[PATCH] D36454: [X86] Changes to extract Horizontal addition operation for AVX-512.

Craig Topper via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Sat Aug 26 12:31:41 PDT 2017


craig.topper added a comment.

Thinking about this some more. Do we really want to use a horizontal add instruction for a register with itself? Horizontal add is suboptimally implemented in microcode. It's 3 uops while the pshufd and the add are only 2 uops. The 3 uops also mean its limited to the complex decoder on Intel hardware.


https://reviews.llvm.org/D36454





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