C++: Delete incorrect comment and add a bunch of barrier guard tests.

Author: MathiasVP

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

@@ -342,25 +342,7 @@ module GuardsInput implements SharedGuards::InputSig<Cpp::Location, Instruction,
     /** Gets an expression returned from this function. */
     GuardsInput::Expr getAReturnExpr() {
       exists(StoreInstruction store |
-        // We use the `Store` instruction that writes the return value instead of the
-        // `ReturnValue` instruction since the `ReturnValue` instruction is not always
-        // dominated by certain guards. For example:
-        // ```
-        // if(b) {
-        //   return true;
-        // } else {
-        //   return false;
-        // }
-        // ```
-        // this will be translated into IR like:
-        // ```
-        // if(b) {
-        //   x = true;
-        // } else {
-        //   x = false;
-        // }
-        // return x;
-        // ```
+        // A write to the `IRVariable` which represents the return value.
         store.getDestinationAddress().(VariableAddressInstruction).getIRVariable() instanceof
           IRReturnVariable and
         store.getEnclosingFunction() = this and

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

@@ -135,6 +135,32 @@ bool guarded_wrapper(int x) {
   }
 }
 
+bool guarded_wrapper_2(int x) {
+  bool b;
+  if(guarded(x)) {
+    b = true;
+  } else {
+    b = false;
+  }
+  return b;
+}
+
+bool guarded_wrapper_3(int x) {
+  bool b = false;
+  if(guarded(x)) {
+    b = true;
+  }
+  return b;
+}
+
+bool guarded_wrapper_4(int x) {
+  bool b = false;
+  if(guarded(x)) {
+    return true;
+  }
+  return b;
+}
+
 void test_guarded_wrapper() {
   int x = source();
 
@@ -143,4 +169,23 @@ void test_guarded_wrapper() {
   } else {
     sink(x); // $ ast,ir
   }
-}
+
+  if(guarded_wrapper_2(x)) {
+    sink(x); // $ SPURIOUS: ast
+  } else {
+    sink(x); // $ ast,ir
+  }
+
+  if(guarded_wrapper_3(x)) {
+    sink(x); // $ SPURIOUS: ast
+  } else {
+    sink(x); // $ ast,ir
+  }
+
+  if(guarded_wrapper_4(x)) {
+    sink(x); // $ SPURIOUS: ast
+  } else {
+    sink(x); // $ ast,ir
+  }
+}
+

cpp/ql/test/library-tests/dataflow/dataflow-tests/test-source-sink.expected

@@ -16,8 +16,14 @@ astFlow
 | BarrierGuard.cpp:90:11:90:16 | call to source | BarrierGuard.cpp:101:8:101:8 | x |
 | BarrierGuard.cpp:107:11:107:16 | call to source | BarrierGuard.cpp:112:8:112:8 | x |
 | BarrierGuard.cpp:116:11:116:16 | call to source | BarrierGuard.cpp:127:8:127:8 | x |
-| BarrierGuard.cpp:139:11:139:16 | call to source | BarrierGuard.cpp:142:10:142:10 | x |
-| BarrierGuard.cpp:139:11:139:16 | call to source | BarrierGuard.cpp:144:10:144:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:168:10:168:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:170:10:170:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:174:10:174:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:176:10:176:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:180:10:180:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:182:10:182:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:186:10:186:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:188:10:188:10 | x |
 | acrossLinkTargets.cpp:19:27:19:32 | call to source | acrossLinkTargets.cpp:12:8:12:8 | x |
 | clang.cpp:12:9:12:20 | sourceArray1 | clang.cpp:18:8:18:19 | sourceArray1 |
 | clang.cpp:12:9:12:20 | sourceArray1 | clang.cpp:22:8:22:20 | & ... |
@@ -158,7 +164,10 @@ irFlow
 | BarrierGuard.cpp:49:10:49:15 | call to source | BarrierGuard.cpp:55:13:55:13 | x |
 | BarrierGuard.cpp:60:11:60:16 | call to source | BarrierGuard.cpp:64:14:64:14 | x |
 | BarrierGuard.cpp:60:11:60:16 | call to source | BarrierGuard.cpp:66:14:66:14 | x |
-| BarrierGuard.cpp:139:11:139:16 | call to source | BarrierGuard.cpp:144:10:144:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:170:10:170:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:176:10:176:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:182:10:182:10 | x |
+| BarrierGuard.cpp:165:11:165:16 | call to source | BarrierGuard.cpp:188:10:188:10 | x |
 | acrossLinkTargets.cpp:19:27:19:32 | call to source | acrossLinkTargets.cpp:12:8:12:8 | x |
 | clang.cpp:12:9:12:20 | sourceArray1 | clang.cpp:18:8:18:19 | sourceArray1 |
 | clang.cpp:12:9:12:20 | sourceArray1 | clang.cpp:23:17:23:29 | *& ... |