RFR: 8266798: C1: More types of instruction can also apply LoopInvariantCodeMotion [v2]

[Nils Eliasson]

On Tue, 11 May 2021 10:43:55 GMT, Yi Yang <yyang at openjdk.org> wrote:

>> C1 only applies LoopInvariantCodeMotion for instructions whose types are Constant/ArithmeticOp/LoadField/ArrayLength/LoadIndexed. We are possible to apply this optimization for more types of instruction.
>> 
>> Candidates: NegateOp,Convert.
>> 
>> Due to the lack of verification at IR level, it is difficult to write jtreg to check if it transformed, so I can only demonstrate it with a simple program:
>> 
>> // run with -XX:+PrintValueNumbering
>> static int foo10(int t){
>>     int sum=12;
>>     for(int i=0;i<100;i++){
>>         sum += 12;
>>         sum += -t;
>>         sum += (long)t;
>>     }
>>     return sum;
>> }
>> 
>> Before:
>> 
>> [...]
>> * loop invariant code motion for short loop B1
>> processing block B1
>> Value Numbering: insert Constant i10  (size 11, entries 3, nesting 2)
>> Instruction i10 is loop invariant
>> processing block B2
>> Value Numbering: Constant i12 equal to i5  (size 11, entries 3, nesting-diff 1)
>> substitution for 12 set to 5
>> Instruction i12 is loop invariant   // only 12 is recongized
>> Value Numbering: insert Constant i20  (size 11, entries 4, nesting 2)
>> Instruction i20 is loop invariant
>> ** loop successfully optimized
>> [...]
>> 
>> After:
>> 
>> [...]
>> ** loop invariant code motion for short loop B1
>> processing block B1
>> Value Numbering: insert Constant i10  (size 11, entries 3, nesting 2)
>> Instruction i10 is loop invariant
>>   6    0    i10    100
>> processing block B2
>> Value Numbering: Constant i12 equal to i5  (size 11, entries 3, nesting-diff 1)
>> substitution for i12 set to 105
>> Instruction i12 is loop invariant
>>   11   0    i12    12
>> Instruction i14 is loop invariant
>> . 16   0    i14    -i4
>> Value Numbering: insert Convert l17  (size 11, entries 4, nesting 2)
>> Instruction l17 is loop invariant
>> . 22   0    l17    i2l(i4)
>> Value Numbering: insert Constant i20  (size 11, entries 5, nesting 2)
>> Instruction i20 is loop invariant
>>   26   0    i20    1
>> [...]
>
> Yi Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   tchar() before id()

Looks good.

-------------

Marked as reviewed by neliasso (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/3965