[RISCV][VLS] Support RISCV VLS calling convention (#100346)

This patch adds a function attribute `riscv_vls_cc` for RISCV VLS
calling
convention which takes 0 or 1 argument, the argument is the `ABI_VLEN`
which is the `VLEN` for passing the fixed-vector arguments, it wraps the
argument as a scalable vector(VLA) using the `ABI_VLEN` and uses the
corresponding mechanism to handle it. The range of `ABI_VLEN` is [32,
65536],
if not specified, the default value is 128.

Here is an example of VLS argument passing:
Non-VLS call:
```
  void original_call(__attribute__((vector_size(16))) int arg) {}
=>
  define void @original_call(i128 noundef %arg) {
  entry:
    ...
    ret void
  }
```
VLS call:
```
  void __attribute__((riscv_vls_cc(256))) vls_call(__attribute__((vector_size(16))) int arg) {}
=>
  define riscv_vls_cc void @vls_call(<vscale x 1 x i32> %arg) {
  entry:
    ...
    ret void
  }
}
```

The first Non-VLS call passes generic vector argument of 16 bytes by
flattened integer.
On the contrary, the VLS call uses `ABI_VLEN=256` which wraps the
vector to <vscale x 1 x i32> where the number of scalable vector
elements
is calaulated by: `ORIG_ELTS * RVV_BITS_PER_BLOCK / ABI_VLEN`.
Note: ORIG_ELTS = Vector Size / Type Size = 128 / 32 = 4.

PsABI PR: https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/418
C-API PR: https://github.com/riscv-non-isa/riscv-c-api-doc/pull/68

1 files changed, 15 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 46ad11e..f4d4a36 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -1593,6 +1593,21 @@ static unsigned getDwarfCC(CallingConv CC) {
     return llvm::dwarf::DW_CC_LLVM_PreserveNone;
   case CC_RISCVVectorCall:
     return llvm::dwarf::DW_CC_LLVM_RISCVVectorCall;
+#define CC_VLS_CASE(ABI_VLEN) case CC_RISCVVLSCall_##ABI_VLEN:
+    CC_VLS_CASE(32)
+    CC_VLS_CASE(64)
+    CC_VLS_CASE(128)
+    CC_VLS_CASE(256)
+    CC_VLS_CASE(512)
+    CC_VLS_CASE(1024)
+    CC_VLS_CASE(2048)
+    CC_VLS_CASE(4096)
+    CC_VLS_CASE(8192)
+    CC_VLS_CASE(16384)
+    CC_VLS_CASE(32768)
+    CC_VLS_CASE(65536)
+#undef CC_VLS_CASE
+    return llvm::dwarf::DW_CC_LLVM_RISCVVLSCall;
   }
   return 0;
 }