Hi Matthias, Thanks for the review!
On Tue, 2019-04-30 at 12:52 +0000, Baesken, Matthias wrote: > Hi Severin, looks okay to me (not a reviewer however). > In our proprietary JVM8 we had set (on > Linux) BUILD_LIBFDLIBM_OPTIMIZATION := > HIGH and FDLIBM_CFLAGS += -ffp-contract=off for a long time > and did not observe any issues . Good to know. We do the same in Fedora, fwiw. > (but we always build with gcc 4.8.x so cannot tell much about lower > gcc versions ). > > But I really wonder - wouldn’t it be better in the long run to go > for a min. gcc versions >= 4.6 (or even 4.8) in OpenJDK8 ? > > Maybe some people from the distros could comment on this . Perhaps, but it's hard to effectively figure out what that minimal version should be. Note that this change for the alternative of -ffp-contract=off was introduced to JDK 8 by SAP. See: https://bugs.openjdk.java.net/browse/JDK-8172053 Reading that bug it appears that minimum gcc is version 4.3? Either way, this patch will do the right thing(tm) for both as far as I could tell. It would use -mno-fused-madd -fno-strict-aliasing over --ffp- contract=off. My focus for this backport was to not break existing behaviour. Supporting -ffp-contract=off only would also break our upstream build machinery, as for them we build on RHEL 6 with gcc 4.4.7. >From our point of view JDK 8 minimal GCC would be 4.4.7 :) Thanks, Severin > > Best regards, Matthias > > > > -----Original Message----- > > From: ppc-aix-port-dev <ppc-aix-port-dev-boun...@openjdk.java.net> > > On > > Behalf Of Severin Gehwolf > > Sent: Dienstag, 30. April 2019 13:38 > > To: jdk8u-dev <jdk8u-...@openjdk.java.net>; build-dev <build- > > d...@openjdk.java.net> > > Cc: ppc-aix-port-dev <ppc-aix-port-...@openjdk.java.net> > > Subject: [8u] RFR: 8210416: [linux] Poor StrictMath performance due > > to non- > > optimized compilation > > > > Hi, > > > > Could I please get a review for this 8u backport related to fdlibm > > optimization on Linux? The JDK 12 patch doesn't apply as-is as the > > JDK > > 8 build system is drastically different from JDK 11+. > > > > Bug: https://bugs.openjdk.java.net/browse/JDK-8210416 > > webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK- > > 8210416/jdk8/02/ > > > > The main differences to the original fix are: a) optimization level > > and > > b) additional hook for older GCC. This backport keeps the > > optimization > > level at -O3 (HIGH) over -O2 (LOW) for JDK 8u as this would > > otherwise > > regress Linux ppc64{,le} which currently use -O3. As the current > > code > > has the implicit assumption of ppc64 being compiled on older GCCs > > too > > (JDK-8172053), this backport maintains compatibility in this > > regard. If > > -ffp-contract=off is not available, a machine specific set of flags > > is > > being used if the compiler supports them (-mno-fused-madd -fno- > > strict- > > aliasing). > > > > For older GCCs (< 4.6) specific machine flags are being used. That > > is, > > for ppc64{,le} and x86{,_64}. ppc64{,le} machine specific flags > > have > > already been determined (See JDK-8172053). x86_64 and x86 have the > > same > > machine specific flags available, so I've used them there too[1]. > > > > Testing: build/test on gcc 8.x Linux x86_64. build/test on gcc > > 4.4.7 > > x86_64/ppc64. Manual inspection of build logs for fdlibm files > > (e.g. > > w_asin.c). > > > > Thoughts? > > > > Thanks, > > Severin > > > > [1] > > https://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/i386-and-x86_002d64- > > Options.html#i386-and-x86_002d64-Options > > > > > > > >
