Rollup merge of #157733 - hanna-kruppe:fixme-nocapture, r=mati865

Remove old FIXMEs about nocapture attribute

As discussed in the long-closed issue referenced by the FIXMEs (#25759), it would be unsound to add nocapture to all reference arguments. The canonical example is taking &T and returning *const T, i.e., `std::ptr::from_ref`. Some of the removed test cases suggest that named vs elided vs static lifetime on the reference would make a difference for capturing, which is incompatible with all modern takes on Rust opsem.

Hypothetically, we could add some kind of escape analysis on MIR to determine which arguments can be marked as nocapture. But LLVM can do that too (often better), so why should we? Plus, if we started doing such analysis, the test that had the FIXMEs would not be a good place to exercise it, as all the function bodies are trivial.

Part of #44366

Author: JonathanBrouwer

tests/codegen-llvm/function-arguments.rs

@@ -81,7 +81,6 @@ pub fn option_nonzero_int(x: Option<NonZero<u64>>) -> Option<NonZero<u64>> {
 }
 
 // CHECK: @readonly_borrow(ptr noalias nofree noundef readonly align 4{{( captures\(address, read_provenance\))?}} dereferenceable(4) %_1)
-// FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn readonly_borrow(_: &i32) {}
 
@@ -91,16 +90,6 @@ pub fn readonly_borrow_ret() -> &'static i32 {
     loop {}
 }
 
-// CHECK: @static_borrow(ptr noalias nofree noundef readonly align 4{{( captures\(address, read_provenance\))?}} dereferenceable(4) %_1)
-// static borrow may be captured
-#[no_mangle]
-pub fn static_borrow(_: &'static i32) {}
-
-// CHECK: @named_borrow(ptr noalias nofree noundef readonly align 4{{( captures\(address, read_provenance\))?}} dereferenceable(4) %_1)
-// borrow with named lifetime may be captured
-#[no_mangle]
-pub fn named_borrow<'r>(_: &'r i32) {}
-
 // CHECK: @unsafe_borrow(ptr noundef nonnull align 2 %_1)
 // unsafe interior means this isn't actually readonly and there may be aliases ...
 #[no_mangle]
@@ -112,7 +101,6 @@ pub fn unsafe_borrow(_: &UnsafeInner) {}
 pub fn mutable_unsafe_borrow(_: &mut UnsafeInner) {}
 
 // CHECK: @mutable_borrow(ptr noalias nofree noundef align 4 dereferenceable(4) %_1)
-// FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn mutable_borrow(_: &mut i32) {}
 
@@ -139,7 +127,6 @@ pub fn notunpin_borrow(_: &NotUnpin) {}
 pub fn indirect_struct(_: S) {}
 
 // CHECK: @borrowed_struct(ptr noalias nofree noundef readonly align 4{{( captures\(address, read_provenance\))?}} dereferenceable(32) %_1)
-// FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn borrowed_struct(_: &S) {}
 
@@ -196,14 +183,12 @@ pub fn helper(_: usize) {}
 // CHECK: @slice(
 // CHECK-SAME: ptr noalias nofree noundef nonnull readonly{{( captures\(address, read_provenance\))?}} %_1.0,
 // CHECK-SAME: [[USIZE]] noundef range({{i32 0, -2147483648|i64 0, -9223372036854775808}}) %_1.1)
-// FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn slice(_: &[u8]) {}
 
 // CHECK: @mutable_slice(
 // CHECK-SAME: ptr noalias nofree noundef nonnull %_1.0,
 // CHECK-SAME: [[USIZE]] noundef range({{i32 0, -2147483648|i64 0, -9223372036854775808}}) %_1.1)
-// FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn mutable_slice(_: &mut [u8]) {}
 
@@ -221,12 +206,10 @@ pub fn raw_slice(_: *const [u8]) {}
 // CHECK: @str(
 // CHECK-SAME: ptr noalias nofree noundef nonnull readonly{{( captures\(address, read_provenance\))?}} %_1.0,
 // CHECK-SAME: [[USIZE]] noundef range({{i32 0, -2147483648|i64 0, -9223372036854775808}}) %_1.1)
-// FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn str(_: &[u8]) {}
 
 // CHECK: @trait_borrow(ptr noundef nonnull %_1.0, {{.+}} noalias nofree noundef readonly align {{.*}} dereferenceable({{.*}}) %_1.1)
-// FIXME #25759 This should also have `nocapture`
 #[no_mangle]
 pub fn trait_borrow(_: &dyn Drop) {}