compiler: implement analysis-local comptime-mutable memory

lib/std/Target.zig

@@ -1317,7 +1317,8 @@ pub const Cpu = struct {
             for (decls, 0..) |decl, i| {
                 array[i] = &@field(cpus, decl.name);
             }
-            return &array;
+            const finalized = array;
+            return &finalized;
         }
     };
 

lib/std/enums.zig

@@ -41,7 +41,8 @@ pub inline fn valuesFromFields(comptime E: type, comptime fields: []const EnumFi
         for (&result, fields) |*r, f| {
             r.* = @enumFromInt(f.value);
         }
-        return &result;
+        const final = result;
+        return &final;
     }
 }
 

lib/std/fmt.zig

@@ -1829,7 +1829,8 @@ pub inline fn comptimePrint(comptime fmt: []const u8, args: anytype) *const [cou
         var buf: [count(fmt, args):0]u8 = undefined;
         _ = bufPrint(&buf, fmt, args) catch unreachable;
         buf[buf.len] = 0;
-        return &buf;
+        const final = buf;
+        return &final;
     }
 }
 

lib/std/meta.zig

@@ -465,7 +465,8 @@ pub fn fieldNames(comptime T: type) *const [fields(T).len][:0]const u8 {
         var names: [fieldInfos.len][:0]const u8 = undefined;
         // This concat can be removed with the next zig1 update.
         for (&names, fieldInfos) |*name, field| name.* = field.name ++ "";
-        break :blk &names;
+        const final = names;
+        break :blk &final;
     };
 }
 
@@ -506,7 +507,8 @@ pub fn tags(comptime T: type) *const [fields(T).len]T {
         for (fieldInfos, 0..) |field, i| {
             res[i] = @field(T, field.name);
         }
-        break :blk &res;
+        const final = res;
+        break :blk &final;
     };
 }
 

lib/std/unicode.zig

@@ -1358,7 +1358,8 @@ pub fn utf8ToUtf16LeStringLiteral(comptime utf8: []const u8) *const [calcUtf16Le
         var utf16le: [len:0]u16 = [_:0]u16{0} ** len;
         const utf16le_len = utf8ToUtf16Le(&utf16le, utf8[0..]) catch |err| @compileError(err);
         assert(len == utf16le_len);
-        break :blk &utf16le;
+        const final = utf16le;
+        break :blk &final;
     };
 }
 

lib/std/zig/AstGen.zig

@@ -8296,22 +8296,27 @@ fn localVarRef(
                     });
                 }
 
-                const ptr_inst = if (num_namespaces_out != 0) try tunnelThroughClosure(
-                    gz,
-                    ident,
-                    num_namespaces_out,
-                    .{ .ref = local_ptr.ptr },
-                    .{ .token = local_ptr.token_src },
-                ) else local_ptr.ptr;
-
                 switch (ri.rl) {
                     .ref, .ref_coerced_ty => {
+                        const ptr_inst = if (num_namespaces_out != 0) try tunnelThroughClosure(
+                            gz,
+                            ident,
+                            num_namespaces_out,
+                            .{ .ref = local_ptr.ptr },
+                            .{ .token = local_ptr.token_src },
+                        ) else local_ptr.ptr;
                         local_ptr.used_as_lvalue = true;
                         return ptr_inst;
                     },
                     else => {
-                        const loaded = try gz.addUnNode(.load, ptr_inst, ident);
-                        return rvalueNoCoercePreRef(gz, ri, loaded, ident);
+                        const val_inst = if (num_namespaces_out != 0) try tunnelThroughClosure(
+                            gz,
+                            ident,
+                            num_namespaces_out,
+                            .{ .ref_load = local_ptr.ptr },
+                            .{ .token = local_ptr.token_src },
+                        ) else try gz.addUnNode(.load, local_ptr.ptr, ident);
+                        return rvalueNoCoercePreRef(gz, ri, val_inst, ident);
                     },
                 }
             }
@@ -8390,6 +8395,7 @@ fn tunnelThroughClosure(
     /// The value being captured.
     value: union(enum) {
         ref: Zir.Inst.Ref,
+        ref_load: Zir.Inst.Ref,
         decl_val: Zir.NullTerminatedString,
         decl_ref: Zir.NullTerminatedString,
     },
@@ -8400,7 +8406,8 @@ fn tunnelThroughClosure(
     },
 ) !Zir.Inst.Ref {
     switch (value) {
-        .ref => |v| if (v.toIndex() == null) return v, // trivia value; do not need tunnel
+        .ref => |v| if (v.toIndex() == null) return v, // trivial value; do not need tunnel
+        .ref_load => |v| assert(v.toIndex() != null), // there are no constant pointer refs
         .decl_val, .decl_ref => {},
     }
 
