[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, 4 insertions, 1 deletions

diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index ceb3185..ef0591e 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -288,6 +288,10 @@ Attribute Attribute::getWithNoFPClass(LLVMContext &Context,
   return get(Context, NoFPClass, ClassMask);
 }
 
+Attribute Attribute::getWithCaptureInfo(LLVMContext &Context, CaptureInfo CI) {
+  return get(Context, Captures, CI.toIntValue());
+}
+
 Attribute
 Attribute::getWithAllocSizeArgs(LLVMContext &Context, unsigned ElemSizeArg,
                                 const std::optional<unsigned> &NumElemsArg) {
@@ -2373,7 +2377,6 @@ AttributeMask AttributeFuncs::typeIncompatible(Type *Ty, AttributeSet AS,
     // Attributes that only apply to pointers.
     if (ASK & ASK_SAFE_TO_DROP)
       Incompatible.addAttribute(Attribute::NoAlias)
-          .addAttribute(Attribute::NoCapture)
           .addAttribute(Attribute::NonNull)
           .addAttribute(Attribute::ReadNone)
           .addAttribute(Attribute::ReadOnly)