Hi, On Fri, Nov 08, 2024 at 11:18:09PM +1300, David Rowley wrote: > I tried with [1] and the > latest gcc does not seem to be smart enough to figure this out. I > tried adding some additional len checks that the compiler can use as a > cue and won't need to emit code for the checks providing the function > does get inlined. That was enough to get the compiler to not emit the > loops when they'll not be used. See the -DCHECK_LEN flag I'm passing > in the 2nd compiler window. I just don't know if putting something > like that into the code is a good idea as if the function wasn't > inlined for some reason, the extra len checks would have to be > compiled into the function. > > David > > [1] https://godbolt.org/z/xa81ro8GK
Looking at it, that looks like an issue. I mean, without the -DCHECK_LEN flag then the SIMD code will read up to 48 bytes beyond the struct's memory (which is 16 bytes): This is fine: " movdqu xmm0, XMMWORD PTR [rdi] " But I don't think it is: " movdqu xmm2, XMMWORD PTR [rdi+16] movdqu xmm1, XMMWORD PTR [rdi+32] movdqu xmm3, XMMWORD PTR [rdi+48] " given that the struct size is only 16 bytes. Thoughts? Regards, -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
