RTL to have one array-array assignment instead of bit blasted assignm…

…ents (#487)

lib/src/synthesizers/systemverilog.dart

@@ -882,6 +882,7 @@ class _SynthModuleDefinition {
     }
 
     // The order of these is important!
+    _collapseArrays();
     _collapseAssignments();
     _assignSubmodulePortMapping();
     _replaceNetConnections();
@@ -1103,6 +1104,59 @@ class _SynthModuleDefinition {
     }
   }
 
+  /// Merges bit blasted array assignments into one single assignment when
+  /// it's full array-full array assignment
+  void _collapseArrays() {
+    final boringArrayPairs = <(_SynthLogic, _SynthLogic)>[];
+
+    var prevAssignmentCount = 0;
+    while (prevAssignmentCount != assignments.length) {
+      final reducedAssignments = <_SynthAssignment>[];
+
+      final groupedAssignments =
+          <(_SynthLogic, _SynthLogic), List<_SynthAssignment>>{};
+
+      for (final assignment in assignments) {
+        final src = assignment.src;
+        final dst = assignment.dst;
+
+        if (src is _SynthLogicArrayElement && dst is _SynthLogicArrayElement) {
+          final srcArray = src.parentArray;
+          final dstArray = dst.parentArray;
+
+          assert(srcArray.logics.length == 1, 'should be 1');
+          assert(dstArray.logics.length == 1, 'should be 1');
+
+          if (srcArray.logics.first.elements.length !=
+                  dstArray.logics.first.elements.length ||
+              boringArrayPairs.contains((srcArray, dstArray))) {
+            reducedAssignments.add(assignment);
+          } else {
+            groupedAssignments[(srcArray, dstArray)] ??= [];
+            groupedAssignments[(srcArray, dstArray)]!.add(assignment);
+          }
+        } else {
+          reducedAssignments.add(assignment);
+        }
+      }
+
+      for (final MapEntry(key: (srcArray, dstArray), value: arrAssignments)
+          in groupedAssignments.entries) {
+        if (arrAssignments.length == srcArray.logics.first.elements.length) {
+          reducedAssignments.add(_SynthAssignment(srcArray, dstArray));
+        } else {
+          reducedAssignments.addAll(arrAssignments);
+          boringArrayPairs.add((srcArray, dstArray));
+        }
+      }
+
+      prevAssignmentCount = assignments.length;
+      assignments
+        ..clear()
+        ..addAll(reducedAssignments);
+    }
+  }
+
   /// Collapses assignments that don't need to remain present.
   void _collapseAssignments() {
     // there might be more assign statements than necessary, so let's ditch them
@@ -1183,7 +1237,8 @@ class _SynthLogicArrayElement extends _SynthLogic {
 
   @override
   String get name {
-    final n = '${parentArray.name}[${logic.arrayIndex!}]';
+    final parentArrayname = parentArray.replacement?.name ?? parentArray.name;
+    final n = '$parentArrayname[${logic.arrayIndex!}]';
     assert(
       Sanitizer.isSanitary(
           n.substring(0, n.contains('[') ? n.indexOf('[') : null)),

test/array_collapsing_test.dart

@@ -0,0 +1,109 @@
+// Copyright (C) 2024 Intel Corporation
+// SPDX-License-Identifier: BSD-3-Clause
+//
+// array_collapsing_test.dart
+// Tests for array collapsing
+//
+// 2024 June 5
+// Author: Shankar Sharma <[email protected]>
+
+import 'package:rohd/rohd.dart';
+import 'package:rohd/src/utilities/simcompare.dart';
+import 'package:test/test.dart';
+
+class ArrayModule extends Module {
+  ArrayModule(LogicArray a) {
+    final inpA = addInputArray('a', a, dimensions: a.dimensions);
+    addOutputArray('b', dimensions: a.dimensions) <= inpA;
+
+    final inoutA = addInOutArray('c', a, dimensions: a.dimensions);
+    addOutputArray('d', dimensions: [a.dimensions.last]) <=
+        inoutA.elements.first;
+  }
+}
+
+class ArrayModuleWithNetIntermediates extends Module {
+  ArrayModuleWithNetIntermediates(LogicArray a, LogicArray b) {
+    a = addInOutArray('a', a,
+        dimensions: a.dimensions,
+        elementWidth: a.elementWidth,
+        numUnpackedDimensions: a.numUnpackedDimensions);
+
+    final intermediate = LogicArray.net(
+      a.dimensions,
+      a.elementWidth,
+      name: 'intermediate',
+      naming: Naming.reserved,
+    );
+
+    b = addInOutArray('b', b,
+        dimensions: a.dimensions,
+        elementWidth: a.elementWidth,
+        numUnpackedDimensions: a.numUnpackedDimensions);
+
+    intermediate <= a;
+    b <= intermediate;
+  }
+}
+
+void main() {
+  tearDown(() async {
+    await Simulator.reset();
+  });
+  test('array nets with intermediate collapse', () async {
+    final mod = ArrayModuleWithNetIntermediates(
+        LogicArray([3, 3], 1), LogicArray([3, 3], 1));
+    await mod.build();
+
+    final sv = mod.generateSynth();
+    expect(sv,
+        contains('net_connect #(.WIDTH(9)) net_connect (intermediate, a);'));
+    expect(sv,
+        contains('net_connect #(.WIDTH(9)) net_connect_0 (b, intermediate);'));
+
+    final vectors = [
+      Vector({'a': 0}, {'b': 0}),
+      Vector({'a': 123}, {'b': 123}),
+    ];
+    await SimCompare.checkFunctionalVector(mod, vectors);
+    SimCompare.checkIverilogVector(mod, vectors);
+  });
+
+  test('array nets with intermediate collapse with unpacked', () async {
+    final mod = ArrayModuleWithNetIntermediates(
+        LogicArray([3, 3], 1, numUnpackedDimensions: 2),
+        LogicArray([3, 3], 1, numUnpackedDimensions: 2));
+    await mod.build();
+
+    final sv = mod.generateSynth();
+    expect(sv,
+        contains('net_connect #(.WIDTH(9)) net_connect (intermediate, a);'));
+    expect(sv,
+        contains('net_connect #(.WIDTH(9)) net_connect_0 (b, intermediate);'));
+
+    final vectors = [
+      Vector({'a': 0}, {'b': 0}),
+      Vector({'a': 123}, {'b': 123}),
+    ];
+    await SimCompare.checkFunctionalVector(mod, vectors);
+  });
+
+  test('collapse test 2d', () async {
+    final mod = ArrayModule(LogicArray([4, 4], 1));
+    await mod.build();
+
+    final sv = mod.generateSynth();
+
+    expect(sv, contains('assign d = c[0];'));
+    expect(sv, contains('assign b = a;'));
+
+    final vectors = [
+      Vector({'a': 0}, {'b': 0}),
+      Vector({'a': 123}, {'b': 123}),
+      Vector({'c': 6}, {'d': 6}),
+    ];
+
+    await SimCompare.checkFunctionalVector(mod, vectors);
+    SimCompare.checkIverilogVector(mod, vectors);
+  });
+}