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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/99881] Regression compare -O2 -ftree-vectorize with -O2
 on SKX/CLX
Date: Tue, 06 Apr 2021 10:06:19 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99881

--- Comment #4 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Richard Biener from comment #3)
> But 2 element construction _should_ be cheap.  What is missing is the move
> cost from GPR to XMM regs (but we do not have a good idea whether the sou=
rces
> are memory, so it's not as clear-cut here either).
>=20
> IMHO a better approach might be to up unaligned vector store/load costs?
>=20
> For the testcase at hand why does a throughput of 1 pose a problem?  Ther=
e's
> only one punpckldq instruction around?
>=20

There're several lea/add(which also may use port 5) instructions around
punckldq, considering that FAST LEA and Int ALU will be common in address
computation, throughput of 1 for punckldq will be a bottleneck.

refer to https://godbolt.org/z/hK9r5vTzd for original case

> Note that for the case of non-loop vectorization of 'double' the two elem=
ent
> vector CTORs are common and important to handle cheaply.  See also all the
> discussion in PR98856=