From 973af312ebd28b1fc0f97b5f348b329d5684a6fb Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@meta.com>
Date: Mon, 8 Jan 2024 18:14:22 -0800
Subject: [PATCH] Simplify basic_format_args

---
 include/fmt/core.h | 45 +++++++++++++++++++++------------------------
 1 file changed, 21 insertions(+), 24 deletions(-)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index 03a47557d1ee0..bfafb57bf5d78 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -1727,15 +1727,19 @@ template <typename Context> class basic_format_args {
   // argument types are passed in the descriptor. This reduces binary code size
   // per formatting function call.
   unsigned long long desc_;
-  union {
-    // If is_packed() returns true then argument values are stored in values_;
-    // otherwise they are stored in args_. This is done to improve cache
-    // locality and reduce compiled code size since storing larger objects
-    // may require more code (at least on x86-64) even if the same amount of
-    // data is actually copied to stack. It saves ~10% on the bloat test.
-    const detail::value<Context>* values_;
-    const format_arg* args_;
-  };
+
+  // If is_packed() returns true then arguments are stored as `detail::value`;
+  // otherwise they are stored as `format_arg` objects. This is done to improve
+  // cache locality and reduce compiled code size since storing larger objects
+  // may require more code (at least on x86-64) even if the same amount of
+  // data is actually copied to stack. It saves ~10% on the bloat test.
+  const void* args_;
+
+  auto get_value(int index) const -> const detail::value<Context>& {
+    return is_packed()
+               ? static_cast<const detail::value<Context>*>(args_)[index]
+               : static_cast<const format_arg*>(args_)[index].value_;
+  }
 
   constexpr auto is_packed() const -> bool {
     return (desc_ & detail::is_unpacked_bit) == 0;
@@ -1750,12 +1754,6 @@ template <typename Context> class basic_format_args {
     return static_cast<detail::type>((desc_ >> shift) & mask);
   }
 
-  constexpr FMT_INLINE basic_format_args(unsigned long long desc,
-                                         const detail::value<Context>* values)
-      : desc_(desc), values_(values) {}
-  constexpr basic_format_args(unsigned long long desc, const format_arg* args)
-      : desc_(desc), args_(args) {}
-
  public:
   constexpr basic_format_args() : desc_(0), args_(nullptr) {}
 
@@ -1767,8 +1765,8 @@ template <typename Context> class basic_format_args {
   template <size_t N, typename... Args>
   constexpr FMT_INLINE basic_format_args(
       const format_arg_store_impl<Context, N, Args...>& store)
-      : basic_format_args(format_arg_store_impl<Context, N, Args...>::desc,
-                          store.args()) {}
+      : desc_(format_arg_store_impl<Context, N, Args...>::desc),
+        args_(store.args()) {}
 
   /**
    \rst
@@ -1778,7 +1776,7 @@ template <typename Context> class basic_format_args {
    */
   constexpr FMT_INLINE basic_format_args(
       const dynamic_format_arg_store<Context>& store)
-      : basic_format_args(store.get_types(), store.data()) {}
+      : desc_(store.get_types()), args_(store.data()) {}
 
   /**
    \rst
@@ -1786,20 +1784,20 @@ template <typename Context> class basic_format_args {
    \endrst
    */
   constexpr basic_format_args(const format_arg* args, int count)
-      : basic_format_args(detail::is_unpacked_bit | detail::to_unsigned(count),
-                          args) {}
+      : desc_(detail::is_unpacked_bit | detail::to_unsigned(count)),
+        args_(args) {}
 
   /** Returns the argument with the specified id. */
   FMT_CONSTEXPR auto get(int id) const -> format_arg {
     format_arg arg;
     if (!is_packed()) {
-      if (id < max_size()) arg = args_[id];
+      if (id < max_size()) arg = static_cast<const format_arg*>(args_)[id];
       return arg;
     }
     if (id >= detail::max_packed_args) return arg;
     arg.type_ = type(id);
     if (arg.type_ == detail::type::none_type) return arg;
-    arg.value_ = values_[id];
+    arg.value_ = static_cast<const detail::value<Context>*>(args_)[id];
     return arg;
   }
 
@@ -1812,8 +1810,7 @@ template <typename Context> class basic_format_args {
   template <typename Char>
   FMT_CONSTEXPR auto get_id(basic_string_view<Char> name) const -> int {
     if (!has_named_args()) return -1;
-    const auto& named_args =
-        (is_packed() ? values_[-1] : args_[-1].value_).named_args;
+    const auto& named_args = get_value(-1).named_args;
     for (size_t i = 0; i < named_args.size; ++i) {
       if (named_args.data[i].name == name) return named_args.data[i].id;
     }