Update calling conventions for wasm functions slightly #6676
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This resolves two issues from recent changes in bytecodealliance#6649: * First the s390x calling convention for wasm functions is changed back to `WasmtimeSystemV` from `Fast`. This was an accidental omission from bytecodealliance#6649 where the conclusion was that s390x will continue using a calling convention with little-endian lane order for lane arguments. The only calling convention that supports this today is `WasmtimeSystemV`, although the `Tail` calling convention will likely use it in the future as well. * Second the apple-aarch64 platform now uses the `Fast` calling convention instead of `AppleAarch64` calling convention. That convention was specified in bytecodealliance#4195 but local testing shows that is not necessary in the sense that tests all pass with the `Fast` calling convention. This means that the prior comment why the `AppleAarch64` calling convention is required is no longer accurate and in the absence of a reason not to I went ahead and switched it to `Fast`. In the near future all wasm functions will unconditionally use the `Tail` calling convention and at that time the lane order can be specified on s390x to be little-endian to satisfy all the constraints here. Additionally any unwinding directives, if necessary for aarch64, can be specified as needed.
fitzgen
approved these changes
Jul 6, 2023
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This resolves two issues from recent changes in #6649:
First the s390x calling convention for wasm functions is changed back to
WasmtimeSystemVfromFast. This was an accidental omission from Remove Wasmtime ABIs from Cranelift #6649 where the conclusion was that s390x will continue using a calling convention with little-endian lane order for lane arguments. The only calling convention that supports this today isWasmtimeSystemV, although theTailcalling convention will likely use it in the future as well.Second the apple-aarch64 platform now uses the
Fastcalling convention instead ofAppleAarch64calling convention. That convention was specified in CFI improvements to the AArch64 fiber implementation #4195 but local testing shows that is not necessary in the sense that tests all pass with theFastcalling convention. This means that the prior comment why theAppleAarch64calling convention is required is no longer accurate and in the absence of a reason not to I went ahead and switched it toFast.In the near future all wasm functions will unconditionally use the
Tailcalling convention and at that time the lane order can be specified on s390x to be little-endian to satisfy all the constraints here. Additionally any unwinding directives, if necessary for aarch64, can be specified as needed.