Questions about APX ABI

[huoyaoyuan]

I see latest MSVC changelog mentions ABI of APX: https://devblogs.microsoft.com/cppblog/msvc-build-tools-version-14-52-release-candidate-now-available/#x64-and-x86

APX support now spans the ABI, assembler, disassembler, and debugging tools. R30 and R31 are nonvolatile, register assignment treats them as killed across setjmp, MASM and the disassembler handle eligible extended-register encodings, and DIA reads APX register context.

The words claims that R30/R31 are non-volatile. In current JIT code, all the APX eGPRs are volatile:

runtime/src/coreclr/jit/targetamd64.h

Line 289 in 46cd67b

#define REG_VAR_ORDER_CALLEE_TRASH REG_EAX,REG_ECX,REG_EDX,REG_R8,REG_R10,REG_R9,REG_R11,REG_R16,REG_R17,REG_R18,REG_R19,REG_R20,REG_R21,REG_R22,REG_R23,REG_R24,REG_R25,REG_R26,REG_R27,REG_R28,REG_R29,REG_R30,REG_R31

What would be the final ABI of APX? What does it mean for interop and pure managed code? @dotnet/intel Can you provide some information on this?

[jkotas]

R30/R31 are non-volatile

Yes, it is finalized Windows ABI for APX, the JIT has not been updated yet.

[DeepakRajendrakumaran]

To add to @jkotas, this is a to-do tracked here as part of Unwind V3 Support(see 2b) - #134986