Separate the language Type from the ABI halide_type_t

[alexreinking]

• ABI halide_type_t drops lanes -> {code, bits, reserved} (still 4 bytes; halide_buffer_t layout unchanged). Halide::Type is decoupled and stores its own fields; must be explicitly erased with as_abi (asserts scalar), Trace event/packet carry their own lanes.
• Halide::Type is reduced to 8 bytes: the handle_type pointer is replaced by a 4-byte index into a process-wide handle-type intern table.
• The IR matcher / constant folder uses Halide::Type directly; This keeps handle C++-type metadata fidelity through matcher reconstruction.

One open problem remains for future work due to lack of testing:

• d3d12 buffer element types treated as scalar (multi-channel texture format selection is a follow-up). @slomp maybe you know something about this? I don't think it's tested at all.

Fixes #9202
Fixes #9203

Breaking changes

The Type and halide_type_t arguments have been significantly reworked. This is both an ABI and an API break.

Checklist

• Tests added or updated (not required for docs, CI config, or typo fixes)
• Documentation updated (if public API changed)
• Python bindings updated (if public API changed)
• Benchmarks are included here if the change is intended to affect performance.
• Commits include AI attribution where applicable (see Code of Conduct)

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 72 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@5476bf3). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/IRMatch.h	87.23%	16 Missing and 2 partials ⚠️
src/Type.cpp	67.50%	5 Missing and 8 partials ⚠️
src/runtime/HalideRuntime.h	45.83%	9 Missing and 4 partials ⚠️
src/Type.h	81.39%	4 Missing and 4 partials ⚠️
src/Callable.h	64.28%	2 Missing and 3 partials ⚠️
src/CodeGen_LLVM.cpp	16.66%	2 Missing and 3 partials ⚠️
src/CodeGen_C.cpp	85.18%	1 Missing and 3 partials ⚠️
src/CPlusPlusMangle.cpp	92.00%	1 Missing and 1 partial ⚠️
src/WasmExecutor.cpp	83.33%	2 Missing ⚠️
src/Buffer.h	66.66%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9205   +/-   ##
=======================================
  Coverage        ?   70.32%           
=======================================
  Files           ?      255           
  Lines           ?    78928           
  Branches        ?    18879           
=======================================
  Hits            ?    55504           
  Misses          ?    17874           
  Partials        ?     5550           

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[slomp]

d3d12 buffer element types treated as scalar

IIRC, the no-scalar buffer formats would only be applicable in specific instances of vectorized inputs/outputs.
I do remember testing the behavior waaay back when, but I don't think actual tests were added to the repository.

[alexreinking]

IIRC, the no-scalar buffer formats would only be applicable in specific instances of vectorized inputs/outputs.
I do remember testing the behavior waaay back when, but I don't think actual tests were added to the repository.

I wonder whether they actually work on main... In any case, we'll need a Type-driven (rather than halide_type_t-driven) way of communicating that information to D3D12.

[alexreinking]

Rebased and pushed to include #9108 in CI. The only other failure was a very mysterious case in HVX. It's complaining about an incorrect function signature for qurt_hvx_lock. This was first corrected in #7601 and then later reverted in #7614.

If it happens again, I'll investigate further.

[alexreinking]

All green now.

edit: some filesystem issue on win-worker-3