[CFG] [analyzer] Fix a crash on finding construction context for implicit constructor conversion.

[NoQ]

Summary

While landing D43428 as rC325966, i caused an internal compiler error of an MSVC 2015 compiler on a buildbot. Then i tried to hotfix it in rC325969 (which didn't help) and in rC325978 (which suddenly helped, i.e. simply moving the existing code around has suppressed the crash). Then i committed D43481 as rC326016 and MSVC crashed again. Then i committed rC326021 as a hotfix, and it seemed to help again.

The problem is, i lost some code in rC326021. Namely i forgot to check that the cast that's mentioned in D43481 / rC326016 is a NoOp-kind cast.

Bring back the check for the cast kind, add a test for it.

The test exposes an interesting edge case that we don't support yet: implicit constructor conversion. For now we only support explicit constructor conversion (i.e. functional cast as in D43480). For whatever reason, in this case the AST doesn't contain a CXXBindTemporaryExpr even if the object requires destruction, so the assertion in ConstructionContext::createFromLayers that says that any construction context with an MTE but without the respective BTE should be of an object with a trivial destructor (which isn't a problem here because the object is lifetime-extended anyway).

[george.karpenkov]

Should there be a FIXME note saying that other casts should be supported?

[NoQ]

Add the comment.

cfe/trunk/lib/Analysis/CFG.cpp

void CFGBuilder::findConstructionContexts(
   }
   case Stmt::CXXFunctionalCastExprClass: {
     auto *Cast = cast<CXXFunctionalCastExpr>(Child);
     findConstructionContexts(Layer, Cast->getSubExpr());
     break;
   }
   case Stmt::ImplicitCastExprClass: {
     auto *Cast = cast<ImplicitCastExpr>(Child);
+    // TODO: We need to support CK_ConstructorConversion, maybe other kinds?
+    if (Cast->getCastKind() == CK_NoOp)
       findConstructionContexts(Layer, Cast->getSubExpr());
     break;
   }
   case Stmt::CXXBindTemporaryExprClass: {
     auto *BTE = cast<CXXBindTemporaryExpr>(Child);
     findConstructionContexts(
         ConstructionContextLayer::create(cfg->getBumpVectorContext(),
                                          BTE, Layer),
         BTE->getSubExpr());

cfe/trunk/test/Analysis/cfg-rich-constructors.cpp

 // CHECK-NEXT:     5: [B7.4] (ImplicitCastExpr, NoOp, const class temporary_object_expr_with_dtors::D)
 // CHECK-NEXT:     6: [B7.5].operator bool
 // CHECK-NEXT:     7: [B7.5]
 // CHECK-NEXT:     8: [B7.7] (ImplicitCastExpr, UserDefinedConversion, _Bool)
 // CHECK-NEXT:     T: [B7.8] ? ... : ...
 void constructorInTernaryCondition() {
   const D &d = D(1) ? D(2) : D(3);
 }
+
 } // end namespace temporary_object_expr_with_dtors
+
+namespace implicit_constructor_conversion {
+
+class A {};
+A get();
+
+class B {
+public:
+  B(const A &);
+  ~B() {}
+};
+
+// FIXME: Find construction context for the implicit constructor conversion.
+// CHECK: void implicitConstructionConversionFromFunctionValue()
+// CHECK:          1: get
+// CHECK-NEXT:     2: [B1.1] (ImplicitCastExpr, FunctionToPointerDecay, class implicit_constructor_conver
+// CHECK-NEXT:     3: [B1.2]()
+// CHECK-NEXT:     4: [B1.3] (ImplicitCastExpr, NoOp, const class implicit_constructor_conversion::A)
+// CHECK-NEXT:     5: [B1.4]
+// CHECK-NEXT:     6: [B1.5] (CXXConstructExpr, class implicit_constructor_conversion::B)
+// CHECK-NEXT:     7: [B1.6] (ImplicitCastExpr, ConstructorConversion, class implicit_constructor_convers
+// CHECK-NEXT:     8: [B1.7] (ImplicitCastExpr, NoOp, const class implicit_constructor_conversion::B)
+// CHECK-NEXT:     9: [B1.8]
+// CHECK-NEXT:    10: const implicit_constructor_conversion::B &b = get();
+// CHECK-NEXT:    11: [B1.10].~B() (Implicit destructor)
+void implicitConstructionConversionFromFunctionValue() {
+  const B &b = get(); // no-crash
+}
+
+} // end namespace implicit_constructor_conversion