This patch adds an initial implementation for a new helper type for

generating GIMPLE statements.

The type is called gimple_builder.  There are two main variants:
gimple_builder_normal and gimple_builder_ssa.  The difference between
the two is the temporaries they create.  The 'normal' builder creates
temporaries in normal form (i.e., VAR_DECLs).  The 'ssa' builder
creates SSA names.

The basic functionality is described in
http://gcc.gnu.org/wiki/cxx-conversion/gimple-generation.  I expect it
to evolve as I address feedback on this initial implementation.

The patch implements the initial builder.  It has enough functionality
to simplify the generation of 3 address assignments (the bulk of all
generated code).

To use the builder:

1- Declare an instance 'gb' of gimple_builder_normal or
   gimple_builder_ssa.  E.g., gimple_builder_ssa gb;

2- Use gb.add_* to add a new statement to it.  This
   returns an SSA name or VAR_DECL with the value of the added
   statement.

3- Call gb.insert_*() to insert the sequence of statements in the
   builder into a statement iterator.

For instance, in asan.c we generate the expression:

(shadow != 0) & (base_addr & 7) + (size_in_bytes - 1)) >= shadow).

with the following code:

-----------------------------------------------------------------------------
      gimple_builder_ssa gb(location);
      t = gb.add (NE_EXPR, shadow, 0);
      tree t1 = gb.add (BIT_AND_EXPR, base_addr, 7);
      t1 = gb.add_type_cast (shadow_type, t1);
      if (size_in_bytes > 1)
	t1 = gb.add (PLUS_EXPR, t1, size_in_bytes - 1);
      t1 = gb.add (GE_EXPR, t1, shadow);
      t = gb.add (BIT_AND_EXPR, t, t1);
      gb.insert_after (&gsi, GSI_NEW_STMT);
-----------------------------------------------------------------------------

In contrast, the original code needed to generate the same expression
is significantly longer:

-----------------------------------------------------------------------------
      g = gimple_build_assign_with_ops (NE_EXPR,
					make_ssa_name (boolean_type_node,
						       NULL),
					shadow,
					build_int_cst (shadow_type, 0));
      gimple_set_location (g, location);
      gsi_insert_after (&gsi, g, GSI_NEW_STMT);
      t = gimple_assign_lhs (g);

      g = gimple_build_assign_with_ops (BIT_AND_EXPR,
					make_ssa_name (uintptr_type,
						       NULL),
					base_addr,
					build_int_cst (uintptr_type, 7));
      gimple_set_location (g, location);
      gsi_insert_after (&gsi, g, GSI_NEW_STMT);

      g = gimple_build_assign_with_ops (NOP_EXPR,
					make_ssa_name (shadow_type,
						       NULL),
					gimple_assign_lhs (g), NULL_TREE);
      gimple_set_location (g, location);
      gsi_insert_after (&gsi, g, GSI_NEW_STMT);
      if (size_in_bytes > 1)
	{
	  g = gimple_build_assign_with_ops (PLUS_EXPR,
					    make_ssa_name (shadow_type,
							   NULL),
					    gimple_assign_lhs (g),
					    build_int_cst (shadow_type,
							   size_in_bytes - 1));
	  gimple_set_location (g, location);
	  gsi_insert_after (&gsi, g, GSI_NEW_STMT);
	}

      g = gimple_build_assign_with_ops (GE_EXPR,
					make_ssa_name (boolean_type_node,
						       NULL),
					gimple_assign_lhs (g),
					shadow);
      gimple_set_location (g, location);
      gsi_insert_after (&gsi, g, GSI_NEW_STMT);

      g = gimple_build_assign_with_ops (BIT_AND_EXPR,
					make_ssa_name (boolean_type_node,
						       NULL),
					t, gimple_assign_lhs (g));
      gimple_set_location (g, location);
      gsi_insert_after (&gsi, g, GSI_NEW_STMT);
      t = gimple_assign_lhs (g);
-----------------------------------------------------------------------------

I expect to add more facilities to the builder.  Mainly, generation of
control flow altering statements which will automatically reflect on
the CFG.

I do not think the helper should replace all code generation, but it
should serve as a shorter/simpler way of generating GIMPLE IL in the
common cases.

git-svn-id: https://gcc.gnu.org/svn/gcc/branches/cxx-conversion@196640 138bc75d-0d04-0410-961f-82ee72b054a4

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