From f0bfba258330884df9c9d14a0aafd741ca9bbdc9 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 3 Oct 2024 09:47:06 -0400
Subject: [PATCH] Disable jump threading UnOp::Not for non-bool

---
 .../rustc_mir_transform/src/jump_threading.rs |  8 ++++
 ...bitwise_not.JumpThreading.panic-abort.diff | 46 +++++++++++++++++++
 ...itwise_not.JumpThreading.panic-unwind.diff |  3 +-
 3 files changed, 55 insertions(+), 2 deletions(-)
 create mode 100644 tests/mir-opt/jump_threading.bitwise_not.JumpThreading.panic-abort.diff

diff --git a/compiler/rustc_mir_transform/src/jump_threading.rs b/compiler/rustc_mir_transform/src/jump_threading.rs
index 1844b97887a..9b9b0b705bf 100644
--- a/compiler/rustc_mir_transform/src/jump_threading.rs
+++ b/compiler/rustc_mir_transform/src/jump_threading.rs
@@ -494,8 +494,16 @@ fn process_assign(
             }
             // Transfer the conditions on the copy rhs, after inversing polarity.
             Rvalue::UnaryOp(UnOp::Not, Operand::Move(place) | Operand::Copy(place)) => {
+                if !place.ty(self.body, self.tcx).ty.is_bool() {
+                    // Constructing the conditions by inverting the polarity
+                    // of equality is only correct for bools. That is to say,
+                    // `!a == b` is not `a != b` for integers greater than 1 bit.
+                    return;
+                }
                 let Some(conditions) = state.try_get_idx(lhs, &self.map) else { return };
                 let Some(place) = self.map.find(place.as_ref()) else { return };
+                // FIXME: I think This could be generalized to not bool if we
+                // actually perform a logical not on the condition's value.
                 let conds = conditions.map(self.arena, Condition::inv);
                 state.insert_value_idx(place, conds, &self.map);
             }
diff --git a/tests/mir-opt/jump_threading.bitwise_not.JumpThreading.panic-abort.diff b/tests/mir-opt/jump_threading.bitwise_not.JumpThreading.panic-abort.diff
new file mode 100644
index 00000000000..047441e6099
--- /dev/null
+++ b/tests/mir-opt/jump_threading.bitwise_not.JumpThreading.panic-abort.diff
@@ -0,0 +1,46 @@
+- // MIR for `bitwise_not` before JumpThreading
++ // MIR for `bitwise_not` after JumpThreading
+  
+  fn bitwise_not() -> i32 {
+      let mut _0: i32;
+      let mut _1: i32;
+      let mut _2: bool;
+      let mut _3: i32;
+      let mut _4: i32;
+      scope 1 {
+          debug a => _1;
+      }
+  
+      bb0: {
+          StorageLive(_1);
+          _1 = const 0_i32;
+          _1 = const 1_i32;
+          StorageLive(_2);
+          StorageLive(_3);
+          StorageLive(_4);
+          _4 = copy _1;
+          _3 = Not(move _4);
+          StorageDead(_4);
+          _2 = Eq(move _3, const 0_i32);
+          switchInt(move _2) -> [0: bb2, otherwise: bb1];
+      }
+  
+      bb1: {
+          StorageDead(_3);
+          _0 = const 1_i32;
+          goto -> bb3;
+      }
+  
+      bb2: {
+          StorageDead(_3);
+          _0 = const 0_i32;
+          goto -> bb3;
+      }
+  
+      bb3: {
+          StorageDead(_2);
+          StorageDead(_1);
+          return;
+      }
+  }
+  
diff --git a/tests/mir-opt/jump_threading.bitwise_not.JumpThreading.panic-unwind.diff b/tests/mir-opt/jump_threading.bitwise_not.JumpThreading.panic-unwind.diff
index fb64fff7e11..047441e6099 100644
--- a/tests/mir-opt/jump_threading.bitwise_not.JumpThreading.panic-unwind.diff
+++ b/tests/mir-opt/jump_threading.bitwise_not.JumpThreading.panic-unwind.diff
@@ -22,8 +22,7 @@
           _3 = Not(move _4);
           StorageDead(_4);
           _2 = Eq(move _3, const 0_i32);
--         switchInt(move _2) -> [0: bb2, otherwise: bb1];
-+         goto -> bb1;
+          switchInt(move _2) -> [0: bb2, otherwise: bb1];
       }
   
       bb1: {