tqchen opened a new pull request, #19638:
URL: https://github.com/apache/tvm/pull/19638
## Summary
Phase out `src/arith/scalable_expression.{h,cc}`. The arith layer no longer
attempts to prove anything about scalable vectors — proofs that depended on
`Target::Current()` are removed. Scalable vectors remain a first-class concept;
arith just doesn't reason about their lengths.
## Use-site summary
Only 16 call sites total across 7 symbols (9 live, 7 proof-related).
| Symbol | Live callers (kept) | Proof callers (deleted) | New home |
|---|---|---|---|
| `ExtractVscaleFactor` | 4 × `arith/rewrite_simplify.cc` + 2 ×
`tirx/ir/expr.cc` | — | file-local in each |
| `IsVScaleCall` | 1 × `tirx/op/op.cc` + 1 ×
`tirx/transform/vectorize_loop.cc` | — | inline at use sites |
| `ContainsVscaleCall` | 4 × `arith/rewrite_simplify.cc` + 1 ×
`s_tir/schedule/ir_comparator.cc` | — | inline at use sites |
| `TargetHasVLA` | 2 × `tirx/transform/vectorize_loop.cc` | analyzer.cc +
const_int_bound.cc | local in vectorize_loop.cc |
| `GetVScaleValues` | 1 × `target/llvm/codegen_aarch64.cc` | analyzer.cc +
const_int_bound.cc | inlined at codegen_aarch64 |
| `CanProveVscaleExpressionFromKnownValues` | — | analyzer.cc | DELETE |
| `SubstituteVScaleWithKnownValue` | — | internal only | DELETE |
## Changes (6 commits)
1. Move `ExtractVscaleFactor` to file-local anonymous-namespace helpers in
`rewrite_simplify.cc` and `tirx/ir/expr.cc`. Function is small; per-file
duplication is cleaner than a shared header.
2. Inline `IsVScaleCall` / `ContainsVscaleCall` / `TargetHasVLA` at call
sites (1-3 line predicates, anonymous-namespace per consumer `.cc`).
3. Drop the scalable-vector proof scaffolding from `arith/analyzer.cc`
(substitution-proof loop) and `arith/const_int_bound.cc` (vscale branch).
`vscale()` calls fall back to `Everything()` — no special bound narrowing.
4. Delete `scalable_expression.{h,cc}`. Inline the `GetVScaleValues` body at
`codegen_aarch64.cc` (computes `max_val = vector_width / 8` floor-rounded to a
power of two for the LLVM `vscale_range` attribute).
5. Mark `pytest.mark.xfail` on 19 tests that relied on the deleted
substitution-proof loop.
6. `pre-commit` line-length cleanup.
## Compatibility / intentional regression
This is a hard break for any consumer of the deleted symbols. They were
already in a private header (`src/arith/scalable_expression.h`, not under
`include/`).
19 tests that proved vscale-bearing inequalities on SVE / RVV are xfailed.
The proofs were target-dependent and the new policy is that arith does not
attempt them.
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