Output register allocation constrain fix for HotSpot

[Christian Thalinger]

On Mar 26, 2011, at 4:10 AM, David Holmes wrote:
> Hi Deepak,
> 
> I've filed "7031385 incorrect register allocation in release_store_fence on linux x86" for this issue.

I just stumbled over this same bug on one of our Ubuntu machines using GCC 4.5.1.  What's the status of this fix?

/home/twisti/hotspot-comp/7018355/src/os_cpu/linux_x86/vm/orderAccess_linux_x86.inline.hpp: Assembler messages:
/home/twisti/hotspot-comp/7018355/src/os_cpu/linux_x86/vm/orderAccess_linux_x86.inline.hpp:160: Error: bad register name `%dil'
/home/twisti/hotspot-comp/7018355/src/os_cpu/linux_x86/vm/orderAccess_linux_x86.inline.hpp:160: Error: bad register name `%dil'

-- Christian

> 
> David Holmes
> 
> Deepak Bhole said the following on 03/26/11 12:59:
>> Hi,
>> When trying to build IcedTea with GCC 4.6, we encountered an error that
>> stems from incorrect register allocation in release_store_fence(volatile
>> jbyte*  p, jbyte  v) in orderAccess_linux_x86.inline.hpp.
>> Specifically, the inline assembly call trying to do an atomic 8-bit
>> exchange sets the output register constrain to r. The older versions GCC
>> (by chance) ended up assigning the l-part of one of the a/b/c/d
>> registers. However with 4.6, it attempts to do this with the
>> %*bp register. This is fine on x86_64, but on i686 the bp register
>> cannot be addressed in 8-bit (%bpl). This leads to a compilation
>> failure:
>> /builddir/build/BUILD/icedtea6-1.10/openjdk-ecj/hotspot/src/os_cpu/linux_x86/vm/orderAccess_linux_x86.inline.hpp: Assembler messages:
>> /builddir/build/BUILD/icedtea6-1.10/openjdk-ecj/hotspot/src/os_cpu/linux_x86/vm/orderAccess_linux_x86.inline.hpp:160: Error: bad register name `%bpl'
>> /builddir/build/BUILD/icedtea6-1.10/openjdk-ecj/hotspot/src/os_cpu/linux_x86/vm/orderAccess_linux_x86.inline.hpp:160: Error: bad register name `%bpl'
>> It is possible to make it work on both 32 and 64-bit by constraining the
>> output register further to only be one of a/b/c/d (=q).
>> Though it was only that function that caused an error, I think it'd be
>> best to change both uses of xchgb in orderAccess_linux_x86.inline.hpp to
>> use =q. Here is the webrev for it:
>> http://cr.openjdk.java.net/~dbhole/register-allocation-fix/webrev.00/
>> If there are no issues, I'd be happy to push the above change.
>> Cheers,
>> Deepak