Scriptcomp optimizations refactor

[mtijanic]

• Remove constant folding from the optimization lists; it's a core language feature. You can't disable it.
• Group the optimizations into groups: NONE, SAFE, AGGRESSIVE, EXPERIMENTAL
• Default to SAFE everywhere. This is just dead code elimination, which was default prior to all the compiler improvements
• Provide CLI args for -O{0..3} to pick the groups

  -O N                        Optimisation levels [default: 1]
                                0: Optimise nothing
                                1: Safe optimisations only, as used by the game and toolset
                                    +RemoveDeadCode
                                2: Aggressive optimisations; faster and smaller code size
                                    +RemoveDeadCode
                                    +RemoveDeadBranches
                                3: Experimental optimisations; untested or known to break something
                                    +RemoveDeadCode
                                    +MeldInstructions
                                    +RemoveDeadBranches

This is in response to #148 , but it only fixes it insofar that it disables the problematic behavior by default.

Testing

nwscript test corpus. Also ran manually with all four different -O options and looked at disassembly.

Changelog

Changed

• nwn_script_comp: the default optimization level has been lowered from 2 to 1***

Licence

• I am licencing my change under the project's MIT licence, including all changes to GPL-3.0 licenced parts of the codebase.

[Copilot]

Pull Request Overview

This PR refactors the script compiler optimization system by removing constant folding as an optional optimization (since it's a core language feature) and reorganizing optimizations into four distinct levels (0-3) with clearer groupings and more conservative defaults.

Key changes:

• Removes constant folding from optimization flags and makes it always enabled
• Introduces grouped optimization levels: NONE (O0), SAFE (O1), AGGRESSIVE (O2), and EXPERIMENTAL (O3)
• Changes default optimization level from 2 to 1 for safer compilation behavior

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
nwn_script_comp.nim	Updates CLI help text and adds support for new optimization levels O1 and O3
neverwinter/nwscript/native/scriptcompfinalcode.cpp	Removes force parameter from ConstantFoldNode calls to always enable constant folding
neverwinter/nwscript/native/scriptcompcore.cpp	Changes default optimization flags and removes conditional constant folding logic
neverwinter/nwscript/native/scriptcomp.h	Redefines optimization flag constants and introduces grouped optimization levels
neverwinter/nwscript/compilerapi.cpp	Updates default optimization level from EVERYTHING to AGGRESSIVE
neverwinter/nwscript/compiler.nim	Updates OptimizationFlag enum and defines new optimization level constants

[Copilot]

The bit flag value 0x00000002 is now being reused for MELD_INSTRUCTIONS after removing FOLD_CONSTANTS. Consider adding a comment explaining this change or ensuring this doesn't break binary compatibility with existing code.

Suggested change

	// Post processes generated instructions to merge sequences into shorter equivalents
	// Post processes generated instructions to merge sequences into shorter equivalents
	// Note: The bit flag value 0x00000002 was previously used for FOLD_CONSTANTS.
	// After removing FOLD_CONSTANTS, this value is now reused for MELD_INSTRUCTIONS.
	// Ensure this does not break binary compatibility with existing code or data.

[mtijanic]

No ABI requirements, can reuse these freely.

[Copilot]

The enum value for MeldInstructions has changed from 0x4 to 0x2. This could cause issues if the enum values are persisted or used in binary interfaces. Ensure this change is intentional and documented.

Suggested change

	MeldInstructions = 0x2
	MeldInstructions = 0x4