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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/77579] Missed multiple add (int) for CSEd case Date: Tue, 16 May 2023 20:06:10 +0000 [thread overview] Message-ID: <bug-77579-4-CbZo6pLFDk@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-77579-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77579 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|ASSIGNED |NEW Assignee|pinskia at gcc dot gnu.org |unassigned at gcc dot gnu.org --- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Thinking about this some more, doing the multiply multiple times is actually slower on most cores. So this is not something you want to do normally but with a constant multiply you do for small power of 2 constant. E.g.: ``` void f(int x, int y, int z, int *s) { int t = y * 2; s[0] = t + x; s[1] = x - t; } ``` You should get: add w2, w0, w1 lsl 1 sub w0, w0, w1 lsl 1 stp w2, w0, [x3] And no seperate lsl instruction as the cost to do the lsl is free in this case. Anyways I am not working on this any more.
parent reply other threads:[~2023-05-16 20:06 UTC|newest] Thread overview: expand[flat|nested] mbox.gz Atom feed [parent not found: <bug-77579-4@http.gcc.gnu.org/bugzilla/>]
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