I'm also seeing performance regressions in the shootout benchmarks that I can't identify in the asm. The new asm looks better but performs worse, with a ~15% slowdown.
I fired up the performance counters in my CPU and the free Intel code for inspecting them showed that my CPU utilization took about a 10% hit, even while executing fewer total instructions. 1) Jan, perhaps we're seeing the same sort of behavior — the shootout benchmarks have extremely hot loops (hundreds of millions of iterations IIRC). I used ticky profiling too, and saw no suspicious changes in any counters. 2) Dear Low-level Gurus: How feasible is it that a ~15% slowdown in a program with a very hot loop is due to incidentally inhibiting some caching behavior (instr? data?)? Or perhaps effecting alignment? FTR my CPU is a Core i7-2620M, Sandy Bridge. Thanks all. On Wed, Jun 19, 2013 at 9:27 AM, Jan Stolarek <[email protected]>wrote: > > If it's not sorted out, can you open a ticket, put in the relevant info > (so > > we don't need to look at the email trail), and we can tackle it when you > > get here. > Currently there's a temporary workaround: I'm using new folding rules for > all primitive types, > except for Integer, in which case I left the old folding rules unchanged. > This of course should > be modified to make all rules uniform, but for now it at least passes > validation. I didn't fill > the ticket, because the bug does not exist yet :) It only manifests itself > in my patches, which > have not been applied yet. I'll add all the information from this > discussion to my github fork of > GHC and then move it to Trac once the bug makes it to HEAD. > > What worries me more about my patches is the performance regression in > kahan, because I see no > obvious differences in the generated assembly. > > Janek > > > > > Simon > > > > -----Original Message----- > > From: [email protected] [mailto:[email protected]] > On > > Behalf Of Jan Stolarek Sent: 20 May 2013 12:35 > > To: Ian Lynagh > > Cc: [email protected] > > Subject: Re: Integer constant folding in the presence of new primops > > > > > If you remove everything but the quotInteger test from > > > integerConstantFolding and compile with -ddump-rule-rewrites then > > > you'll see that the eqInteger rule fires before quotInteger. This is > > > presumably comparing against 0, as the definition of quot for Integer > > > (in GHC.Real) is > > > _ `quot` 0 = divZeroError > > > n `quot` d = n `quotInteger` d > > > > Yes, I noticed these two rules firing together - perhaps that's the > > explanation why. I created a small program for testing: > > > > main = print quotInt > > quotInt :: Integer > > quotInt = 100063 `quot` 156 > > > > I noticed that when I define eqInteger wrapper to be NOINLINE, the call > to > > quot is translated to Core as: > > > > Main.quotInt = > > GHC.Real.$fIntegralInteger_$cquot > > (__integer 100063) (__integer 156) > > > > but when I change the wrapper to INLINE I get: > > > > Main.quotInt = > > GHC.Real.$fNumRatio_$cquot <-------- NumRatio instead of > > IntegralInteger (__integer 100063) (__integer 156) > > > > All rule firing happens later (I used -ddump-simpl-iterations > > -ddump-rule-firings), except that for $fNumRatio_$cquot the quot rules > > don't fire. > > > > > Do you also still have eqInteger wired in? It sounds like you might > > > have given them both the same unique? > > > > No, they didn't have the same unique. I modified the existing rules to > work > > on the new primops and ignore their wrappers. At the moment I reverted > > these changes so that I can make progress and leave this problem for > later. > > > > Janek > > > > _______________________________________________ > > ghc-devs mailing list > > [email protected] > > http://www.haskell.org/mailman/listinfo/ghc-devs > > > > _______________________________________________ > ghc-devs mailing list > [email protected] > http://www.haskell.org/mailman/listinfo/ghc-devs >
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