Implement the Wasm `simd` proposal

[Robbepop]

This is about adding support for the simd Wasm proposal.

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The simd Wasm proposal has been stabilized (Phase 5) since a long time now. Many Wasm producers already can produce simd capable Wasm binaries and it is likely to gain even more traction.

Wasmi originally did not intend to support simd and was hoping for an eventual uptake of the alternative flexible-vectors Wasm proposal. However, it seems unlikely at this point that the alternative design will see significant development in the near to medium future.

Having simd support in wasmi is the final missing Wasm proposal required to make Wasmi Wasm 2.0 compatible which would be great for advertisement. Obviously, simd users could use Wasmi. In some past tests we actually saw decreased file sizes by using simd proposal when generating Wasm, so it might also have a nice side benefit. Especially Wasm based game engines that rely on Wasmi might find simd support very useful.

Due to the massive size of the Wasm simd proposal it will be put behind a crate feature flag simd. This is important for users who do not need simd support as this will significantly impact Wasmi compile time and Wasm execution performance as well as memory usage during Wasm execution.

Subtasks

• Prepare Wasmi for efficient handling of 128-bit registers #1392
• wasmi_core: add support for the Wasm simd proposal #1395
• wasmi_ir: add support for the Wasm simd proposal #1409
• Fix compile time regression for wasmi_ir crate #1412
• Add Wasm simd proposal's official Wasm spec testsuite tests #1413
• Fix wasmi_core's no_std build when simd is enabled #1414
• Add wasmi Wasm simd proposal support skeleton #1415
• Do _not_ visit Wasm relaxed-simd proposal operators in translation #1416
• Add Val[Type]::V128 to Wasmi crates #1418
• Add support for V128 to wasmi_wast crate #1419
• Fix VisitSimdOperator trait propagation in Wasmi translation #1420
• Add support for most Wasm simd instructions to the wasmi crate #1421
• Implement SIMD comparison instruction translation and execution #1422
• Fix some SIMD instruction execution issues #1423
• Implement SIMD replace_lane instruction translation and execution #1424
• Implement v128.storeN_lane SIMD instruction translation and execution #1425
• Implement translation and execution of some SIMD load instructions #1426
• Implement translation and execution for v128.loadN_lane instructions #1427
• Enable Wasm simd fuzzing #1428
• Fix some SIMD bugs found by fuzzing #1429
• Update README and document Wasmi crate features #1430

[ZheniaZuser]

Will it be possible to deterministically execute wasm with simd?

[Robbepop]

@ZheniaZuser yes, since the Wasm simd proposal is deterministic it will be determinstic when implemented in Wasmi. Note though that the extensional Wasm relaxed-simd proposal contains some non-deterministic op-codes.

[ZheniaZuser]

So, relaxed one will not be deterministic in Wasmi? (Perhaps this could be done with emulation of relaxed-simd ?)

[Robbepop]

So, relaxed one will not be deterministic in Wasmi? (Perhaps this could be done with emulation of relaxed-simd ?)

I cannot really say that because I have not yet taken a deep look at it. What I can say that everything that can be implemented deterministically, will be.

[Robbepop]

Today I merged #1392 which allows for 128-bit register cells. With this we should be able to implement Wasm simd for Wasmi now.

[Robbepop]

I just merged #1409 which addds Wasmi IR instruction variants for all the Wasm simd proposal instructions. This enables to start with the Wasm to Wasmi bytecode translation of all the Wasm simd proposal instructions. However, first we need to fix a compilation time regression: #1409 (comment)

[Robbepop]

Update: I am nearly done implementing Wasm simd proposal for Wasmi. The only remaining SIMD instructions to implement are most of the load and store SIMD instruction translation and execution. Definition and implementation is already done for them.

[Robbepop]

With #1427 all SIMD related Wasm spec testsuite tests are now passing. 🥳
This does not necessarily mean that Wasmi implements the entire Wasm simd proposal flawlessly, yet. Intense fuzz testing needed for some time to draw conclusions.

[Robbepop]

The Wasm simd proposal has been implemented and will be available to users in the next Wasmi release of v0.43.0.