[mono][interp] Intrinsify Vector128.Store/StoreUnsafe on wasm

[lewing]

Rebased onto main now that #132500 has merged; this is a single commit touching 3 files.

Problem

Vector128.Store and Vector128.StoreUnsafe were deliberately left out of the PackedSimd alias table because their operands are reversed relative to the method they would lower to:

PackedSimd.Store (T* address, Vector128<T> source)
Vector128.Store (this Vector128<T> source, T* destination)

The alias path only renames the method, and emit_common_simd_epilogue assigns sregs in signature order, so aliasing them as-is would have passed the vector where the destination address is expected. They therefore fell back to managed code, which routes through Unsafe.WriteUnaligned — an intrinsic the interpreter does not implement — making a documented-as-fast API roughly six times slower than the PackedSimd equivalent.

Fix

Add them to the alias table and swap the two sregs after the epilogue has run. sregs are var indices consumed positionally by MINT_SIMD_INTRINS_P_PP (interp.c:6141), so the swap is a permutation: it changes their order, not the set of vars used, leaving liveness and refcounting unaffected. It runs during IL→IR generation, before every optimization pass.

It also matches what the jiterpreter already expects — SimdIntrinsic3.StoreANY in jiterpreter-trace-generator.ts loads arg 2 as the address and arg 3 as the vector.

Store is registered for every element type (ANY), so the reorder is guarded on the shape actually being a store: two parameters, void return, and a raw address (T* or ref T) as the second parameter. The three-argument StoreUnsafe(source, destination, elementOffset) has no PackedSimd counterpart and is rejected by the parameter count, falling back to managed code as before.

System.Numerics.Vector.Store/StoreUnsafe share the identical shape and route through the same emit path, so they are lowered too. StoreAligned/StoreAlignedNonTemporal are absent from the alias table and continue to fall back to managed code — importantly, since StoreAligned has a runtime alignment check that must throw.

Alignment

interp_packedsimd_store assigned through a v128_t*, claiming 16-byte alignment that neither PackedSimd.Store nor Vector128.StoreUnsafe guarantee. It now uses wasm_v128_store, which stores through a __packed__ __may_alias__ struct. This mirrors interp_packedsimd_load128's existing use of wasm_v128_load, and matches the jiterpreter's v128_store with an alignment hint of 1. Misaligned access is well-defined at the wasm ISA level, so this was C UB rather than a live bug.

Measurements

browser-wasm under V8, interpreter, 1,000,000 iterations, 2 warmups, best of 5, same harness before and after on the same machine:

Operation	Before	After	Speedup
Vector128.Store<int>	3.243 ns	0.521 ns	6.2x
Vector128.StoreUnsafe<int>	3.253 ns	0.518 ns	6.3x
PackedSimd.Store<int> (control)	0.485 ns	0.527 ns	unchanged

The control's ~8% drift bounds run-to-run noise; the 6x is far outside it. No loop-overhead baseline is subtracted — an empty-loop control measured higher than the store loops, since the jiterpreter doesn't trace it.

Validation

• browser-wasm mono+libs Release: 0 errors, 0 warnings
• native osx-arm64 mono Release: 0 errors, 0 warnings
• System.Runtime.Intrinsics: 13024/13024 passing (13021 baseline + 3 new)
• System.Numerics.Vectors: 7449/7449 passing
• IR (MONO_VERBOSE_METHOD): simd_intrins_p_pp [74 <- 73 72], 191 — descending sregs confirm the swap; the three-argument overload still emits a managed call
• System.Numerics.Vector<T>.StoreUnsafe likewise emits simd_intrins_p_pp [19 <- 18 14], 191

Tests

Three tests covering Store, StoreUnsafe, and StoreUnsafe with an element offset, across twelve element types, at every 16-byte alignment, with guard bytes on both sides so a misplaced or oversized store is caught. The element-offset arm uses StoreUnsafe(ref *(destination - 1), elementOffset: 1) so a dropped offset argument shows up as a misplaced store. They pass on an unmodified runtime as well, so they validate behavior rather than implementation.

Note

This pull request was authored with the assistance of GitHub Copilot.

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[Copilot]

Pull request overview

This PR enables Mono interpreter SIMD lowering for Vector128.Store / Vector128.StoreUnsafe (and the analogous System.Numerics.Vector APIs) on wasm by routing them through the existing PackedSimd lowering path while correcting for the reversed operand order, and fixes the wasm store helper to avoid C UB on unaligned destinations.

Changes:

• Add Store / StoreUnsafe to the PackedSimd alias table and swap the two operand sregs after emit_common_simd_epilogue assigns them in signature order.
• Update interp_packedsimd_store to use wasm_v128_store (unaligned-safe) instead of assigning through a v128_t*.
• Add new Vector128 tests covering Store, StoreUnsafe, and StoreUnsafe with element offset across multiple element types and destination alignments.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/mono/mono/mini/interp/transform-simd.c	Enables aliasing of Store/StoreUnsafe and performs a post-epilogue sreg swap so the PackedSimd helper receives (address, vector) ordering.
src/mono/mono/mini/interp/interp-simd.c	Replaces a potentially-alignment-assuming store through v128_t* with wasm_v128_store for well-defined unaligned stores.
src/libraries/System.Runtime.Intrinsics/tests/Vectors/Vector128Tests.cs	Adds regression tests validating correct store placement and size across alignments, types, and the element-offset overload behavior.

[lewing]

/backport to release/11.0-rc1

[github-actions]

Started backporting to release/11.0-rc1 (link to workflow run)

[github-actions]

@lewing backporting to release/11.0-rc1 failed, the patch most likely resulted in conflicts. Please backport manually!

git am output

$ git cherry-pick be1c680101458a735200e68a74460919be249315Auto-merging src/libraries/System.Runtime.Intrinsics/tests/Vectors/Vector128Tests.csCONFLICT (content): Merge conflict in src/libraries/System.Runtime.Intrinsics/tests/Vectors/Vector128Tests.csAuto-merging src/mono/mono/mini/interp/interp-simd.cAuto-merging src/mono/mono/mini/interp/transform-simd.cCONFLICT (content): Merge conflict in src/mono/mono/mini/interp/transform-simd.cerror: could not apply be1c6801014... [mono][interp] Intrinsify Vector128.Store/StoreUnsafe on wasm (#132502)hint: After resolving the conflicts, mark them withhint: "git add/rm <pathspec>", then runhint: "git cherry-pick --continue".hint: You can instead skip this commit with "git cherry-pick --skip".hint: To abort and get back to the state before "git cherry-pick",hint: run "git cherry-pick --abort".hint: Disable this message with "git config set advice.mergeConflict false"
$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patchApplying: [mono][interp] Intrinsify Vector128.Store/StoreUnsafe on wasmUsing index info to reconstruct a base tree...M	src/libraries/System.Runtime.Intrinsics/tests/Vectors/Vector128Tests.csM	src/mono/mono/mini/interp/interp-simd.cM	src/mono/mono/mini/interp/transform-simd.cFalling back to patching base and 3-way merge...Auto-merging src/libraries/System.Runtime.Intrinsics/tests/Vectors/Vector128Tests.csCONFLICT (content): Merge conflict in src/libraries/System.Runtime.Intrinsics/tests/Vectors/Vector128Tests.csAuto-merging src/mono/mono/mini/interp/interp-simd.cAuto-merging src/mono/mono/mini/interp/transform-simd.cCONFLICT (content): Merge conflict in src/mono/mono/mini/interp/transform-simd.cerror: Failed to merge in the changes.hint: Use 'git am --show-current-patch=diff' to see the failed patchhint: When you have resolved this problem, run "git am --continue".hint: If you prefer to skip this patch, run "git am --skip" instead.hint: To restore the original branch and stop patching, run "git am --abort".hint: Disable this message with "git config set advice.mergeConflict false"Patch failed at 0001 [mono][interp] Intrinsify Vector128.Store/StoreUnsafe on wasmError: The process '/usr/bin/git' failed with exit code 128

Link to workflow output