RFR: 8210416: [linux] Poor StrictMath performance due to non-optimized compilation

[Severin Gehwolf]

On Thu, 2018-09-06 at 09:55 -0700, Erik Joelsson wrote:
> On 2018-09-06 03:12, Severin Gehwolf wrote:
> > Hi David,
> > 
> > On Thu, 2018-09-06 at 07:32 +1000, David Holmes wrote:
> > > Hi Severin,
> > > 
> > > Might as well raise this here too as it's really a build philosophy
> > > issue. Shouldn't flags like -ffp-contract=off (and the existing AIX
> > > -qfloat=nomaf) be toolchain specific rather than platform specific?
> > 
> > Looks like Clang has -ffp-contract:
> > https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-ffp-contract
> > 
> > Is there any other (supported) toolchain other than gcc and clang on
> > linux? As for AIX I suppose there is only on supported toolchain?
> 
> We don't have a big variety of toolchain/platform combinations that we 
> actively support no, but we still try to be conscious of when a flag is 
> toolchain specific and when it's platform specific. There is certainly 
> interest in using other compilers on Linux, and GCC could potentially be 
> used on other platforms as well. Until we actually try it, it can be 
> hard to know for sure if a flag actually applies in other cases for the 
> toolchain and/or platform, but we can at least try our best guess.

Thanks, Erik. GCC supports -ffp-contract since 4.6. Clang has -ffp-
contract too. Question is beginning from which version. That's why I'd
expect for those flags to work on linux. Is there anything else I need
to check?

Would it be preferred if I moved this into a block like this?

ifeq ($(TOOLCHAIN_TYPE), gcc)
  [...]
endif

Thanks,
Severin

> /Erik
> > Thanks,
> > Severin
> > 
> > > Thanks,
> > > David
> > > 
> > > On 5/09/2018 11:12 PM, Severin Gehwolf wrote:
> > > > Hi,
> > > > 
> > > > Cross-posting this review-thread on core-libs-dev and build-dev as
> > > > this
> > > > is a build change, but affects fdlibm which is core-libs.
> > > > 
> > > > With JDK-8170153 optimization for fdlibm code has been turned on
> > > > for
> > > > ppc64 s390 and aarch64. This patch intends to turn it on on all
> > > > arches
> > > > on Linux. I've not observed any precision issues. Is there a good
> > > > reason to not use -O3 -ffp-contract=off everywhere?
> > > > 
> > > > Bug:    https://bugs.openjdk.java.net/browse/JDK-8210416
> > > > webrev:
> > > > http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8210416/webrev.01/
> > > > 
> > > > Testing: - java/lang/Math, java/lang/StrictMath tests (all pass).
> > > >            - Currently running through submit repo.
> > > > 
> > > > A simple micro benchmark from JDK-8170153[1] shows these numbers
> > > > for
> > > > StrictMath:
> > > > 
> > > > Function      | before     | after
> > > > ----------------------------------------------
> > > > sin           | 0m33.382s  | 0m18.731s
> > > > cos           | 0m31.562s  | 0m18.796s
> > > > tan           | 0m33.657s  | 0m21.093s
> > > > atan          | 0m5.714s   | 0m4.902s
> > > > log           | 0m6.212s   | 0m4.439s
> > > > log10         | 0m7.946s   | 0m5.543s
> > > > sqrt          | 0m0.481s   | 0m0.449s
> > > > cbrt          | 0m5.295s   | 0m5.214s
> > > > tanh          | 0m1.404s   | 0m1.307s
> > > > log1p         | 0m6.457s   | 0m5.131s
> > > > IEEEremainder | 0m10.629s  | 0m6.048s
> > > > atan2         | 0m8.037s   | 0m5.668s
> > > > hypot         | 0m2.171s   | 0m2.147s
> > > > 
> > > > Thoughts?
> > > > 
> > > > Thanks,
> > > > Severin
> > > > 
> > > > 
> 
>