LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Aaron Sawdey
Honza, Seeing your recent patches relating to inliner heuristics for LTO, I thought I should mention some related work I'm doing. By way of introduction, I've recently joined the IBM LTC's PPC Toolchain team, working on gcc performance. We have not generally seen good results using LTO on

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Jan Hubicka
Hello, Honza, Seeing your recent patches relating to inliner heuristics for LTO, I thought I should mention some related work I'm doing. By way of introduction, I've recently joined the IBM LTC's PPC Toolchain team, working on gcc performance. We have not generally seen good results

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Xinliang David Li
Do you witness similar problems with LTO +FDO? My concern is it can be tricky to get the register pressure estimate right. The register pressure problem is created by downstream components (code motions etc) but only exposed by the inliner. If you want to get it 'right' (i.e., not exposing the

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Xinliang David Li
On Fri, Apr 18, 2014 at 10:26 AM, Jan Hubicka hubi...@ucw.cz wrote: Hello, Honza, Seeing your recent patches relating to inliner heuristics for LTO, I thought I should mention some related work I'm doing. By way of introduction, I've recently joined the IBM LTC's PPC Toolchain team,

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Aaron Sawdey
On Fri, 2014-04-18 at 19:26 +0200, Jan Hubicka wrote: This is intresting. I sort of planned to add register pressure logic but always tought it is somewhat hard to do at GIMPLE level in a way that would work for all CPUs. Yes, this is just meant to try to measure something that is

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Aaron Sawdey
What I've observed on power is that LTO alone reduces performance and LTO+FDO is not significantly different than FDO alone. I agree that an exact estimate of the register pressure would be a difficult problem. I'm hoping that something that approximates potential register pressure downstream

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Jan Hubicka
What I've observed on power is that LTO alone reduces performance and LTO+FDO is not significantly different than FDO alone. On SPEC2k6? This is quite surprising, for our (well SUSE's) spec testers (AMD64) LTO seems off-noise win on SPEC2k6

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Jan Hubicka
What I've observed on power is that LTO alone reduces performance and LTO+FDO is not significantly different than FDO alone. I agree that an exact estimate of the register pressure would be a difficult problem. I'm hoping that something that approximates potential register pressure

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Xinliang David Li
On Fri, Apr 18, 2014 at 12:27 PM, Jan Hubicka hubi...@ucw.cz wrote: What I've observed on power is that LTO alone reduces performance and LTO+FDO is not significantly different than FDO alone. On SPEC2k6? This is quite surprising, for our (well SUSE's) spec testers (AMD64) LTO seems

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Xinliang David Li
On Fri, Apr 18, 2014 at 12:51 PM, Jan Hubicka hubi...@ucw.cz wrote: What I've observed on power is that LTO alone reduces performance and LTO+FDO is not significantly different than FDO alone. I agree that an exact estimate of the register pressure would be a difficult problem. I'm hoping

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Jan Hubicka
On Fri, Apr 18, 2014 at 12:27 PM, Jan Hubicka hubi...@ucw.cz wrote: What I've observed on power is that LTO alone reduces performance and LTO+FDO is not significantly different than FDO alone. On SPEC2k6? This is quite surprising, for our (well SUSE's) spec testers (AMD64) LTO seems

Re: LTO inliner -- sensitivity to increasing register pressure

2014-04-18 Thread Xinliang David Li
On Fri, Apr 18, 2014 at 2:16 PM, Jan Hubicka hubi...@ucw.cz wrote: On Fri, Apr 18, 2014 at 12:27 PM, Jan Hubicka hubi...@ucw.cz wrote: What I've observed on power is that LTO alone reduces performance and LTO+FDO is not significantly different than FDO alone. On SPEC2k6? This is quite