Fix dehash of a suffix after a hashed name (#8556)

src/V3String.cpp

@@ -656,7 +656,7 @@ string VHashSha512::digestSymbol24() {
                          | (static_cast<int>(binhash[pos + 2] & 0xc0) >> 6)];
         result += digits[((binhash[pos + 2] & 0x3f))];
         // Keep symbols short-ish, with 24 chars/144 bits we won't have hash collisions
-        if (result.size() >= 24) break;
+        if (result.size() >= DIGEST_SYMBOL24_LENGTH) break;
     }
     // Any leftover bits don't matter for our purpose
     return result;
@@ -732,6 +732,7 @@ void VHashSha512::selfTest() {
 
 string VName::dehash(const string& in) {
     static constexpr const char VHSH[] = "__Vhsh";
+    static constexpr size_t VHSH_LEN = sizeof(VHSH) - 1 + VHashSha512::DIGEST_SYMBOL24_LENGTH;
     static const size_t DOT_LEN = std::strlen("__DOT__");
     std::string dehashed;
 
@@ -748,7 +749,11 @@ string VName::dehash(const string& in) {
         const auto begin_vhsh
             = std::search(search_begin, search_end, std::begin(VHSH), std::end(VHSH) - 1);
         if (begin_vhsh != search_end) {
-            const std::string vhsh{begin_vhsh, search_end};
+            // V3SplitVar appends a bit range to a name hashedName already hashed, so the
+            // hash does not always reach the end of the component.
+            const auto end_vhsh
+                = begin_vhsh + std::min<size_t>(std::distance(begin_vhsh, search_end), VHSH_LEN);
+            const std::string vhsh{begin_vhsh, end_vhsh};
             const auto& it = s_dehashMap.find(vhsh);
             UASSERT(it != s_dehashMap.end(), "String not in reverse hash map '" << vhsh << "'");
             // Is this not the first component, but the first to require dehashing?
@@ -760,6 +765,8 @@ string VName::dehash(const string& in) {
             dehashed += std::string{search_begin, begin_vhsh};
             // Append the bit that was lost to truncation but retrieved from the dehash map.
             dehashed += it->second;
+            // Append what follows the hash, such as a split variable bit range.
+            dehashed += std::string{end_vhsh, search_end};
         }
         // This component doesn't need dehashing but a previous one might have.
         else if (!dehashed.empty()) {

src/V3String.h

@@ -178,6 +178,10 @@ public:
     }
     ~VHashSha512() = default;
 
+    // CONSTANTS
+    // Characters digestSymbol24 keeps, 6 bits each, so 144 bits and no collisions in practice
+    static constexpr size_t DIGEST_SYMBOL24_LENGTH = 24;
+
     // METHODS
     string digestBase64();  // Return digest formatted in Base64 (non-URL flavor)
     string digestBinary();  // Return digest as 64 character binary

test_regress/t/t_trace_hashed_name.py

@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of either the GNU Lesser General Public License Version 3
+# or the Perl Artistic License Version 2.0.
+# SPDX-FileCopyrightText: 2026 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile(verilator_flags2=['--trace-vcd'])
+
+test.execute()
+
+test.passes()

test_regress/t/t_trace_hashed_name.v

@@ -0,0 +1,28 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain.
+// SPDX-FileCopyrightText: 2026 Ethan Sifferman
+// SPDX-License-Identifier: CC0-1.0
+
+// Every name here is over the 128 character limit at which VName hashes it, so the
+// passes that append to a name append to a hash: V3SplitVar a bit range or an element
+// index, V3Class a package suffix.
+
+class class_with_a_name_long_enough_that_verilator_replaces_it_with_a_hash_because_it_is_over_the_one_hundred_twenty_eight_character_limit;
+  int x;
+endclass
+
+module t;
+  logic [1:0] packed_signal_with_a_name_long_enough_that_verilator_replaces_it_with_a_hash_because_it_is_over_the_one_hundred_twenty_eight_char_limit /*verilator split_var*/;
+  logic unpacked_array_with_a_name_long_enough_that_verilator_replaces_it_with_a_hash_because_it_is_over_the_one_hundred_twenty_eight_char_limit [1:0] /*verilator split_var*/;
+  class_with_a_name_long_enough_that_verilator_replaces_it_with_a_hash_because_it_is_over_the_one_hundred_twenty_eight_character_limit obj;
+
+  always_comb packed_signal_with_a_name_long_enough_that_verilator_replaces_it_with_a_hash_because_it_is_over_the_one_hundred_twenty_eight_char_limit[0] = 1'b1;
+  always_comb unpacked_array_with_a_name_long_enough_that_verilator_replaces_it_with_a_hash_because_it_is_over_the_one_hundred_twenty_eight_char_limit[0] = 1'b1;
+
+  initial begin
+    obj = new;
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule