[clang][Interp] Implement integral->complex casts (#75590)

Allocate storage for them, initialize the first member with the given
value and the second member to 0.

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -294,6 +294,29 @@ bool ByteCodeExprGen<Emitter>::VisitCastExpr(const CastExpr *CE) {
   case CK_ToVoid:
     return discard(SubExpr);
 
+  case CK_IntegralRealToComplex:
+  case CK_FloatingRealToComplex: {
+    // We're creating a complex value here, so we need to
+    // allocate storage for it.
+    if (!Initializing) {
+      std::optional<unsigned> LocalIndex =
+          allocateLocal(CE, /*IsExtended=*/true);
+      if (!LocalIndex)
+        return false;
+      if (!this->emitGetPtrLocal(*LocalIndex, CE))
+        return false;
+    }
+
+    // Init the complex value to {SubExpr, 0}.
+    if (!this->visitArrayElemInit(0, SubExpr))
+      return false;
+    // Zero-init the second element.
+    PrimType T = classifyPrim(SubExpr->getType());
+    if (!this->visitZeroInitializer(T, SubExpr->getType(), SubExpr))
+      return false;
+    return this->emitInitElem(T, 1, SubExpr);
+  }
+
   default:
     assert(false && "Cast not implemented");
   }
@@ -846,6 +869,10 @@ bool ByteCodeExprGen<Emitter>::VisitInitListExpr(const InitListExpr *E) {
 
   if (T->isAnyComplexType()) {
     unsigned NumInits = E->getNumInits();
+
+    if (NumInits == 1)
+      return this->delegate(E->inits()[0]);
+
     QualType ElemQT = E->getType()->getAs<ComplexType>()->getElementType();
     PrimType ElemT = classifyPrim(ElemQT);
     if (NumInits == 0) {

clang/test/AST/Interp/complex.cpp

@@ -55,21 +55,20 @@ static_assert(ignoredCast() == 0, "");
 static_assert((int)I1 == 1, "");
 static_assert((float)D == 1.0f, "");
 
+static_assert(__real((_Complex unsigned)5) == 5);
+static_assert(__imag((_Complex unsigned)5) == 0);
 
 /// Standalone complex expressions.
 static_assert(__real((_Complex float){1.0, 3.0}) == 1.0, "");
 
 
-#if 0
-/// FIXME: This should work in the new interpreter.
 constexpr _Complex double D2 = {12};
 static_assert(__real(D2) == 12, "");
-static_assert(__imag(D2) == 12, "");
+static_assert(__imag(D2) == 0, "");
 
 constexpr _Complex int I3 = {15};
 static_assert(__real(I3) == 15, "");
-static_assert(__imag(I3) == 15, "");
-#endif
+static_assert(__imag(I3) == 0, "");
 
 /// FIXME: This should work in the new interpreter as well.
 // constexpr _Complex _BitInt(8) A = 0;// = {4};