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

Lindenmaier, Goetz goetz.lindenmaier at sap.com
Thu Sep 10 06:51:59 UTC 2015

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?

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