RFR: 8271589: fatal error with variable shift count integer rotate operation.

[Jatin Bhateja]

On Mon, 2 Aug 2021 16:17:10 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Problem seen on targets which do not support variable vector shifts, in such a case vector rotation node inferred by auto-vectorizer are not disintegrable into LeftShift/RightShift and Or operations.
>
> src/hotspot/share/opto/superword.cpp line 2491:
> 
>> 2489:         Node* in1 = low_adr->in(1);
>> 2490:         Node* in2 = p->at(0)->in(2);
>> 2491:         assert(in2->bottom_type()->isa_int(), "Shift must always be an int value");
> 
> Why you removed the assert? What other types can be seen here?
> The following code (specifically `in2->get_int()`) will fail if it is not Integer type.

The shift is either an int value or a vector of an int value. If it's a vector !in2->is_Con() will make the condition true and no need to check for get_int due to short-circuiting.

> src/hotspot/share/opto/vectornode.cpp line 1163:
> 
>> 1161:   } else if (VectorNode::is_invariant_vector(cnt)) {
>> 1162:     // Scalar variable shift, handle replicates generated by auto vectorizer.
>> 1163:     assert(VectorNode::is_invariant_vector(cnt), "Broadcast expected");
> 
> This assert is not needed anymore since you already checked for this case.

Will remove this before checking in the final version of the patch.

> Is this case from Vector API? I think in Java we can have only Int type for shifts.

This is to handle long rotates, SLP will insert a ConvI2L before broadcasting shift value into a long vector. In case of constant int value, ConvI2L::Value will create a constant of TypeLong and which is what is being handled here.

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PR: https://git.openjdk.java.net/jdk/pull/4956