Merge pull request #2755 from jbj/BarrierGuard-SSA

C++: Don't use GVN in AST DataFlow BarrierNode

Author: MathiasVP

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

@@ -6,7 +6,6 @@ private import cpp
 private import semmle.code.cpp.dataflow.internal.FlowVar
 private import semmle.code.cpp.models.interfaces.DataFlow
 private import semmle.code.cpp.controlflow.Guards
-private import semmle.code.cpp.valuenumbering.GlobalValueNumbering
 
 cached
 private newtype TNode =
@@ -689,9 +688,9 @@ class BarrierGuard extends GuardCondition {
 
   /** Gets a node guarded by this guard. */
   final ExprNode getAGuardedNode() {
-    exists(GVN value, boolean branch |
-      result.getExpr() = value.getAnExpr() and
-      this.checks(value.getAnExpr(), branch) and
+    exists(SsaDefinition def, Variable v, boolean branch |
+      result.getExpr() = def.getAUse(v) and
+      this.checks(def.getAUse(v), branch) and
       this.controls(result.getExpr().getBasicBlock(), branch)
     )
   }

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

@@ -48,7 +48,7 @@ struct XY {
 void bg_stackstruct(XY s1, XY s2) {
   s1.x = source();
   if (guarded(s1.x)) {
-    sink(s1.x); // no flow
+    sink(s1.x); // no flow [FALSE POSITIVE in AST]
   } else if (guarded(s1.y)) {
     sink(s1.x); // flow
   } else if (guarded(s2.y)) {

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

@@ -3,6 +3,7 @@
 | BarrierGuard.cpp:25:10:25:15 | source | BarrierGuard.cpp:21:17:21:22 | source |
 | BarrierGuard.cpp:31:10:31:15 | source | BarrierGuard.cpp:29:16:29:21 | source |
 | BarrierGuard.cpp:33:10:33:15 | source | BarrierGuard.cpp:29:16:29:21 | source |
+| BarrierGuard.cpp:51:13:51:13 | x | BarrierGuard.cpp:49:10:49:15 | call to source |
 | BarrierGuard.cpp:53:13:53:13 | x | BarrierGuard.cpp:49:10:49:15 | call to source |
 | BarrierGuard.cpp:55:13:55:13 | x | BarrierGuard.cpp:49:10:49:15 | call to source |
 | BarrierGuard.cpp:62:14:62:14 | x | BarrierGuard.cpp:60:11:60:16 | call to source |

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

@@ -1,3 +1,4 @@
+| BarrierGuard.cpp:49:10:49:15 | BarrierGuard.cpp:51:13:51:13 | AST only |
 | BarrierGuard.cpp:60:11:60:16 | BarrierGuard.cpp:62:14:62:14 | AST only |
 | clang.cpp:12:9:12:20 | clang.cpp:22:8:22:20 | AST only |
 | clang.cpp:28:27:28:32 | clang.cpp:30:27:30:34 | AST only |