Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

Ah of course that explains it. On Fri, 4 Aug 2017, 11:22 Dave Cheney, wrote: > Gcc on OS X is an alias for clang as Apple does not ship any GPLv3 > software with their os. > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group.

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

Gcc on OS X is an alias for clang as Apple does not ship any GPLv3 software with their os. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

I seem to have a disguised gcc/clang thing... gcc --version gcc --version Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/usr/include/c++/4.2.1

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

even at -O3 gcc wouldn't do it, probably because pow is implemented in another compilation unit. On Fri, Aug 4, 2017 at 6:49 PM, Sebastien Binet wrote: > > > On Fri, Aug 4, 2017 at 10:47 AM, Dave Cheney wrote: >> >> I'm disappointed that both compilers didn't

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

On Fri, Aug 4, 2017 at 10:47 AM, Dave Cheney wrote: > I'm disappointed that both compilers didn't compile both original samples > to a noop. > clang did it, though. -s -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

I'm disappointed that both compilers didn't compile both original samples to a noop. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

And the guess how it's arriving at that optimization: Step 0: base code x := 2.5 res := 0.0 for n := 0; n < NMAX; n++ { for i := 0; i < 4; i++ { res += math.Pow(x, float(i)) } } Step 1: unroll inner-loop x := 2.5 res := 0.0 for n := 0; n < NMAX; n++ { res += math.Pow(x, float(0)) res +=

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

Use the Assembly Luke. https://godbolt.org/g/nGFMbf It looks like clang manages to compute a table of powers of x. Which, is very very impressive. Which is roughly https://play.golang.org/p/CZkiJKfe7s -- except clang, also does inner loop unrolling. + Egon On Friday, 4 August 2017 11:16:10

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

I've put these files and a bash script for convenience here: https://gist.github.com/cpmech/b13b6e17789c0bdfa469b2f1b6b71587 Thanks again. On Friday, August 4, 2017 at 6:16:10 PM UTC+10, Dorival Pedroso wrote: > > wait, what?! > > the same code: > > #include "stdio.h" > #include "math.h" > int

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

wait, what?! the same code: #include "stdio.h" #include "math.h" int main() { double res = 0.0; double x = 2.5; int Nmax = 1000; for (int N=0; N

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

On Fri, Aug 4, 2017 at 9:51 AM, Henrik Johansson wrote: > Actually I get the same as the original program on my mac. > > time ./ccode > sum=606329794183272.375000 > ./ccode 0.17s user 0.00s system 98% cpu 0.170 total > > The Go version -O2 -Wall > time ./pow >

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

Sebastien is right! Thanks a lot! I forgot that the optimizer does eliminate some code at times. (and forgot this https://dave.cheney.net/2013/06/30/how-to-write-benchmarks-in-go) This is the C code now (compiled with gcc -O2 run_std_pow.c -o run_std_pow -lm): #include "stdio.h" #include

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

Actually I get the same as the original program on my mac. time ./ccode sum=606329794183272.375000 ./ccode 0.17s user 0.00s system 98% cpu 0.170 total The Go version -O2 -Wall time ./pow sum=6.063297941832724e+14./pow 5.47s user 0.01s system 99% cpu 5.490 total fre 4 aug. 2017 kl 09:38

Re: [go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

Dorival, On Fri, Aug 4, 2017 at 8:20 AM, Dorival Pedroso wrote: > I've noticed that this C code: > > #include "math.h" > int main() { > double x = 2.5; > int Nmax = 1000; > for (int N=0; N for (int i=0; i<20;

[go-nuts] How to optimize as with -O2 from Gcc? (50x speedup)

I've noticed that this C code: #include "math.h" int main() { double x = 2.5; int Nmax = 1000; for (int N=0; N