[CAUTION] RE: RFR JDK-8209786: gcc 7.3 compiler errors

[Lindenmaier, Goetz]

Hi,

maybe use -1LL or 0xfff...ULL ...

But please, this is still not the right list to discuss this.

Best regards,
  Goetz.

> -----Original Message-----
> From: Keith Campbell <keithc at ca.ibm.com>
> Sent: Donnerstag, 23. August 2018 15:04
> To: Andrew Leonard <andrew_m_leonard at uk.ibm.com>
> Cc: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>;
> joe.darcy at oracle.com; Schmidt, Lutz <lutz.schmidt at sap.com>; s390x-port-
> dev at openjdk.java.net
> Subject: Re: [CAUTION] RE: RFR JDK-8209786: gcc 7.3 compiler errors
> 
> I agree, -(1>>3) isn't what we want, but leaving it as it was isn't guaranteed to
> yield the desired result.
> 
> Instead, I suggest the right shifts should be applied to unsigned values:
>    -   mlib_u64 emask = (mlib_u64)((mlib_s64)(-1)) >> ((8 - (size - i)) * 8);
>    +   mlib_u64 emask = ((mlib_u64)(-1)) >> ((8 - (size - i)) * 8)
> 
> -Keith
> 
> 
> 	----- Original message -----
> 	From: Andrew Leonard/UK/IBM
> 	To: "Schmidt, Lutz" <lutz.schmidt at sap.com>, joe.darcy at oracle.com
> 	Cc: "Lindenmaier, Goetz" <goetz.lindenmaier at sap.com>, "s390x-
> port-dev at openjdk.java.net" <s390x-port-dev at openjdk.java.net>, Keith
> Campbell/Ottawa/IBM at IBMCA
> 	Subject: Re: [CAUTION] RE: RFR JDK-8209786: gcc 7.3 compiler errors
> 	Date: Thu, Aug 23, 2018 4:05 AM
> 
> 	Thanks for the reviews guys,
> 	Lutz, yes, those "undefined" behaviour's is what gcc7.3 is now
> highlighting, and we're trying to fix.
> 
> 	Goetz, I see what you're saying, I think we should leave the right
> shifts alone then, although as stated in Lutz's doc reference they are
> implementation-defined, I think the original code is trying to achieve the
> former 000111...111, I doubt it was trying to achieve 0!
> 	before, -1 >> 3 will result in something like 000111...111
> 	   now -(1>>3) will result in 000....0000
> 
> 	It is the left shirt of -ve values that is the real concern.
> 
> 	Joe, also suggested we should tackle this by changing the compiler
> options rather than changing libfdlibm, which maybe the alternative as this
> source has not changed for a long time and maybe best to let working code
> remain unchanged, i'd have to investigate a compiler option fix...
> 
> 	Keith, do you have any other views?
> 
> 	Thanks
> 	Andrew
> 
> 	Andrew Leonard
> 	Java Runtimes Development
> 	IBM Hursley
> 	IBM United Kingdom Ltd
> 	Phone internal: 245913, external: 01962 815913
> 	internet email: andrew_m_leonard at uk.ibm.com
> 
> 
> 	"Schmidt, Lutz" ---22/08/2018 16:50:27---Hi Andrew,  just recently I
> was confronted with a similar "shift issue" which prompted me to read th
> 
> 	From: "Schmidt, Lutz" <lutz.schmidt at sap.com>
> 	To: "Lindenmaier, Goetz" <goetz.lindenmaier at sap.com>, Andrew
> Leonard <andrew_m_leonard at uk.ibm.com>, "s390x-port-
> dev at openjdk.java.net" <s390x-port-dev at openjdk.java.net>
> 	Date: 22/08/2018 16:50
> 	Subject: Re: [CAUTION] RE: RFR JDK-8209786: gcc 7.3 compiler errors
> ________________________________
> 
> 
> 
> 
> 	Hi Andrew,
> 	just recently I was confronted with a similar "shift issue" which
> prompted me to read the language standard (again). I have summarized my
> understanding in a little text file which you may find attached. Have fun
> reading!
> 	Best Regards,
> 	Lutz
> 
> 	On 22.08.18, 09:18, "s390x-port-dev on behalf of Lindenmaier, Goetz"
> <s390x-port-dev-bounces at openjdk.java.net on behalf of
> goetz.lindenmaier at sap.com> wrote:
> 
> 	   Hi Andrew,
> 
> 	   please post this RFR to core-libs-dev.
> 
> 	   s390x-prot-dev is only for questions about the port etc.
> 	   It is not for reviews that go to jdk/jdk.
> 
> 	   Also, I'm not sure that your change in java.desktop is correct.
> 	   You now negate after shifting.
> 
> 	   -      mlib_u64 emask = (mlib_u64)((mlib_s64)(-1)) >> ((8 - (size - i)) *
> 8);
> 	   +      mlib_u64 emask = (mlib_u64)-(((mlib_s64)1) >> ((8 - (size - i)) *
> 8));
> 
> 	   before, -1 >> 3 will result in something like 000111...111
> 	   now -(1>>3) will result in 000....0000
> 
> 	   Best regards,
> 	     Goetz.
> 
> 
> 
> 
> 
> 
> 
> 
> 	   > -----Original Message-----
> 	   > From: s390x-port-dev <s390x-port-dev-
> bounces at openjdk.java.net> On
> 	   > Behalf Of Andrew Leonard
> 	   > Sent: Dienstag, 21. August 2018 15:05
> 	   > To: s390x-port-dev at openjdk.java.net
> 	   > Subject: RFR JDK-8209786: gcc 7.3 compiler errors
> 	   >
> 	   > Hi,
> 	   > We have discovered issues with gcc 7.3 on zLinux, combined with
> OpenJDK's
> 	   > default compiler options has highlighted a couple of native code
> issues,
> 	   > with:
> 	   >   - validating loop test array bounds
> 	   >   - left shifts of negative values
> 	   > I have created bug https://bugs.openjdk.java.net/browse/JDK-
> 8209786
> 	   > and attached the webrev fix here:
> 	   > http://cr.openjdk.java.net/~aleonard/gcc73/webrev.00/
> 	   >
> 	   > I'd like to request a sponsor for this fix please?
> 	   >
> 	   > Many thanks
> 	   > Andrew
> 	   >
> 	   > Andrew Leonard
> 	   > Java Runtimes Development
> 	   > IBM Hursley
> 	   > IBM United Kingdom Ltd
> 	   > Phone internal: 245913, external: 01962 815913
> 	   > internet email: andrew_m_leonard at uk.ibm.com
> 	   >
> 	   >
> 	   > Unless stated otherwise above:
> 	   > IBM United Kingdom Limited - Registered in England and Wales
> with number
> 	   > 741598.
> 	   > Registered office: PO Box 41, North Harbour, Portsmouth,
> Hampshire PO6
> 	   > 3AU
> 
> 
> 	[attachment "cppShiftOperations.txt" deleted by Andrew
> Leonard/UK/IBM]
> 
>