Do not unroll simple array assignments in V3Slice (#7359)

See also #5644

src/V3Const.cpp

@@ -1630,6 +1630,9 @@ class ConstVisitor final : public VNVisitor {
         if (!thensp->lhsp()->sameGateTree(elsesp->lhsp())) return false;
         if (!thensp->rhsp()->gateTree()) return false;
         if (!elsesp->rhsp()->gateTree()) return false;
+        // Must not create an expression with unpacked array type
+        if (VN_IS(thensp->rhsp()->dtypep()->skipRefp(), UnpackArrayDType)) return false;
+        if (VN_IS(elsesp->rhsp()->dtypep()->skipRefp(), UnpackArrayDType)) return false;
         if (m_underRecFunc) return false;  // This optimization may lead to infinite recursion
         // Only do it if not calls and both pure, otherwise undoes V3LiftExpr
         return !VN_IS(thensp->rhsp(), NodeFTaskRef)  //

src/V3Gate.cpp

@@ -692,11 +692,17 @@ class GateInline final {
                 }
             }
 
+            AstVarScope* const vscp = vVtxp->varScp();
+            AstNodeExpr* const substp = okVisitor.substitutionp();
+
+            // Only inline arrays if a simple variable
+            if (VN_IS(vscp->dtypep()->skipRefp(), UnpackArrayDType)) {
+                if (!VN_IS(substp, NodeVarRef)) continue;
+            }
+
             // Process it
             ++m_statInlined;
 
-            AstVarScope* const vscp = vVtxp->varScp();
-            AstNodeExpr* const substp = okVisitor.substitutionp();
             if (debug() >= 9) {
                 vscp->dumpTree("substituting: ");
                 substp->dumpTree("        with: ");

src/V3Slice.cpp

@@ -260,6 +260,16 @@ class SliceVisitor final : public VNVisitor {
             return false;
         }
 
+        // Skip if this is a simple a = b assignment of identical arrays
+        if (AstVarRef* const lhsp = VN_CAST(nodep->lhsp(), VarRef)) {
+            if (AstVarRef* const rhsp = VN_CAST(nodep->rhsp(), VarRef)) {
+                if (!hasSc && lhsp->dtypep()->skipRefp()->sameTree(rhsp->dtypep()->skipRefp())) {
+                    m_okInitArray = true;  // VL_RESTORER in visit(AstNodeAssign)
+                    return false;
+                }
+            }
+        }
+
         UINFO(4, "Slice optimizing " << nodep);
         ++m_statAssigns;
 

test_regress/t/t_opt_slice.py

@@ -13,6 +13,6 @@ test.scenarios('simulator')
 
 test.compile(verilator_flags2=['--sc', '--stats'])
 
-test.file_grep(test.stats, r'Optimizations, Slice array assignments\s+(\d+)', 5)
+test.file_grep(test.stats, r'Optimizations, Slice array assignments\s+(\d+)', 2)
 
 test.passes()