[clang] [clang][bytecode] Start implementing __builtin_bit_cast (PR #112126)

[Erich Keane via cfe-commits]

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@@ -6400,6 +6403,67 @@ bool Compiler<Emitter>::emitDestruction(const Descriptor *Desc,
   return this->emitRecordDestruction(Desc->ElemRecord, Loc);
 }
 
+//  This function is constexpr if and only if To, From, and the types of
+//  all subobjects of To and From are types T such that...
+//  (3.1) - is_union_v<T> is false;
+//  (3.2) - is_pointer_v<T> is false;
+//  (3.3) - is_member_pointer_v<T> is false;
+//  (3.4) - is_volatile_v<T> is false; and
+//  (3.5) - T has no non-static data members of reference type
+template <class Emitter>
+bool Compiler<Emitter>::emitBuiltinBitCast(const CastExpr *E) {
+  const Expr *SubExpr = E->getSubExpr();
+  QualType FromType = SubExpr->getType();
+  QualType ToType = E->getType();
+  std::optional<PrimType> ToT = classify(ToType);
+
+  assert(!DiscardResult && "Implement");
+
+  if (ToType->isNullPtrType()) {
+    if (!this->discard(SubExpr))
+      return false;
+
+    return this->emitNullPtr(nullptr, E);
+  }
+
+  if (FromType->isNullPtrType() && ToT) {
+    if (!this->discard(SubExpr))
+      return false;
+
+    return visitZeroInitializer(*ToT, ToType, E);
+  }
+  assert(!ToType->isReferenceType());
+
+  // Get a pointer to the value-to-cast on the stack.
+  if (!this->visit(SubExpr))
+    return false;
+
+  if (!ToT || ToT == PT_Ptr) {
+    // Conversion to an array or record type.
+    assert(false && "Implement");
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erichkeane wrote:

same here.

https://github.com/llvm/llvm-project/pull/112126