add noexcept to frequently used constructors

Author: Daniel Kroening

src/util/dstring.h

@@ -25,7 +25,7 @@ class dstringt final
   #ifdef __GNUC__
   constexpr
   #endif
-  dstringt():no(0)
+  dstringt() noexcept:no(0)
   {
   }
 

src/util/expr.h

@@ -45,7 +45,7 @@ class exprt:public irept
   typedef std::vector<exprt> operandst;
 
   // constructors
-  exprt() { }
+  exprt() noexcept { }
   explicit exprt(const irep_idt &_id):irept(_id) { }
   exprt(const irep_idt &_id, const typet &_type):irept(_id)
   {

src/util/irep.h

@@ -103,7 +103,7 @@ class irept
   bool is_nil() const { return id()==ID_nil; }
   bool is_not_nil() const { return id()!=ID_nil; }
 
-  explicit irept(const irep_idt &_id)
+  explicit irept(const irep_idt &_id) noexcept
 #ifdef SHARING
     :data(&empty_d)
 #endif
@@ -113,12 +113,12 @@ class irept
 
   #ifdef SHARING
   // constructor for blank irep
-  irept():data(&empty_d)
+  irept() noexcept:data(&empty_d)
   {
   }
 
   // copy constructor
-  irept(const irept &irep):data(irep.data)
+  irept(const irept &irep) noexcept:data(irep.data)
   {
     if(data!=&empty_d)
     {
@@ -135,7 +135,7 @@ class irept
   // Copy from rvalue reference.
   // Note that this does avoid a branch compared to the
   // standard copy constructor above.
-  irept(irept &&irep):data(irep.data)
+  irept(irept &&irep) noexcept:data(irep.data)
   {
     #ifdef IREP_DEBUG
     std::cout << "COPY MOVE\n";
@@ -165,7 +165,7 @@ class irept
   #ifdef USE_MOVE
   // Note that the move assignment operator does avoid
   // three branches compared to standard operator above.
-  irept &operator=(irept &&irep)
+  irept &operator=(irept &&irep) noexcept
   {
     #ifdef IREP_DEBUG
     std::cout << "ASSIGN MOVE\n";