Put checks that detect UB under their own flag below debug_assertions

Author: saethlin

compiler/rustc_codegen_cranelift/src/base.rs

@@ -789,7 +789,7 @@ fn codegen_stmt<'tcx>(
  layout.offset_of_subfield(fx, fields.iter()).bytes()
  }
  NullOp::UbChecks => {
- let val = fx.tcx.sess.opts.debug_assertions;
+ let val = fx.tcx.sess.ub_checks();
  let val = CValue::by_val(
  fx.bcx.ins().iconst(types::I8, i64::try_from(val).unwrap()),
  fx.layout_of(fx.tcx.types.bool),

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -682,7 +682,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
  bx.cx().const_usize(val)
  }
  mir::NullOp::UbChecks => {
- let val = bx.tcx().sess.opts.debug_assertions;
+ let val = bx.tcx().sess.ub_checks();
  bx.cx().const_bool(val)
  }
  };

compiler/rustc_const_eval/src/interpret/step.rs

@@ -258,7 +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::UbChecks => Scalar::from_bool(self.tcx.sess.opts.debug_assertions),
+ mir::NullOp::UbChecks => Scalar::from_bool(self.tcx.sess.ub_checks()),
  };
  self.write_scalar(val, &dest)?;
  }

compiler/rustc_feature/src/builtin_attrs.rs

@@ -25,6 +25,7 @@ pub type GatedCfg = (Symbol, Symbol, GateFn);
 const GATED_CFGS: &[GatedCfg] = &[
  // (name in cfg, feature, function to check if the feature is enabled)
  (sym::overflow_checks, sym::cfg_overflow_checks, cfg_fn!(cfg_overflow_checks)),
+ (sym::ub_checks, sym::cfg_ub_checks, cfg_fn!(cfg_ub_checks)),
  (sym::target_thread_local, sym::cfg_target_thread_local, cfg_fn!(cfg_target_thread_local)),
  (
  sym::target_has_atomic_equal_alignment,

compiler/rustc_feature/src/unstable.rs

@@ -381,6 +381,8 @@ declare_features! (
  (unstable, cfg_target_has_atomic_equal_alignment, "1.60.0", Some(93822)),
  /// Allows `cfg(target_thread_local)`.
  (unstable, cfg_target_thread_local, "1.7.0", Some(29594)),
+ /// Allows the use of `#[cfg(ub_checks)` to check if UB checks are enabled.
+ (unstable, cfg_ub_checks, "CURRENT_RUSTC_VERSION", Some(123499)),
  /// Allow conditional compilation depending on rust version
  (unstable, cfg_version, "1.45.0", Some(64796)),
  /// Allows to use the `#[cfi_encoding = ""]` attribute.

compiler/rustc_interface/src/tests.rs

@@ -847,6 +847,7 @@ fn test_unstable_options_tracking_hash() {
  tracked!(trap_unreachable, Some(false));
  tracked!(treat_err_as_bug, NonZero::new(1));
  tracked!(tune_cpu, Some(String::from("abc")));
+ tracked!(ub_checks, Some(false));
  tracked!(uninit_const_chunk_threshold, 123);
  tracked!(unleash_the_miri_inside_of_you, true);
  tracked!(use_ctors_section, Some(true));

compiler/rustc_mir_transform/src/check_alignment.rs

@@ -16,7 +16,7 @@ impl<'tcx> MirPass<'tcx> for CheckAlignment {
  if sess.target.llvm_target == "i686-pc-windows-msvc" {
  return false;
  }
- sess.opts.debug_assertions
+ sess.ub_checks()
  }
 
  fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {

compiler/rustc_mir_transform/src/instsimplify.rs

@@ -149,7 +149,7 @@ impl<'tcx> InstSimplifyContext<'tcx, '_> {
 
  fn simplify_ub_check(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
  if let Rvalue::NullaryOp(NullOp::UbChecks, _) = *rvalue {
- let const_ = Const::from_bool(self.tcx, self.tcx.sess.opts.debug_assertions);
+ let const_ = Const::from_bool(self.tcx, self.tcx.sess.ub_checks());
  let constant = ConstOperand { span: source_info.span, const_, user_ty: None };
  *rvalue = Rvalue::Use(Operand::Constant(Box::new(constant)));
  }

compiler/rustc_session/src/config.rs

@@ -1236,6 +1236,10 @@ fn default_configuration(sess: &Session) -> Cfg {
  ins_none!(sym::overflow_checks);
  }
 
+ if sess.ub_checks() {
+ ins_none!(sym::ub_checks);
+ }
+
  ins_sym!(sym::panic, sess.panic_strategy().desc_symbol());
 
  // JUSTIFICATION: before wrapper fn is available

compiler/rustc_session/src/options.rs

@@ -1994,6 +1994,9 @@ written to standard error output)"),
  "in diagnostics, use heuristics to shorten paths referring to items"),
  tune_cpu: Option<String> = (None, parse_opt_string, [TRACKED],
  "select processor to schedule for (`rustc --print target-cpus` for details)"),
+ #[rustc_lint_opt_deny_field_access("use `Session::ub_checks` instead of this field")]
+ ub_checks: Option<bool> = (None, parse_opt_bool, [TRACKED],
+ "emit runtime checks for Undefined Behavior (default: -Cdebug-assertions)"),
  ui_testing: bool = (false, parse_bool, [UNTRACKED],
  "emit compiler diagnostics in a form suitable for UI testing (default: no)"),
  uninit_const_chunk_threshold: usize = (16, parse_number, [TRACKED],