This PR removes the old `nocapture` attribute, replacing it with the new
`captures` attribute introduced in #116990. This change is
intended to be essentially NFC, replacing existing uses of `nocapture`
with `captures(none)` without adding any new analysis capabilities.
Making use of non-`none` values is left for a followup.
Some notes:
* `nocapture` will be upgraded to `captures(none)` by the bitcode
reader.
* `nocapture` will also be upgraded by the textual IR reader. This is to
make it easier to use old IR files and somewhat reduce the test churn in
this PR.
* Helper APIs like `doesNotCapture()` will check for `captures(none)`.
* MLIR import will convert `captures(none)` into an `llvm.nocapture`
attribute. The representation in the LLVM IR dialect should be updated
separately.
This commit makes the `generic` target to support FP and LSX, as
discussed in #110211. Thereby, it allows 128-bit vector to be enabled by
default in the loongarch64 backend.
The `TTI` hooks are used during vectorization for calculating register
pressure. The default implementation defined wrong value for register
number (all register class are 8 registers).
This patch also defines LoongArch's own register classes.
With enough codegen complete, we can now correctly report the size of
vector registers for LSX/LASX, allowing auto vectorization (The
`auto-vec` feature needs to be enabled simultaneously).
As described, the `auto-vec` feature is an experimental one. To ensure
that automatic vectorization is not enabled by default, because the
information provided by the current `TTI` cannot yield additional
benefits for automatic vectorization.
