[8u] RFR: 8210416: [linux] Poor StrictMath performance due to non-optimized compilation

[Andrew John Hughes]

On 30/04/2019 12:37, Severin Gehwolf wrote:
> 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+.
> 

It's not "drastically different" as regards the top-level and jdk areas.
HotSpot is another matter.

The main difference in this change is we're supporting gcc < 4.6, which
is sensible.

> 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
> 
> 
> 
> 
> 

Looks good to me. This is how JDK-8172053 should have been handled to
begin with, rather than making assumptions (and indeed, that's how I
fixed it [0] [1])

[0] http://icedtea.classpath.org/hg/icedtea8-forest/rev/d5760f7cce54
[1] http://icedtea.classpath.org/hg/icedtea8-forest/jdk/rev/3642a826880b
-- 
Andrew :)

Senior Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

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