[PATCH] D34336: [x86] transform vector inc/dec to use -1 constant (PR33483)

[Ayman Musa via Phabricator via llvm-commits]

aymanmus added a comment.

Taken from Intel's optimization manual:

> There is another dependency breaking idiom - the "ones idiom".
>  • CMPEQ XMM1, XMM1; "ones idiom" set all elements to all "ones"
>  In this case, the micro-op must execute, however, since it is known that regardless of the input data the
>  output data is always "all ones" the micro-op dependency upon its sources does not exist as with the zero
>  idiom and it can execute as soon as it finds a free execution port.

No mentioning for vpternlog in the manual, but I think it would behave the same.


https://reviews.llvm.org/D34336