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 * Fix outdated slice syntax in docs.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, 28 deletions

diff --git a/test/cases/underscore.zig b/test/cases/underscore.zig
deleted file mode 100644
index da1c97659c..0000000000
--- a/test/cases/underscore.zig
+++ /dev/null
@@ -1,28 +0,0 @@
-const std = @import("std");
-const assert = std.debug.assert;
-
-test "ignore lval with underscore" {
-    _ = false;
-}
-
-test "ignore lval with underscore (for loop)" {
-    for ([]void{}) |_, i| {
-        for ([]void{}) |_, j| {
-            break;
-        }
-        break;
-    }
-}
-
-test "ignore lval with underscore (while loop)" {
-    while (optionalReturnError()) |_| {
-        while (optionalReturnError()) |_| {
-            break;
-        } else |_| {}
-        break;
-    } else |_| {}
-}
-
-fn optionalReturnError() !?u32 {
-    return error.optionalReturnError;
-}