syn: Add slot check to parse

Assisted-by: Claude (various models)
Signed-off-by: Martin Povišer <povik@cutebit.org>

Author: povik

src/syn/src/ir/Parse.cc

@@ -539,7 +539,13 @@ class Parser
       error("unknown cell keyword: " + keyword);
     }
 
-    (void) id;
+    const uint32_t expected_slots = std::max(width, 1u);
+    if (g->tableSize() != id + expected_slots) {
+      error("'" + keyword + "' declared output width " + std::to_string(width)
+            + " but produced " + std::to_string(g->tableSize() - id) + " slot"
+            + (g->tableSize() - id == 1 ? "" : "s"));
+    }
+
     expectNewline();
   }
 

src/syn/test/parse_test.cc

@@ -2,6 +2,7 @@
 // Copyright (c) 2026, The OpenROAD Authors
 
 #include <sstream>
+#include <stdexcept>
 
 #include "gtest/gtest.h"
 #include "syn/ir/Graph.h"
@@ -189,4 +190,13 @@ TEST(ParseTest, NonConsecutiveIds)
   }
 }
 
+TEST(ParseTest, RejectsDeclaredWidthMismatch)
+{
+  std::istringstream is(
+      "%3:8 = input \"a\"\n"
+      "%11:8 = input \"b\"\n"
+      "%19:16 = mul %3:8 %11:8\n");
+  EXPECT_THROW({ (void) Graph::parse(is); }, std::runtime_error);
+}
+
 }  // namespace syn