Fix string type inconsistency: standardize on i8* and remove struct-b…

[dev-m03]

Pull Request description

This PR fixes a type inconsistency in the LLVM IR builder related to string handling.

Previously, a struct-based STRING_TYPE ({ i32, i8* }) existed in the type system, but all actual string operations in the codebase (concatenation, comparison, casts, puts, function arguments and returns) were already using plain i8*. This created a mismatch between the declared type model and the real LLVM IR being generated.

This change removes the unused struct-based string type and standardizes the string representation across the entire IR builder to i8* (C-style null-terminated char pointer), aligning the type system with the existing implementation.

No logic or behavior was changed — only type consistency was corrected.

[dev-m03]

@yuvimittal
The main/linter CI failure appears unrelated to this change. The job fails during dependency installation with a Python 3.13 / pip metadata error (Bad metadata entry 'version' while uninstalling sniffio). This occurs before tests run and seems to be an environment issue rather than a code issue.
Please check if this is due to CI infra issue or not?

[github-actions]

OSL ChatGPT Reviewer

NOTE: This is generated by an AI program, so some comments may not make sense.

src/irx/builders/llvmliteir.py

• High risk: get_data_type("string"/"utf8string") now returns i8* instead of the previous length+ptr struct. This is a breaking ABI/behavior change and can introduce correctness and safety bugs (null-termination assumptions, OOB reads, O(n) length scans). If intentional, please document and ensure all producers/consumers were migrated; otherwise, restore the struct or gate behind a feature flag (L.132).

• Material bug risk: constructing ir.IntType(8).as_pointer() ad hoc risks subtle type mismatches elsewhere and makes equality checks brittle. Define and reuse a single canonical C-string type.
  Suggested change (add field) (L.90):
  def CSTRING_TYPE(self) -> ir.types.Type:
  """Canonical C string type (char*)"""
  Suggested init (L.212):
  def initialize(self) -> None:
  """Initialize LLVM types"""
  self._llvm.CSTRING_TYPE = ir.IntType(8).as_pointer()
  Then use self._llvm.CSTRING_TYPE in get_data_type and all string helper signatures (L.132, L.1614, L.1630, L.1645, L.1659).

• Robustness: when reusing existing declarations via get_global, validate the signature matches the expected FunctionType to avoid silent mismatches.
  Suggested helper (place near the string helpers) (L.1608):
  def _get_or_declare(self, name: str, ftype: ir.FunctionType) -> ir.Function:
  """Return function with exact expected signature, or raise on mismatch"""
  existing = self._llvm.module.globals.get(name)
  if existing:
  if not isinstance(existing, ir.Function) or existing.function_type != ftype:
  raise ValueError(f"Mismatched declaration for {name}")
  return existing
  return ir.Function(self._llvm.module, ftype, name)

• Minor but correctness-affecting: In cast handling, avoid constructing new IntType each time; use the canonical CSTRING_TYPE for the pointee check to prevent accidental mismatches (L.2204).
  Suggested change (L.2204):
  def _is_cstring(self, t: ir.types.Type) -> bool:
  """Check if type is a canonical C string (char*)"""
  return isinstance(t, ir.PointerType) and t.pointee == self._llvm.CSTRING_TYPE.pointee

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