[analyzer] Improve subscripting null arrays for catching null dereferences.

Array-to-pointer cast now works correctly when the pointer to the array
is concrete, eg. null, which allows further symbolic calculations involving
such values.

Inlined defensive checks are now detected correctly when the resulting null
symbol is being array-subscripted before dereference.

Differential Revision: https://reviews.llvm.org/D32291

llvm-svn: 301251

2 files changed, 12 insertions, 10 deletions

diff --git a/clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp b/clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp
index ec9fd6c75e0..d00182a871c 100644
--- a/clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp
+++ b/clang/lib/StaticAnalyzer/Core/BugReporterVisitors.cpp
@@ -61,7 +61,9 @@ const Expr *bugreporter::getDerefExpr(const Stmt *S) {
         return U->getSubExpr()->IgnoreParenCasts();
     }
     else if (const MemberExpr *ME = dyn_cast<MemberExpr>(E)) {
-      if (ME->isArrow() || isDeclRefExprToReference(ME->getBase())) {
+      if (ME->isImplicitAccess()) {
+        return ME;
+      } else if (ME->isArrow() || isDeclRefExprToReference(ME->getBase())) {
         return ME->getBase()->IgnoreParenCasts();
       } else {
         // If we have a member expr with a dot, the base must have been
@@ -73,9 +75,9 @@ const Expr *bugreporter::getDerefExpr(const Stmt *S) {
       return IvarRef->getBase()->IgnoreParenCasts();
     }
     else if (const ArraySubscriptExpr *AE = dyn_cast<ArraySubscriptExpr>(E)) {
-      return AE->getBase();
+      return getDerefExpr(AE->getBase());
     }
-    else if (isDeclRefExprToReference(E)) {
+    else if (isa<DeclRefExpr>(E)) {
       return E;
     }
     break;
@@ -974,14 +976,11 @@ bool bugreporter::trackNullOrUndefValue(const ExplodedNode *N,
     // This code interacts heavily with this hack; otherwise the value
     // would not be null at all for most fields, so we'd be unable to track it.
     if (const auto *Op = dyn_cast<UnaryOperator>(Ex))
-      if (Op->getOpcode() == UO_AddrOf && Op->getSubExpr()->isLValue()) {
-        Ex = Op->getSubExpr()->IgnoreParenCasts();
-        while (const auto *ME = dyn_cast<MemberExpr>(Ex)) {
-          Ex = ME->getBase()->IgnoreParenCasts();
-        }
-      }
+      if (Op->getOpcode() == UO_AddrOf && Op->getSubExpr()->isLValue())
+        if (const Expr *DerefEx = getDerefExpr(Op->getSubExpr()))
+          Ex = DerefEx;
 
-    if (ExplodedGraph::isInterestingLValueExpr(Ex) || CallEvent::isCallStmt(Ex))
+    if (Ex && (ExplodedGraph::isInterestingLValueExpr(Ex) || CallEvent::isCallStmt(Ex)))
       Inner = Ex;
   }
 
diff --git a/clang/lib/StaticAnalyzer/Core/RegionStore.cpp b/clang/lib/StaticAnalyzer/Core/RegionStore.cpp
index dd7e9dd1178..3000e13d32c 100644
--- a/clang/lib/StaticAnalyzer/Core/RegionStore.cpp
+++ b/clang/lib/StaticAnalyzer/Core/RegionStore.cpp
@@ -1338,6 +1338,9 @@ RegionStoreManager::getSizeInElements(ProgramStateRef state,
 ///  the array).  This is called by ExprEngine when evaluating casts
 ///  from arrays to pointers.
 SVal RegionStoreManager::ArrayToPointer(Loc Array, QualType T) {
+  if (Array.getAs<loc::ConcreteInt>())
+    return Array;
+
   if (!Array.getAs<loc::MemRegionVal>())
     return UnknownVal();