RFR: JDK-8202016: Use obj+offset in interpreter array access

[B. Blaser]

Hi,

On 14 May 2018 at 13:19, Andrew Dinn <adinn at redhat.com> wrote:
> On 14/05/18 11:15, Roman Kennke wrote:
>> Am 07.05.2018 um 21:47 schrieb Roman Kennke:
>>> In the TemplateTable::aastore() and
>>> InterpreterMacroAssembler::load_resolved_reference_at_index(), the
>>> element address is flattened, and then passed to the BarrierSetAssembler
>>> for actual access. GCs like Shenandoah need the original obj though.
>>>
>>> The proposed change replaces the flattening with base+index+disp
>>> addressing, and removes the shift and add computations. In the case of
>>> aastore, we need to re-fetch the rcx/index from the stack because it
>>> gets trashed on the way.
>>>
>>> Testing: passed: hotspot/jtreg:tier1
>>>
>>> Can I please get a review?
>>> Thanks, Roman
> Well, that x86 code change looks ok/ish/ -- although the need to reload
> from the stack is a tad disappointing.

Maybe I'm a bit late, but I think we could use r8 & r9 to avoid some
unnecessary stack access, as next.
What do you think (tier1 seems OK)?

Regards,
Bernard


diff -r 24151f48582b src/hotspot/cpu/x86/templateTable_x86.cpp
--- a/src/hotspot/cpu/x86/templateTable_x86.cpp    Mon May 14 21:56:07
2018 +0200
+++ b/src/hotspot/cpu/x86/templateTable_x86.cpp    Mon May 14 23:03:40
2018 +0200
@@ -1098,6 +1098,11 @@
   __ movl(rcx, at_tos_p1()); // index
   __ movptr(rdx, at_tos_p2()); // array

+#ifdef _LP64
+  __ movptr(r8, rax);
+  __ movl(r9, rcx);
+#endif
+
   Address element_address(rdx, rcx,
                           UseCompressedOops? Address::times_4 :
Address::times_ptr,
                           arrayOopDesc::base_offset_in_bytes(T_OBJECT));
@@ -1125,8 +1130,13 @@
   __ bind(ok_is_subtype);

   // Get the value we will store
+#ifdef _LP64
+  __ movptr(rax, r8);
+  __ movl(rcx, r9);
+#else
   __ movptr(rax, at_tos());
   __ movl(rcx, at_tos_p1()); // index
+#endif
   // Now store using the appropriate barrier
   do_oop_store(_masm, element_address, rax, IN_HEAP_ARRAY);
   __ jmp(done);


> [...]
>
> regards,
>
>
> Andrew Dinn
> -----------
> Senior Principal Software Engineer
> Red Hat UK Ltd
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