@@ -8433,6 +8440,7 @@ fn tunnelThroughClosure(
     // captures as required, starting with the outermost namespace.
     const root_capture = Zir.Inst.Capture.wrap(switch (value) {
         .ref => |v| .{ .instruction = v.toIndex().? },
+        .ref_load => |v| .{ .instruction_load = v.toIndex().? },
         .decl_val => |str| .{ .decl_val = str },
         .decl_ref => |str| .{ .decl_ref = str },
     });

lib/std/zig/Zir.zig

@@ -3058,20 +3058,23 @@ pub const Inst = struct {
 
     /// Represents a single value being captured in a type declaration's closure.
     pub const Capture = packed struct(u32) {
-        tag: enum(u2) {
+        tag: enum(u3) {
             /// `data` is a `u16` index into the parent closure.
             nested,
             /// `data` is a `Zir.Inst.Index` to an instruction whose value is being captured.
             instruction,
+            /// `data` is a `Zir.Inst.Index` to an instruction representing an alloc whose contents is being captured.
+            instruction_load,
             /// `data` is a `NullTerminatedString` to a decl name.
             decl_val,
             /// `data` is a `NullTerminatedString` to a decl name.
             decl_ref,
         },
-        data: u30,
+        data: u29,
         pub const Unwrapped = union(enum) {
             nested: u16,
             instruction: Zir.Inst.Index,
+            instruction_load: Zir.Inst.Index,
             decl_val: NullTerminatedString,
             decl_ref: NullTerminatedString,
         };
@@ -3085,6 +3088,10 @@ pub const Inst = struct {
                     .tag = .instruction,
                     .data = @intCast(@intFromEnum(inst)),
                 },
+                .instruction_load => |inst| .{
+                    .tag = .instruction_load,
+                    .data = @intCast(@intFromEnum(inst)),
+                },
                 .decl_val => |str| .{
                     .tag = .decl_val,
                     .data = @intCast(@intFromEnum(str)),
@@ -3099,6 +3106,7 @@ pub const Inst = struct {
             return switch (cap.tag) {
                 .nested => .{ .nested = @intCast(cap.data) },
                 .instruction => .{ .instruction = @enumFromInt(cap.data) },
+                .instruction_load => .{ .instruction_load = @enumFromInt(cap.data) },
                 .decl_val => .{ .decl_val = @enumFromInt(cap.data) },
                 .decl_ref => .{ .decl_ref = @enumFromInt(cap.data) },
             };

src/Air.zig

@@ -1084,9 +1084,11 @@ pub const Inst = struct {
         inferred_alloc: InferredAlloc,
 
         pub const InferredAllocComptime = struct {
-            decl_index: InternPool.DeclIndex,
             alignment: InternPool.Alignment,
             is_const: bool,
+            /// This is `undefined` until we encounter a `store_to_inferred_alloc`,
+            /// at which point the pointer is created and stored here.
+            ptr: InternPool.Index,
         };
 
         pub const InferredAlloc = struct {

src/Compilation.zig

@@ -1382,7 +1382,6 @@ pub fn create(gpa: Allocator, arena: Allocator, options: CreateOptions) !*Compil
                 .global_zir_cache = global_zir_cache,
                 .local_zir_cache = local_zir_cache,
                 .emit_h = emit_h,
-                .tmp_hack_arena = std.heap.ArenaAllocator.init(gpa),
                 .error_limit = error_limit,
                 .llvm_object = null,
             };