bracket verify_attributes/3 interrupts with allocation and deallocation of stack frames.

src/prolog/and_stack.rs

@@ -8,6 +8,7 @@ pub struct Frame {
     pub global_index: usize,
     pub e: usize,
     pub cp: LocalCodePtr,
+    pub special_form_cp: LocalCodePtr,
     perms: Vec<Addr>
 }
 
@@ -17,9 +18,15 @@ impl Frame {
             global_index,
             e: e,
             cp: cp,
+            special_form_cp: LocalCodePtr::default(),
             perms: (1 .. n+1).map(|i| Addr::StackCell(fr, i)).collect()
         }
     }
+
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.perms.len()
+    }
 }
 
 pub struct AndStack(Vec<Frame>);

src/prolog/debray_allocator.rs

@@ -34,6 +34,7 @@ impl DebrayAllocator {
         }
     }
 
+    #[inline]
     fn is_in_use(&self, r: usize) -> bool {
         let in_use_range = r <= self.arity && r >= self.arg_c;
         in_use_range || self.in_use.contains(&r)

src/prolog/machine/attributed_variables.rs

@@ -4,10 +4,9 @@ pub static VERIFY_ATTRS: &str = include_str!("attributed_variables.pl");
 
 pub(super) type Bindings = Vec<(usize, Addr)>;
 
-pub(super) struct AttrVarInitializer {
+pub(super) struct AttrVarInitializer {    
     pub(super) bindings: Bindings,
-    cp_stack: Vec<CodePtr>,
-    pub(super) registers: Registers,
+    pub(super) cp: LocalCodePtr,
     pub(super) verify_attrs_loc: usize
 }
 
@@ -15,20 +14,13 @@ impl AttrVarInitializer {
     pub(super) fn new(p: usize) -> Self {
         AttrVarInitializer {
             bindings: vec![],
+            cp: LocalCodePtr::default(),
             verify_attrs_loc: p,
-            cp_stack: vec![],
-            registers: vec![Addr::HeapCell(0); MAX_ARITY + 1]
         }
     }
 
-    #[inline]
-    pub(super) fn pop_code_ptr(&mut self) -> CodePtr {
-        self.cp_stack.pop().unwrap()
-    }
-
     #[inline]
     pub(super) fn reset(&mut self) {
-        self.cp_stack.clear();
         self.bindings.clear();
     }
 }
@@ -37,7 +29,7 @@ impl MachineState {
     pub(super) fn push_attr_var_binding(&mut self, h: usize, addr: Addr)
     {
         if self.attr_var_init.bindings.is_empty() {
-            self.attr_var_init.cp_stack.push(self.p.clone() + 1);
+            self.attr_var_init.cp = self.p.local() + 1;
             self.p = CodePtr::VerifyAttrInterrupt(self.attr_var_init.verify_attrs_loc);
         }
 
@@ -54,18 +46,32 @@ impl MachineState {
         (var_list_addr, value_list_addr)
     }
 
+    pub(super)
+    fn calculate_register_threshold(&self) -> usize {
+        let mut count = 0;
+        
+        for r in 1 .. MAX_ARITY + 1 {
+            if let &Addr::HeapCell(0) = &self[RegType::Temp(r)] {
+                break;
+            }
+
+            count += 1;
+        }
+
+        count
+    }
+    
     pub(super)
     fn verify_attributes(&mut self)
     {
         /* STEP 1: Undo bindings in machine.
            STEP 2: Write the list of bindings to two lists in the heap, one for vars, one for values.
-           STEP 3: Swap the machine's Registers for attr_var_init's Registers.
-           STEP 4: Pass the addresses of the lists to iterate in the attr_vars special form.
+           STEP 3: Pass the addresses of the lists to iterate in the attr_vars special form.
                    Call verify_attributes/3 wherever applicable.
-           STEP 5: Redo the bindings.
-           STEP 6: Call the goals.
-           STEP 7: Pop the top of AttrVarInitializer::cp_stack to self.p.
-           STEP 8: Swap the AttrVarInitializer's Registers back for the machine's Registers.
+           STEP 4: Redo the bindings.
+           STEP 5: Call the goals.
+           STEP 6: Pop the top of AttrVarInitializer::cp_stack to self.p.
+           STEP 7: Swap the AttrVarInitializer's Registers back for the machine's Registers.
          */
 
         // STEP 1.
@@ -75,10 +81,8 @@ impl MachineState {
 
         // STEP 2.
         let (var_list_addr, value_list_addr) = self.populate_var_and_value_lists();
-        // STEP 3.
-        mem::swap(&mut self.registers, &mut self.attr_var_init.registers);
 
-        // STEP 4.
+        // STEP 3.
         self[temp_v!(1)] = var_list_addr;
         self[temp_v!(2)] = value_list_addr;
     }

src/prolog/machine/machine_state_impl.rs

@@ -2175,7 +2175,7 @@ impl MachineState {
         self.e = self.and_stack.len() - 1;
     }
 
-    fn deallocate(&mut self) {
+    pub(super) fn deallocate(&mut self) {
         let e = self.e;
 
         self.cp = self.and_stack[e].cp.clone();

src/prolog/machine/mod.rs

@@ -586,6 +586,17 @@ impl MachineState {
                 CodePtr::Local(_) =>
                     break,
                 CodePtr::VerifyAttrInterrupt(p) => {
+                    let rs  = self.calculate_register_threshold();
+
+                    self.allocate(rs); // store temp vars in perm vars slots.
+
+                    let e = self.e;
+                    self.and_stack[e].special_form_cp = self.attr_var_init.cp;
+
+                    for i in 1 .. self.and_stack[e].len() + 1 {
+                        self.and_stack[e][i] = self[RegType::Temp(i)].clone();
+                    }
+
                     self.verify_attributes();
 
                     self.num_of_args = 2;

src/prolog/machine/system_calls.rs

@@ -450,9 +450,15 @@ impl MachineState {
                                     CWILCallPolicy.")
                 },
             &SystemClauseType::RestoreCodePtrFromSpecialFormCP => {
-                self.p = self.attr_var_init.pop_code_ptr();
-                mem::swap(&mut self.registers, &mut self.attr_var_init.registers);
+                let e = self.e;
+                
+                for i in 1 .. self.and_stack[e].len() + 1 {
+                    self[RegType::Temp(i)] = self.and_stack[e][i].clone();
+                }
 
+                self.p = CodePtr::Local(self.and_stack[e].special_form_cp);
+                self.deallocate();
+                
                 return Ok(());
             },
             &SystemClauseType::RestoreCutPolicy => {

src/prolog/write.rs

@@ -13,6 +13,23 @@ fn error_string(e: &String) -> String {
     format!("error: exception thrown: {}", e)
 }
 
+impl fmt::Display for LocalCodePtr {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            LocalCodePtr::DirEntry(p) =>
+                write!(f, "LocalCodePtr::DirEntry({})", p),
+            LocalCodePtr::InSituDirEntry(p) =>
+                write!(f, "LocalCodePtr::InSituDirEntry({})", p),
+            LocalCodePtr::TopLevel(cn, p) =>
+                write!(f, "LocalCodePtr::TopLevel({}, {})", cn, p),
+            LocalCodePtr::UserGoalExpansion(p) =>
+                write!(f, "LocalCodePtr::UserGoalExpansion({})", p),
+            LocalCodePtr::UserTermExpansion(p) =>
+                write!(f, "LocalCodePtr::UserTermExpansion({})", p),
+        }
+    }
+}
+
 impl fmt::Display for IndexPtr {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {