Track LLVM backend retirement and migration to Whale #93

Current status

LLVM 21 remains Wave's default native backend and is required for supported compilation, target, ABI, and release workflows. Alpha now has an opt-in Wave-to-Whale IR adapter; this does not replace LLVM's native or release coverage.

Wave intends to move native toolchain responsibilities to Whale over time and exclude LLVM from the eventual bootstrap path.

Migration scope

• Define a backend-neutral compiler-to-toolchain interface.
• Preserve target, relocation, code model, ABI, inline assembly, object, linker, and diagnostic contracts.
• Reuse target and ABI fixtures across LLVM and Whale where possible.
• Add explicit backend selection during the transition.
• Establish feature-parity and artifact-compatibility gates.
• Define the bootstrap path and supported host requirements.
• Deprecate LLVM only after Whale passes the required language, ABI, platform, and release tests.

Completion criteria

• Whale can compile the maintained Wave corpus for supported targets.
• Backend-neutral ABI fixtures, including the work tracked in Specify and validate the Wave ABI independently from the C ABI #350 and Define a backend-neutral Wave ABI fixture format #368, pass.
• Release and bootstrap workflows no longer require LLVM.
• Users receive a documented migration path.
• LLVM removal is a deliberate final step, not an intermediate breakage.

This issue records the long-term toolchain direction. Concrete migration components should be opened as focused implementation issues.

Alpha adapter progress

PR #859 introduced the Linux amd64/O0 IR-only adapter (#861). PR #860 implements checked shifts (#863), checked float-to-integer casts (#864) and format-3 reader integration (#862). Generated IR verification and guard probes do not establish native execution parity. LLVM remains the default.

Focused alpha follow-ups

• Adapt the Whale dependency and IR tests to format 4 #868 — Adapt the Whale dependency and IR tests to format 4
• Execute Wave-generated integer IR with the bounded Whale oracle #869 — Execute Wave-generated integer IR with the bounded Whale oracle
• Lower integer division and remainder in the Whale adapter #870 — Lower integer division and remainder in the Whale adapter
• Lower floating division and remainder in the Whale adapter #871 — Lower floating division and remainder in the Whale adapter
• Lower scalar compound assignments in the Whale adapter #872 — Lower scalar compound assignments in the Whale adapter
• Lower for loops with correct continue targets in Whale #873 — Lower for loops with correct continue targets in Whale
• Consume typed global scalar constants in Whale lowering #874 — Consume typed global scalar constants in Whale lowering
• Accept resolved scalar type aliases in Whale programs #875 — Accept resolved scalar type aliases in Whale programs
• Lower omitted default arguments for direct Whale calls #876 — Lower omitted default arguments for direct Whale calls
• Allow grouped void calls in Whale expression statements #877 — Allow grouped void calls in Whale expression statements
• Lower the existing char scalar type and literals in Whale #878 — Lower the existing char scalar type and literals in Whale
• Lower typed scalar pointer operations through Whale #879 — Lower typed scalar pointer operations through Whale
• Lower fixed arrays and checked indexing in Whale #880 — Lower fixed arrays and checked indexing in Whale
• Lower typed struct construction and field access in Whale #881 — Lower typed struct construction and field access in Whale
• Lower scalar integer match statements through Whale #882 — Lower scalar integer match statements through Whale
• Lower uninitialized local declarations with Whale initialization tracking #883 — Lower uninitialized local declarations with Whale initialization tracking
• Define and implement Whale lowering for Wave integers wider than 128 bits #884 — Define and implement Whale lowering for Wave integers wider than 128 bits
• Name unsupported constructs in Whale diagnostics #885 — Name unsupported constructs in Whale diagnostics
• Expose Whale target and emit-kind capability queries #886 — Expose Whale target and emit-kind capability queries
• Update README development status and add a Whale IR example #887 — Update README development status and add a Whale IR example
• Test that failed Whale multi-input lowering preserves all outputs #894 — Test that failed Whale multi-input lowering preserves all outputs
• Report Whale verification resource limits separately from internal errors #895 — Report Whale verification resource limits separately from internal errors