gdb: some global_block improvements

Some refactors around struct global_block, all in one patch because they
all tie in together and are relatively trivial.

 - Make block::global_block() and blockvector::global_block() return
   `global_block *`, instead of `block *`.  There is no cost in doing
   so, and it's a bit more precise.  Callers of these methods that need
   a `global_block *` won't need to cast themselves.

 - Add some block::as_global_block methods, as a way to get a
   `global_block *` from a `block *` when you know it's a global block.
   This is basically a static cast with an assert.

 - Move set_compunit_symtab to global_block, since it requires the
   block to be a global block anyway.  Rename to just `set_compunit` (I
   think that compunit_symtab should just be renamed compunit...).

 - Move the get_block_compunit_symtab free function to be a method of
   global_block.

 - Make global_block::compunit_symtab private and rename.

 - Simplify initialize_block_iterator.

Change-Id: I1667a86b5c1a02d0d460cfad55b5d3d48867583d
Approved-By: Tom Tromey <tom@tromey.com>

4 files changed, 68 insertions, 64 deletions

diff --git a/gdb/block.c b/gdb/block.c
index acf21e2..d4baaae 100644
--- a/gdb/block.c
+++ b/gdb/block.c
@@ -41,13 +41,10 @@ struct block_namespace_info : public allocate_on_obstack<block_namespace_info>
 struct objfile *
 block::objfile () const
 {
-  const struct global_block *global_block;
-
   if (function () != nullptr)
     return function ()->objfile ();
 
-  global_block = (struct global_block *) this->global_block ();
-  return global_block->compunit_symtab->objfile ();
+  return this->global_block ()->compunit ()->objfile ();
 }
 
 /* See block.  */
@@ -364,7 +361,7 @@ block::static_block () const
 
 /* See block.h.  */
 
-const struct block *
+const struct global_block *
 block::global_block () const
 {
   const block *block = this;
@@ -372,33 +369,40 @@ block::global_block () const
   while (block->superblock () != NULL)
     block = block->superblock ();
 
-  return block;
+  return block->as_global_block ();
 }
 
 /* See block.h.  */
 
-const struct block *
-block::function_block () const
+struct global_block *
+block::as_global_block ()
 {
-  const block *block = this;
+  gdb_assert (this->is_global_block ());
 
-  while (block != nullptr && block->function () == nullptr)
-    block = block->superblock ();
+  return static_cast<struct global_block *>(this);
+}
 
-  return block;
+/* See block.h.  */
+
+const struct global_block *
+block::as_global_block () const
+{
+  gdb_assert (this->is_global_block ());
+
+  return static_cast<const struct global_block *>(this);
 }
 
 /* See block.h.  */
 
-void
-block::set_compunit_symtab (struct compunit_symtab *cu)
+const struct block *
+block::function_block () const
 {
-  struct global_block *gb;
+  const block *block = this;
 
-  gdb_assert (superblock () == NULL);
-  gb = (struct global_block *) this;
-  gdb_assert (gb->compunit_symtab == NULL);
-  gb->compunit_symtab = cu;
+  while (block != nullptr && block->function () == nullptr)
+    block = block->superblock ();
+
+  return block;
 }
 
 /* See block.h.  */
@@ -416,21 +420,6 @@ block::static_link () const
   return (struct dynamic_prop *) objfile_lookup_static_link (objfile, this);
 }
 
-/* Return the compunit of the global block.  */
-
-static struct compunit_symtab *
-get_block_compunit_symtab (const struct block *block)
-{
-  struct global_block *gb;
-
-  gdb_assert (block->superblock () == NULL);
-  gb = (struct global_block *) block;
-  gdb_assert (gb->compunit_symtab != NULL);
-  return gb->compunit_symtab;
-}
-
-
-
 /* Initialize a block iterator, either to iterate over a single block,
    or, for static and global blocks, all the included symtabs as
    well.  */
@@ -441,30 +430,26 @@ initialize_block_iterator (const struct block *block,
 			   const lookup_name_info *name)
 {
   enum block_enum which;
-  struct compunit_symtab *cu;
 
   iter->idx = -1;
   iter->name = name;
 
-  if (block->superblock () == NULL)
-    {
-      which = GLOBAL_BLOCK;
-      cu = get_block_compunit_symtab (block);
-    }
-  else if (block->superblock ()->superblock () == NULL)
-    {
-      which = STATIC_BLOCK;
-      cu = get_block_compunit_symtab (block->superblock ());
-    }
+  if (block->is_global_block ())
+    which = GLOBAL_BLOCK;
+  else if (block->is_static_block ())
+    which = STATIC_BLOCK;
   else
     {
       iter->d.block = block;
+
       /* A signal value meaning that we're iterating over a single
 	 block.  */
       iter->which = FIRST_LOCAL_BLOCK;
       return;
     }
 
