[IR] Convert from nocapture to captures(none) (#123181)

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.

1 files changed, 0 insertions, 2 deletions

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 31c9640..9461280 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -768,8 +768,6 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_NO_BUILTIN;
   case Attribute::NoCallback:
     return bitc::ATTR_KIND_NO_CALLBACK;
-  case Attribute::NoCapture:
-    return bitc::ATTR_KIND_NO_CAPTURE;
   case Attribute::NoDivergenceSource:
     return bitc::ATTR_KIND_NO_DIVERGENCE_SOURCE;
   case Attribute::NoDuplicate: