RFR: 8347405: MergeStores with reverse bytes order value [v5]

[Emanuel Peter]

On Fri, 10 Jan 2025 12:51:11 GMT, kuaiwei <duke at openjdk.org> wrote:

>> src/hotspot/share/opto/memnode.cpp line 3044:
>> 
>>> 3042:     shift_out = 0;
>>> 3043:     return true;
>>> 3044:   }
>> 
>> Can you tell me why you added this?
>
> When I debug a case, I found a base node is a LoadNode, and the rest shift nodes are derived from it. Because the LoadNode is not recognized as a shift node, all of them can not be merged.  Here I parse node with Int or Long type as "base << 0".

Ah, I see. Can you add a comment in the code for that?
`// (base << 0)`

Actually, I was wondering why we did not discover this before....
And found this code:

  Node const* base_n1;
  jint shift_n1;
  if (n1 == base_n2) {
    // n1 = base = base >> 0
    base_n1 = n1;
    shift_n1 = 0;

Do we still need this, or could we now remove that section with your change here? Just don't want to patternmatch the same in multiple places if not necessary ;)

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PR Review Comment: https://git.openjdk.org/jdk/pull/23030#discussion_r1921912026