RFR: 8347459: C2: missing transformation for chain of shifts/multiplications by constants [v5]

[Emanuel Peter]

On Fri, 7 Mar 2025 12:34:36 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Marc Chevalier has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   + comment on why not zerocon
>
> src/hotspot/share/opto/memnode.cpp line 3534:
> 
>> 3532: //  31                     8 7        0
>> 3533: // v[0..7] is meaningful, but v[8..31] is not. In this case, num_rejected_bits == 24
>> 3534: // If we do the shift left then right by 24 bits, we get:
> 
> It could be nice if you explicitly denoted the 3 cases, maybe even using some indentation for emphasis:
> 
> Case 1: conIL == conIR
> Case 2: conIL > conIR
> Case 3: conIL < conIR

It could also be nice to say what you are trying to show / prove here.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23728#discussion_r1984986704