This PR fixes invalid pointer arithmetic emitted by C-family codegen for
vector-typed `tvm_access_ptr`.
A vector access pointer is lowered to `address_of(BufferLoad(...))` with
a `Ramp` index describing its lane indices. For example, `Ramp(4, 1, 2)`
represents scalar elements `[4, 5]`, so its address should be the
address of the first lane, `&A[4]`.
LLVM codegen already extracts `Ramp::base` in this case. However,
`CodeGenC` previously passed the complete ramp to pointer arithmetic,
which could generate invalid CUDA code such as:
```cpp
(float*)A + make_int2(4, 5)
```
This PR makes `CodeGenC` use `Ramp::base` when generating the address of
a vector `BufferLoad`. The normalized index is applied to both the
direct pointer-offset path and the general `GetBufferRef` path.
The existing scalar-buffer plus `Ramp` lowering is preserved. This
avoids regressions for padded vector types such as `float32x3` and
packed vector types such as `int4x4`, while making C-family codegen
consistent with LLVM codegen.
Regression tests cover:
- `float32x2` C codegen.
- Padded `float32x3` LLVM codegen.
- Packed `int4x4` CUDA codegen.
Shushi Hong
23fc37c4cf