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 * Fix outdated slice syntax in docs.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, 115 insertions, 50 deletions

diff --git a/src/all_types.hpp b/src/all_types.hpp
index 91b24e3110..4b134361a3 100644
--- a/src/all_types.hpp
+++ b/src/all_types.hpp
@@ -56,9 +56,6 @@ struct IrExecutable {
     size_t next_debug_id;
     size_t *backward_branch_count;
     size_t backward_branch_quota;
-    bool invalid;
-    bool is_inline;
-    bool is_generic_instantiation;
     ZigFn *fn_entry;
     Buf *c_import_buf;
     AstNode *source_node;
@@ -78,6 +75,10 @@ struct IrExecutable {
     IrBasicBlock *coro_suspend_block;
     IrBasicBlock *coro_final_cleanup_block;
     ZigVar *coro_allocator_var;
+
+    bool invalid;
+    bool is_inline;
+    bool is_generic_instantiation;
 };
 
 enum OutType {
@@ -90,6 +91,9 @@ enum OutType {
 enum ConstParentId {
     ConstParentIdNone,
     ConstParentIdStruct,
+    ConstParentIdErrUnionCode,
+    ConstParentIdErrUnionPayload,
+    ConstParentIdOptionalPayload,
     ConstParentIdArray,
     ConstParentIdUnion,
     ConstParentIdScalar,
@@ -108,6 +112,15 @@ struct ConstParent {
             size_t field_index;
         } p_struct;
         struct {
+            ConstExprValue *err_union_val;
+        } p_err_union_code;
+        struct {
+            ConstExprValue *err_union_val;
+        } p_err_union_payload;
+        struct {
+            ConstExprValue *optional_val;
+        } p_optional_payload;
+        struct {
             ConstExprValue *union_val;
         } p_union;
         struct {
@@ -118,13 +131,11 @@ struct ConstParent {
 
 struct ConstStructValue {
     ConstExprValue *fields;
-    ConstParent parent;
 };
 
 struct ConstUnionValue {
     BigInt tag;
     ConstExprValue *payload;
-    ConstParent parent;
 };
 
 enum ConstArraySpecial {
@@ -138,7 +149,6 @@ struct ConstArrayValue {
     union {
         struct {
             ConstExprValue *elements;
-            ConstParent parent;
         } s_none;
         Buf *s_buf;
     } data;
@@ -153,19 +163,29 @@ enum ConstPtrSpecial {
     ConstPtrSpecialBaseArray,
     // The pointer points to a field in an underlying struct.
     ConstPtrSpecialBaseStruct,
+    // The pointer points to the error set field of an error union
+    ConstPtrSpecialBaseErrorUnionCode,
+    // The pointer points to the payload field of an error union
+    ConstPtrSpecialBaseErrorUnionPayload,
+    // The pointer points to the payload field of an optional
+    ConstPtrSpecialBaseOptionalPayload,
     // This means that we did a compile-time pointer reinterpret and we cannot
     // understand the value of pointee at compile time. However, we will still
     // emit a binary with a compile time known address.
     // In this case index is the numeric address value.
-    // We also use this for null pointer. We need the data layout for ConstCastOnly == true
-    // types to be the same, so all optionals of pointer types use x_ptr
-    // instead of x_optional
     ConstPtrSpecialHardCodedAddr,
     // This means that the pointer represents memory of assigning to _.
     // That is, storing discards the data, and loading is invalid.
     ConstPtrSpecialDiscard,
     // This is actually a function.
     ConstPtrSpecialFunction,
+    // This means the pointer is null. This is only allowed when the type is ?*T.
+    // We use this instead of ConstPtrSpecialHardCodedAddr because often we check
+    // for that value to avoid doing comptime work.
+    // We need the data layout for ConstCastOnly == true
+    // types to be the same, so all optionals of pointer types use x_ptr
+    // instead of x_optional.
+    ConstPtrSpecialNull,
 };
 
 enum ConstPtrMut {
@@ -200,6 +220,15 @@ struct ConstPtrValue {
             size_t field_index;
         } base_struct;
         struct {
+            ConstExprValue *err_union_val;
+        } base_err_union_code;
+        struct {
+            ConstExprValue *err_union_val;
+        } base_err_union_payload;
+        struct {
+            ConstExprValue *optional_val;
+        } base_optional_payload;
+        struct {
             uint64_t addr;
         } hard_coded_addr;
         struct {
@@ -209,7 +238,7 @@ struct ConstPtrValue {
 };
 
 struct ConstErrValue {
-    ErrorTableEntry *err;
+    ConstExprValue *error_set;
     ConstExprValue *payload;
 };
 
@@ -265,6 +294,7 @@ struct ConstGlobalRefs {
 struct ConstExprValue {
     ZigType *type;
     ConstValSpecial special;
+    ConstParent parent;
     ConstGlobalRefs *global_refs;
 
     union {
@@ -433,7 +463,7 @@ enum NodeType {
     NodeTypeArrayType,
     NodeTypeErrorType,
     NodeTypeIfErrorExpr,
-    NodeTypeTestExpr,
+    NodeTypeIfOptional,
     NodeTypeErrorSetDecl,
     NodeTypeCancel,
     NodeTypeResume,
@@ -677,7 +707,7 @@ struct AstNodeUse {
     AstNode *expr;
 
     TldResolution resolution;
-    IrInstruction *value;
+    ConstExprValue *value;
 };
 
 struct AstNodeIfBoolExpr {
@@ -1610,7 +1640,7 @@ struct CodeGen {
     HashMap<FnTypeId *, ZigType *, fn_type_id_hash, fn_type_id_eql> fn_type_table;
     HashMap<Buf *, ErrorTableEntry *, buf_hash, buf_eql_buf> error_table;
     HashMap<GenericFnTypeId *, ZigFn *, generic_fn_type_id_hash, generic_fn_type_id_eql> generic_table;
-    HashMap<Scope *, IrInstruction *, fn_eval_hash, fn_eval_eql> memoized_fn_eval_table;
+    HashMap<Scope *, ConstExprValue *, fn_eval_hash, fn_eval_eql> memoized_fn_eval_table;
     HashMap<ZigLLVMFnKey, LLVMValueRef, zig_llvm_fn_key_hash, zig_llvm_fn_key_eql> llvm_fn_table;
     HashMap<Buf *, AstNode *, buf_hash, buf_eql_buf> exported_symbol_names;
     HashMap<Buf *, Tld *, buf_hash, buf_eql_buf> external_prototypes;
@@ -1802,10 +1832,9 @@ enum VarLinkage {
 
 struct ZigVar {
     Buf name;
-    ConstExprValue *value;
+    ConstExprValue *const_value;
+    ZigType *var_type;
     LLVMValueRef value_ref;
-    bool src_is_const;
-    bool gen_is_const;
     IrInstruction *is_comptime;
     // which node is the declaration of the variable
     AstNode *decl_node;
@@ -1815,17 +1844,21 @@ struct ZigVar {
     Scope *parent_scope;
     Scope *child_scope;
     LLVMValueRef param_value_ref;
-    bool shadowable;
     size_t mem_slot_index;
     IrExecutable *owner_exec;
     size_t ref_count;
-    VarLinkage linkage;
-    uint32_t align_bytes;
 
     // In an inline loop, multiple variables may be created,
     // In this case, a reference to a variable should follow
     // this pointer to the redefined variable.
     ZigVar *next_var;
+
+    uint32_t align_bytes;
+    VarLinkage linkage;
+
+    bool shadowable;
+    bool src_is_const;
+    bool gen_is_const;
 };
 
 struct ErrorTableEntry {
@@ -1891,10 +1924,11 @@ struct ScopeBlock {
     ZigList<IrInstruction *> *incoming_values;
     ZigList<IrBasicBlock *> *incoming_blocks;
 
-    bool safety_off;
     AstNode *safety_set_node;
-    bool fast_math_on;
     AstNode *fast_math_set_node;
+
+    bool safety_off;
+    bool fast_math_on;
 };
 
 // This scope is created from every defer expression.
@@ -2030,8 +2064,19 @@ struct IrBasicBlock {
     IrInstruction *must_be_comptime_source_instr;
 };
 
+// These instructions are in transition to having "pass 1" instructions
+// and "pass 2" instructions. The pass 1 instructions are suffixed with Src
+// and pass 2 are suffixed with Gen.
+// Once all instructions are separated in this way, they'll have different
+// base types for better type safety.
+// Src instructions are generated by ir_gen_* functions in ir.cpp from AST.
+// ir_analyze_* functions consume Src instructions and produce Gen instructions.
+// ir_render_* functions in codegen.cpp consume Gen instructions and produce LLVM IR.
+// Src instructions do not have type information; Gen instructions do.
 enum IrInstructionId {
     IrInstructionIdInvalid,
+    IrInstructionIdDeclVarSrc,
+    IrInstructionIdDeclVarGen,
     IrInstructionIdBr,
     IrInstructionIdCondBr,
     IrInstructionIdSwitchBr,
@@ -2040,7 +2085,6 @@ enum IrInstructionId {
     IrInstructionIdPhi,
     IrInstructionIdUnOp,
     IrInstructionIdBinOp,
-    IrInstructionIdDeclVar,
     IrInstructionIdLoadPtr,
     IrInstructionIdStorePtr,
     IrInstructionIdFieldPtr,
@@ -2069,7 +2113,7 @@ enum IrInstructionId {
     IrInstructionIdAsm,
     IrInstructionIdSizeOf,
     IrInstructionIdTestNonNull,
-    IrInstructionIdUnwrapOptional,
+    IrInstructionIdOptionalUnwrapPtr,
     IrInstructionIdOptionalWrap,
     IrInstructionIdUnionTag,
     IrInstructionIdClz,
@@ -2085,7 +2129,8 @@ enum IrInstructionId {
     IrInstructionIdCompileLog,
     IrInstructionIdErrName,
     IrInstructionIdEmbedFile,
-    IrInstructionIdCmpxchg,
+    IrInstructionIdCmpxchgSrc,
+    IrInstructionIdCmpxchgGen,
     IrInstructionIdFence,
     IrInstructionIdTruncate,
     IrInstructionIdIntCast,
@@ -2114,7 +2159,8 @@ enum IrInstructionId {
     IrInstructionIdErrWrapPayload,
     IrInstructionIdFnProto,
     IrInstructionIdTestComptime,
-    IrInstructionIdPtrCast,
+    IrInstructionIdPtrCastSrc,
+    IrInstructionIdPtrCastGen,
     IrInstructionIdBitCast,
     IrInstructionIdWidenOrShorten,
     IrInstructionIdIntToPtr,
@@ -2194,6 +2240,22 @@ struct IrInstruction {
     bool is_gen;
 };
 
