Another array access performance issue.

[IntegratedQuantum]

Zig Version

0.11.0-dev.753+331861161

Steps to Reproduce and Observed Behavior

I thought this was covered by #12215, but now that it is fixed I still get terrible performance.
Here is a simple benchmark:

const std = @import("std");

const len = 32*32*32;

fn getIndex(i: u16) u16 {
	return i;
}

pub const Chunk = struct {
	blocks: [len]u16 = undefined,
};

pub noinline fn regenerateMainMesh(chunk: *Chunk) u32 {
	var sum: u32 = 0;
	var i: u16 = 0;
	while(i < len) : (i += 1) {
		sum += chunk.blocks[getIndex(i)]; // ← workaround: (&chunk.blocks)[...]
	}
	return sum;
}

pub fn main() void {
	var chunk: Chunk = Chunk{};
	for(chunk.blocks) |*block, i| {
		block.* = @intCast(u16, i);
	}
	const start = std.time.nanoTimestamp();
	const sum = regenerateMainMesh(&chunk);
	const end = std.time.nanoTimestamp();
	std.log.err("Time: {} Sum: {}", .{end - start, sum});
}

Even in release-fast the performance is terrible:

$ zig run test.zig -OReleaseFast
error: Time: 104980842 Sum: 536854528

godbolt reveals that, like in #12215, there is a memcpy when accessing the array.

Expected Behavior

When applying the workaround

- sum += chunk.blocks[getIndex(i)]; // ← workaround: (&chunk.blocks)[...]
+ sum += (&chunk.blocks)[getIndex(i)]; // ← workaround: (&chunk.blocks)[...]

the performance is significantly better:

$ zig run test.zig -OReleaseFast
error: Time: 4188 Sum: 536854528

[shwqf]

I guess .field_ptr should be generated in fieldAccess in this case.

working on it.

[andrewrk]

Fix reverted in f93a36c