Add hoist_invariants() directive for semiring reductions by alexreinking · Pull Request #9190 · halide/Halide

alexreinking · 2026-07-04T02:53:22Z

This PR adds a scheduling directive similar to rfactor that hoists invariant factors according to a detected distributive (semiring) law into the write-back part of the accumulation step. This enables writing straightforward quantized kernels in the algorithm language and factoring them into efficient kernels.

This is meant to work towards optimizing quantized mat-mul and mat-vec kernels (especially those from GGML).

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 · 2026-07-04T04:06:56Z

Codecov Report

❌ Patch coverage is 84.86842% with 23 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (alexreinking/change-type@70a3120). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/Func.cpp	84.86%	8 Missing and 15 partials ⚠️

Additional details and impacted files

@@                     Coverage Diff                     @@
##             alexreinking/change-type    #9190   +/-   ##
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  Files                               ?      259           
  Lines                               ?    78797           
  Branches                            ?    19218           
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  Hits                                ?    54816           
  Misses                              ?    18223           
  Partials                            ?     5758

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abadams · 2026-08-07T19:09:14Z

+    Buffer<float> kernel(diameter);
+    kernel.set_min(-radius);
+    constexpr std::array<int, diameter> binomial_weights = {
+        1, 14, 91, 364, 1001, 2002, 3003, 3432,


Better to just use arbitrary or random numbers here, or the lack of high freqs in the output might disguise output-is-shifted-over errors.

abadams · 2026-08-07T19:09:32Z

+    }
+
+    constexpr int stride = 2;
+    constexpr int radius = 7;


Make radius much larger - 50 or 100. Make the output size smaller if that makes it take too long to run.

abadams

Sadly need to delete the separable downsample test, because it doesn't do what we hoped, but LGTM for the rest of it.

Introduce Stage::hoist_invariants(), which applies a semiring distributive law to hoist loop-invariant factors out of associative reductions. The returned intermediate accumulates the factor-free reduction over the original RDom, while the write-back applies the factor once. Support +/*, min/+, max/+, or/&&, and and/|| laws, including factors nested within associative chains. Add reusable binary-operator helpers, the Python binding, and correctness tests.

Add a quantized (int8 x int8 -> f32) mat-vec performance test targeting ARM's SDOT instruction, scheduled by composing eager_inline(), hoist_invariants(), rfactor(), and change_type(). eager_inline() folds the Wt and VecDq producers into Acc's update so their scale factors -- WtScale(i) and VecScale -- surface as explicit leaves that hoist_invariants() can then lift out of the reduction as the invariant product WtScale(i) * VecScale. rfactor() splits the now scale-free reduction by block, and change_type(Int(32)) retypes the innermost per-block dot product so CodeGen_ARM matches it to SDOT. The generated assembly contains sdot instructions, the Hoisted/PlainRfactor numerical cross-check passes, and the composed schedule is several times faster than the non-hoisting variant. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

…elf_reference A prior rebase silently merged this call site as a 3-argument Call::make() after the Function overload gained a required follow_global_wrappers parameter. This is a Func's self-reference to the rfactor intermediate, so it must not follow global wrappers, matching the other self-reference call sites. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

alexreinking requested review from abadams and shoaibkamil July 4, 2026 02:53

alexreinking added the release_notes For changes that may warrant a note in README for official releases. label Jul 4, 2026

alexreinking changed the title ~~Alexreinking/rfactor hoisting~~ Allow hoisting invariant factors in rfactor Jul 4, 2026

alexreinking marked this pull request as draft July 6, 2026 14:22

alexreinking added the dev_meeting Topic to be discussed at the next dev meeting label Jul 6, 2026

alexreinking force-pushed the alexreinking/rfactor-hoisting branch 2 times, most recently from 9e244ff to 328fd0a Compare July 20, 2026 15:28

alexreinking force-pushed the alexreinking/rfactor-hoisting branch 3 times, most recently from f2cbdc3 to f271649 Compare July 29, 2026 19:07

alexreinking changed the base branch from main to alexreinking/change-type July 29, 2026 19:07

alexreinking changed the title ~~Allow hoisting invariant factors in rfactor~~ Add hoist_invariants() directive Jul 29, 2026

alexreinking changed the title ~~Add hoist_invariants() directive~~ Add hoist_invariants() directive for semiring reductions Jul 29, 2026

alexreinking force-pushed the alexreinking/rfactor-hoisting branch from f271649 to 9660010 Compare July 29, 2026 19:33

alexreinking force-pushed the alexreinking/rfactor-hoisting branch from 9660010 to 12834ac Compare July 29, 2026 19:59

alexreinking mentioned this pull request Jul 30, 2026

Add eager_inline() directive for schedule-time inlining #9256

Merged

4 tasks

alexreinking force-pushed the alexreinking/rfactor-hoisting branch from 12834ac to d049c0c Compare July 30, 2026 12:45

alexreinking force-pushed the alexreinking/rfactor-hoisting branch from d049c0c to 460d780 Compare July 30, 2026 13:35

alexreinking force-pushed the alexreinking/rfactor-hoisting branch 2 times, most recently from 8f48f71 to 25be6cb Compare July 30, 2026 15:20

alexreinking force-pushed the alexreinking/rfactor-hoisting branch 3 times, most recently from a26996d to 9787945 Compare July 30, 2026 16:57

alexreinking force-pushed the alexreinking/rfactor-hoisting branch from 7d6e34b to c8dc9c6 Compare August 4, 2026 22:13

alexreinking force-pushed the alexreinking/rfactor-hoisting branch from c8dc9c6 to 7e94a45 Compare August 7, 2026 07:52

abadams reviewed Aug 7, 2026

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alexreinking force-pushed the alexreinking/rfactor-hoisting branch from 7e94a45 to 7a912b0 Compare August 8, 2026 19:31

alexreinking force-pushed the alexreinking/rfactor-hoisting branch 3 times, most recently from 519d92d to bd73073 Compare August 8, 2026 20:37

alexreinking force-pushed the alexreinking/rfactor-hoisting branch from bd73073 to 0c7be4f Compare August 9, 2026 14:09

alexreinking force-pushed the alexreinking/rfactor-hoisting branch from 0c7be4f to 1a19df0 Compare August 9, 2026 14:10

abadams approved these changes Aug 10, 2026

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alexreinking force-pushed the alexreinking/rfactor-hoisting branch 2 times, most recently from e80fe7d to 3cbcddf Compare August 10, 2026 21:01

alexreinking and others added 5 commits August 13, 2026 10:23

Refactor SubstituteSelfReference

34068e0

Add RFactorProjection and update rfactor() implementation

7d02eda

Add TODO for hoisting tuple-sums

75a0dd4

alexreinking force-pushed the alexreinking/rfactor-hoisting branch from 3cbcddf to fb002b3 Compare August 13, 2026 14:23

alexreinking force-pushed the alexreinking/rfactor-hoisting branch from fb002b3 to e0bc603 Compare August 13, 2026 14:25

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Add hoist_invariants() directive for semiring reductions - #9190

Add hoist_invariants() directive for semiring reductions#9190
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