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[Bug target/46091] missed optimization: x86 bt/btc/bts instructions
- From: "ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 14 Aug 2017 18:10:43 +0000
- Subject: [Bug target/46091] missed optimization: x86 bt/btc/bts instructions
- Auto-submitted: auto-generated
- References: <bug-46091-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46091
--- Comment #11 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Uroš Bizjak from comment #10)
> I'll look into this a bit some more. However, these insn should be rare, so
> do not expect any noticeable application speed-up ...
From the Agner lists, it is not clear if "bitop mem, imm" is faster than
"movabs r, imm + logic_op mem, r". Looking at several tables, it looks that
that it is not; for some AMD and older Intel targets, RMW bitop looses
considerably.