RFR: change verifier for withfield to check that value types match instead of doing an is_assignable check

[David Simms]

Looks good Harold, thanks for the comments in the tests (helps with the 
raw bytecode)

On 27/03/18 15:59, harold seigel wrote:
> Hi,
>
> Please review this small verifier change for the withfield opcode to 
> check that the reference on the stack is the same as the class pointed 
> to by withfield's constant pool fieldref.  Previously, the verifier 
> did an is_assignable_from() check, but this potentially caused some 
> class loads and returned true if the fieldref's class was 
> java.lang.Object.
>
> Open Webrev: 
> http://cr.openjdk.java.net/~hseigel/valueTypes_lworld.wfield.jlo/webrev/index.html
>
> Here's a sample error message emitted when the two references are not 
> the same:
>
>    Exception in thread "main" java.lang.VerifyError: Bad value type on
>    operand stack in withfield
>    Exception Details:
>       Location:
>         wthFldBadFldRef2.makeValue(I)LwthFldBadFldRef2; @6: withfield
>       Reason:
>         Type 'otherVT' (current frame, stack[0]) and type
>    'wthFldBadFldRef2' (constant pool 2) must be identical value types.
>       Current Frame:
>         bci: @6
>         flags: { }
>         locals: { integer, 'otherVT' }
>         stack: { 'otherVT', integer }
>       Bytecode:
>         0000000: cb00 1b4c 2b1a cc00 024c 2bb0
>
> This webrev was tested with hotspot JTReg tests and multiple JDK JTReg 
> tests.
>
> Thanks, Harold
>
>