stage2: dbg_stmt ZIR instructions have line/col

instead of node indexes.

 * AstGen: dbg_stmt instructions now have line and column indexes,
   relative to the parent declaration. This allows codegen to emit debug
   info without having the source bytes, tokens, or AST nodes loaded
   in memory.
 * ZIR: each decl has the absolute line number. This allows computing
   line numbers from offsets without consulting source code bytes.

Memory management: creating a function definition does not prematurely
set the Decl arena. Instead the function is allocated with the general
purpose allocator.

Codegen no longer looks at source code bytes for any reason. They can
remain unloaded from disk.

1 files changed, 4 insertions, 28 deletions

diff --git a/src/link/Elf.zig b/src/link/Elf.zig
index 7fbf17015e..3f87fd390b 100644
--- a/src/link/Elf.zig
+++ b/src/link/Elf.zig
@@ -2221,21 +2221,8 @@ pub fn updateDecl(self: *Elf, module: *Module, decl: *Module.Decl) !void {
         // For functions we need to add a prologue to the debug line program.
         try dbg_line_buffer.ensureCapacity(26);
 
-        const line_off: u28 = blk: {
-            const tree = decl.namespace.file_scope.tree;
-            const node_tags = tree.nodes.items(.tag);
-            const node_datas = tree.nodes.items(.data);
-            const token_starts = tree.tokens.items(.start);
-
-            // TODO Look into improving the performance here by adding a token-index-to-line
-            // lookup table. Currently this involves scanning over the source code for newlines.
-            const fn_decl = decl.src_node;
-            assert(node_tags[fn_decl] == .fn_decl);
-            const block = node_datas[fn_decl].rhs;
-            const lbrace = tree.firstToken(block);
-            const line_delta = std.zig.lineDelta(tree.source, 0, token_starts[lbrace]);
-            break :blk @intCast(u28, line_delta);
-        };
+        const func = decl.val.castTag(.function).?.data;
+        const line_off = @intCast(u28, decl.src_line + func.lbrace_line);
 
         const ptr_width_bytes = self.ptrWidthBytes();
         dbg_line_buffer.appendSliceAssumeCapacity(&[_]u8{
@@ -2750,19 +2737,8 @@ pub fn updateDeclLineNumber(self: *Elf, module: *Module, decl: *const Module.Dec
 
     if (self.llvm_object) |_| return;
 
-    const tree = decl.namespace.file_scope.tree;
-    const node_tags = tree.nodes.items(.tag);
-    const node_datas = tree.nodes.items(.data);
-    const token_starts = tree.tokens.items(.start);
-
-    // TODO Look into improving the performance here by adding a token-index-to-line
-    // lookup table. Currently this involves scanning over the source code for newlines.
-    const fn_decl = decl.src_node;
-    assert(node_tags[fn_decl] == .fn_decl);
-    const block = node_datas[fn_decl].rhs;
-    const lbrace = tree.firstToken(block);
-    const line_delta = std.zig.lineDelta(tree.source, 0, token_starts[lbrace]);
-    const casted_line_off = @intCast(u28, line_delta);
+    const func = decl.val.castTag(.function).?.data;
+    const casted_line_off = @intCast(u28, decl.src_line + func.lbrace_line);
 
     const shdr = &self.sections.items[self.debug_line_section_index.?];
     const file_pos = shdr.sh_offset + decl.fn_link.elf.off + self.getRelocDbgLineOff();