alt Hacker News> I always code with the mindset “the compiler is smarter than me.”
...I don't know... for instance the MSVC compiler creates this output for the last two 'non-trivial' functions with '/Ox':
add w8,w1,w0
cmp w0,#0
cseleq w0,w1,w8
A better mindset is "don't trust the compiler for code that's actually performance sensitive".
You shouldn't validate each line of compiler output, but at least for the 'hot areas' in the code base that definitely pays off, because sometimes compilers do really weird shit for no good reason (often because of 'interference' between unrelated optimizer passes) - and often you don't need to dig deep to stumble over weird output like in the example above.
I see the msvc arm compiler has not improved much in 20 years. The msvc arm was pretty odd when we used it in ~2003. We did not trust it at all. Think we had to get 4 or so compiler fixes out of MS for that project plus 3 or 4 library fixes. The x86 one was pretty solid. We were targeting 4 different CPU platforms at the same time so we could find things like that decently quickly. Most of the the time it was something we did that was weird. But even then we would find them. That one looks like maybe the optimizer back filled a nop slot?