[tuples] gimple_assign_subcode for GIMPLE_SINGLE_RHS

[Zdenek Dvorak]

Hi,

> So, what about adding a GIMPLE_COPY code?  The code would have 0
> operands and used only for its numeric value.

another possibility would be to make GIMPLE_COPY an unary operator, and
get rid of the SINGLE_RHS case altogether (of course, unlike any other
unary operator, it would not require its operand to be gimple_val, so
special handling might still be necessary at some places. but it might
be less cumbersome),

Zdenek