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[ARTICLE · art-68573] src=twitter.com ↗ pub= topic=artificial-intelligence verified=true sentiment=↑ positive

GPT-5.6 found an Intel CPU microcode bug causing a performance regression

GPT-5.6 identified an Intel CPU microcode bug causing a performance regression, which was resolved by building with the -mbranches-within-32B-boundaries flag. The workaround slows conditional jumps straddling a 32-byte boundary, requiring specific program layout to restore speed.

read1 min views1 publishedJul 22, 2026
GPT-5.6 found an Intel CPU microcode bug causing a performance regression
Image: source

Had a strange performance regression from a seemingly innocuous code change, and GPT-5.6 tracked it down to a microcode workaround for an Intel CPU bug. The workaround can make conditional jumps that straddle a 32-byte boundary much slower, so programs have to be laid out around it. Tried building with -mbranches-within-32B-boundaries and wouldn't you know it, we're fast again! The future is so fucking cool!

source & further reading
twitter.com — original article
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