[MLIR][NVVM] Add support for multiple return values in `inline_ptx` (#153774)

This PR adds the ability for `nvvm.inline_ptx` to return multiple
values, matching the expected semantics in PTX while respecting LLVM’s
constraints.

LLVM’s `inline_asm` op does not natively support multiple returns —
instead, it requires packing results into an LLVM `struct` and then
extracting them. This PR implements automatic packing/unpacking so that
multiple return values can be expressed naturally in MLIR without extra
user boilerplate.

**Example**
MLIR:

```
%r1, %r2 = nvvm.inline_ptx  "{
   .reg .pred p;
   setp.ge.s32 p, $2, $3;
   selp.s32 $0, $2, $3, p;
   selp.s32 $1, $2, $3, !p;
}" (%a, %b) : i32, i32 -> i32, i32

%r3 = llvm.add %r1, %r2 : i32
```

Lowered LLVM IR:

```
%1 = llvm.inline_asm has_side_effects asm_dialect = att "{\0A\09 .reg .pred p;\0A\09 setp.ge.s32 p, $2, $3;\0A\09 selp.s32 $0, $2, $3, p;\0A\09 selp.s32 $1, $2, $3, !p;\0A\09}\0A", "=r,=r,r,r" %a, %b : (i32, i32) -> !llvm.struct<(i32, i32)>
%2 = llvm.extractvalue %1[0] : !llvm.struct<(i32, i32)>
%3 = llvm.extractvalue %1[1] : !llvm.struct<(i32, i32)>
%4 = llvm.add %2, %3 : i32
```

0 files changed, 0 insertions, 0 deletions