Modify model of std::vector

Summary:
Turns out, analyzer was getting confused with complicated
model and it was reporting empty access in places it
shouldn't. Fixing backend is not trivial (tracing mode is the answer),
but the model can be simplified.
It introduces the problem that get() method doesn't return fresh value
every time, but we should be able to change backend later to deal with it.

Reviewed By: sblackshear

Differential Revision: D3328228

fbshipit-source-id: dddbaf8

infer/models/cpp/include/infer_model/vector.h

@@ -76,27 +76,19 @@ class vector {
   typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 
   /* INFER SPECIFIC HELPER FUNCTIONS */
-  bool isEmpty = true;
 
   // required to keep sizeof(std::vector) same as in standard
   value_type* beginPtr = nullptr;
   value_type* endPtr = nullptr;
+  value_type* __ignore;
 
-  value_type* get() const {
-    if (isEmpty) {
-      return nullptr;
-    }
-    // infer will angelically assume that __infer_skip__get_nondet_val
-    // returns non-null with unknown value which means there will be no
-    // null dereference
-    return __infer_skip__get_nondet_val<value_type>();
-  }
+  value_type* get() const { return beginPtr; }
 
   void allocate(size_type size) {
     if (size > 0) {
-      isEmpty = false;
+      beginPtr = __infer_skip__get_nondet_val<value_type>();
     } else {
-      isEmpty = true;
+      beginPtr = nullptr;
     }
   }
 
@@ -200,7 +192,7 @@ class vector {
   const_reverse_iterator crend() const noexcept { return rend(); }
 
   size_type size() const noexcept {
-    if (!isEmpty) {
+    if (beginPtr) {
       return 10;
     }
     return 0;
@@ -208,7 +200,7 @@ class vector {
 
   size_type capacity() const noexcept {}
 
-  bool empty() const noexcept { return isEmpty; }
+  bool empty() const noexcept { return beginPtr == nullptr; }
   size_type max_size() const noexcept;
   void reserve(size_type __n);
   void shrink_to_fit() noexcept;
@@ -259,7 +251,7 @@ class vector {
   iterator erase(const_iterator __position);
   iterator erase(const_iterator __first, const_iterator __last);
 
-  void clear() noexcept { isEmpty = true; }
+  void clear() noexcept { allocate(0); }
 
   void resize(size_type __sz);
   void resize(size_type __sz, const_reference __x);
@@ -326,25 +318,25 @@ vector<_Tp, _Allocator>::vector(
 
 template <class _Tp, class _Allocator>
 vector<_Tp, _Allocator>::vector(const vector& __x) {
-  isEmpty = __x.isEmpty;
+  beginPtr = __x.beginPtr;
 }
 
 template <class _Tp, class _Allocator>
 vector<_Tp, _Allocator>::vector(const vector& __x, const allocator_type& __a) {
-  isEmpty = __x.isEmpty;
+  beginPtr = __x.beginPtr;
 }
 
 template <class _Tp, class _Allocator>
 inline vector<_Tp, _Allocator>::vector(vector&& __x) noexcept {
-  isEmpty = __x.isEmpty;
-  __x.isEmpty = true;
+  beginPtr = __x.beginPtr;
+  __x.beginPtr = nullptr;
 }
 
 template <class _Tp, class _Allocator>
 inline vector<_Tp, _Allocator>::vector(vector&& __x,
                                        const allocator_type& __a) {
-  isEmpty = __x.isEmpty;
-  __x.isEmpty = true;
+  beginPtr = __x.beginPtr;
+  __x.beginPtr = nullptr;
 }
 
 template <class _Tp, class _Allocator>
@@ -363,15 +355,15 @@ inline vector<_Tp, _Allocator>& vector<_Tp, _Allocator>::operator=(
     vector&& __x) noexcept /*((__noexcept_move_assign_container<_Allocator,
                               __alloc_traits>::value)) */
 {
-  isEmpty = __x.isEmpty;
-  __x.isEmpty = true;
+  beginPtr = __x.beginPtr;
+  __x.beginPtr = nullptr;
   return *this;
 }
 
 template <class _Tp, class _Allocator>
 inline vector<_Tp, _Allocator>& vector<_Tp, _Allocator>::operator=(
     const vector& __x) {
-  isEmpty = __x.isEmpty;
+  beginPtr = __x.beginPtr;
   return *this;
 }
 
@@ -516,7 +508,7 @@ typename vector<_Tp, _Allocator>::iterator vector<_Tp, _Allocator>::emplace(
 template <class _Tp, class _Allocator>
 typename vector<_Tp, _Allocator>::iterator vector<_Tp, _Allocator>::insert(
     const_iterator __position, size_type __n, const_reference __x) {
-  if (isEmpty) {
+  if (empty()) {
     allocate(__n);
   }
 }
@@ -545,9 +537,9 @@ void vector<_Tp, _Allocator>::resize(size_type __sz, const_reference __x) {
 
 template <class _Tp, class _Allocator>
 void vector<_Tp, _Allocator>::swap(vector& __x) {
-  bool tmp = __x.isEmpty;
-  __x.isEmpty = isEmpty;
-  isEmpty = tmp;
+  value_type* tmp = __x.beginPtr;
+  __x.beginPtr = beginPtr;
+  beginPtr = tmp;
 }
 
 template <class _Allocator>

infer/tests/codetoanalyze/cpp/errors/vector/empty_access.cpp

@@ -108,3 +108,17 @@ int size_check1_nonempty() {
   }
   return 1;
 }
+
+int vector_param_access(std::vector<int>& v) {
+  return v.back(); // shouldn't report anything here
+}
+
+int vector_as_param_empty() {
+  std::vector<int> v;
+  return vector_param_access(v);
+}
+
+int vector_as_param_nonempty() {
+  std::vector<int> v(1);
+  return vector_param_access(v);
+}

infer/tests/endtoend/cpp/VectorEmptyAccessTest.java

@@ -55,6 +55,7 @@ public class VectorEmptyAccessTest {
         "assign_empty",
         "empty_check_access_empty",
         "size_check0_empty",
+        "vector_as_param_empty",
     };
     InferResults inferResults = InferRunner.runInferCPP(inferCmd);
     assertThat(