From 0f38f686964664f68e013ec3c63cfe655001f165 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Mon, 12 Jul 2021 19:51:31 -0700
Subject: stage2: Air and Liveness are passed ephemerally

to the link infrastructure, instead of being stored with Module.Fn. This
moves towards a strategy to make more efficient use of memory by not
storing Air or Liveness data in the Fn struct, but computing it on
demand, immediately sending it to the backend, and then immediately
freeing it.

Backends which want to defer codegen until flush() such as SPIR-V
must move the Air/Liveness data upon `updateFunc` being called and keep
track of that data in the backend implementation itself.
---
 src/codegen/c.zig | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

(limited to 'src/codegen/c.zig')

diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index e3f2423746..4743494f35 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -6,7 +6,6 @@ const log = std.log.scoped(.c);
 const link = @import("../link.zig");
 const Module = @import("../Module.zig");
 const Compilation = @import("../Compilation.zig");
-const Air = @import("../Air.zig");
 const Value = @import("../value.zig").Value;
 const Type = @import("../type.zig").Type;
 const TypedValue = @import("../TypedValue.zig");
@@ -14,6 +13,8 @@ const C = link.File.C;
 const Decl = Module.Decl;
 const trace = @import("../tracy.zig").trace;
 const LazySrcLoc = Module.LazySrcLoc;
+const Air = @import("../Air.zig");
+const Liveness = @import("../Liveness.zig");
 
 const Mutability = enum { Const, Mut };
 
@@ -37,7 +38,7 @@ const BlockData = struct {
     result: CValue,
 };
 
-pub const CValueMap = std.AutoHashMap(*Inst, CValue);
+pub const CValueMap = std.AutoHashMap(Air.Inst.Index, CValue);
 pub const TypedefMap = std.ArrayHashMap(
     Type,
     struct { name: []const u8, rendered: []u8 },
@@ -93,6 +94,8 @@ pub fn fmtIdent(ident: []const u8) std.fmt.Formatter(formatIdent) {
 /// It is not available when generating .h file.
 pub const Object = struct {
     dg: DeclGen,
+    air: Air,
+    liveness: Liveness,
     gpa: *mem.Allocator,
     code: std.ArrayList(u8),
     value_map: CValueMap,
@@ -102,7 +105,7 @@ pub const Object = struct {
     next_block_index: usize = 0,
     indent_writer: IndentWriter(std.ArrayList(u8).Writer),
 
-    fn resolveInst(o: *Object, inst: *Inst) !CValue {
+    fn resolveInst(o: *Object, inst: Air.Inst.Index) !CValue {
         if (inst.value()) |_| {
             return CValue{ .constant = inst };
         }
-- 
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