RFR: 8282204: Use lea instructions for arithmetic operations on x86_64 [v11]

[Quan Anh Mai]

On Sat, 12 Mar 2022 00:54:41 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   reviews
>
> src/hotspot/cpu/x86/assembler_x86.cpp line 2393:
> 
>> 2391:   InstructionMark im(this);
>> 2392: #ifdef _LP64
>> 2393:   emit_int8(0x67); // addr32
> 
> By removing the 0x67 prefix, we are now doing 64 bit computation even for 32 bit inputs. Wouldn't this cause partial register stalls (see section 3.5.2.4 end of section).

Partial writes only happen with data size smaller than 32-bit since 32-bit writes are zero-extended to full register width. As a result, there should be no additional stalls here.

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PR: https://git.openjdk.java.net/jdk/pull/7560