+struct IrInstructionDeclVarSrc {
+    IrInstruction base;
+
+    ZigVar *var;
+    IrInstruction *var_type;
+    IrInstruction *align_value;
+    IrInstruction *init_value;
+};
+
+struct IrInstructionDeclVarGen {
+    IrInstruction base;
+
+    ZigVar *var;
+    IrInstruction *init_value;
+};
+
 struct IrInstructionCondBr {
     IrInstruction base;
 
@@ -2302,20 +2364,11 @@ struct IrInstructionBinOp {
     IrInstruction base;
 
     IrInstruction *op1;
-    IrBinOp op_id;
     IrInstruction *op2;
+    IrBinOp op_id;
     bool safety_check_on;
 };
 
-struct IrInstructionDeclVar {
-    IrInstruction base;
-
-    ZigVar *var;
-    IrInstruction *var_type;
-    IrInstruction *align_value;
-    IrInstruction *init_value;
-};
-
 struct IrInstructionLoadPtr {
     IrInstruction base;
 
@@ -2335,7 +2388,6 @@ struct IrInstructionFieldPtr {
     IrInstruction *container_ptr;
     Buf *field_name_buffer;
     IrInstruction *field_name_expr;
-    bool is_const;
 };
 
 struct IrInstructionStructFieldPtr {
@@ -2378,13 +2430,13 @@ struct IrInstructionCall {
     ZigFn *fn_entry;
     size_t arg_count;
     IrInstruction **args;
-    bool is_comptime;
     LLVMValueRef tmp_ptr;
-    FnInline fn_inline;
-    bool is_async;
 
     IrInstruction *async_allocator;
     IrInstruction *new_stack;
+    FnInline fn_inline;
+    bool is_async;
+    bool is_comptime;
 };
 
 struct IrInstructionConst {
@@ -2527,9 +2579,9 @@ struct IrInstructionSliceType {
     IrInstruction base;
 
     IrInstruction *align_value;
+    IrInstruction *child_type;
     bool is_const;
     bool is_volatile;
-    IrInstruction *child_type;
 };
 
 struct IrInstructionAsm {
@@ -2557,10 +2609,12 @@ struct IrInstructionTestNonNull {
     IrInstruction *value;
 };
 
-struct IrInstructionUnwrapOptional {
+// Takes a pointer to an optional value, returns a pointer
+// to the payload.
+struct IrInstructionOptionalUnwrapPtr {
     IrInstruction base;
 
-    IrInstruction *value;
+    IrInstruction *base_ptr;
     bool safety_check_on;
 };
 
@@ -2651,7 +2705,7 @@ struct IrInstructionEmbedFile {
     IrInstruction *name;
 };
 
-struct IrInstructionCmpxchg {
+struct IrInstructionCmpxchgSrc {
     IrInstruction base;
 
     IrInstruction *type_value;
@@ -2661,14 +2715,19 @@ struct IrInstructionCmpxchg {
     IrInstruction *success_order_value;
     IrInstruction *failure_order_value;
 
-    // if this instruction gets to runtime then we know these values:
-    ZigType *type;
-    AtomicOrder success_order;
-    AtomicOrder failure_order;
-
     bool is_weak;
+};
 
+struct IrInstructionCmpxchgGen {
+    IrInstruction base;
+
+    IrInstruction *ptr;
+    IrInstruction *cmp_value;
+    IrInstruction *new_value;
     LLVMValueRef tmp_ptr;
+    AtomicOrder success_order;
+    AtomicOrder failure_order;
+    bool is_weak;
 };
 
 struct IrInstructionFence {
@@ -2851,7 +2910,7 @@ struct IrInstructionTestErr {
 struct IrInstructionUnwrapErrCode {
     IrInstruction base;
 
-    IrInstruction *value;
+    IrInstruction *err_union;
 };
 
 struct IrInstructionUnwrapErrPayload {
@@ -2899,13 +2958,19 @@ struct IrInstructionTestComptime {
     IrInstruction *value;
 };
 
-struct IrInstructionPtrCast {
+struct IrInstructionPtrCastSrc {
     IrInstruction base;
 
     IrInstruction *dest_type;
     IrInstruction *ptr;
 };
 
+struct IrInstructionPtrCastGen {
+    IrInstruction base;
+
+    IrInstruction *ptr;
+};
+
 struct IrInstructionBitCast {
     IrInstruction base;