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WIP: Reduce IL size of LexFilter - #20920

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T-Gro wants to merge 41 commits into
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T-Gro:t-gro-guarded-match-delivery
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WIP: Reduce IL size of LexFilter#20920
T-Gro wants to merge 41 commits into
dotnet:mainfrom
T-Gro:t-gro-guarded-match-delivery

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@T-Gro T-Gro commented Nov 3, 2026

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Description

Fixes #20632

LexFilter.hwTokenFetch runs for every token the parser reads. At 110 KB of IL it was too large for the JIT to optimize. Three changes:

  • Shared guards. A when guard reached from several decision paths is compiled once as a helper. A repeated rest-of-match is compiled once and reached by a branch in the same method. Guard order and count, active-pattern calls, mutable state, tail calls, quotations and debug points do not change.
  • Compact union switches. A union test emitted one jump-table entry per union case. The table now ends at the highest tested case, and up to four sparse cases use compare-and-branch. Dense switches do not change; no IL baselines change.
  • LexFilter cleanup. Remove the internal --tokenize-debug switch and its 102 trace statements. End the balancing-rule match so the offside rules compile once, not once per token kind.
IL bytes main this PR
hwTokenFetch 110,353 (MinOpts) 20,985 (FullOpts)
All of LexFilter 196,561 73,488 (−63%)
FSharp.Compiler.Service 5,429,307 5,166,264 (−4.8%)
FSharp.Core 616,182 575,365 (−6.6%)
Time ratio, this PR / … main .NET 10.0.403 SDK compiler
Parse 224 compiler files, .NET 11 0.60 [0.59, 0.61] 0.60 [0.59, 0.60]
Parse 224 compiler files, .NET 10 0.61 [0.60, 0.61] 0.60 [0.59, 0.61]
Typecheck a 547-line script, .NET 11 0.94 [0.91, 1.00] 0.88 [0.83, 0.93]

20 randomized fresh-process pairs per row, ReadyToRun off, ratio of medians, 95% bootstrap interval. Parse allocations are unchanged.

Checklist

  • Test cases added
  • Performance benchmarks added in case of performance changes
  • Release notes entry updated

T-Gro and others added 30 commits October 16, 2026 23:04
@T-Gro
Reduce guarded pattern-match code duplication
0ca7b4c 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Cover guarded match effects and scope across runtimes
68d0697 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Merge current main for guarded-match qualification
cb8bd39 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Fix cross-platform compiler test setup
a6ead96 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Use exact casing for SDK test import
8b2c537 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Use a local HTML sample for static argument regression
daa40de 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Merge current main before guarded-match compaction
9f56d3b 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Keep guarded-match change focused on compiler behavior
dc3efc5 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Simplify guarded-match grouping and separate test fixtures
11f9483 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Reuse quotation context checks and compact test templates
575f797 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Merge current main for guarded-match integration
048f4ad 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Share guarded-match decisions inside the original method
c07e72b 
Share repeated guards and exact residual states without a source-pattern whitelist or union-layout prediction. Preserve action ownership, source lambda boundaries, recursive initialization and original method continuations.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Fix incomplete match targets after join promotion
b75e155 
Keep the actual MatchBuilder target index with the incomplete clause instead of assuming it follows the source clauses. Reuse that clause for its bindings and guard.

Add baseline guarded-match regressions using the existing templated fixtures. Leave generic guard and action sharing, and its dependent coverage, in the upper layer.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Preserve sequence lowering across guarded-match joins
d19f938 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Integrate the local guarded-match regression layer
a1911b4 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Keep decision joins inside delegate receivers
ed7afa0 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Expand decision joins before runtime-async consumption
84b16de 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Limit decision-join parameter scopes to their bodies
97e17f9 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Preserve caller sequence points for shared guards
8a2eeba 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Factor guarded-match reference IDs and reuse test settings
1c640aa 
Keep separate typed identity tables and their growth schedules. Reuse the existing test execution helper without changing the harness's real-signature mode.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Skip match-sharing tables when promotion is disabled
023d9c7 
Keep the four typed memo tables in optional struct state. Simple matches and diagnostic passes now use the existing disabled path without constructing unused sharing caches.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Keep match-sharing state out of the CLR surface
7a123cb 
Use the existing BCL struct tuple for the four distinct dictionary roles. This retains disabled-path allocation savings without emitting a public anonymous-record type.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Avoid memo wrapper calls when match sharing is disabled
29855da 
Call the existing frontier investigator directly on disabled paths. Keep the enabled memoization path and its defensive fallback unchanged.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Keep match memo transport reference-sized
5decc95 
Use an ordinary option around the existing struct tuple. Disabled matches still allocate no memo state; recursive calls pass one reference instead of copying the wide value option. Enabled matches add one Some cell. This is a measured exception to the usual value-option preference.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Use response files for determinism test references
f785275 
Reuse the narrow correction from 84140c45554fc2a9b2ec38750af0a74508c601cc. All 31 current determinism cases pass without changing compiler behavior or test assertions.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Use a union-case test for match promotion
b089082 
Avoid structural equality in per-clause producer setup. Keep the existing allocation and join mechanisms unchanged.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Preserve attributed tail calls in decision joins
fff777c 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Allocate join locals without synthetic bindings
322df24 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Merge main into guarded-match optimization
d18aafb 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Merge main into guarded-match optimization
3dab58d
T-Gro and others added 10 commits November 3, 2026 11:42
@T-Gro
Merge main into guarded-match optimization
8ab920b
@T-Gro
Revert unrelated determinism test change
4e11dd0 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Compact guarded-match sharing diff
d2d1b09 
Reuse ExistsExpr, route promotion through the existing memo dispatcher, keep main's clause-group shape, and drop redundant annotations, comments and opens.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Compact guarded-match tests
c3046ef 
Share the context fixture for the growth case, inline single-use fixtures, and table the option matrices.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Remove the LexFilter debug trace
e1f14d7 
Drop the --tokenize-debug option, its TokenizeOption case and the 102 offside-rule trace statements.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Compile the offside rules once in hwTokenFetch
edcc10c 
The token-specific balancing clauses now end their own match, so the stack-only offside rules are no longer copied into every token branch.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Emit compact union tag switches
48effe6 
Stop the jump table at the highest tested tag, and use compare-and-branch for up to four sparse tags.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Add release notes for switch and LexFilter changes
29fb27c 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Minimize guarded-match tests
72ba061 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
Merge main
31ab5c4
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github-actions Bot commented Nov 3, 2026 •
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✅ No release notes required

@T-Gro
Link release notes to PR 20920
843987e 
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

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LexFilter's hwTokenFetch is too large for the JIT to optimize and zeroes a large stack frame for every token

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