RFR(XXS): 8135179: Fix conversion warning after 8067341

[Lindenmaier, Goetz]

Hi Volker, 

thanks for this fix!  It's good.

Could somebody please sponsor this one-liner? Thanks!

Best regards,
  Goetz.

-----Original Message-----
From: hotspot-dev [mailto:hotspot-dev-bounces at openjdk.java.net] On Behalf Of Volker Simonis
Sent: Dienstag, 8. September 2015 18:57
To: HotSpot Open Source Developers
Subject: RFR(XXS): 8135179: Fix conversion warning after 8067341

Hi,

can somebody please review and sponsor the following trivial fix:

http://cr.openjdk.java.net/~simonis/webrevs/2015/8135179/
https://bugs.openjdk.java.net/browse/JDK-8135179

Change "8067341: Modify PLAB sizing algorithm to waste less"
introduced the following code:

size_t const cur_plab_sz = (double)total_waste_allowed /
G1LastPLABAverageOccupancy;

which triggers a conversion warning with older versions of GCC and
potentially other compilers as well:

hotspot-rt/src/share/vm/gc/g1/g1EvacStats.cpp: In member function
'virtual void G1EvacStats::adjust_desired_plab_sz()':
hotspot-rt/src/share/vm/gc/g1/g1EvacStats.cpp:96: warning: converting
to 'size_t' from 'double'
make[4]: *** [g1EvacStats.o] Error 1

The warning can be easily fixed as follows:

size_t const cur_plab_sz = (sizte_t)((double)total_waste_allowed /
G1LastPLABAverageOccupancy);

Thank you and best regards,
Volker


PS: as a side note I want to mention that we are currently disabling
'-Wconversion' for GCC 4.3 and later because it produces too many
warnings which are by default treated as errors. All the warnings
produced by '-Wconversion' are about narrowing conversions which may
result in a potential data loss.

It may be a good idea to fix all these implicit narrowing conversions
and re-enable -Wconversion warning by default.

But unfortunately there's quite some code which has to be changed in
order to meet the requirements of '-Wconversion'. A quick research
showed that there are currently 137 different implicit narrowing
conversions spread over 1785 different code locations.

For more details see "8135181: Re-enable '-Wconversion' for GCC 4.3
and later" (https://bugs.openjdk.java.net/browse/JDK-8135181) which
I've opened to track the issue.

What's the general opinion? Would it be worth wile to fix all these
conversion warnings by inserting implicit casts?