Debug mode - Referencing field copies the object (self hosted backend)

[avahe-kellenberger]

Zig Version

0.15.1

Steps to Reproduce and Observed Behavior

I'm not sure if this is a duplicate of #25111 but I didn't think it was, based on the first comment...

The following code (in debug mode, not using llvm) has fn slow running significantly slower than fn fast:

const std = @import("std");

pub fn main() !void {
    var foo: Foo = .init();

    var slow_data: [100]i128 = undefined;
    for (0..100) |i| slow_data[i] = foo.slow();

    var fast_data: [100]i128 = undefined;
    for (0..100) |i| fast_data[i] = foo.fast();

    std.mem.sort(i128, &slow_data, {}, std.sort.asc(i128));
    std.mem.sort(i128, &fast_data, {}, std.sort.asc(i128));

    std.log.err("min: {} - max: {} - median: {}", .{ slow_data[0], slow_data[99], slow_data[49] });
    std.log.err("min: {} - max: {} - median: {}", .{ fast_data[0], fast_data[99], fast_data[49] });
}

const Map = struct {
    pub const Self = @This();
    tile_size: f32,
    data: [144 * 144 * 16]u8 = undefined,
    pub fn init(tile_size: f32) Self {
        return .{ .tile_size = tile_size };
    }
};

const Foo = struct {
    pub const Self = @This();

    map: Map,

    pub fn init() Self {
        return .{ .map = .init(16.0) };
    }

    pub fn slow(self: *Self) i128 {
        const start_time = std.time.nanoTimestamp();
        const map_size = self.map.tile_size;
        _ = map_size;
        return std.time.nanoTimestamp() - start_time;
    }

    pub fn fast(self: *Self) i128 {
        const start_time = std.time.nanoTimestamp();
        const map_size = &(self.map).tile_size;
        _ = map_size;
        return std.time.nanoTimestamp() - start_time;
    }
};

zig run foo.zig -freference-trace
error: min: 5811 - max: 150233 - median: 6301
error: min: 60 - max: 81 - median: 70

zig run -OReleaseSafe foo.zig
error: min: 10 - max: 40 - median: 20
error: min: 10 - max: 30 - median: 20

zig run -fllvm foo.zig
error: min: 20 - max: 140 - median: 30
error: min: 20 - max: 31 - median: 30

I haven't delved into the assembly, but I'm assuming this is causing a copy of Map (used Map.data to emphasize the slowdown)

Expected Behavior

Self hosted backend debug mode should have speeds somewhat similar to debug + llvm, or ReleaseSafe

[xdBronch]

im guessing this was indeed #25111/#25154, results look a lot more reasonable now

~ $ zig run a.zig
error: min: 51 - max: 228 - median: 52
error: min: 51 - max: 54 - median: 52
~ $ zig run a.zig -fllvm
error: min: 29 - max: 138 - median: 31
error: min: 30 - max: 43 - median: 31