backport copy elision changes

This commit contains everything from the copy-elision-2
branch that does not have to do with copy elision directly,
but is generally useful for master branch.

 * All const values know their parents, when applicable, not
   just structs and unions.
 * Null pointers in const values are represented explicitly,
   rather than as a HardCodedAddr value of 0.
 * Rename "maybe" to "optional" in various code locations.
 * Separate DeclVarSrc and DeclVarGen
 * Separate PtrCastSrc and PtrCastGen
 * Separate CmpxchgSrc and CmpxchgGen
 * Represent optional error set as an integer, using the 0 value.
   In a const value, it uses nullptr.
 * Introduce type_has_one_possible_value and use it where applicable.
 * Fix debug builds not setting memory to 0xaa when storing
   undefined.
 * Separate the type of a variable from the const value of a variable.
 * Use copy_const_val where appropriate.
 * Rearrange structs to pack data more efficiently.
 * Move test/cases/* to test/behavior/*
 * Use `std.debug.assertOrPanic` in behavior tests instead of
   `std.debug.assert`.
 * Fix outdated slice syntax in docs.

1 files changed, 0 insertions, 21 deletions

diff --git a/test/cases/struct_contains_null_ptr_itself.zig b/test/cases/struct_contains_null_ptr_itself.zig
deleted file mode 100644
index 21175974b3..0000000000
--- a/test/cases/struct_contains_null_ptr_itself.zig
+++ /dev/null
@@ -1,21 +0,0 @@
-const std = @import("std");
-const assert = std.debug.assert;
-
-test "struct contains null pointer which contains original struct" {
-    var x: ?*NodeLineComment = null;
-    assert(x == null);
-}
-
-pub const Node = struct {
-    id: Id,
-    comment: ?*NodeLineComment,
-
-    pub const Id = enum {
-        Root,
-        LineComment,
-    };
-};
-
-pub const NodeLineComment = struct {
-    base: Node,
-};