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From: "unlvsur at live dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug rtl-optimization/103550] 2 more instructions generated by gcc
 than clang
Date: Sat, 04 Dec 2021 13:56:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103550

--- Comment #10 from cqwrteur <unlvsur at live dot com> ---
(In reply to Roger Sayle from comment #9)
> Note adding -fno-tree-reassoc results in fewer instructions than clang.

maybe I am a little bit picky since I keep writing "portable assembly code"
with C++. I just frequently compare assembly generated by the compiler to
manually written assembly. However, I think that is how we got an improveme=
nt
on the GCC compiler since I do frequently find out suboptimal codegen with =
it.

The 21 instructions look really good. Do not know whether we can squeeze it
further.

Do not get me wrong. Actually, clang runs much slower for my sha512 in gene=
ral
(since they generate much more instructions (around 10% more)). I just comp=
are
GCC to openssl's manually written assembly (well it is actually generated by
perl script) and i feel it moves more registers.=