Auto merge of #131201 - compiler-errors:unop-not, r=cjgillot

Disable jump threading `UnOp::Not` for non-bool

Fix #131195, where jumpthreading was optimizing `!a == b` into `a != b` for non-bool, where this is definitely not true.

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);
             }

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;
+      }
+  }
+  

tests/mir-opt/jump_threading.bitwise_not.JumpThreading.panic-unwind.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;
+      }
+  }
+  

tests/mir-opt/jump_threading.rs

@@ -531,6 +531,16 @@ fn floats() -> u32 {
     if x == 0.0 { 0 } else { 1 }
 }
 
+pub fn bitwise_not() -> i32 {
+    // CHECK-LABEL: fn bitwise_not(
+    // CHECK: switchInt(
+
+    // Test for #131195, which was optimizing `!a == b` into `a != b`.
+    let mut a: i32 = 0;
+    a = 1;
+    if !a == 0 { 1 } else { 0 }
+}
+
 fn main() {
     // CHECK-LABEL: fn main(
     too_complex(Ok(0));
@@ -562,3 +572,4 @@ fn main() {
 // EMIT_MIR jump_threading.assume.JumpThreading.diff
 // EMIT_MIR jump_threading.aggregate_copy.JumpThreading.diff
 // EMIT_MIR jump_threading.floats.JumpThreading.diff
+// EMIT_MIR jump_threading.bitwise_not.JumpThreading.diff