[TCLCORE] New Bytecode Branch Ready for Review

[Donal F. <don...@ma...>]

Hi everyone,

The branch for the new bytecodes (with the wonderfully wieldy name no-variable-width-instruction-issue) is ready for someone to give it a bit of a review.  It's quite a large one, so here's a summary:

The branch deprecates all operations that have a single byte for a jump offset, a variable index or an argument count (except for string concatenation). These are replaced with versions that use four-byte offsets/indices/counts. The affected instructions are:

  *
INST_PUSH1
  *
INST_INVOKE_STK1
  *
INST_LOAD_SCALAR1
  *
INST_LOAD_SCALAR_STK (wasn't issues by our compiler anyway)
  *
INST_LOAD_ARRAY1
  *
INST_STORE_SCALAR1
  *
INST_STORE_SCALAR_STK (another never-generated one)
  *
INST_STORE_ARRAY1
  *
INST_INCR_SCALAR1
  *
INST_INCR_ARRAY1
  *
INST_INCR_SCALAR1_IMM
  *
INST_INCR_ARRAY1_IMM
  *
INST_APPEND_SCALAR1
  *
INST_APPEND_ARRAY1
  *
INST_LAPPEND_SCALAR1
  *
INST_LAPPEND_ARRAY1
  *
INST_RETURN_CODE_BRANCH
  *
INST_TAILCALL
  *
INST_TCLOO_NEXT
  *
INST_TCLOO_NEXT_CLASS

Some of these are replaced with their existing 4-byte versions. Some have new versions (now with 4-byte args):

  *
INST_INCR_SCALAR
  *
INST_INCR_ARRAY
  *
INST_INCR_SCALAR_IMM
  *
INST_INCR_ARRAY_IMM
  *
INST_TAILCALL
  *
INST_TCLOO_NEXT
  *
INST_TCLOO_NEXT_CLASS

The replacement for INST_RETURN_CODE_BRANCH is INST_JUMP_TABLE_NUM that is a general numeric-keyed jump table. (Take note for the Tcl Compiler and TBCLoad: there's a new AUX type).

I also add these new opcodes:

  *
INST_SWAP - Swap the top two items on the stack.
  *
INST_ERROR_PREFIX_EQ - Special equality for [try/trap]
  *
INST_TCLOO_ID - Get the creation ID of an object; not common, but easy
  *
INST_DICT_PUT - [dict replace] as an opcode, simplifying [try]
  *
INST_DICT_REMOVE - [dict remove] as an opcode, to fill out the suite available
  *
INST_IS_EMPTY - access to Tcl_IsEmpty (and enhancements to bytecode optimiser to use it)

Some of the operations are made available to [tcl::unsupported::assemble]. Only the error prefix comparator isn't; that's got safety requirements on its argument that I'm not bothering to make the assembler understand.

As far as I can tell, the test suite is passing. At least on Windows and excluding some tests that don't run on this laptop.

I have not performance-tested the code!  This machine has aggressive speed-stepping forced on by institutional group policy. Sorry about that.

Donal.