From f90ba235d04165e654af0787e1e381159cbc5202 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Thu, 2 Nov 2023 18:23:50 -0700
Subject: [PATCH] zig reduce proof of concept

---
 src/reduce.zig | 83 +++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 69 insertions(+), 14 deletions(-)

diff --git a/src/reduce.zig b/src/reduce.zig
index e50817503a..f238125528 100644
--- a/src/reduce.zig
+++ b/src/reduce.zig
@@ -3,20 +3,38 @@ const Allocator = std.mem.Allocator;
 const assert = std.debug.assert;
 
 const usage =
-    \\zig reduce [source_file] [transformation]
+    \\zig reduce [source_file] [interestingness]
     \\
 ;
 
+const Interestingness = enum { interesting, boring, unknown };
+
 // Roadmap:
-// - add the main loop that checks for interestingness
-// - add transformations
 // - add thread pool
 // - add support for `@import` detection and other files
+// - more fancy transformations
 // - reduce flags sent to the compiler
+//   - @import inlining
+//   - deleting unused functions and other globals
+//   - removing statements or blocks of code
+//   - replacing operands of `and` and `or` with `true` and `false`
+//   - replacing if conditions with `true` and `false`
+// - integrate the build system?
 
 pub fn main(gpa: Allocator, arena: Allocator, args: []const []const u8) !void {
     const file_path = args[2];
-    const transformation_index = try std.fmt.parseInt(u32, args[3], 0);
+    const interestingness_argv_template = args[3..];
+
+    var interestingness_argv: std.ArrayListUnmanaged([]const u8) = .{};
+    try interestingness_argv.ensureUnusedCapacity(arena, interestingness_argv_template.len + 1);
+    interestingness_argv.appendSliceAssumeCapacity(interestingness_argv_template);
+    interestingness_argv.appendAssumeCapacity(file_path);
+
+    var rendered = std.ArrayList(u8).init(gpa);
+    defer rendered.deinit();
+
+    var prev_rendered = std.ArrayList(u8).init(gpa);
+    defer prev_rendered.deinit();
 
     const source_code = try std.fs.cwd().readFileAllocOptions(
         arena,
@@ -33,19 +51,56 @@ pub fn main(gpa: Allocator, arena: Allocator, args: []const []const u8) !void {
     if (tree.errors.len != 0) {
         @panic("syntax errors occurred");
     }
-    var rendered = std.ArrayList(u8).init(gpa);
-    defer rendered.deinit();
-    rendered.clearRetainingCapacity();
 
-    var gut_functions: std.AutoHashMapUnmanaged(u32, void) = .{};
-    try gut_functions.put(arena, transformation_index, {});
+    var next_gut_fn_index: u32 = 0;
+    var fixups: std.zig.Ast.Fixups = .{};
 
-    try tree.renderToArrayList(&rendered, .{
-        .gut_functions = gut_functions,
-    });
+    while (true) {
+        try fixups.gut_functions.put(arena, next_gut_fn_index, {});
 
-    const stdout = std.io.getStdOut();
-    try stdout.writeAll(rendered.items);
+        rendered.clearRetainingCapacity();
+        try tree.renderToArrayList(&rendered, fixups);
 
+        if (std.mem.eql(u8, rendered.items, prev_rendered.items)) {
+            std.debug.print("no remaining transformations\n", .{});
+            break;
+        }
+        prev_rendered.clearRetainingCapacity();
+        try prev_rendered.appendSlice(rendered.items);
+
+        try std.fs.cwd().writeFile(file_path, rendered.items);
+
+        const result = try std.process.Child.run(.{
+            .allocator = arena,
+            .argv = interestingness_argv.items,
+        });
+        if (result.stderr.len != 0)
+            std.debug.print("{s}", .{result.stderr});
+        const interestingness: Interestingness = switch (result.term) {
+            .Exited => |code| switch (code) {
+                0 => .interesting,
+                1 => .unknown,
+                else => .boring,
+            },
+            else => b: {
+                std.debug.print("interestingness check aborted unexpectedly\n", .{});
+                break :b .boring;
+            },
+        };
+        std.debug.print("{s}\n", .{@tagName(interestingness)});
+        switch (interestingness) {
+            .interesting => {
+                next_gut_fn_index += 1;
+            },
+            .unknown, .boring => {
+                // revert the change and try the next transformation
+                assert(fixups.gut_functions.remove(next_gut_fn_index));
+                next_gut_fn_index += 1;
+
+                rendered.clearRetainingCapacity();
+                try tree.renderToArrayList(&rendered, fixups);
+            },
+        }
+    }
     return std.process.cleanExit();
 }