about Calling Convention about riscv-elf-psabi-doc HOT 5 CLOSED

This was cross posted to both riscv-gcc #155 and riscv-elf-psabi-doc #91.

No, the gcc -fipa-sra option is not violating the ABI. There are multiple ways to look at this.

1. The ABI documents the external interface to an object file. A compiler is free to choose a different interface for functions internal to an object file.
2. The compiler is changing the function type signature, from one with a struct arg to one with multiple scalar args, and then using the standard ABI on the new type signature.

Either way you look at this, it is invisible to the programmer, as the compiler ensures that everything is correct, and emits appropriate DWARF2 debug info to make the new function type look like the old one.

from riscv-elf-psabi-doc.

This was cross posted to both riscv-gcc #155 and riscv-elf-psabi-doc #91.

No, the gcc -fipa-sra option is not violating the ABI. There are multiple ways to look at this.

1. The ABI documents the external interface to an object file. A compiler is free to choose a different interface for functions internal to an object file.
2. The compiler is changing the function type signature, from one with a struct arg to one with multiple scalar args, and then using the standard ABI on the new type signature.

Either way you look at this, it is invisible to the programmer, as the compiler ensures that everything is correct, and emits appropriate DWARF2 debug info to make the new function type look like the old one.

this means that if the function is local, you can not follow the calling convention at all. as long as the program is correct, the compiler can decide how to use all the registers, right?

example:
so if the function is local, it is detected in advance that the number of CALLEE registers used in the called function is less than the total number of hardware CALLEE registers, the compiler may also use CALLEE registers for function parameter passing?

from riscv-elf-psabi-doc.

so if the function is local, it is detected in advance that the number of CALLEE registers used in the called function is less than the total number of hardware CALLEE registers, the compiler may also use CALLEE registers or temporary registers for function parameter passing?

Yeah, compiler might use other than a0-a7 to pass register, IIRC it will happen in LLVM for local functions.

from riscv-elf-psabi-doc.

so if the function is local, it is detected in advance that the number of CALLEE registers used in the called function is less than the total number of hardware CALLEE registers, the compiler may also use CALLEE registers or temporary registers for function parameter passing?

Yeah, compiler might use other than a0-a7 to pass register, IIRC it will happen in LLVM for local functions.

has the 8.0 version of the latest release of LLVM been implemented? or included in the 9.0 version of the implementation plan

from riscv-elf-psabi-doc.

so if the function is local, it is detected in advance that the number of CALLEE registers used in the called function is less than the total number of hardware CALLEE registers, the compiler may also use CALLEE registers or temporary registers for function parameter passing?

Yeah, compiler might use other than a0-a7 to pass register, IIRC it will happen in LLVM for local functions.

has the 8.0 version of the latest release of LLVM been implemented? or included in the 9.0 version of the implementation plan

8.0 includes substantial RISC-V support, but it is not compiled by default (we are still an "experimental" backend). We intend to become non-experimental in the 9.0 release cycle.

from riscv-elf-psabi-doc.