[clang][Interp] Array initialization via CXXConstructExpr

[tbaeder]

Ping

[aaron.ballman]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

950–951

This should go through ASTContext::getConstantArrayType(). It may also be worth a comment mentioning that VLAs can't have initializers and an unbounded array has known bounds if it has an initializer, as I suspect that's the reason you're not handling either of those here?

clang/test/AST/Interp/arrays.cpp

188–200

I'd like to see a test for when the class ends with a flexible array member (ctor shouldn't be called for that case because we don't know how many trailing objects there will be). That could show up as an unbounded member.

Also, a test case where the ctor will execute UB, to demonstrate we properly diagnose arrays of default-constructed objects.

[tbaeder]

clang/lib/AST/Interp/ByteCodeExprGen.cpp

950–951

I'm not handling them because they are untested everywhere. :/

clang/test/AST/Interp/arrays.cpp

188–200

I added a test for a UB constructor, but a flexible array member shows up as a non-ConstantArrayType member, so the code runs into one or the other assertion.

[aaron.ballman]

LGTM!

clang/lib/AST/Interp/ByteCodeExprGen.cpp

if (Optional<PrimType> ElemT = classify(CAT->getElementType())) {
         if (!this->emitInitElem(*ElemT, I, Initializer))
           return false;
       }
     } else {
       assert(false && "default initializer for non-primitive type");
     }
 
     return true;
+  } else if (const auto *Ctor = dyn_cast<CXXConstructExpr>(Initializer)) {
+    const ConstantArrayType *CAT =
+        Ctx.getASTContext().getAsConstantArrayType(Ctor->getType());
+    assert(CAT);
+    size_t NumElems = CAT->getSize().getZExtValue();
+    const Function *Func = getFunction(Ctor->getConstructor());
+    if (!Func || !Func->isConstexpr())
+      return false;
+
+    // FIXME(perf): We're calling the constructor once per array element here,
+    //   in the old intepreter we had a special-case for trivial constructors.
+    for (size_t I = 0; I != NumElems; ++I) {
+      if (!this->emitDupPtr(Initializer))
+        return false;
+      if (!this->emitConstUint64(I, Initializer))
+        return false;
+      if (!this->emitAddOffsetUint64(Initializer))
+        return false;
+      if (!this->emitNarrowPtr(Initializer))
+        return false;
+
+      // Constructor arguments.
+      for (const auto *Arg : Ctor->arguments()) {
+        if (!this->visit(Arg))
+          return false;
+      }
+
+      if (!this->emitCall(Func, Initializer))
+        return false;
+    }
+    return true;
   }
 
   assert(false && "Unknown expression for array initialization");
   return false;
 }
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::visitRecordInitializer(const Expr *Initializer) {

clang/test/AST/Interp/arrays.cpp

namespace DefaultInit {
   };
 
   int f() {
      constexpr B<int,10> arr = {};
      constexpr int x = arr.a[0];
   }
 };
 
+class A {
+public:
+  int a;
+  constexpr A(int m = 2) : a(10 + m) {}
+};
+class AU {
+public:
+  int a;
+  constexpr AU() : a(5 / 0) {} // expected-warning {{division by zero is undefined}} \
+                               // expected-note {{division by zero}} \
+                               // ref-error {{never produces a constant expression}} \
+                               // ref-note 2{{division by zero}} \
+                               // ref-warning {{division by zero is undefined}}
+};
+class B {
+public:
+  A a[2];
+  constexpr B() {}
+};
+constexpr B b;
+static_assert(b.a[0].a == 12, "");
+static_assert(b.a[1].a == 12, "");
+
+class BU {
+public:
+  AU a[2];
+  constexpr BU() {} // expected-note {{in call to 'AU()'}} \
+                    // ref-note {{in call to 'AU()'}}
+};
+constexpr BU bu; // expected-error {{must be initialized by a constant expression}} \
+                 // expected-note {{in call to 'BU()'}} \
+                 // ref-error {{must be initialized by a constant expression}} \
+                 // ref-note {{in call to 'BU()'}}
+
 namespace IncDec {
   // FIXME: Pointer arithmethic needs to be supported in inc/dec
   //   unary operators
 #if 0
   constexpr int getNextElem(const int *A, int I) {
     const int *B = (A + I);
     ++B;
     return *B;
   }
   constexpr int E[] = {1,2,3,4};
 
   static_assert(getNextElem(E, 1) == 3);
 #endif
 };