Re: [v3 PATCH] Reduce the size of variant, it doesn't need an index of type size_t internally.

[Jonathan Wakely]

On 11/01/17 10:29 +0000, Jonathan Wakely wrote:

On 11/01/17 00:19 +0200, Ville Voutilainen wrote:

@@ -1086,7 +1099,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return !this->_M_valid(); }

     constexpr size_t index() const noexcept
-      { return this->_M_index; }
+      {
+       if (this->_M_index ==
+           typename _Base::_Storage::__index_type(variant_npos))
+         return variant_npos;
+       return this->_M_index;

GCC doesn't seem to be smart enough to optimize the branch away here.

But that's only for 32-bit x86. It optimizes well for x86_64, so no
need to obfuscate it.