LGTM

Address @SixWeining's comments.

Address @SixWeining's commonts.

Rebase.
Similar to VLDI, the immediate operand of XVLDI is treated as a signed number.

Address @SixWeining's comments.

Fixed an error caused by intuition, thank you very much for @xen0n's prompt reminder.

Just adding some comments.

rebase

Address @xen0n's comments.

Thanks.

We have decided to keep it unchanged. Thank you, everyone.

1. Add register definition, and fix the old interface parameters.
2. Specify instruction properties.

rebase

specify instruction properties.

fix typo

Address @xen0n's comments.

There will be separate test patches in the future.

If we want to ignore empty structures, it is not enough to only modify psABI, because the current implementations of gcc and clang do not ignore empty structures in all cases. For example:

struct { struct{}; int i; }; // in this case, the empty struct is not ignored.
struct { struct{}; float f; }; // ignored.

This is the same behavior as RISC-V. While attempting to pass a struct through FPRs, the empty field is ignored. But if passing through FPR does not work and it's passed through GPRs, the empty fields are not ignored:

I think the paragraph means:

class Empty {};
int test(Empty empty, int a);

Then we should put a into a1, not a0. And we are indeed doing so.

yes. with this patch, a will be passed with a1 register.

In D151298#4367225, @xry111 wrote:

In D151298#4367215, @wangleiat wrote:

In D151298#4367163, @xry111 wrote:

Blocking this as it's a deliberate decision made in D132285.

Is there any imperative reason we must really pass the empty struct? The C++ standard only treats struct {} as size 1 for the semantics of pointer comparison. While there is no pointers to registers, ignoring it in the register calling convention will make no harm.

And AFAIK it will be an undefined behavior attempting to (mis)use the padding space of/after the empty struct to pass any information.

Our current modifications are closer to the description of Itanium C++ ABI, and we try to keep it consistent with the description of the calling convention under reasonable premise.

Hmm, could you provide a link to the section saying this in the Itanium C++ ABI?

In D151298#4367163, @xry111 wrote:

Blocking this as it's a deliberate decision made in D132285.

Is there any imperative reason we must really pass the empty struct? The C++ standard only treats struct {} as size 1 for the semantics of pointer comparison. While there is no pointers to registers, ignoring it in the register calling convention will make no harm.

And AFAIK it will be an undefined behavior attempting to (mis)use the padding space of/after the empty struct to pass any information.

LGTM

LGTM