Auto merge of #122629 - RalfJung:assert-unsafe-precondition, r=saethlin

refactor check_{lang,library}_ub: use a single intrinsic

This enacts the plan I laid out [here](https://github.com/rust-lang/rust/pull/122282#issuecomment-1996917998): use a single intrinsic, called `ub_checks` (in aniticpation of https://github.com/rust-lang/compiler-team/issues/725), that just exposes the value of `debug_assertions` (consistently implemented in both codegen and the interpreter). Put the language vs library UB logic into the library.

This makes it easier to do something like https://github.com/rust-lang/rust/pull/122282 in the future: that just slightly alters the semantics of `ub_checks` (making it more approximating when crates built with different flags are mixed), but it no longer affects whether these checks can happen in Miri or compile-time.

The first commit just moves things around; I don't think these macros and functions belong into `intrinsics.rs` as they are not intrinsics.

r? `@saethlin`

3 files changed, 3 insertions, 13 deletions

diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
index 54bac70da38..9114ffff6fd 100644
--- a/compiler/rustc_const_eval/src/interpret/step.rs
+++ b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -258,17 +258,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         let val = layout.offset_of_subfield(self, fields.iter()).bytes();
                         Scalar::from_target_usize(val, self)
                     }
-                    mir::NullOp::UbCheck(kind) => {
-                        // We want to enable checks for library UB, because the interpreter doesn't
-                        // know about those on its own.
-                        // But we want to disable checks for language UB, because the interpreter
-                        // has its own better checks for that.
-                        let should_check = match kind {
-                            mir::UbKind::LibraryUb => self.tcx.sess.opts.debug_assertions,
-                            mir::UbKind::LanguageUb => false,
-                        };
-                        Scalar::from_bool(should_check)
-                    }
+                    mir::NullOp::UbChecks => Scalar::from_bool(self.tcx.sess.opts.debug_assertions),
                 };
                 self.write_scalar(val, &dest)?;
             }
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
index a93e8138aa4..da8e28d0298 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@@ -558,7 +558,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
             Rvalue::Cast(_, _, _) => {}
 
             Rvalue::NullaryOp(
-                NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(_) | NullOp::UbCheck(_),
+                NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(_) | NullOp::UbChecks,
                 _,
             ) => {}
             Rvalue::ShallowInitBox(_, _) => {}
diff --git a/compiler/rustc_const_eval/src/transform/validate.rs b/compiler/rustc_const_eval/src/transform/validate.rs
index 4bc49f90607..c8eeaa4a45e 100644
--- a/compiler/rustc_const_eval/src/transform/validate.rs
+++ b/compiler/rustc_const_eval/src/transform/validate.rs
@@ -1168,7 +1168,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
             Rvalue::Repeat(_, _)
             | Rvalue::ThreadLocalRef(_)
             | Rvalue::AddressOf(_, _)
-            | Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::UbCheck(_), _)
+            | Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::UbChecks, _)
             | Rvalue::Discriminant(_) => {}
         }
         self.super_rvalue(rvalue, location);