arm64ec support?

[p0nce]

On Windows the x86_64 and arm64ec are made to interoperate (each can host the other in the same process).
arm64ec may well be there for a long time.

[JohanEngelen]

Some implementation hints:

• triple: arm64ec-windows-msvc. LLVM has a bool Triple::isWindowsArm64EC() function.
• quote from clang PR: For the Arm64EC ABI, ARM64 functions have an alternate name. For C code, this name is just the original name prefixed with "#". For C++ code, we stick a "$$h" modifier in the middle of the mangling. https://reviews.llvm.org/D125418
• ABI conventions: https://github.com/MicrosoftDocs/cpp-docs/blob/main/docs/build/arm64ec-windows-abi-conventions.md
• some more info: https://learn.microsoft.com/en-us/windows/arm/arm64ec-abi
• entry and exit thunks... don't know how much we have to do vs. what LLVM already does for us...

[kassane]

extra reference about LLD support [WiP]:

• [lld-link][arm64ec] error: msvcrtd.lib: machine type arm64 conflicts with arm64ec llvm/llvm-project#113658 (comment)

[p0nce]

It seems to me D compilers will need a way to separate arm64 (version identifier AArch64 from arm64ec (could be AArch64ec ?)

[JohanEngelen]

It seems to me D compilers will need a way to separate arm64 (version identifier AArch64 from arm64ec (could be AArch64ec ?)

Yes indeed. The precedent of ABI version identifiers seems to follow ARCH_ABINAME naming, e.g. ARM_HardFloat. https://dlang.org/spec/version.html#predefined-versions So maybe AArch64_ARM64CE.