[analyzer] Re-enable lifetime extension for temporaries without destructors.

When an object's class provides no destructor, it's less important to
materialize that object properly because we don't have to model the destructor
correctly, so previously we skipped the support for these syntax patterns.

Additionally, fix support for construction contexts of "static temporaries"
(temporaries that are lifetime-extended by static references) because
it turned out that we only had tests for them without destructors, which caused
us to regress when we re-introduced the construction context for such
temporaries.

Differential Revision: https://reviews.llvm.org/D47658


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@335796 91177308-0d34-0410-b5e6-96231b3b80d8

lib/StaticAnalyzer/Core/ExprEngineCXX.cpp

@@ -218,12 +218,6 @@ std::pair<ProgramStateRef, SVal> ExprEngine::prepareForObjectConstruction(
       const CXXBindTemporaryExpr *BTE = TCC->getCXXBindTemporaryExpr();
       const MaterializeTemporaryExpr *MTE = TCC->getMaterializedTemporaryExpr();
 
-      if (!BTE) {
-        // FIXME: Lifetime extension for temporaries without destructors
-        // is not implemented yet.
-        MTE = nullptr;
-      }
-
       if (MTE) {
         if (const ValueDecl *VD = MTE->getExtendingDecl()) {
           assert(MTE->getStorageDuration() != SD_FullExpression);
@@ -238,16 +232,20 @@ std::pair<ProgramStateRef, SVal> ExprEngine::prepareForObjectConstruction(
         }
       }
 
+      SVal V = UnknownVal();
       if (MTE && MTE->getStorageDuration() != SD_FullExpression) {
         // If the temporary is lifetime-extended, don't save the BTE,
         // because we don't need a temporary destructor, but an automatic
         // destructor.
         BTE = nullptr;
+
+        if (MTE->getStorageDuration() == SD_Static ||
+            MTE->getStorageDuration() == SD_Thread)
+          V = loc::MemRegionVal(MRMgr.getCXXStaticTempObjectRegion(E));
       }
 
-      // FIXME: Support temporaries lifetime-extended via static references.
-      // They'd need a getCXXStaticTempObjectRegion().
-      SVal V = loc::MemRegionVal(MRMgr.getCXXTempObjectRegion(E, LCtx));
+      if (V.isUnknown())
+        V = loc::MemRegionVal(MRMgr.getCXXTempObjectRegion(E, LCtx));
 
       if (BTE)
         State = addObjectUnderConstruction(State, BTE, LCtx, V);

test/Analysis/lifetime-extension.cpp

@@ -234,25 +234,24 @@ void f2() {
 } // end namespace maintain_original_object_address_on_move
 
 namespace maintain_address_of_copies {
-class C;
 
-struct AddressVector {
-  C *buf[10];
+template <typename T> struct AddressVector {
+  const T *buf[10];
   int len;
 
   AddressVector() : len(0) {}
 
-  void push(C *c) {
-    buf[len] = c;
+  void push(const T *t) {
+    buf[len] = t;
     ++len;
   }
 };
 
 class C {
-  AddressVector &v;
+  AddressVector<C> &v;
 
 public:
-  C(AddressVector &v) : v(v) { v.push(this); }
+  C(AddressVector<C> &v) : v(v) { v.push(this); }
   ~C() { v.push(this); }
 
 #ifdef MOVES
@@ -268,11 +267,11 @@ public:
 #endif
   } // no-warning
 
-  static C make(AddressVector &v) { return C(v); }
+  static C make(AddressVector<C> &v) { return C(v); }
 };
 
 void f1() {
-  AddressVector v;
+  AddressVector<C> v;
   {
     C c = C(v);
   }
@@ -296,7 +295,7 @@ void f1() {
 }
 
 void f2() {
-  AddressVector v;
+  AddressVector<C> v;
   {
     const C &c = C::make(v);
   }
@@ -320,7 +319,7 @@ void f2() {
 }
 
 void f3() {
-  AddressVector v;
+  AddressVector<C> v;
   {
     C &&c = C::make(v);
   }
@@ -343,12 +342,12 @@ void f3() {
 #endif
 }
 
-C doubleMake(AddressVector &v) {
+C doubleMake(AddressVector<C> &v) {
   return C::make(v);
 }
 
 void f4() {
-  AddressVector v;
+  AddressVector<C> v;
   {
     C c = doubleMake(v);
   }
@@ -382,4 +381,18 @@ void f4() {
   // expected-warning@-12{{UNKNOWN}}
 #endif
 }
+
+class NoDtor {
+  AddressVector<NoDtor> &v;
+
+public:
+  NoDtor(AddressVector<NoDtor> &v) : v(v) { v.push(this); }
+};
+
+void f5() {
+  AddressVector<NoDtor> v;
+  const NoDtor &N = NoDtor(v);
+  clang_analyzer_eval(v.buf[0] == &N); // expected-warning{{TRUE}}
+}
+
 } // end namespace maintain_address_of_copies

test/Analysis/temporaries-callback-order.cpp

@@ -8,11 +8,7 @@ struct Sub : Super {
 };
 
 void testTemporaries() {
-  // This triggers RegionChanges twice:
-  // - Once for zero-initialization of the structure.
-  // - Once for creating a temporary region and copying the structure there.
-  // FIXME: This code shouldn't really produce the extra temporary, however
-  // that's how we behave for now.
+  // This triggers RegionChanges once for zero-initialization of the structure.
   Sub().m();
 }
 
@@ -29,7 +25,6 @@ void seeIfCheckBindWorks() {
 
 // testTemporaries():
 // CHECK-NEXT: RegionChanges
-// CHECK-NEXT: RegionChanges
 
 // Make sure there's no further output.
 // CHECK-NOT: Bind