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From: "andysem at mail dot ru" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/108401] gcc defeats vector constant generation with
 intrinsics
Date: Mon, 16 Jan 2023 10:42:59 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108401

--- Comment #7 from andysem at mail dot ru ---
To be clear, I'm not asking the compiler to recognize the particular patter=
n of
alternating 0x00 and 0xFF bytes. Because hardcoding this particular pattern
won't improve generated code in other cases.

Rather, I'm asking to tune down code transformations for intrinsics. If the
developer wrote a sequence of intrinsics to generate a constant then he
probably wanted that sequence instead of a simple _mm_set1_epi32 or a load =
from
memory.

But, if you're going to improve constant generation, please make it so that=
 it
can recognize not only the particular pattern described in this bug. More
importantly, it should recognize the all-ones case (as a single pcmpeq) as a
starting point. Then it can apply shifts to achieve the final result from t=
he
all-ones vector - shifts of any width, length or direction, including
psrldq/pslldq. This would improve generated code in a wider range of cases.=