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58 lines
2.1 KiB
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58 lines
2.1 KiB
Markdown
← [Back to Twitter thread index](../README.md)
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---
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title: "So I can liter error checks around stuff with little actual cost,"
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author: "NOTimothyLottes"
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handle: "@NOTimothyLottes"
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post_url: "https://x.com/NOTimothyLottes/status/2076893128515112995"
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post_id: "2076893128515112995"
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timestamp: "2026-07-14 04:54:43"
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post_count: 6
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reply_count: 0
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repost_count: 0
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like_count: 3
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view_count: 419
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---
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# @NOTimothyLottes — So I can liter error checks around stuff with little actual cost,
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## Post 1 (2026-07-14 04:36:51)
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Another round of getting optimized error checking. Disassembly [after syscall] shows that it works.
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(1.) Volatile store __LINE__
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(2.) Volatile store "error code"
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(3.) TEST if error
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(4.) Conditional forward branch on error [static prediction untaken]
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AS_MINIMAL_AS_ONE_CAN_GET
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## Post 2 (2026-07-14 04:43:38) — reply to Post 1
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A macro cheat sheet to try to explain how it works ...
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## Post 3 (2026-07-14 04:46:54) — reply to Post 2
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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.
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## Post 4 (2026-07-14 04:50:23) — reply to Post 3
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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.
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## Post 5 (2026-07-14 04:52:35) — reply to Post 4
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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().
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## Post 6 (2026-07-14 04:54:43) — reply to Post 5
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So I can liter error checks around stuff with little actual cost,
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(1.) Two stores
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(2.) A CMP or TEST
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(3.) An ignored on no-error branch on the first execution! [this code almost never runs 2 times].
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