RFR: 8261142: AArch64: Incorrect instruction encoding when right-shifting vectors with shift amount equals to the element width [v9]

[Andrew Haley]

On Tue, 23 Feb 2021 10:29:05 GMT, Dong Bo <dongbo at openjdk.org> wrote:

> Hi, @theRealAph
> 
> I've rebased the tests so that sshr/ushr/sshl/ssra/usra are accessed in one jtreg `test/hotspot/jtreg/compiler/vectorapi/TestVectorShiftImm.java`.
> Local tests by manually injected error shows all instructions are covered by the jtreg case. Suggestions?

I'm not seeing ```sra``` used anywhere.

The problem I see with the tests is that the methods are large. This causes C2 to do a lot of spilling. Also, because the resuling code is intertwined and complex, it's very hard to debug.

It would be far better to do something like this:
    void long_shift_add(long arrLongs[][], LongVector vba, LongVector vbb, int i) {
        vba.add(vbb.lanewise(VectorOperators.LSHR, 37)).intoArray(arrLongs[op], 2 * i);
        vba.add(vbb.lanewise(VectorOperators.LSHR, 64)).intoArray(arrLongs[op  + 1], 2 * i);
        vba.add(vbb.lanewise(VectorOperators.LSHR, 99)).intoArray(arrLongs[op  + 2], 2 * i);
        vba.add(vbb.lanewise(VectorOperators.LSHR, 128)).intoArray(arrLongs[op + 3], 2 * i);
        vba.add(vbb.lanewise(VectorOperators.LSHR, 157)).intoArray(arrLongs[op + 4], 2 * i);
        vba.add(vbb.lanewise(VectorOperators.LSHR, 192)).intoArray(arrLongs[op + 5], 2 * i);
    }

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PR: https://git.openjdk.java.net/jdk/pull/2472