MIG depth rewriting without area increase. (#58)

lsils · Aug 2, 2018 · ab2647d · ab2647d
1 parent 46c0f67
commit ab2647d
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Showing 3 changed files with 49 additions and 6 deletions.
diff --git a/docs/changelog.rst b/docs/changelog.rst
@@ -16,7 +16,7 @@ v0.1 (not yet released)
     - LUT mapping (`lut_mapping`) `#7 <https://github.com/lsils/mockturtle/pull/7>`_
     - Akers synthesis (`akers_synthesis`) `#9 <https://github.com/lsils/mockturtle/pull/9>`_
     - Create LUT network from mapped network (`collapse_mapped_network`) `#13 <https://github.com/lsils/mockturtle/pull/13>`_
-    - MIG algebraic depth rewriting (`mig_algebraic_depth_rewriting`) `#16 <https://github.com/lsils/mockturtle/pull/16>`_
+    - MIG algebraic depth rewriting (`mig_algebraic_depth_rewriting`) `#16 <https://github.com/lsils/mockturtle/pull/16>`_ `#58 <https://github.com/lsils/mockturtle/pull/58>`_
     - Cleanup dangling nodes (`cleanup_dangling`) `#16 <https://github.com/lsils/mockturtle/pull/16>`_
     - Node resynthesis (`node_resynthesis`) `#17 <https://github.com/lsils/mockturtle/pull/17>`_
     - Reconvergency-driven cut computation (`reconv_cut`) `#24 <https://github.com/lsils/mockturtle/pull/24>`_

diff --git a/include/mockturtle/algorithms/mig_algebraic_rewriting.hpp b/include/mockturtle/algorithms/mig_algebraic_rewriting.hpp
@@ -78,6 +78,9 @@ struct mig_algebraic_depth_rewriting_params
    * number of dangling nodes are taken into account.
    */
   float overhead{2.0f};
+
+  /*! \brief Allow area increase while optimizing depth. */
+  bool allow_area_increase{true};
 };
 
 namespace detail
@@ -192,6 +195,10 @@ class mig_algebraic_depth_rewriting_impl
     if ( ntk.level( ntk.get_node( ocs[2] ) ) <= ntk.level( ntk.get_node( ocs[1] ) ) + 1 )
       return false;
 
+    /* child must have single fanout, if no area overhead is allowed */
+    if ( !ps.allow_area_increase && ntk.fanout_size( ntk.get_node( ocs[2] ) ) != 1 )
+      return false;
+
     /* get children of last child */
     auto ocs2 = ordered_children( ntk.get_node( ocs[2] ) );
 
@@ -218,11 +225,14 @@ class mig_algebraic_depth_rewriting_impl
     }
 
     /* distributivity */
-    auto opt = ntk.create_maj( ocs2[2],
-                               ntk.create_maj( ocs[0], ocs[1], ocs2[0] ),
-                               ntk.create_maj( ocs[0], ocs[1], ocs2[1] ) );
-    ntk.substitute_node( n, opt );
-    ntk.update();
+    if ( ps.allow_area_increase )
+    {
+      auto opt = ntk.create_maj( ocs2[2],
+                                 ntk.create_maj( ocs[0], ocs[1], ocs2[0] ),
+                                 ntk.create_maj( ocs[0], ocs[1], ocs2[1] ) );
+      ntk.substitute_node( n, opt );
+      ntk.update();
+    }
     return true;
   }
 

diff --git a/test/algorithms/quality.cpp b/test/algorithms/quality.cpp
@@ -9,6 +9,7 @@
 #include <mockturtle/algorithms/cut_enumeration.hpp>
 #include <mockturtle/algorithms/cut_rewriting.hpp>
 #include <mockturtle/algorithms/lut_mapping.hpp>
+#include <mockturtle/algorithms/mig_algebraic_rewriting.hpp>
 #include <mockturtle/algorithms/node_resynthesis.hpp>
 #include <mockturtle/algorithms/node_resynthesis/akers.hpp>
 #include <mockturtle/algorithms/node_resynthesis/mig_npn.hpp>
@@ -163,4 +164,36 @@ TEST_CASE( "Test quality of MIG resubstitution", "[quality]" )
   CHECK( v == std::vector<uint32_t>{{6, 208, 398, 317, 502, 333, 704, 1007, 1741, 2322, 1460}} );
 }
 
+TEST_CASE( "Test quality of MIG algebraic depth rewriting", "[quality]" )
+{
+  const auto v = foreach_benchmark<mig_network>( []( auto& ntk, auto ) {
+    depth_view depth_ntk{ntk};
+    const auto before = depth_ntk.depth();
+    mig_algebraic_depth_rewriting( depth_ntk );
+    ntk = cleanup_dangling( ntk );
+    depth_ntk.update();
+    return before - depth_ntk.depth();
+  } );
+
+  CHECK( v == std::vector<uint32_t>{{0, 4, 1, 8, 2, 4, 3, 11, 6, 35, 7}} );
+}
+
+TEST_CASE( "Test quality of MIG algebraic depth rewriting without area increase", "[quality]" )
+{
+  const auto v = foreach_benchmark<mig_network>( []( auto& ntk, auto ) {
+    depth_view depth_ntk{ntk};
+    const auto size_before = ntk.num_gates();
+    const auto before = depth_ntk.depth();
+    mig_algebraic_depth_rewriting_params ps;
+    ps.allow_area_increase = false;
+    mig_algebraic_depth_rewriting( depth_ntk, ps );
+    ntk = cleanup_dangling( ntk );
+    depth_ntk.update();
+    CHECK( ntk.num_gates() <= size_before );
+    return before - depth_ntk.depth();
+  } );
+
+  CHECK( v == std::vector<uint32_t>{{0, 1, 0, 5, 0, 0, 2, 6, 3, 0, 6}} );
+}
+
 #endif