From 6f01ff61b3d9d722031fdb39747283c911b97049 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Mon, 4 Jul 2022 08:57:10 -0400
Subject: [PATCH] interpret: fix CheckedBinOp behavior when overflow checking
 is disabled

---
 compiler/rustc_const_eval/src/interpret/intrinsics.rs | 4 +++-
 compiler/rustc_const_eval/src/interpret/operator.rs   | 8 ++++++++
 compiler/rustc_const_eval/src/interpret/step.rs       | 4 +++-
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
index e51c51cf45e..6744aace849 100644
--- a/compiler/rustc_const_eval/src/interpret/intrinsics.rs
+++ b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -217,7 +217,9 @@ pub fn emulate_intrinsic(
                     sym::mul_with_overflow => BinOp::Mul,
                     _ => bug!(),
                 };
-                self.binop_with_overflow(bin_op, &lhs, &rhs, dest)?;
+                self.binop_with_overflow(
+                    bin_op, /*force_overflow_checks*/ true, &lhs, &rhs, dest,
+                )?;
             }
             sym::saturating_add | sym::saturating_sub => {
                 let l = self.read_immediate(&args[0])?;
diff --git a/compiler/rustc_const_eval/src/interpret/operator.rs b/compiler/rustc_const_eval/src/interpret/operator.rs
index dec7fa8c4aa..454243ddca6 100644
--- a/compiler/rustc_const_eval/src/interpret/operator.rs
+++ b/compiler/rustc_const_eval/src/interpret/operator.rs
@@ -12,9 +12,13 @@
 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// Applies the binary operation `op` to the two operands and writes a tuple of the result
     /// and a boolean signifying the potential overflow to the destination.
+    ///
+    /// `force_overflow_checks` indicates whether overflow checks should be done even when
+    /// `tcx.sess.overflow_checks()` is `false`.
     pub fn binop_with_overflow(
         &mut self,
         op: mir::BinOp,
+        force_overflow_checks: bool,
         left: &ImmTy<'tcx, M::PointerTag>,
         right: &ImmTy<'tcx, M::PointerTag>,
         dest: &PlaceTy<'tcx, M::PointerTag>,
@@ -26,6 +30,10 @@ pub fn binop_with_overflow(
             "type mismatch for result of {:?}",
             op,
         );
+        // As per https://github.com/rust-lang/rust/pull/98738, we always return `false` in the 2nd
+        // component when overflow checking is disabled.
+        let overflowed = overflowed && (force_overflow_checks || self.tcx.sess.overflow_checks());
+        // Write the result to `dest`.
         if let Abi::ScalarPair(..) = dest.layout.abi {
             // We can use the optimized path and avoid `place_field` (which might do
             // `force_allocation`).
diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
index 98f69456e49..2ee7ed57ab5 100644
--- a/compiler/rustc_const_eval/src/interpret/step.rs
+++ b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -185,7 +185,9 @@ pub fn eval_rvalue_into_place(
                 let left = self.read_immediate(&self.eval_operand(left, None)?)?;
                 let layout = binop_right_homogeneous(bin_op).then_some(left.layout);
                 let right = self.read_immediate(&self.eval_operand(right, layout)?)?;
-                self.binop_with_overflow(bin_op, &left, &right, &dest)?;
+                self.binop_with_overflow(
+                    bin_op, /*force_overflow_checks*/ false, &left, &right, &dest,
+                )?;
             }
 
             UnaryOp(un_op, ref operand) => {