RFR: 8323220: Reassociate loop invariants involved in Cmps and Add/Subs [v10]

[Emanuel Peter]

On Fri, 16 Feb 2024 00:58:13 GMT, Joshua Cao <duke at openjdk.org> wrote:

>> // inv1 == (x + inv2) => ( inv1 - inv2 ) == x
>> // inv1 == (x - inv2) => ( inv1 + inv2 ) == x
>> // inv1 == (inv2 - x) => (-inv1 + inv2 ) == x
>> 
>> 
>> For example,
>> 
>> 
>> fn(inv1, inv2)
>>   while(...)
>>       x = foobar()
>>       if inv1 == x + inv2
>>            blackhole()
>> 
>> 
>> We can transform this into
>> 
>> 
>> fn(inv1, inv2)
>>   t = inv1 - inv2
>>   while(...)
>>       x = foobar()
>>       if t == x
>>            blackhole()
>> 
>> 
>> Here is an example: https://github.com/openjdk/jdk/blob/b78896b9aafcb15f453eaed6e154a5461581407b/src/java.base/share/classes/java/lang/invoke/LambdaFormEditor.java#L910. LHS `1` and RHS `pos` are both loop invariant
>> 
>> Passes tier1 locally on Linux machine. Passes GHA on my fork.
>
> Joshua Cao has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision:
> 
>  - Update test to utilize @setup method for arguments
>  - Merge branch 'master' into licm
>  - Add correctness test for some random tests with random inputs
>  - Add some correctness tests where we do reassociate
>  - Remove unused TestInfo parameter. Have some tests exit mid-loop.
>  - Merge branch 'master' into licm
>  - Small fixes and add check methods for tests
>  - reassociate_add_sub -> reassociate_add_sub_cmp
>  - Formatting and fix typo
>  - Assert for n2. Variables for n1/n2 opcode. More concise comments.
>    Overflow/random tests
>  - ... and 2 more: https://git.openjdk.org/jdk/compare/dca35b21...ad073ef2

Good work with the @Setup methods! Thanks for the work :)

test/hotspot/jtreg/compiler/loopopts/InvariantCodeMotionReassociateCmp.java line 66:

> 64:             }
> 65:             // Setup inputs to be equals sometimes to avoid uncommon traps
> 66:             inv2 = inv1;

You may want to use the `SetupInfo` instead, and make this deterministic. Just in the case where the randomness here fails in all cases - then you would not have any equal case.
Also: why can `inv1` not be zero?

test/hotspot/jtreg/compiler/loopopts/InvariantCodeMotionReassociateCmp.java line 71:

> 69:         }
> 70:         return new Object[] { inv1, inv2 };
> 71:     }

Suggestion:

    }

test/hotspot/jtreg/compiler/loopopts/InvariantCodeMotionReassociateCmp.java line 80:

> 78:         int invDiff = inv2 - inv1;
> 79:         if ((invDiff < size && returnValue != invDiff) || (invDiff
> 80:                     >= size && returnValue != size)) {

Suggestion:

        if ((invDiff <  size && returnValue != invDiff) ||
            (invDiff >= size && returnValue != size)) {

test/hotspot/jtreg/compiler/loopopts/InvariantCodeMotionReassociateCmp.java line 88:

> 86:         int invDiff = inv2 - inv1;
> 87:         if ((invDiff != 0 && returnValue != 0) || (invDiff
> 88:                     == 0 && returnValue != 1)) {

Suggestion:

        if ((invDiff != 0 && returnValue != 0) ||
            (invDiff == 0 && returnValue != 1)) {

test/hotspot/jtreg/compiler/loopopts/InvariantCodeMotionReassociateCmp.java line 179:

> 177:         int i = 0;
> 178:         for (; i < size; ++i) {
> 179:             // Reassociate to `inv1 + inv2 == i`

Suggestion:

            // Reassociate to `inv2 - inv1 == i`

Or otherwise you'd have to explain why you do the `@IR(counts = {IRNode.SUB_I, "1"})` here

test/hotspot/jtreg/compiler/loopopts/InvariantCodeMotionReassociateCmp.java line 200:

> 198:         for (; i < size; ++i) {
> 199:             // Reassociate to `inv1 + inv2 == i`
> 200:             if (i - inv2 == -inv1) {

Suggestion:

            // Reassociate to `inv2 - inv1 == i`
            if (i - inv2 == -inv1) {

test/hotspot/jtreg/compiler/loopopts/InvariantCodeMotionReassociateCmp.java line 301:

> 299:         for (; i < 500; ++i) {
> 300:             // Reassociate to `inv1 + inv2 != i`
> 301:             if (i - inv2 != -inv1) {

Suggestion:

            // Reassociate to `inv1 - inv2 != i`
            if (i - inv2 != -inv1) {

test/hotspot/jtreg/compiler/loopopts/InvariantCodeMotionReassociateCmp.java line 321:

> 319:         for (; i < size; ++i) {
> 320:             // Reassociate to `inv1 + inv2 != i`
> 321:             if (i - inv2 != -inv1) {

Suggestion:

            // Reassociate to `inv1 - inv2 != i`
            if (i - inv2 != -inv1) {

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

Changes requested by epeter (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17375#pullrequestreview-1884447939
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1492054432
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1492045838
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1492050058
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1492052093
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1492066185
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1492066675
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1492067942
PR Review Comment: https://git.openjdk.org/jdk/pull/17375#discussion_r1492068397