PR47143: Don't crash while constant-evaluating value-initialization of

an array of unknown bound as the initializer of an array new expression.

Author: zygoloid

clang/lib/AST/ExprConstant.cpp

@@ -8987,6 +8987,7 @@ bool PointerExprEvaluator::VisitCXXNewExpr(const CXXNewExpr *E) {
   const Expr *Init = E->getInitializer();
   const InitListExpr *ResizedArrayILE = nullptr;
   const CXXConstructExpr *ResizedArrayCCE = nullptr;
+  bool ValueInit = false;
 
   QualType AllocType = E->getAllocatedType();
   if (Optional<const Expr*> ArraySize = E->getArraySize()) {
@@ -9030,7 +9031,14 @@ bool PointerExprEvaluator::VisitCXXNewExpr(const CXXNewExpr *E) {
     //   -- the new-initializer is a braced-init-list and the number of
     //      array elements for which initializers are provided [...]
     //      exceeds the number of elements to initialize
-    if (Init && !isa<CXXConstructExpr>(Init)) {
+    if (!Init) {
+      // No initialization is performed.
+    } else if (isa<CXXScalarValueInitExpr>(Init) ||
+               isa<ImplicitValueInitExpr>(Init)) {
+      ValueInit = true;
+    } else if (auto *CCE = dyn_cast<CXXConstructExpr>(Init)) {
+      ResizedArrayCCE = CCE;
+    } else {
       auto *CAT = Info.Ctx.getAsConstantArrayType(Init->getType());
       assert(CAT && "unexpected type for array initializer");
 
@@ -9053,8 +9061,6 @@ bool PointerExprEvaluator::VisitCXXNewExpr(const CXXNewExpr *E) {
       // special handling for this case when we initialize.
       if (InitBound != AllocBound)
         ResizedArrayILE = cast<InitListExpr>(Init);
-    } else if (Init) {
-      ResizedArrayCCE = cast<CXXConstructExpr>(Init);
     }
 
     AllocType = Info.Ctx.getConstantArrayType(AllocType, ArrayBound, nullptr,
@@ -9115,7 +9121,11 @@ bool PointerExprEvaluator::VisitCXXNewExpr(const CXXNewExpr *E) {
       return false;
   }
 
-  if (ResizedArrayILE) {
+  if (ValueInit) {
+    ImplicitValueInitExpr VIE(AllocType);
+    if (!EvaluateInPlace(*Val, Info, Result, &VIE))
+      return false;
+  } else if (ResizedArrayILE) {
     if (!EvaluateArrayNewInitList(Info, Result, *Val, ResizedArrayILE,
                                   AllocType))
       return false;

clang/test/SemaCXX/constant-expression-cxx2a.cpp

@@ -950,6 +950,20 @@ namespace dynamic_alloc {
     p = new ((std::align_val_t)n) char[n];
     p = new char(n);
   }
+
+  namespace PR47143 {
+    constexpr char *f(int n) {
+      return new char[n]();
+    }
+    const char *p = f(3);
+    constexpr bool test() {
+      char *p = f(3);
+      bool result = !p[0] && !p[1] && !p[2];
+      delete [] p;
+      return result;
+    }
+    static_assert(test());
+  }
 }
 
 struct placement_new_arg {};