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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/98856] [11 Regression] botan AES-128/XTS is
 slower by ~17% since r11-6649-g285fa338b06b804e72997c4d876ecf08a9c083af
Date: Thu, 04 Mar 2021 15:36:01 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98856

--- Comment #18 from Richard Biener <rguenth at gcc dot gnu.org> ---
There's another thing - we end up with

        vmovq   %rax, %xmm3
        vpinsrq $1, %rdx, %xmm3, %xmm0

but that has way worse latency than the alternative you'd get w/o SSE 4.1:

        vmovq   %rax, %xmm3
        vmovq   %rdx, %xmm7
        punpcklqdq  %xmm7, %xmm3

for example on Zen3 vmovq and vpisnrq have latencies of 3 while punpck
has a latency of only one.  So the second variant should have 2 cycles
less latency.

Testcase:

typedef long v2di __attribute__((vector_size(16)));

v2di foo (long a, long b)
{
  return (v2di){a, b};
}

Even on Skylake it's 2 (movq) + 3 (vpinsr), so there it's 6 vs. 3.  Not
sure if we should somehow do this late somehow (peephole or splitter) since
it requires one more %xmm register.=