RFR: 8283726: x86_64 intrinsics for compareUnsigned method in Integer and Long [v3]

[Jatin Bhateja]

On Wed, 22 Jun 2022 03:01:36 GMT, Quan Anh Mai <duke at openjdk.org> wrote:

>> Hi,
>> 
>> This patch implements intrinsics for `Integer/Long::compareUnsigned` using the same approach as the JVM does for long and floating-point comparisons. This allows efficient and reliable usage of unsigned comparison in Java, which is a basic operation and is important for range checks such as discussed in #8620 .
>> 
>> Thank you very much.
>
> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   add comparison for direct value of compare

src/hotspot/cpu/x86/x86_64.ad line 13027:

> 13025: // Manifest a CmpU result in an integer register.  Very painful.
> 13026: // This is the test to avoid.
> 13027: instruct cmpU3_reg_reg(rRegI dst, rRegI src1, rRegI src2, rFlagsReg flags)

Do you plan to add 32 bit support?
Integer pattern can be moved to common file x86.ad and 64 pattern can handled in 32/64 bit AD files.

src/hotspot/cpu/x86/x86_64.ad line 13043:

> 13041:     __ cmpl($src1$$Register, $src2$$Register);
> 13042:     __ movl($dst$$Register, -1);
> 13043:     __ jccb(Assembler::below, done);

By placing compare adjacent to conditional jump in-order frontend can trigger macro-fusion. 
Kindly refer section 3.4.2.2 of Intel's optimization manual.

src/hotspot/cpu/x86/x86_64.ad line 13095:

> 13093:     __ cmpq($src1$$Register, $src2$$Register);
> 13094:     __ movl($dst$$Register, -1);
> 13095:     __ jccb(Assembler::below, done);

Same as above.

src/hotspot/share/opto/subnode.hpp line 185:

> 183:   }
> 184:   virtual int Opcode() const;
> 185:   virtual uint ideal_reg() const { return Op_RegI; }

Value routine to handle constant folding.

src/hotspot/share/opto/subnode.hpp line 247:

> 245:     init_class_id(Class_Sub);
> 246:   }
> 247:   virtual int Opcode() const;

In-lining may connect the inputs to constant, hence a Value routine may be useful here.

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PR: https://git.openjdk.org/jdk/pull/9068