fix fuzzing speed with prior runs

Author: gooncreeper

lib/build-web/fuzz.zig

@@ -1,5 +1,6 @@
 // Server timestamp.
 var start_fuzzing_timestamp: i64 = undefined;
+var start_fuzzing_n_runs: u64 = undefined;
 
 const js = struct {
     extern "fuzz" fn requestSources() void;
@@ -36,6 +37,7 @@ pub fn sourceIndexMessage(msg_bytes: []u8) error{OutOfMemory}!void {
     const source_locations: []const Coverage.SourceLocation = @alignCast(std.mem.bytesAsSlice(Coverage.SourceLocation, msg_bytes[source_locations_start..source_locations_end]));
 
     start_fuzzing_timestamp = header.start_timestamp;
+    start_fuzzing_n_runs = header.start_n_runs;
     try updateCoverageSources(directories, files, source_locations, string_bytes);
     js.ready();
 }
@@ -270,7 +272,7 @@ fn updateStats() error{OutOfMemory}!void {
 
     const avg_speed: f64 = speed: {
         const ns_elapsed: f64 = @floatFromInt(nsSince(start_fuzzing_timestamp));
-        const n_runs: f64 = @floatFromInt(hdr.n_runs);
+        const n_runs: f64 = @floatFromInt(hdr.n_runs -% start_fuzzing_n_runs);
         break :speed n_runs / (ns_elapsed / std.time.ns_per_s);
     };
 

lib/std/Build/Fuzz.zig

@@ -67,6 +67,7 @@ const CoverageMap = struct {
     /// Elements are indexes into `source_locations` pointing to the unit tests that are being fuzz tested.
     entry_points: std.ArrayListUnmanaged(u32),
     start_timestamp: i64,
+    start_n_runs: u64,
 
     fn deinit(cm: *CoverageMap, gpa: Allocator) void {
         std.posix.munmap(cm.mapped_memory);
@@ -318,6 +319,7 @@ pub fn sendUpdate(
                 .source_locations_len = @intCast(coverage_map.source_locations.len),
                 .string_bytes_len = @intCast(coverage_map.coverage.string_bytes.items.len),
                 .start_timestamp = coverage_map.start_timestamp,
+                .start_n_runs = coverage_map.start_n_runs,
             };
             var iovecs: [5][]const u8 = .{
                 @ptrCast(&header),
@@ -399,6 +401,7 @@ fn prepareTables(fuzz: *Fuzz, run_step: *Step.Run, coverage_id: u64) error{ OutO
         .source_locations = undefined, // populated below
         .entry_points = .{},
         .start_timestamp = ws.now(),
+        .start_n_runs = undefined, // populated below
     };
     errdefer gop.value_ptr.coverage.deinit(fuzz.gpa);
 
@@ -468,6 +471,7 @@ fn prepareTables(fuzz: *Fuzz, run_step: *Step.Run, coverage_id: u64) error{ OutO
 
     for (sorted_pcs.items(.index), sorted_pcs.items(.sl)) |i, sl| source_locations[i] = sl;
     gop.value_ptr.source_locations = source_locations;
+    gop.value_ptr.start_n_runs = header.n_runs;
 
     ws.notifyUpdate();
 }

lib/std/Build/abi.zig

@@ -218,6 +218,7 @@ pub const fuzz = struct {
         string_bytes_len: u32,
         /// When, according to the server, fuzzing started.
         start_timestamp: i64 align(4),
+        start_n_runs: u64 align(4),
     };
 
     /// WebSocket server->client.