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

This PR removes the old `nocapture` attribute, replacing it with the new
`captures` attribute introduced in llvm#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.

Author: nikic

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

@@ -5752,8 +5752,7 @@ bool AANoCapture::isImpliedByIR(Attributor &A, const IRPosition &IRP,
   if (IRP.getPositionKind() == IRP_CALL_SITE_ARGUMENT)
     if (Argument *Arg = IRP.getAssociatedArgument()) {
       SmallVector<Attribute, 1> Attrs;
-      A.getAttrs(IRPosition::argument(*Arg),
-                 {Attribute::Captures, Attribute::ByVal}, Attrs,
+      A.getAttrs(IRP, {Attribute::Captures, Attribute::ByVal}, Attrs,
                  /* IgnoreSubsumingPositions */ true);
       bool ArgNoCapture = any_of(Attrs, [](Attribute Attr) {
         return Attr.getKindAsEnum() == Attribute::ByVal ||

llvm/test/Transforms/Attributor/liveness.ll

@@ -2364,7 +2364,7 @@ define internal void @call_via_pointer_with_dead_args_internal_a(ptr %a, ptr %b,
 ;
 ; CGSCC-LABEL: define {{[^@]+}}@call_via_pointer_with_dead_args_internal_a
 ; CGSCC-SAME: (ptr [[A:%.*]], ptr noundef nonnull align 128 dereferenceable(4) [[B:%.*]]) {
-; CGSCC-NEXT:    call void @called_via_pointer(ptr [[A]], ptr nofree noundef nonnull align 128 captures(none) dereferenceable(4) [[B]], ptr nofree captures(none) [[A]], i64 noundef -1, ptr nofree noundef null)
+; CGSCC-NEXT:    call void @called_via_pointer(ptr [[A]], ptr nofree noundef nonnull align 128 dereferenceable(4) [[B]], ptr nofree [[A]], i64 noundef -1, ptr nofree noundef null)
 ; CGSCC-NEXT:    ret void
 ;
   call void %fp(ptr %a, ptr %b, ptr %a, i64 -1, ptr null)

llvm/test/Transforms/Attributor/nonnull.ll

@@ -1058,7 +1058,7 @@ define internal void @optnone(ptr dereferenceable(4) %a) optnone noinline {
 ; CHECK: Function Attrs: noinline optnone
 ; CHECK-LABEL: define {{[^@]+}}@optnone
 ; CHECK-SAME: (ptr noundef nonnull dereferenceable(4) [[A:%.*]]) #[[ATTR12:[0-9]+]] {
-; CHECK-NEXT:    call void @use_i32_ptr(ptr nofree noundef nonnull captures(none) [[A]])
+; CHECK-NEXT:    call void @use_i32_ptr(ptr nofree noundef nonnull [[A]])
 ; CHECK-NEXT:    ret void
 ;
   call void @use_i32_ptr(ptr %a)