[PATCH] D132285: [LoongArch] Implement ABI lowering

[Lu Weining via Phabricator via cfe-commits]

SixWeining created this revision.
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Reuse most of RISCV's implementation with several exceptions:

On RISCV, integer scalars passed in registers have signext/zeroext
when promoted, but are anyext if passed on the stack. This is defined
in early RISCV ABI specification. But after this change [1], integers
should also be signext/zeroext if passed on the stack. So I think
RISCV's ABI lowering should be updated [2].

In LoongArch ABI spec, we can see that integer scalars narrower than
GRLEN bits are zero/sign-extended no matter passed in registers or on
the stack.

There is another difference worth mentioning is that `char` is signed
by default on LoongArch while it is unsigned on RISCV.

This patch also adds `_BitInt` type support to LoongArch and handle it
in LoongArchABIInfo::classifyArgumentType.

[1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/commit/cec39a064ee0e5b0129973fffab7e3ad1710498f
[2] https://github.com/llvm/llvm-project/issues/57261

Depends on D130255 <https://reviews.llvm.org/D130255>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D132285

Files:
  clang/lib/Basic/Targets/LoongArch.h
  clang/lib/CodeGen/TargetInfo.cpp
  clang/test/CodeGen/LoongArch/abi-lp64d.c
  clang/test/CodeGen/ext-int-cc.c
  clang/test/CodeGenCXX/LoongArch/abi-lp64d-struct-inherit.cpp

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