correct (\+)/1 (#2141)

src/codegen.rs

@@ -950,10 +950,15 @@ impl<'b> CodeGenerator<'b> {
                                     code.push_back(instr!("proceed"));
                                 }
                             }
-                            &QueryTerm::LocalCut(var_num) => {
+                            &QueryTerm::LocalCut { var_num, cut_prev } => {
                                 let code = branch_code_stack.code(code);
                                 let r = self.marker.get_binding(var_num);
-                                code.push_back(instr!("cut", r));
+
+                                code.push_back(if cut_prev {
+                                    instr!("cut_prev", r)
+                                } else {
+                                    instr!("cut", r)
+                                });
 
                                 if self.marker.in_tail_position {
                                     if self.marker.var_data.allocates {

src/forms.rs

@@ -202,7 +202,7 @@ pub enum QueryTerm {
     // register, clause type, subterms, clause call policy.
     Clause(Cell<RegType>, ClauseType, Vec<Term>, CallPolicy),
     Fail,
-    LocalCut(usize),  // var_num
+    LocalCut { var_num: usize, cut_prev: bool },  // var_num
     GlobalCut(usize), // var_num
     GetCutPoint { var_num: usize, prev_b: bool },
     GetLevel(usize), // var_num

src/machine/disjuncts.rs

@@ -154,8 +154,11 @@ enum TraversalState {
     Fail,
     GetCutPoint { var_num: usize, prev_b: bool },
     Cut { var_num: usize, is_global: bool },
+    CutPrev(usize),
     ResetCallPolicy(CallPolicy),
     Term(Term),
+    OverrideGlobalCutVar(usize),
+    ResetGlobalCutVarOverride(Option<usize>),
     RemoveBranchNum,            // pop the current_branch_num and from the root set.
     AddBranchNum(BranchNumber), // set current_branch_num, add it to the root set
     RepBranchNum(BranchNumber), // replace current_branch_num and the latest in the root set
@@ -171,6 +174,7 @@ pub struct VariableClassifier {
     var_num: usize,
     root_set: RootSet,
     global_cut_var_num: Option<usize>,
+    global_cut_var_num_override: Option<usize>,
 }
 
 #[derive(Debug, Default)]
@@ -252,6 +256,7 @@ impl VariableClassifier {
             root_set: RootSet::new(),
             var_num: 0,
             global_cut_var_num: None,
+            global_cut_var_num_override: None,
         }
     }
 
@@ -517,6 +522,12 @@ impl VariableClassifier {
                     self.probe_in_situ_var(var_num);
                     build_stack.push_chunk_term(QueryTerm::GetCutPoint { var_num, prev_b });
                 }
+                TraversalState::OverrideGlobalCutVar(var_num) => {
+                    self.global_cut_var_num_override = Some(var_num);
+                }
+                TraversalState::ResetGlobalCutVarOverride(old_override) => {
+                    self.global_cut_var_num_override = old_override;
+                }
                 TraversalState::Cut { var_num, is_global } => {
                     if self.try_set_chunk_at_inlined_boundary() {
                         build_stack.add_chunk();
@@ -527,9 +538,18 @@ impl VariableClassifier {
                     build_stack.push_chunk_term(if is_global {
                         QueryTerm::GlobalCut(var_num)
                     } else {
-                        QueryTerm::LocalCut(var_num)
+                        QueryTerm::LocalCut { var_num, cut_prev: false }
                     });
                 }
+                TraversalState::CutPrev(var_num) => {
+                    if self.try_set_chunk_at_inlined_boundary() {
+                        build_stack.add_chunk();
+                    }
+
+                    self.probe_in_situ_var(var_num);
+
+                    build_stack.push_chunk_term(QueryTerm::LocalCut { var_num, cut_prev: true });
+                }
                 TraversalState::Fail => {
                     build_stack.push_chunk_term(QueryTerm::Fail);
                 }
@@ -684,14 +704,13 @@ impl VariableClassifier {
                             )));
                             state_stack.push(TraversalState::BuildDisjunct(build_stack_len));
                             state_stack.push(TraversalState::Fail);
-                            state_stack.push(TraversalState::Cut {
-                                var_num: self.var_num,
-                                is_global: false,
-                            });
+                            state_stack.push(TraversalState::CutPrev(self.var_num));
+                            state_stack.push(TraversalState::ResetGlobalCutVarOverride(self.global_cut_var_num_override));
                             state_stack.push(TraversalState::Term(not_term));
+                            state_stack.push(TraversalState::OverrideGlobalCutVar(self.var_num));
                             state_stack.push(TraversalState::GetCutPoint {
                                 var_num: self.var_num,
-                                prev_b: true,
+                                prev_b: false,
                             });
 
                             self.current_chunk_type = ChunkType::Mid;
@@ -786,17 +805,23 @@ impl VariableClassifier {
                             ));
                         }
                         Term::Literal(_, Literal::Atom(atom!("!")) | Literal::Char('!')) => {
-                            if self.global_cut_var_num.is_none() {
-                                self.global_cut_var_num = Some(self.var_num);
-                                self.var_num += 1;
-                            }
+                            let (var_num, is_global) =
+                                if let Some(var_num) = self.global_cut_var_num_override {
+                                    (var_num, false)
+                                } else if let Some(var_num) = self.global_cut_var_num {
+                                    (var_num, true)
+                                } else {
+                                    let var_num = self.var_num;
 
-                            self.probe_in_situ_var(self.global_cut_var_num.unwrap());
+                                    self.global_cut_var_num = Some(var_num);
+                                    self.var_num += 1;
 
-                            state_stack.push(TraversalState::Cut {
-                                var_num: self.global_cut_var_num.unwrap(),
-                                is_global: true,
-                            });
+                                    (var_num, true)
+                                };
+
+                            self.probe_in_situ_var(var_num);
+
+                            state_stack.push(TraversalState::Cut { var_num, is_global });
                         }
                         Term::Literal(_, Literal::Atom(name)) => {
                             if update_chunk_data(self, name, 0) {

src/machine/dispatch.rs

@@ -1188,6 +1188,21 @@ impl Machine {
 
                         self.machine_st.p += 1;
                     }
+                    &Instruction::CutPrev(r) => {
+                        let value = self.machine_st[r];
+                        self.machine_st.cut_prev_body(value);
+
+                        if self.machine_st.fail {
+                            self.machine_st.backtrack();
+                            continue;
+                        }
+
+                        if (self.machine_st.run_cleaners_fn)(self) {
+                            continue;
+                        }
+
+                        self.machine_st.p += 1;
+                    }
                     &Instruction::Allocate(num_cells) => {
                         self.machine_st.allocate(num_cells);
                     }

src/machine/machine_state.rs

@@ -941,6 +941,25 @@ impl MachineState {
             }
         );
     }
+
+    #[inline(always)]
+    pub(super) fn cut_prev_body(&mut self, value: HeapCellValue) {
+        let b = self.b;
+
+        read_heap_cell!(value,
+            (HeapCellValueTag::CutPoint, b0) => {
+                let b0 = b0.get_num() as usize;
+                let b0 = self.stack.index_or_frame(b0).prelude.b;
+
+                if b > b0 {
+                    self.b = b0;
+                }
+            }
+            _ => {
+                self.fail = true;
+            }
+        );
+    }
 }
 
 #[derive(Debug)]