+  compunit_symtab *cu = block->global_block ()->compunit ();
+
   /* If this is an included symtab, find the canonical includer and
      use it instead.  */
   while (cu->user != NULL)
diff --git a/gdb/block.h b/gdb/block.h
index ae676c4..c3babad 100644
--- a/gdb/block.h
+++ b/gdb/block.h
@@ -264,25 +264,26 @@ struct block : public allocate_on_obstack<block>
     return sup->is_global_block ();
   }
 
-  /* Return the static block associated with block.  */
+  /* Return the global block associated with block.  */
 
-  const struct block *global_block () const;
+  const struct global_block *global_block () const;
 
   /* Return true if this block is a global block.  */
 
   bool is_global_block () const
   { return superblock () == nullptr; }
 
+  /* Return this block as a global_block.  This block must be a global
+     block.  */
+  struct global_block *as_global_block ();
+  const struct global_block *as_global_block () const;
+
   /* Return the function block for this block.  Returns nullptr if
      there is no enclosing function, i.e., if this block is a static
      or global block.  */
 
   const struct block *function_block () const;
 
-  /* Set the compunit of this block, which must be a global block.  */
-
-  void set_compunit_symtab (struct compunit_symtab *);
-
   /* Return a property to evaluate the static link associated to this
      block.
 
@@ -346,13 +347,31 @@ private:
 };
 
 /* The global block is singled out so that we can provide a back-link
-   to the compunit symtab.  */
+   to the compunit.  */
 
 struct global_block : public block
 {
-  /* This holds a pointer to the compunit symtab holding this block.  */
+  /* Set the compunit of this global block.
+
+     The compunit must not have been set previously.  */
+  void set_compunit (compunit_symtab *cu)
+  {
+    gdb_assert (m_compunit == nullptr);
+    m_compunit = cu;
+  }
+
+  /* Return the compunit of this global block.
 
-  struct compunit_symtab *compunit_symtab = nullptr;
+     The compunit must have been set previously.  */
+  compunit_symtab *compunit () const
+  {
+    gdb_assert (m_compunit != nullptr);
+    return m_compunit;
+  }
+
+private:
+  /* This holds a pointer to the compunit holding this block.  */
+  compunit_symtab *m_compunit = nullptr;
 };
 
 struct blockvector
@@ -394,12 +413,15 @@ struct blockvector
   { return m_num_blocks; }
 
   /* Return the global block of this blockvector.  */
-  struct block *global_block ()
-  { return this->block (GLOBAL_BLOCK); }
+  struct global_block *global_block ()
+  { return static_cast<struct global_block *> (this->block (GLOBAL_BLOCK)); }
 
   /* Const version of the above.  */
-  const struct block *global_block () const
-  { return this->block (GLOBAL_BLOCK); }
+  const struct global_block *global_block () const
+  {
+    return static_cast<const struct global_block *>
+      (this->block (GLOBAL_BLOCK));
+  }
 
   /* Return the static block of this blockvector.  */
   struct block *static_block ()
diff --git a/gdb/buildsym.c b/gdb/buildsym.c
index 1c762ad..02d6848 100644
--- a/gdb/buildsym.c
+++ b/gdb/buildsym.c
@@ -951,11 +951,7 @@ buildsym_compunit::end_compunit_symtab_with_blockvector
   cu->set_producer (m_producer);
 
   cu->set_blockvector (blockvector);
-  {
-    struct block *b = blockvector->global_block ();
-
-    b->set_compunit_symtab (cu);
-  }
+  blockvector->global_block ()->set_compunit (cu);
 
   cu->set_macro_table (release_macros ());
 
diff --git a/gdb/jit.c b/gdb/jit.c
index d451332..89c967d 100644
--- a/gdb/jit.c
+++ b/gdb/jit.c
@@ -613,6 +613,7 @@ finalize_symtab (struct gdb_symtab *stab, struct objfile *objfile)
 	new_block = new (&objfile->objfile_obstack) global_block;
       else
 	new_block = new (&objfile->objfile_obstack) block;
+
       new_block->set_multidict
 	(mdict_create_linear (&objfile->objfile_obstack, NULL));
       new_block->set_superblock (block_iter);
@@ -624,7 +625,7 @@ finalize_symtab (struct gdb_symtab *stab, struct objfile *objfile)
       bv->set_block (i, new_block);
 
       if (i == GLOBAL_BLOCK)
-	new_block->set_compunit_symtab (cust);
+	new_block->as_global_block ()->set_compunit (cust);
     }
 
   /* Fill up the superblock fields for the real blocks, using the