RFR: 8332268: C2: Add missing optimizations for UDivI/L and UModI/L and unify the shared logic with the signed nodes [v8]

[Quan Anh Mai]

On Thu, 28 Nov 2024 16:23:59 GMT, theoweidmannoracle <duke at openjdk.org> wrote:

>> test/hotspot/jtreg/compiler/c2/irTests/UDivINodeIdealizationTests.java line 129:
>> 
>>> 127:             IRNode.DIV_BY_ZERO_TRAP, "1"
>>> 128:     })
>>> 129:     // Hotspot should keep the division because it may cause a division by zero trap
>> 
>> This comment is actually incorrect, the division is kept because the transformation is wrong.
>
> Which part of the transformation do you think is wrong? Do you think there might also be overflow issues and that's why it cannot be replaced with x?
> 
> (I took over this comment and test from the pre-existing test for the signed version: test/hotspot/jtreg/compiler/c2/irTests/DivINodeIdealizationTests.java.)

Yupp it can overflow, if it does not then we can totally do this transformation. I think you should remove this line from the newly added test, feel free to also remove it from the old one.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22061#discussion_r1862472357