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From: "ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/95632] Redundant zero extension
Date: Tue, 16 Jun 2020 07:21:04 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95632

--- Comment #6 from Uro=C5=A1 Bizjak <ubizjak at gmail dot com> ---
(In reply to Uro=C5=A1 Bizjak from comment #5)
> (In reply to Mel Chen from comment #2)
> > Is it possible to pretend that we have a pattern that can match xor (re=
g:SI
> > 80), (reg: SI 72), 0xa001 in combine pass?
> > And then, if the constant part is too large to put in to the immediate =
part,
> > it can be split to 2 xor in split pass.
>=20
> Please note that the combine pass has its own (rather limited) splitter, =
it
> is documented in the second part of "Defining How to Split Instructions"
> paragraph. The example is dealing with the instruction that has too large
> immediate part, and looks similar to your problem.

Oh, I missed the discussion above. In this case, x86 implements pre-reload
splits, please see patterns decorated with ix86_pre_reload_split condition.=