RFR: Fix unsigned comparison in plab.cpp

[Zhengyu Gu]

Good.

-Zhengyu

On 05/18/2018 08:23 AM, Aleksey Shipilev wrote:
> 32-bit builds started to fail with:
> 
> /pool/buildbot/slaves/sobornost/shenandoah-jdkX/build/src/hotspot/share/gc/shared/plab.cpp:87:29:
> error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>       assert(_hard_end - _top >= oopDesc::header_size() + Universe::heap()->oop_extra_words(),
>              ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Fix:
> 
> diff -r 19704db7c2c2 src/hotspot/share/gc/shared/plab.cpp
> --- a/src/hotspot/share/gc/shared/plab.cpp	Fri May 18 14:02:15 2018 +0200
> +++ b/src/hotspot/share/gc/shared/plab.cpp	Fri May 18 14:19:41 2018 +0200
> @@ -84,7 +84,7 @@
>   size_t PLAB::retire_internal() {
>     size_t result = 0;
>     if (_top < _hard_end) {
> -    assert(_hard_end - _top >= oopDesc::header_size() + Universe::heap()->oop_extra_words(),
> +    assert(pointer_delta(_hard_end, _top) >= (size_t)(oopDesc::header_size() +
> Universe::heap()->oop_extra_words()),
>              "better have enough space left to fill with dummy");
>       HeapWord* obj = Universe::heap()->tlab_post_allocation_setup(_top);
>       CollectedHeap::fill_with_object(obj, _hard_end);
> 
> 
> Testing: x86_32, x86_64 builds
> 
> Thanks,
> -Aleksey
>