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

[Jatin Bhateja via Phabricator via llvm-commits]

jbhateja added a comment.

In https://reviews.llvm.org/D36454#853351, @craig.topper wrote:

> 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.


Yes, I agree. latency and number of micro codes are better without hadd, only lesser code size is advantage with hadd with same operands.
Do you suggest adding a check in isHorizontalBinOp to not recognize a valid pttern for horizontal add/sub if operands of are same.


https://reviews.llvm.org/D36454