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---
title: "So I can liter error checks around stuff with little actual cost,"
author: "NOTimothyLottes"
handle: "@NOTimothyLottes"
post_url: "https://x.com/NOTimothyLottes/status/2076893128515112995"
post_id: "2076893128515112995"
timestamp: "2026-07-14 04:54:43"
post_count: 6
reply_count: 0
repost_count: 0
like_count: 3
view_count: 419
---

# @NOTimothyLottes — So I can liter error checks around stuff with little actual cost,

## Post 1 (2026-07-14 04:36:51)

Another round of getting optimized error checking. Disassembly [after syscall] shows that it works. 
(1.) Volatile store __LINE__
(2.) Volatile store "error code"
(3.) TEST if error
(4.) Conditional forward branch on error [static prediction untaken]
AS_MINIMAL_AS_ONE_CAN_GET

![Media 1](./media/2076888631508107561_1.png)

## Post 2 (2026-07-14 04:43:38) — reply to Post 1

A macro cheat sheet to try to explain how it works ...

![Media 1](./media/2076890340057878586_1.png)

## Post 3 (2026-07-14 04:46:54) — reply to Post 2

I have a collection of force inline wrappers that test returns from syscalls/functions for error and return the return. These all leverage builtin_expect so the compiler knows to make them fall through in the common case.

![Media 1](./media/2076891161898143906_1.png)

## Post 4 (2026-07-14 04:50:23) — reply to Post 3

Those force inlines call Err() on terminal error. The Err() function ensures the {__LINE__, error} stores are visible, then triggers the console drawing code to kill the app with printed error. Then it sleeps until the termination.

![Media 1](./media/2076892038314741815_1.png)

## Post 5 (2026-07-14 04:52:35) — reply to Post 4

Compiler eventually screws up, but at least it gets the fast path correct, and the slow error path gets an extra call. Effectively it conditionally forward branches to a distant call to Err() instead of just branching to the Err().

## Post 6 (2026-07-14 04:54:43) — reply to Post 5

So I can liter error checks around stuff with little actual cost,
(1.) Two stores
(2.) A CMP or TEST
(3.) An ignored on no-error branch on the first execution! [this code almost never runs 2 times].