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

[Shafik Yaghmour via cfe-commits]

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@@ -283,6 +283,28 @@ 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;
+    }
+
+    if (!this->visitArrayElemInit(0, SubExpr))
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shafik wrote:

Why the different init for first and second element? Complex is basiclly an array underneath: https://eel.is/c++draft/complex.numbers#general-4 but I am not sure I understand the difference in how we init the first and second element. 

Seems like a comment would be helpful.

https://github.com/llvm/llvm-project/pull/75590