Avoid repeated lookups during irep serialisation

irep serialisation spends most of its time in numbering, which in turn spends
this time in finding map entries. Make sure finding map entries happens only
once per call to number().

Author: tautschnig

src/util/irep_hash_container.cpp

@@ -18,19 +18,18 @@ size_t irep_hash_container_baset::number(const irept &irep)
 {
   // the ptr-hash provides a speedup of up to 3x
 
-  ptr_hasht::const_iterator it=ptr_hash.find(&irep.read());
+  auto entry = ptr_hash.emplace(
+    std::piecewise_construct,
+    std::forward_as_tuple(&irep.read()),
+    std::forward_as_tuple(0, irep));
 
-  if(it!=ptr_hash.end())
-    return it->second.number;
+  if(!entry.second && entry.first->second.final_number)
+    return entry.first->second.number;
 
-  packedt packed;
-  pack(irep, packed);
-  size_t id=numbering.number(packed);
+  const size_t id = numbering.number(pack(irep));
 
-  ptr_hash.emplace(
-    std::piecewise_construct,
-    std::forward_as_tuple(&irep.read()),
-    std::forward_as_tuple(id, irep));
+  entry.first->second.number = id;
+  entry.first->second.final_number = true;
 
   return id;
 }
@@ -44,9 +43,7 @@ size_t irep_hash_container_baset::vector_hasht::operator()(
   return result;
 }
 
-void irep_hash_container_baset::pack(
-  const irept &irep,
-  packedt &packed)
+irep_hash_container_baset::packedt irep_hash_container_baset::pack(const irept &irep)
 {
   const irept::subt &sub=irep.get_sub();
   const irept::named_subt &named_sub=irep.get_named_sub();
@@ -61,7 +58,7 @@ void irep_hash_container_baset::pack(
 #else
     const std::size_t named_sub_size = named_sub.size();
 #endif
-    packed.reserve(1 + 1 + sub.size() + 1 + named_sub_size * 2);
+    packedt packed(1 + 1 + sub.size() + 1 + named_sub_size * 2);
 
     packed.push_back(irep_id_hash()(irep.id()));
 
@@ -75,6 +72,8 @@ void irep_hash_container_baset::pack(
       packed.push_back(irep_id_hash()(sub_irep.first)); // id
       packed.push_back(number(sub_irep.second));        // sub-irep
     }
+
+    return packed;
   }
   else
   {
@@ -83,7 +82,7 @@ void irep_hash_container_baset::pack(
 
     // we pack: the irep id, the sub size, the subs, the named-sub size, and
     // each of the non-comment named subs with their ids
-    packed.reserve(1 + 1 + sub.size() + 1 + non_comment_count * 2);
+    packedt packed(1 + 1 + sub.size() + 1 + non_comment_count * 2);
 
     packed.push_back(irep_id_hash()(irep.id()));
 
@@ -98,5 +97,7 @@ void irep_hash_container_baset::pack(
         packed.push_back(irep_id_hash()(sub_irep.first)); // id
         packed.push_back(number(sub_irep.second));        // sub-irep
       }
+
+    return packed;
   }
 }

src/util/irep_hash_container.h

@@ -49,6 +49,7 @@ class irep_hash_container_baset
   {
     std::size_t number;
     irept irep; // copy to keep addresses stable
+    bool final_number = false;
 
     irep_entryt(std::size_t _number, const irept &_irep)
       : number(_number), irep(_irep)
@@ -72,7 +73,7 @@ class irep_hash_container_baset
   typedef hash_numbering<packedt, vector_hasht> numberingt;
   numberingt numbering;
 
-  void pack(const irept &irep, packedt &);
+  packedt pack(const irept &irep);
 
   bool full;
 };