[PATCH] D63080: [analyzer] Track indices of arrays

[Kristóf Umann via Phabricator via cfe-commits]

Szelethus created this revision.
Szelethus added reviewers: NoQ, dcoughlin, xazax.hun, rnkovacs, baloghadamsoftware, Charusso.
Szelethus added a project: clang.
Herald added subscribers: cfe-commits, gamesh411, dkrupp, donat.nagy, mikhail.ramalho, a.sidorin, szepet, whisperity.

Observe the test file before this patch:
F9155603: image.png <https://reviews.llvm.org/F9155603>

I think this patch really improves on this case. The problem however, that some subexpressions of expressions should be tracked (like `n` in `arr[n]` here) is a broader one, and there may be other some cases I could add.


Repository:
  rC Clang

https://reviews.llvm.org/D63080

Files:
  clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp
  clang/test/Analysis/diagnostics/track_subexpressions.cpp


Index: clang/test/Analysis/diagnostics/track_subexpressions.cpp
===================================================================
--- clang/test/Analysis/diagnostics/track_subexpressions.cpp
+++ clang/test/Analysis/diagnostics/track_subexpressions.cpp
@@ -17,3 +17,35 @@
   (void)(TCP_MAXWIN << shift_amount); // expected-warning{{The result of the left shift is undefined due to shifting by '255', which is greater or equal to the width of type 'int'}}
                                       // expected-note at -1{{The result of the left shift is undefined due to shifting by '255', which is greater or equal to the width of type 'int'}}
 }
+
+namespace array_index_tracking {
+void consume(int);
+
+int getIndex(int x) {
+  int a;
+  if (x > 0) // expected-note {{Assuming 'x' is > 0}}
+             // expected-note at -1 {{Taking true branch}}
+    a = 3; // expected-note {{The value 3 is assigned to 'a'}}
+  else
+    a = 2;
+  return a; // expected-note {{Returning the value 3 (loaded from 'a')}}
+}
+
+int getInt();
+
+void testArrayIndexTracking() {
+  int arr[10];
+
+  for (int i = 0; i < 3; ++i)
+    // expected-note at -1 3{{Loop condition is true.  Entering loop body}}
+    // expected-note at -2 {{Loop condition is false. Execution continues on line 43}}
+    arr[i] = 0;
+  int x = getInt();
+  int n = getIndex(x); // expected-note {{Calling 'getIndex'}}
+                       // expected-note at -1 {{Returning from 'getIndex'}}
+                       // expected-note at -2 {{'n' initialized to 3}}
+  consume(arr[n]);
+  // expected-note at -1 {{1st function call argument is an uninitialized value}}
+  // expected-warning at -2{{1st function call argument is an uninitialized value}}
+}
+} // end of namespace array_index_tracking
Index: clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp
===================================================================
--- clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp
+++ clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp
@@ -1676,6 +1676,10 @@
   if (const Expr *Receiver = NilReceiverBRVisitor::getNilReceiver(Inner, LVNode))
     trackExpressionValue(LVNode, Receiver, report, EnableNullFPSuppression);
 
+  if (const auto *Arr = dyn_cast<ArraySubscriptExpr>(Inner))
+    trackExpressionValue(
+        LVNode, Arr->getIdx(), report, EnableNullFPSuppression);
+
   // See if the expression we're interested refers to a variable.
   // If so, we can track both its contents and constraints on its value.
   if (ExplodedGraph::isInterestingLValueExpr(Inner)) {


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