[LLVMdev] Inline hint for methods defined in-class (original) (raw)
Xinliang David Li davidxl at google.com
Thu Jul 9 09:23:15 PDT 2015
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On Thu, Jul 9, 2015 at 1:09 AM, David Chisnall <David.Chisnall at cl.cam.ac.uk> wrote:
On 9 Jul 2015, at 08:00, Xinliang David Li <xinliangli at gmail.com> wrote:
You need to be more specific on why the regression is problematic (and more so than missed opportunities). Text size increase (shared and much smaller than heap) is usually not a big issue except for tiny devices which is likely to use Os/Oz in the build. For servers, there are are simple rules to compare cpu vs ram resource cost. Text size increase also means more TLB and i-cache misses. We’ve observed that single-program benchmarks show this quite poorly, but the aggregate increase in i-cache and TLB pressure across the entire system can degrade performance overall on a typical desktop workload (not so relevant for single-application servers, but very relevant for server VMs). I believe some folks at Apple did a more systematic analysis of this, but I don’t know if their detailed results are public.
It may or may not increase itlb/TLB pressure . This should be considered by the inliner when computing the overall cost/benefit, but compiler today is generally very bad at modelling this effect -- especially when profile data is missing.
David
David
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