Merge pull request github#4940 from hvitved/csharp/base-ssa-phi-input

C#: Take phi nodes into account in `Steps::getARead()`

Author: hvitved

csharp/ql/src/semmle/code/csharp/dataflow/internal/Steps.qll

@@ -6,18 +6,17 @@ import csharp
  * Provides functionality for performing simple data flow analysis.
  * This library is used by the dispatch library, which in turn is used by the
  * SSA library, so we cannot make use of the SSA library in this library.
- * Instead, this library relies on a self-contained, minimalistic SSA-like
- * implementation.
+ * Instead, this library relies on the `BaseSsa` library.
  */
 module Steps {
   private import semmle.code.csharp.dataflow.internal.BaseSSA
 
   /**
-   * Gets a read that is guaranteed to read the value assigned at definition `def`.
+   * Gets a read that may read the value assigned at definition `def`.
    */
   private AssignableRead getARead(AssignableDefinition def) {
     exists(BaseSsa::Definition ssaDef |
-      ssaDef.getDefinition() = def and
+      ssaDef.getAnUltimateDefinition().getDefinition() = def and
       result = ssaDef.getARead()
     )
     or

csharp/ql/test/query-tests/Dead Code/DeadStoreOfLocal/DeadStoreOfLocal.cs

@@ -275,6 +275,17 @@ void M9()
     {
         A();
     }
+
+    void M10(bool b)
+    {
+        var x = ""; // GOOD
+        Action action;
+        if (b)
+            action = () => System.Console.WriteLine(x);
+        else
+            action = () => { };
+        action();
+    }
 }
 
 class Patterns

csharp/ql/test/query-tests/Dead Code/DeadStoreOfLocal/DeadStoreOfLocal.expected

@@ -9,11 +9,11 @@
 | DeadStoreOfLocal.cs:142:26:142:27 | Exception ex | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:142:26:142:27 | ex | ex |
 | DeadStoreOfLocal.cs:246:17:246:24 | Int32 y = ... | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:246:17:246:17 | y | y |
 | DeadStoreOfLocal.cs:261:17:261:21 | Int32 x = ... | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:261:17:261:17 | x | x |
-| DeadStoreOfLocal.cs:289:23:289:28 | Object v1 | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:289:27:289:28 | v1 | v1 |
-| DeadStoreOfLocal.cs:303:18:303:23 | Object v2 | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:303:22:303:23 | v2 | v2 |
-| DeadStoreOfLocal.cs:320:9:320:32 | ... = ... | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:316:23:316:23 | b | b |
-| DeadStoreOfLocal.cs:361:13:361:20 | String s = ... | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:361:13:361:13 | s | s |
-| DeadStoreOfLocal.cs:387:13:387:21 | ... = ... | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:385:13:385:13 | s | s |
+| DeadStoreOfLocal.cs:300:23:300:28 | Object v1 | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:300:27:300:28 | v1 | v1 |
+| DeadStoreOfLocal.cs:314:18:314:23 | Object v2 | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:314:22:314:23 | v2 | v2 |
+| DeadStoreOfLocal.cs:331:9:331:32 | ... = ... | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:327:23:327:23 | b | b |
+| DeadStoreOfLocal.cs:372:13:372:20 | String s = ... | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:372:13:372:13 | s | s |
+| DeadStoreOfLocal.cs:398:13:398:21 | ... = ... | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocal.cs:396:13:396:13 | s | s |
 | DeadStoreOfLocalBad.cs:7:13:7:48 | Boolean success = ... | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocalBad.cs:7:13:7:19 | success | success |
 | DeadStoreOfLocalBad.cs:23:32:23:32 | FormatException e | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocalBad.cs:23:32:23:32 | e | e |
 | DeadStoreOfLocalBad.cs:32:22:32:22 | String s | This assignment to $@ is useless, since its value is never read. | DeadStoreOfLocalBad.cs:32:22:32:22 | s | s |