[analyzer] Re-enable constructor inlining when lifetime extension through fields occurs.

[NoQ]

Summary

In code like

const int &x = C().x;

destructors were missing in the CFG, so it was unsafe to inline the constructors, so constructor inlining was disabled in D43689. But i think i found a way to fix the CFG in D44238, so it should be safe to re-enable it now.

[NoQ]

Rebase.

include/clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h

struct EvalCallOptions {
     /// This call is a constructor or a destructor for a single element within
     /// an array, a part of array construction or destruction.
     bool IsArrayCtorOrDtor = false;
 
     /// This call is a constructor or a destructor of a temporary value.
     bool IsTemporaryCtorOrDtor = false;
 
     /// This call is a constructor for a temporary that is lifetime-extended
-    /// by binding a smaller object within it to a reference, for example
-    /// 'const int &x = C().x;'.
-    bool IsTemporaryLifetimeExtendedViaSubobject = false;
-
-    /// This call is a constructor for a temporary that is lifetime-extended
     /// by binding it to a reference-type field within an aggregate,
     /// for example 'A { const C &c; }; A a = { C() };'
     bool IsTemporaryLifetimeExtendedViaAggregate = false;
 
     EvalCallOptions() {}
   };
 
 private:

lib/StaticAnalyzer/Core/ExprEngineCXX.cpp

case ConstructionContext::NewAllocatedObjectKind: {
         // Constructor shall not be called in this case.
       }
       break;
     }
     case ConstructionContext::TemporaryObjectKind: {
       const auto *TOCC = cast<TemporaryObjectConstructionContext>(CC);
       if (const auto *MTE = TOCC->getMaterializedTemporaryExpr()) {
         if (const ValueDecl *VD = MTE->getExtendingDecl()) {
-          // Pattern-match various forms of lifetime extension that aren't
-          // currently supported by the CFG.
-          // FIXME: Is there a better way to retrieve this information from
-          // the MaterializeTemporaryExpr?
           assert(MTE->getStorageDuration() != SD_FullExpression);
-          if (VD->getType()->isReferenceType()) {
-            assert(VD->getType()->isReferenceType());
-            if (VD->getType()->getPointeeType().getCanonicalType() !=
-                MTE->GetTemporaryExpr()->getType().getCanonicalType()) {
-              // We're lifetime-extended via our field. Automatic destructors
-              // aren't quite working in this case.
-              CallOpts.IsTemporaryLifetimeExtendedViaSubobject = true;
-            }
-          } else {
+          if (!VD->getType()->isReferenceType()) {
             // We're lifetime-extended by a surrounding aggregate.
-            // Automatic destructors aren't quite working in this case.
+            // Automatic destructors aren't quite working in this case
+            // on the CFG side. We should warn the caller about that.
+            // FIXME: Is there a better way to retrieve this information from
+            // the MaterializeTemporaryExpr?
             CallOpts.IsTemporaryLifetimeExtendedViaAggregate = true;
           }
         }
       }
       // TODO: Support temporaries lifetime-extended via static references.
       // They'd need a getCXXStaticTempObjectRegion().
       CallOpts.IsTemporaryCtorOrDtor = true;
       return loc::MemRegionVal(MRMgr.getCXXTempObjectRegion(CE, LCtx));

lib/StaticAnalyzer/Core/ExprEngineCallAndReturn.cpp

if (CtorExpr->getConstructionKind() == CXXConstructExpr::CK_Complete) {
         return CIP_DisallowedOnce;
 
       // If we did not find the correct this-region, it would be pointless
       // to inline the constructor. Instead we will simply invalidate
       // the fake temporary target.
       if (CallOpts.IsCtorOrDtorWithImproperlyModeledTargetRegion)
         return CIP_DisallowedOnce;
 
-      // If the temporary is lifetime-extended by binding a smaller object
-      // within it to a reference, automatic destructors don't work properly.
-      if (CallOpts.IsTemporaryLifetimeExtendedViaSubobject)
-        return CIP_DisallowedOnce;
-
-      // If the temporary is lifetime-extended by binding it to a reference-typ
+      // If the temporary is lifetime-extended by binding it to a reference-type
       // field within an aggregate, automatic destructors don't work properly.
       if (CallOpts.IsTemporaryLifetimeExtendedViaAggregate)
         return CIP_DisallowedOnce;
     }
 
     break;
   }
   case CE_CXXDestructor: {

test/Analysis/lifetime-extension.cpp

struct A {
   ~A() {}
 };
 
 void f() {
   const int &x = A().i; // no-crash
   const int &y = A().j[1]; // no-crash
   const int &z = (A().j[1], A().j[0]); // no-crash
 
-  // FIXME: All of these should be TRUE, but constructors aren't inlined.
-  clang_analyzer_eval(x == 1); // expected-warning{{UNKNOWN}}
-  clang_analyzer_eval(y == 3); // expected-warning{{UNKNOWN}}
-  clang_analyzer_eval(z == 2); // expected-warning{{UNKNOWN}}
+  clang_analyzer_eval(x == 1);
+  clang_analyzer_eval(y == 3);
+  clang_analyzer_eval(z == 2);
+#ifdef TEMPORARIES
+  // expected-warning@-4{{TRUE}}
+  // expected-warning@-4{{TRUE}}
+  // expected-warning@-4{{TRUE}}
+#else
+  // expected-warning@-8{{UNKNOWN}}
+  // expected-warning@-8{{UNKNOWN}}
+  // expected-warning@-8{{UNKNOWN}}
+#endif
 }
 } // end namespace pr19539_crash_on_destroying_an_integer
 
 namespace maintain_original_object_address_on_lifetime_extension {
 class C {
   C **after, **before;
 
 public:
#endif
   }
 }
 
 void f5() {
   C *after, *before;
   {
     const bool &x = C(true, &after, &before).x; // no-crash
   }
-  // FIXME: Should be TRUE. Should not warn about garbage value.
-  clang_analyzer_eval(after == before); // expected-warning{{UNKNOWN}}
+  clang_analyzer_eval(after == before);
+#ifdef TEMPORARIES
+  // expected-warning@-2{{TRUE}}
+#else
+  // expected-warning@-4{{UNKNOWN}}
+#endif
 }
 
 struct A { // A is an aggregate.
   const C &c;
 };
 
 void f6() {
   C *after, *before;