Need to sync GC objects to stack only during atomic GC phase.
Need to setup a proper frame structure only for calling finalizers.
Force an exit to the interpreter and let it handle the uncommon cases.
Finally solves the "NYI: gcstep sync with frames" issue.
Add 64 bit lightuserdata handling. Keep the tagged 64 bit value.
Allocate/save/restore 64 bit spill slots for 64 bit lightuserdata.
Fix code generation for 64 bit loads/stores/moves/compares.
Fix code generation for stack pointer adjustments.
Add fixed spill slot definitions for x64. Reduce reserved spill slots.
Disable STRREF + ADD fusion in 64 bit mode (avoid negative 32 bit ofs).
Drop call gates. Use function headers, dispatched like bytecodes.
Emit BC_FUNCF/BC_FUNCV bytecode at PC 0 for all Lua functions.
C functions and ASM fast functions get extra bytecodes.
Modify internal calling convention: new base in BASE (formerly in RA).
Can now use better C function wrapper semantics (dynamic on/off).
Prerequisite for call hooks with zero-overhead if disabled.
Prerequisite for compiling recursive calls.
Prerequisite for efficient 32/64 bit prototype guards.
Spilling a weak ref forces a spill slot, but omits the restore.
Spill slots for snapshot refs override the register, anyway.
Marking snapshot refs weak avoids pointless restores.
Typically reduces storage overhead for snapshot maps by 60%.
The extensible format is a prerequisite for the next redesign steps:
Eliminate IR_FRAME and implement return-to-lower-frame.
All upvalue objects hold a disambiguation hash value now.
It's built from the parent prototype and the slot number.
Different hash values imply the upvalues cannot alias.
Same hash values don't imply anything (collision or different closures).
Upvalue disambiguation makes use of a reduced hash due to IR contraints.
Compile math.sinh(), math.cosh(), math.tanh() and math.random().
Compile various io.*() functions.
Drive the GC forward on string allocations in the parser.
Improve KNUM fuse vs. load heuristics.
Add abstract C call handling to IR.
