fix double multipack conversion of Exprs in LHSs

src/Convert/MultiplePacked.hs

@@ -115,13 +115,18 @@ traverseExprM = traverseNestedExprsM $ stately traverseExpr
 -- LHSs need to be converted too. Rather than duplicating the procedures, we
 -- turn LHSs into expressions temporarily and use the expression conversion.
 traverseLHSM :: LHS -> State Info LHS
-traverseLHSM lhs = do
-    let expr = lhsToExpr lhs
-    expr' <- traverseExprM expr
-    case exprToLHS expr' of
-        Just lhs' -> return lhs'
-        Nothing -> error $ "multi-packed conversion created non-LHS from "
-            ++ (show expr) ++ " to " ++ (show expr')
+traverseLHSM = traverseNestedLHSsM traverseLHSSingleM
+    where
+        -- We can't use traverseExprM directly because that would cause Exprs
+        -- inside of LHSs to be converted twice in a single cycle!
+        traverseLHSSingleM :: LHS -> State Info LHS
+        traverseLHSSingleM lhs = do
+            let expr = lhsToExpr lhs
+            expr' <- stately traverseExpr expr
+            case exprToLHS expr' of
+                Just lhs' -> return lhs'
+                Nothing -> error $ "multi-packed conversion created non-LHS from "
+                    ++ (show expr) ++ " to " ++ (show expr')
 
 traverseExpr :: Info -> Expr -> Expr
 traverseExpr typeMap =

test/basic/multipack_expr_in_lhs.sv

+module top;
+    logic [3:0][7:0] arr;
+    logic [3:0][1:0] idx;
+    assign idx = { 2'b01, 2'b11, 2'b00, 2'b10 };
+    initial begin
+        arr[idx[0]] = 8'hDE;
+        arr[idx[1]] = 8'hAD;
+        arr[idx[2]] = 8'hBE;
+        arr[idx[3]] = 8'hEF;
+        $display("%h", arr);
+    end
+endmodule

test/basic/multipack_expr_in_lhs.v

+module top;
+    reg [31:0] arr;
+    wire [7:0] idx;
+    assign idx = { 2'b01, 2'b11, 2'b00, 2'b10 };
+    initial begin
+        arr[idx[0 * 2 +: 2] * 8 +: 8] = 8'hDE;
+        arr[idx[1 * 2 +: 2] * 8 +: 8] = 8'hAD;
+        arr[idx[2 * 2 +: 2] * 8 +: 8] = 8'hBE;
+        arr[idx[3 * 2 +: 2] * 8 +: 8] = 8'hEF;
+        $display("%h", arr);
+    end
+endmodule