[analyzer] Fix crash when lambda captures a variable-length array.

When a C++ lambda captures a variable-length array, it creates a capture
field to store the size of the array. The initialization expression for this
capture is null, which led the analyzer to crash when initializing the field.
To avoid this, use the size expression from the VLA type to determine the
initialization value.

rdar://problem/23748072

llvm-svn: 254962

clang/lib/StaticAnalyzer/Core/ExprEngineCXX.cpp

@@ -531,9 +531,23 @@ void ExprEngine::VisitLambdaExpr(const LambdaExpr *LE, ExplodedNode *Pred,
   for (LambdaExpr::const_capture_init_iterator i = LE->capture_init_begin(),
                                                e = LE->capture_init_end();
        i != e; ++i, ++CurField) {
-    SVal Field = State->getLValue(*CurField, V);
-    SVal InitExpr = State->getSVal(*i, LocCtxt);
-    State = State->bindLoc(Field, InitExpr);
+    FieldDecl *FieldForCapture = *CurField;
+    SVal FieldLoc = State->getLValue(FieldForCapture, V);
+
+    SVal InitVal;
+    if (!FieldForCapture->hasCapturedVLAType()) {
+      Expr *InitExpr = *i;
+      assert(InitExpr && "Capture missing initialization expression");
+      InitVal = State->getSVal(InitExpr, LocCtxt);
+    } else {
+      // The field stores the length of a captured variable-length array.
+      // These captures don't have initialization expressions; instead we
+      // get the length from the VLAType size expression.
+      Expr *SizeExpr = FieldForCapture->getCapturedVLAType()->getSizeExpr();
+      InitVal = State->getSVal(SizeExpr, LocCtxt);
+    }
+
+    State = State->bindLoc(FieldLoc, InitVal);
   }
 
   // Decay the Loc into an RValue, because there might be a

clang/test/Analysis/lambdas.cpp

@@ -173,6 +173,19 @@ void testFunctionPointerCapture() {
   clang_analyzer_eval(i == 6); // expected-warning{{TRUE}}
 }
 
+// Captured variable-length array.
+
+void testVariableLengthArrayCaptured() {
+  int n = 2;
+  int array[n];
+  array[0] = 7;
+
+  int i = [&]{
+    return array[0];
+  }();
+
+  clang_analyzer_eval(i == 7); // expected-warning{{TRUE}}
+}
 
 // Test inline defensive checks
 int getNum();