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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/95737] PPC: Unnecessary extsw after negative less than Date: Thu, 13 Jan 2022 16:34:29 +0000 [thread overview] Message-ID: <bug-95737-4-uo3RQcqcJr@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-95737-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95737 --- Comment #8 from Segher Boessenkool <segher at gcc dot gnu.org> --- Somewhat more constructive... The problem here is that neg isn't pushed "through" isel insns. This in general means you need to negate both inputs to the isel of course, but there are cases where that is advantageous, like here when both of those inputs are constants (or actually registers, but set to some constant). This is one reason the new set[n]bc[r] insns are so useful to us: it is all one insn, also on RTL level, so it naturally works out in such cases. It also is slightly faster anyway of course, fewer insns and all that, even if for dataflow it is all the same.
next prev parent reply other threads:[~2022-01-13 16:34 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-06-18 8:10 [Bug target/95737] New: " jens.seifert at de dot ibm.com 2020-06-19 16:40 ` [Bug target/95737] " wschmidt at gcc dot gnu.org 2020-06-19 16:42 ` wschmidt at gcc dot gnu.org 2020-06-19 17:43 ` jens.seifert at de dot ibm.com 2020-06-21 15:35 ` wschmidt at linux dot ibm.com 2020-06-21 16:30 ` segher at gcc dot gnu.org 2022-01-06 5:39 ` guihaoc at gcc dot gnu.org 2022-01-13 12:19 ` segher at gcc dot gnu.org 2022-01-13 16:34 ` segher at gcc dot gnu.org [this message] 2022-01-14 9:16 ` guihaoc at gcc dot gnu.org 2022-05-18 5:24 ` cvs-commit at gcc dot gnu.org 2022-07-29 2:52 ` guihaoc at gcc dot gnu.org
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