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[Bug rtl-optimization/50101] GCC 4.5 and 4.6 generate suboptimal code on ppc for countdown loops when the CTR register cannot be used
- From: "meissner at linux dot vnet.ibm.com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Fri, 19 Aug 2011 14:05:51 +0000
- Subject: [Bug rtl-optimization/50101] GCC 4.5 and 4.6 generate suboptimal code on ppc for countdown loops when the CTR register cannot be used
- Auto-submitted: auto-generated
- References: <bug-50101-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50101
--- Comment #8 from Michael Meissner <meissner at linux dot vnet.ibm.com> 2011-08-19 14:05:51 UTC ---
On Thu, Aug 18, 2011 at 08:58:28AM +0000, rguenth at gcc dot gnu.org wrote:
> Did you try pessimizing the non-ctr reg alternatives (and the memory
> alternative even more)? Like adding ! to the non-ctr alternatives
> and ? to the memory one? Not sure if those markers are looked at
> by IRA though.
Yes, I should have mentioned that I tried various combinations of ?, !, and *
and the combinations I tried aborted. I've certainly suspected that IRA now
longer looks at !, ?, and * like the previous register allocator did
previously. It may be that it is special due to being a JUMP_INSN.