RFR: 8299721: [Vector API] assert in switch-default of LibraryCallKit::arch_supports_vector_rotate is too weak to catch bugs

[Jatin Bhateja]

On Fri, 6 Jan 2023 07:53:27 GMT, Jie Fu <jiefu at openjdk.org> wrote:

> Hi all,
> 
> The switch-default path of LibraryCallKit::arch_supports_vector_rotate means runtime error.
> This is because `lshiftopc`@Line136 and `rshiftopc`@Line137 would be undefined if the switch-default path is taken.
> 
> 
>  115   int lshiftopc, rshiftopc;
>  116   switch(elem_bt) {
>  117     case T_BYTE:
>  118       lshiftopc = Op_LShiftI;
>  119       rshiftopc = Op_URShiftB;
>  120       break;
>  121     case T_SHORT:
>  122       lshiftopc = Op_LShiftI;
>  123       rshiftopc = Op_URShiftS;
>  124       break;
>  125     case T_INT:
>  126       lshiftopc = Op_LShiftI;
>  127       rshiftopc = Op_URShiftI;
>  128       break;
>  129     case T_LONG:
>  130       lshiftopc = Op_LShiftL;
>  131       rshiftopc = Op_URShiftL;
>  132       break;
>  133     default:
>  134       assert(false, "Unexpected type");
>  135   }
>  136   int lshiftvopc = VectorNode::opcode(lshiftopc, elem_bt);   <--- lshiftopc is undefine with the default path
>  137   int rshiftvopc = VectorNode::opcode(rshiftopc, elem_bt);   <--- rshiftopc is undefine with the default path
> 
> 
> So to prevent potential bugs, it would be better to stop and print an error msg even with release VMs, which is done by other switch-default statements in the file.
> 
> Thanks.
> Best regards,
> Jie

Rotate operation only works on integral type vectors. But its good to add a fatal msg.
Thanks!

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Marked as reviewed by jbhateja (Reviewer).

PR: https://git.openjdk.org/jdk/pull/11877