Re: 2 optimization bugs ?
George Colpitts <[email protected]>
| Newsgroups | gmane.comp.lang.haskell.cafe |
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| Message-ID | <CAB-d4A7hF7FbTg_MY3gJxhJo+NLCWJu6RkuMeQnFhKpygrf2WQ@mail.gmail.com> |
Thanks Noon. I should have been clearer, I expected 10^6 to be changed to 1000000 at compile time as part of constant folding. Even when done at run time I can't see how that conversion would take that long or why it would allocate so many bytes. On Wed, Jul 3, 2024 at 8:12 AM Noon van der Silk <[email protected]> wrote: > I haven't looked at the second one, but for the first you may be > interested in the source code - > https://hackage.haskell.org/package/ghc-internal-9.1001.0/docs/src/GHC.Internal.Real.html#%5E > - and the comments around [Inlining] and [Powers with small exponent]. > > Notably, it only covers until x^a until a = 5, and indeed with 10^5 the > results of the two different ways of writing the number are the same. > > -- > Noon > > > On Tue, 2 Jul 2024 at 12:35, George Colpitts <[email protected]> > wrote: > >> It seems like I have found two optimization bugs. Before filing bugs , I >> wanted to double check if others agreed and can reproduce the bugs. >> >> Compile and run the attached file: >> >> ghc -O2 optBugs.hs >> Loaded package environment from >> /Users/avie/.ghc/aarch64-darwin-9.10.1/environments/default >> [1 of 2] Compiling Main ( optBugs.hs, optBugs.o ) >> optBugs.hs:45:49: warning: [GHC-18042] [-Wtype-defaults] >> • Defaulting the type variable ‘b0’ to type ‘Integer’ in the >> following constraints >> (Integral b0) arising from a use of ‘^’ at optBugs.hs:45:49 >> (Num b0) arising from the literal ‘6’ at optBugs.hs:45:50 >> • In the first argument of ‘counts’, namely ‘(10 ^ 6)’ >> In the second argument of ‘(.)’, namely ‘counts (10 ^ 6)’ >> In the second argument of ‘(.)’, namely ‘elems . counts (10 ^ 6)’ >> | >> 45 | solve = product . map (+ 1) . elems . counts (10^6) -- 1000000 >> | >> ^ >> >> [2 of 2] Linking optBugs >> avie@Anabela-Air Documents % ./optBugs +RTS -s >> ./optBugs +RTS -s >> 39001250856960000 >> 2,932,564,768 bytes allocated in the heap >> 143,405,696 bytes copied during GC >> 76,022,072 bytes maximum residency (4 sample(s)) >> 11,034,312 bytes maximum slop >> 164 MiB total memory in use (0 MiB lost due to fragmentation) >> >> >> Tot time (elapsed) Avg pause Max >> pause >> Gen 0 263 colls, 0 par 0.032s 0.036s 0.0001s >> 0.0020s >> Gen 1 4 colls, 0 par 0.048s 0.060s 0.0150s >> 0.0368s >> >> >> INIT time 0.003s ( 0.003s elapsed) >> MUT time 3.343s ( 3.333s elapsed) >> GC time 0.080s ( 0.096s elapsed) >> EXIT time 0.002s ( 0.008s elapsed) >> Total time 3.428s ( 3.440s elapsed) >> >> >> %GC time 0.0% (0.0% elapsed) >> >> >> Alloc rate 877,099,801 bytes per MUT second >> >> >> Productivity 97.5% of total user, 96.9% of total elapsed >> >> >> Now change the line >> >> solve = product . map (+ 1) . elems . counts (10^6) -- 1000000 >> >> to >> >> solve = product . map (+ 1) . elems . counts 1000000 >> >> save the file to disk, compile and rerun: >> >> ghc -O2 optBugs.hs >> Loaded package environment from >> /Users/avie/.ghc/aarch64-darwin-9.10.1/environments/default >> [1 of 2] Compiling Main ( optBugs.hs, optBugs.o ) [Source >> file changed] >> [2 of 2] Linking optBugs [Objects changed] >> avie@Anabela-Air Documents % ./optBugs +RTS -s >> ./optBugs +RTS -s >> 39001250856960000 >> 1,920,053,000 bytes allocated in the heap >> 16,488 bytes copied during GC >> 8,028,224 bytes maximum residency (2 sample(s)) >> 393,152 bytes maximum slop >> 22 MiB total memory in use (0 MiB lost due to fragmentation) >> >> >> Tot time (elapsed) Avg pause Max >> pause >> Gen 0 239 colls, 0 par 0.000s 0.001s 0.0000s >> 0.0002s >> Gen 1 2 colls, 0 par 0.000s 0.001s 0.0007s >> 0.0011s >> >> >> INIT time 0.003s ( 0.003s elapsed) >> MUT time 2.011s ( 2.015s elapsed) >> GC time 0.001s ( 0.002s elapsed) >> EXIT time 0.000s ( 0.007s elapsed) >> Total time 2.015s ( 2.027s elapsed) >> >> >> %GC time 0.0% (0.0% elapsed) >> >> >> Alloc rate 954,738,679 bytes per MUT second >> >> >> Productivity 99.8% of total user, 99.4% of total elapsed >> >> >> Allocation decreased by a billion bytes and runtime has decreased by >> almost a third. This is hard to believe. The obvious explanation is that I >> dropped a zero when I wrote out 10^6 but I checked that I have six zeros. >> Also I get the same answer in both cases. >> >> Next uncomment the following two lines in factor: >> >> -- let p = sm ! m >> >> -- sm = smallest maxN >> >> and comment out the line: >> >> let p = smallest maxN ! m >> >> save the file, compile and rerun: >> >> >> ghc -O2 optBugs.hs >> Loaded package environment from >> /Users/avie/.ghc/aarch64-darwin-9.10.1/environments/default >> [1 of 2] Compiling Main ( optBugs.hs, optBugs.o ) [Source >> file changed] >> [2 of 2] Linking optBugs [Objects changed] >> avie@Anabela-Air Documents % ./optBugs +RTS -s >> ./optBugs +RTS -s >> 39001250856960000 >> 16,051,152 bytes allocated in the heap >> 10,040 bytes copied during GC >> 44,328 bytes maximum residency (1 sample(s)) >> 29,400 bytes maximum slop >> 22 MiB total memory in use (0 MiB lost due to fragmentation) >> >> >> Tot time (elapsed) Avg pause Max >> pause >> Gen 0 2 colls, 0 par 0.000s 0.000s 0.0001s >> 0.0002s >> Gen 1 1 colls, 0 par 0.000s 0.001s 0.0015s >> 0.0015s >> >> INIT time 0.003s ( 0.003s elapsed) >> MUT time 0.019s ( 0.018s elapsed) >> GC time 0.000s ( 0.002s elapsed) >> EXIT time 0.001s ( 0.002s elapsed) >> Total time 0.023s ( 0.025s elapsed) >> >> %GC time 0.0% (0.0% elapsed) >> >> Alloc rate 866,786,478 bytes per MUT second >> >> Productivity 78.9% of total user, 72.5% of total elapsed >> >> Allocation has dropped from 2 billion bytes to 16 million and runtime has >> dropped from 2 seconds to 0.02 seconds. I think the optimizer should move >> the call to smallest outside of the "loop" in go. This seems like a bug to >> me. >> >> >> >> >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> To (un)subscribe, modify options or view archives go to: >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> Only members subscribed via the mailman list are allowed to post. > > > > -- > Noon van der Silk > > http://silky.github.io/ > > "My programming language is kindness." > _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.