Missing evaluation on bugs 6914095, 6914113, 6933327, 6935994
vladimir.kozlov at oracle.com
Tue Oct 11 09:54:06 PDT 2011
These bugs have evaluations in Comments section which unfortunately is
not visible outside. I moved my comments to Evaluation section and
included them below.
Vitaly Davidovich wrote:
> On your last one, have you checked to see if it makes a difference? I
> believe using partial registers requires a prefix on the op, making
> the instruction larger. Also there are some partial register stalls
> that can be triggered.
> On Oct 11, 2011 12:00 PM, "Ulf Zibis" <Ulf.Zibis at gmx.de
> <mailto:Ulf.Zibis at gmx.de>> wrote:
> some time ago I have submitted these bugs:
> <http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6914095> -
> HotSpot should reuse invariant loop parameter
It would be nice if 32bit x86 had more registers. Unfortunately we have
to reuse registers otherwise we will get more spills on stack which will
cause more performance regression then keeping value in register. And
x*c+c is very fast (few cycles) on modern cpus.
*** (#3 of 3): 2010-11-09 15:31:21 PST vladimir.kozlov at oracle.com
> <http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6914113> -
> Copy int to byte in 1 step
Will not do this. C2 type system will not allow store int into byte
array. Other platforms require address alignment to 4 bytes for int
store. Also on platforms with different endian the result will be different.
*** (#2 of 2): 2010-08-25 14:51:13 PDT vladimir.kozlov at oracle.com
> <http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6933327> - Use
> shifted addressing modes instead of shift instuctions
Will not fix. Using addressing mode involves addess unit which may have
negative effect if you have memory access instructions near this code.
*** (#2 of 2): 2010-08-25 14:29:34 PDT vladimir.kozlov at oracle.com
> <http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6935994> - Use
> as less bits as necessary
Should not do this since the other part of register will not be
initialized to 0.
*** (#2 of 2): 2010-08-25 14:39:10 PDT vladimir.kozlov at oracle.com
> I do not see, why they have been closed as "Will Not Fix".
> Can someone add content to the 'evaluation' section, or at least
> explain reasons here?
> Much thanks,
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