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

[Jie Fu]

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

-------------

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

Changes: https://git.openjdk.org/jdk/pull/11877/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11877&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8299721
  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/11877.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11877/head:pull/11877

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