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6-post single-author walkthrough of the fast-path error-check pattern: volatile store __LINE__ + error code, TEST, conditional forward branch to a distant Err() call. Companion to the 2063733456144597200 thread which established the macro system via the conversation with @winning_tactic.
110 lines
4.0 KiB
JSON
110 lines
4.0 KiB
JSON
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"post_id": "2076888631508107561",
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"author": "NOTimothyLottes",
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"handle": "NOTimothyLottes",
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"text": "Another round of getting optimized error checking. Disassembly [after syscall] shows that it works. \n(1.) Volatile store __LINE__\n(2.) Volatile store \"error code\"\n(3.) TEST if error\n(4.) Conditional forward branch on error [static prediction untaken]\nAS_MINIMAL_AS_ONE_CAN_GET",
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"timestamp": "2026-07-14 04:36:51",
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"post_id": "2076890340057878586",
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"author": "NOTimothyLottes",
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"handle": "NOTimothyLottes",
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"text": "A macro cheat sheet to try to explain how it works ...",
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"timestamp": "2026-07-14 04:43:38",
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"post_id": "2076891161898143906",
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"author": "NOTimothyLottes",
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"handle": "NOTimothyLottes",
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"text": "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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"timestamp": "2026-07-14 04:46:54",
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"post_id": "2076892038314741815",
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"author": "NOTimothyLottes",
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"handle": "NOTimothyLottes",
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"text": "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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"timestamp": "2026-07-14 04:50:23",
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"post_id": "2076892591216341089",
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"author": "NOTimothyLottes",
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"handle": "NOTimothyLottes",
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"text": "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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"timestamp": "2026-07-14 04:52:35",
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"post_id": "2076893128515112995",
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"author": "NOTimothyLottes",
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"handle": "NOTimothyLottes",
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"text": "So I can liter error checks around stuff with little actual cost,\n(1.) Two stores\n(2.) A CMP or TEST\n(3.) An ignored on no-error branch on the first execution! [this code almost never runs 2 times].",
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"timestamp": "2026-07-14 04:54:43",
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