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 * Fix outdated slice syntax in docs.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, 8 insertions, 1 deletions

diff --git a/src/analyze.hpp b/src/analyze.hpp
index efbc065a63..1bac15ebcc 100644
--- a/src/analyze.hpp
+++ b/src/analyze.hpp
@@ -81,7 +81,7 @@ ZigFn *scope_fn_entry(Scope *scope);
 ImportTableEntry *get_scope_import(Scope *scope);
 void init_tld(Tld *tld, TldId id, Buf *name, VisibMod visib_mod, AstNode *source_node, Scope *parent_scope);
 ZigVar *add_variable(CodeGen *g, AstNode *source_node, Scope *parent_scope, Buf *name,
-    bool is_const, ConstExprValue *init_value, Tld *src_tld);
+    bool is_const, ConstExprValue *init_value, Tld *src_tld, ZigType *var_type);
 ZigType *analyze_type_expr(CodeGen *g, Scope *scope, AstNode *node);
 ZigFn *create_fn(CodeGen *g, AstNode *proto_node);
 ZigFn *create_fn_raw(CodeGen *g, FnInline inline_value);
@@ -222,6 +222,13 @@ enum ReqCompTime {
 };
 ReqCompTime type_requires_comptime(CodeGen *g, ZigType *type_entry);
 
+enum OnePossibleValue {
+    OnePossibleValueInvalid,
+    OnePossibleValueNo,
+    OnePossibleValueYes,
+};
+OnePossibleValue type_has_one_possible_value(CodeGen *g, ZigType *type_entry);
+
 Error ensure_const_val_repr(IrAnalyze *ira, CodeGen *codegen, AstNode *source_node,
         ConstExprValue *const_val, ZigType *wanted_type);