSource1()); // flow [NOT DETECTED]
+  sink(topRef.isSource1()); // flow [NOT DETECTED by AST]
   sink(topRef.isSource2()); // flow [NOT DETECTED by AST]
-  topRef.isSink(source()); // flow [NOT DETECTED]
+  topRef.isSink(source()); // flow [NOT DETECTED by AST]
 
   sink(topRef.notSource1()); // no flow [FALSE POSITIVE]
   sink(topRef.notSource2()); // no flow [FALSE POSITIVE]

cpp/ql/test/library-tests/dataflow/dataflow-tests/test_diff.expected

@@ -7,6 +7,10 @@
 | clang.cpp:39:42:39:47 | clang.cpp:41:18:41:19 | IR only |
 | dispatch.cpp:16:37:16:42 | dispatch.cpp:32:16:32:24 | IR only |
 | dispatch.cpp:16:37:16:42 | dispatch.cpp:40:15:40:23 | IR only |
+| dispatch.cpp:22:37:22:42 | dispatch.cpp:31:16:31:24 | IR only |
+| dispatch.cpp:22:37:22:42 | dispatch.cpp:39:15:39:23 | IR only |
+| dispatch.cpp:33:18:33:23 | dispatch.cpp:23:38:23:38 | IR only |
+| dispatch.cpp:41:17:41:22 | dispatch.cpp:23:38:23:38 | IR only |
 | lambdas.cpp:8:10:8:15 | lambdas.cpp:14:3:14:6 | AST only |
 | lambdas.cpp:8:10:8:15 | lambdas.cpp:18:8:18:8 | AST only |
 | lambdas.cpp:8:10:8:15 | lambdas.cpp:21:3:21:6 | AST only |

cpp/ql/test/library-tests/dataflow/dataflow-tests/test_ir.expected

@@ -14,9 +14,13 @@
 | clang.cpp:45:17:45:18 | Load: m2 | clang.cpp:43:35:43:40 | Call: call to source |
 | dispatch.cpp:11:38:11:38 | Load: x | dispatch.cpp:37:19:37:24 | Call: call to source |
 | dispatch.cpp:11:38:11:38 | Load: x | dispatch.cpp:45:18:45:23 | Call: call to source |
+| dispatch.cpp:23:38:23:38 | Load: x | dispatch.cpp:33:18:33:23 | Call: call to source |
+| dispatch.cpp:23:38:23:38 | Load: x | dispatch.cpp:41:17:41:22 | Call: call to source |
+| dispatch.cpp:31:16:31:24 | Call: call to isSource1 | dispatch.cpp:22:37:22:42 | Call: call to source |
 | dispatch.cpp:32:16:32:24 | Call: call to isSource2 | dispatch.cpp:16:37:16:42 | Call: call to source |
 | dispatch.cpp:35:16:35:25 | Call: call to notSource1 | dispatch.cpp:9:37:9:42 | Call: call to source |
 | dispatch.cpp:36:16:36:25 | Call: call to notSource2 | dispatch.cpp:10:37:10:42 | Call: call to source |
+| dispatch.cpp:39:15:39:23 | Call: call to isSource1 | dispatch.cpp:22:37:22:42 | Call: call to source |
 | dispatch.cpp:40:15:40:23 | Call: call to isSource2 | dispatch.cpp:16:37:16:42 | Call: call to source |
 | dispatch.cpp:43:15:43:24 | Call: call to notSource1 | dispatch.cpp:9:37:9:42 | Call: call to source |
 | dispatch.cpp:44:15:44:24 | Call: call to notSource2 | dispatch.cpp:10:37:10:42 | Call: call to source |