RFR: 8282204: Use lea instructions for arithmetic operations on x86_64 [v10]

[Sandhya Viswanathan]

On Fri, 4 Mar 2022 08:29:40 GMT, Quan Anh Mai <duke at openjdk.java.net> wrote:

>> Hi,
>> 
>> This patch adds several matching rules for x86_64 backend to use `lea` instructions for several fused arithmetic operations. Also, `lea`s don't kill flags and allow different `dst` and `src`, so it is preferred over `sll` if possible, too. 
>> 
>> Thank you very much.
>
> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove unreached rules

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).

src/hotspot/cpu/x86/x86_64.ad line 7527:

> 7525:   predicate(VM_Version::supports_fast_2op_lea());
> 7526:   match(Set dst (AddI base (LShiftI index scale)));
> 7527:   match(Set dst (AddI (LShiftI index scale) base));

I think the commutativity is automatically handled by adlc.

src/hotspot/cpu/x86/x86_64.ad line 7699:

> 7697:   predicate(VM_Version::supports_fast_2op_lea());
> 7698:   match(Set dst (AddL base (LShiftL index scale)));
> 7699:   match(Set dst (AddL (LShiftL index scale) base));

commutativity is automatically handled by adlc.

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