[ExprConstant] Fix assert when initializing constexpr array

[erik.pilkington]

Summary

Previously, clang would assert on the following:

struct S {
  constexpr S (const int& ir = 0) {}
};
constexpr S foo[2];

The problem was that while initializing foo, CallStackFrame::createTemporary() was called twice for the MaterializeTemporaryExpr for 0 in the default constructor (once for each array element) without ending the lifetime of the first. This caused createTemporary() to assert. This patch fixes this problem by separating the lifetime of temporaries created for successive calls to the ctor when initializing arrays.

https://bugs.llvm.org/show_bug.cgi?id=34858

Thanks for taking a look!
Erik

[erik.pilkington]

Ping!

lib/AST/ExprConstant.cpp

if (const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(Type)) {
 
     if (HadZeroInit)
       for (unsigned I = 0; I != N; ++I)
         Value->getArrayInitializedElt(I) = Filler;
 
     // Initialize the elements.
     LValue ArrayElt = Subobject;
     ArrayElt.addArray(Info, E, CAT);
-    for (unsigned I = 0; I != N; ++I)
+    for (unsigned I = 0; I != N; ++I) {
+      BlockScopeRAII Scope(Info);
       if (!VisitCXXConstructExpr(E, ArrayElt, &Value->getArrayInitializedElt(I),
                                  CAT->getElementType()) ||
           !HandleLValueArrayAdjustment(Info, E, ArrayElt,
                                        CAT->getElementType(), 1))
         return false;
+    }
 
     return true;
   }
 
   if (!Type->isRecordType())
     return Error(E);
 
   return RecordExprEvaluator(Info, Subobject, *Value)

test/SemaCXX/constant-expression-cxx1y.cpp

struct Nested {
   }
 };
 constexpr bool evalNested() {
   constexpr Nested N;
   return N.first.x == 43;
 }
 static_assert(evalNested(), "");
 } // namespace PR19741
+
+namespace PR34858 {
+struct S {
+  constexpr S(const int & = 0) {}
+};
+constexpr S s[2];
+}