Allow more variable removal in scoped DFG (#6260)

src/V3DfgVertices.h

@@ -87,10 +87,13 @@ public:
 
     // Variable referenced outside the containing module/netlist.
     bool hasExtRefs() const {
-        if (m_varp->isIO()) return true;  // Ports
-        if (m_varp->isTrace()) return true;  // Traced
-        if (m_varp->isForced()) return true;  // Forced
-        if (hasXRefs()) return true;  // Target of a hierarchical reference
+        // In scoped mode, we can ignrore some of these as they were made explicit by then
+        if (!m_varScopep) {
+            if (m_varp->isIO()) return true;  // Ports
+            if (m_varp->isTrace()) return true;  // Traced
+            if (m_varp->isForced()) return true;  // Forced
+            if (hasXRefs()) return true;  // Target of a hierarchical reference
+        }
         if (m_varp->isPrimaryIO()) return true;  // Top level ports
         if (m_varp->isSigPublic()) return true;  // Public
         return false;

test_regress/t/t_cover_toggle.py

@@ -21,7 +21,7 @@ test.inline_checks()
 test.file_grep_not(test.obj_dir + "/coverage.dat", "largeish")
 
 if test.vlt_all:
-    test.file_grep(test.stats, r'Coverage, Toggle points joined\s+(\d+)', 13)
+    test.file_grep(test.stats, r'Coverage, Toggle points joined\s+(\d+)', 14)
 
 test.run(cmd=[
     os.environ["VERILATOR_ROOT"] + "/bin/verilator_coverage",

test_regress/t/t_inst_tree_inl0_pub1.py

@@ -42,7 +42,7 @@ if test.vlt_all:
     # We expect to combine sequent functions across multiple instances of
     # l2, l3, l4, l5. If this number drops, please confirm this has not broken.
     test.file_grep(test.stats, r'Optimizations, Combined CFuncs\s+(\d+)',
-                   (91 if test.vltmt else 87))
+                   (107 if test.vltmt else 114))
 
     # Everything should use relative references
     check_relative_refs("t", True)