Rollup merge of #109234 - tmiasko:overflow-checks, r=cjgillot

Tweak implementation of overflow checking assertions

Extract and reuse logic controlling behaviour of overflow checking assertions instead of duplicating it three times.

r? `@cjgillot`

compiler/rustc_codegen_cranelift/src/base.rs

@@ -346,17 +346,10 @@ fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
                 crate::abi::codegen_return(fx);
             }
             TerminatorKind::Assert { cond, expected, msg, target, cleanup: _ } => {
-                if !fx.tcx.sess.overflow_checks() {
+                if !fx.tcx.sess.overflow_checks() && msg.is_optional_overflow_check() {
-                    let overflow_not_to_check = match msg {
+                    let target = fx.get_block(*target);
-                        AssertKind::OverflowNeg(..) => true,
+                    fx.bcx.ins().jump(target, &[]);
-                        AssertKind::Overflow(op, ..) => op.is_checkable(),
+                    continue;
-                        _ => false,
-                    };
-                    if overflow_not_to_check {
-                        let target = fx.get_block(*target);
-                        fx.bcx.ins().jump(target, &[]);
-                        continue;
-                    }
                 }
                 let cond = codegen_operand(fx, cond).load_scalar(fx);
 

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -563,15 +563,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         // with #[rustc_inherit_overflow_checks] and inlined from
         // another crate (mostly core::num generic/#[inline] fns),
         // while the current crate doesn't use overflow checks.
-        if !bx.cx().check_overflow() {
+        if !bx.cx().check_overflow() && msg.is_optional_overflow_check() {
-            let overflow_not_to_check = match msg {
+            const_cond = Some(expected);
-                AssertKind::OverflowNeg(..) => true,
-                AssertKind::Overflow(op, ..) => op.is_checkable(),
-                _ => false,
-            };
-            if overflow_not_to_check {
-                const_cond = Some(expected);
-            }
         }
 
         // Don't codegen the panic block if success if known.

compiler/rustc_const_eval/src/interpret/machine.rs

@@ -155,7 +155,7 @@ pub trait Machine<'mir, 'tcx>: Sized {
 
     /// Whether Assert(OverflowNeg) and Assert(Overflow) MIR terminators should actually
     /// check for overflow.
-    fn ignore_checkable_overflow_assertions(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
+    fn ignore_optional_overflow_checks(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
 
     /// Entry point for obtaining the MIR of anything that should get evaluated.
     /// So not just functions and shims, but also const/static initializers, anonymous
@@ -474,7 +474,7 @@ pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
     }
 
     #[inline(always)]
-    fn ignore_checkable_overflow_assertions(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
+    fn ignore_optional_overflow_checks(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
         false
     }
 

compiler/rustc_const_eval/src/interpret/terminator.rs

@@ -138,12 +138,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
 
             Assert { ref cond, expected, ref msg, target, cleanup } => {
-                let ignored = M::ignore_checkable_overflow_assertions(self)
+                let ignored =
-                    && match msg {
+                    M::ignore_optional_overflow_checks(self) && msg.is_optional_overflow_check();
-                        mir::AssertKind::OverflowNeg(..) => true,
-                        mir::AssertKind::Overflow(op, ..) => op.is_checkable(),
-                        _ => false,
-                    };
                 let cond_val = self.read_scalar(&self.eval_operand(cond, None)?)?.to_bool()?;
                 if ignored || expected == cond_val {
                     self.go_to_block(target);

compiler/rustc_middle/src/mir/mod.rs

@@ -1268,6 +1268,13 @@ impl<'tcx> BasicBlockData<'tcx> {
 }
 
 impl<O> AssertKind<O> {
+    /// Returns true if this an overflow checking assertion controlled by -C overflow-checks.
+    pub fn is_optional_overflow_check(&self) -> bool {
+        use AssertKind::*;
+        use BinOp::*;
+        matches!(self, OverflowNeg(..) | Overflow(Add | Sub | Mul | Shl | Shr, ..))
+    }
+
     /// Getting a description does not require `O` to be printable, and does not
     /// require allocation.
     /// The caller is expected to handle `BoundsCheck` separately.
@@ -1992,16 +1999,6 @@ impl BorrowKind {
     }
 }
 
-impl BinOp {
-    /// The checkable operators are those whose overflow checking behavior is controlled by
-    /// -Coverflow-checks option. The remaining operators have either no overflow conditions (e.g.,
-    /// BitAnd, BitOr, BitXor) or are always checked for overflow (e.g., Div, Rem).
-    pub fn is_checkable(self) -> bool {
-        use self::BinOp::*;
-        matches!(self, Add | Sub | Mul | Shl | Shr)
-    }
-}
-
 impl<'tcx> Debug for Rvalue<'tcx> {
     fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
         use self::Rvalue::*;

compiler/rustc_middle/src/mir/syntax.rs

@@ -646,8 +646,7 @@ pub enum TerminatorKind<'tcx> {
     /// When overflow checking is disabled and this is run-time MIR (as opposed to compile-time MIR
     /// that is used for CTFE), the following variants of this terminator behave as `goto target`:
     /// - `OverflowNeg(..)`,
-    /// - `Overflow(op, ..)` if op is a "checkable" operation (add, sub, mul, shl, shr, but NOT
+    /// - `Overflow(op, ..)` if op is add, sub, mul, shl, shr, but NOT div or rem.
-    /// div or rem).
     Assert {
         cond: Operand<'tcx>,
         expected: bool,

src/tools/miri/src/machine.rs

@@ -822,7 +822,7 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
     }
 
     #[inline(always)]
-    fn ignore_checkable_overflow_assertions(ecx: &MiriInterpCx<'mir, 'tcx>) -> bool {
+    fn ignore_optional_overflow_checks(ecx: &MiriInterpCx<'mir, 'tcx>) -> bool {
         !ecx.tcx.sess.overflow_checks()
     }