alt Hacker News-O3 -march=haswell
The second one is your problem. Haswell is 15 years old now. Almost nobody owns a CPU that old. -O3 makes a lot of architecture-dependent decisions, and tying yourself to an antique architecture gives you very bad results.
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My desktop computer is a Sandy Bridge from 2011. I still haven't seen any compelling reason to upgrade.
Not as old but I am still typing this on a MacBook Pro Early 2015 with a Broadwell CPU. It is doing pretty well with Chrome and Firefox, not so much with Safari.
I do. Had to replace the plastics of the laptop and the screen's definition is unacceptable but with Linux and a SSD it's still fine for basic computer usage. Not my daily driver but kept it as a daily drivers for 10 years.
The default is an even older instruction set. Maybe you meant to suggest -march native ?
This era of CPUs has held up surprisingly well. I built an Ivy Bridge desktop in 2012 that still sees daily productivity use (albeit with an NVMe and RAM upgrade).
The author gives a godbolt link. It takes 5 minutes to add two compilers on raptorlake and see that it gives the same result.
https://godbolt.org/z/oof145zjb
So no, Haswell is not the problem. LLVM just doesn't know about the dependency thing.