[Exp] First prototype of new acmp bytecode

John Rose john.r.rose at oracle.com
Wed Feb 21 21:04:58 UTC 2018


That's very clever, I like it!

You might even be able to get rid of the special node type (arity=3),
if the cases where CmpP sees a derived oop can be recognized
as perturbations.  I don't think we do CmpP on derived oops in
any other circumstance (no C-style pointer/limit loops).

On Feb 21, 2018, at 7:58 AM, Tobias Hartmann <tobias.hartmann at oracle.com> wrote:
> 
> ...
> I've quickly prototyped this. Here's an example of a perturbed oop in R11 being live over a call to
> Test::myMethod and being treated as [8]=Derived_oop_[0] in the oop map. It's then re-used in the cmp
> at line 103:
> 
> 03b   	movl    R11, [RDX + #8 (8-bit)]	# compressed klass ptr
> 03f   	movq    R10, R11	# ptr -> long
> 042   	andq    R10, #1	# long
> 046   	movq    R11, RDX	# spill
> 049   	addq    R11, R10	# ptr
> 04c   	cmpq    R11, RCX	# ptr
> 04f   	jne,us  B5  P=0,519876 C=23319,000000
> [...]
> 05b   	movq    [rsp + #8], R11	# spill
> 060   	movq    [rsp + #0], RDX	# spill
>      	nop 	# 3 bytes pad for loops and calls
> 067   	call,static  Test::myMethod
>        # Test::testEq01_1 @ bci:14  L[0]=RBP L[1]=rsp + #0 L[2]=_
>        # OopMap{rbp=Oop [0]=Oop [8]=Derived_oop_[0] off=108}
> [...]
> 103   	cmpq    R11, R10	# ptr
> 
> I still have to sort out some issues (escape analysis isn't happy) but a new webrev will come soon.
> 
> Thanks,
> Tobias



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