diff --git a/.gitignore b/.gitignore
index 48859af2b..e7e3d788a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -41,3 +41,5 @@ verilator-config-version.cmake
 **/_build/*
 **/obj_dir/*
 /.vscode/
+/.idea/
+/cmake-build-*/
diff --git a/include/verilatedos.h b/include/verilatedos.h
index 113d8cd2d..f065ed6f6 100644
--- a/include/verilatedos.h
+++ b/include/verilatedos.h
@@ -577,8 +577,8 @@ static inline double VL_ROUND(double n) {
 //=========================================================================
 // Stringify macros
 
-#define VL_STRINGIFY(x) VL_STRINGIFY2(x)
-#define VL_STRINGIFY2(x) #x
+#define VL_STRINGIFY(...) VL_STRINGIFY2(__VA_ARGS__)
+#define VL_STRINGIFY2(...) #__VA_ARGS__
 
 //=========================================================================
 // Offset of field in type
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index ba230d891..47471a1bd 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -490,11 +490,13 @@ target_include_directories(${verilator}
 )
 
 if (WIN32)
+    target_compile_options(${verilator} PRIVATE /bigobj)
     target_compile_definitions(${verilator} PRIVATE
         YY_NO_UNISTD_H
     )
     target_include_directories(${verilator} PRIVATE ../platform/win32)
     target_link_libraries(${verilator} PRIVATE bcrypt psapi)
+    target_link_options(${verilator} PRIVATE /STACK:10000000)
 endif()
 
 install(TARGETS ${verilator})
diff --git a/src/V3Expand.cpp b/src/V3Expand.cpp
index 812ac86fd..54cb31068 100644
--- a/src/V3Expand.cpp
+++ b/src/V3Expand.cpp
@@ -202,7 +202,9 @@ private:
                            new AstShiftR{fl, lhip,
                                          new AstConst{fl, static_cast<uint32_t>(nbitsonright)},
                                          VL_EDATASIZE}},
-                new AstAnd{fl, new AstConst{fl, AstConst::SizedEData{}, ~VL_MASK_E(loffset)},
+                new AstAnd{fl,
+                           new AstConst{fl, AstConst::SizedEData{},
+                                        static_cast<uint32_t>(~VL_MASK_E(loffset))},
                            new AstShiftL{fl, llowp,
                                          new AstConst{fl, static_cast<uint32_t>(loffset)},
                                          VL_EDATASIZE}}};
diff --git a/src/V3FileLine.cpp b/src/V3FileLine.cpp
index 5de357085..be4a7cd25 100644
--- a/src/V3FileLine.cpp
+++ b/src/V3FileLine.cpp
@@ -20,6 +20,7 @@
 // clang-format off
 #include "V3Error.h"
 #include "V3FileLine.h"
+#include "V3Os.h"
 #include "V3String.h"
 #ifndef V3ERROR_NO_GLOBAL_
 # include "V3Global.h"
@@ -286,12 +287,7 @@ FileLine* FileLine::copyOrSameFileLine() {
     return newp;
 }
 
-string FileLine::filebasename() const VL_MT_SAFE {
-    string name = filename();
-    string::size_type pos;
-    if ((pos = name.rfind('/')) != string::npos) name.erase(0, pos + 1);
-    return name;
-}
+string FileLine::filebasename() const VL_MT_SAFE { return V3Os::filenameNonDir(filename()); }
 
 string FileLine::filebasenameNoExt() const {
     string name = filebasename();
diff --git a/src/V3MergeCond.cpp b/src/V3MergeCond.cpp
index 5f57e82c5..8a237c8ba 100644
--- a/src/V3MergeCond.cpp
+++ b/src/V3MergeCond.cpp
@@ -620,6 +620,7 @@ private:
         // LCOV_EXCL_START
         if (debug()) rhsp->dumpTree("Don't know how to fold expression: ");
         rhsp->v3fatalSrc("Should not try to fold this during conditional merging");
+        return nullptr;
         // LCOV_EXCL_STOP
     }
 
diff --git a/src/V3Options.cpp b/src/V3Options.cpp
index 8d0d3e26f..611f62b20 100644
--- a/src/V3Options.cpp
+++ b/src/V3Options.cpp
@@ -548,8 +548,8 @@ string V3Options::filePath(FileLine* fl, const string& modname, const string& la
     // Find a filename to read the specified module name,
     // using the incdir and libext's.
     // Return "" if not found.
-    if (modname[0] == '/') {
-        // If leading /, obey existing absolute path, so can find getStdPackagePath()
+    if (!V3Os::filenameIsRel(modname)) {
+        // modname is an absolute path, so can find getStdPackagePath()
         string exists = filePathCheckOneDir(modname, "");
         if (exists != "") return exists;
     }
diff --git a/src/V3Os.cpp b/src/V3Os.cpp
index 3fb7ec5ee..01d9db383 100644
--- a/src/V3Os.cpp
+++ b/src/V3Os.cpp
@@ -124,7 +124,9 @@ void V3Os::setenvStr(const string& envvar, const string& value, const string& wh
 //######################################################################
 // Generic filename utilities
 
-string V3Os::filenameFromDirBase(const string& dir, const string& basename) {
+static bool isSlash(char ch) VL_PURE { return ch == '/' || ch == '\\'; }
+
+string V3Os::filenameFromDirBase(const string& dir, const string& basename) VL_PURE {
     // Don't return ./{filename} because if filename was absolute, that makes it relative
     if (dir.empty() || dir == ".") {
         return basename;
@@ -133,22 +135,26 @@ string V3Os::filenameFromDirBase(const string& dir, const string& basename) {
     }
 }
 
-string V3Os::filenameDir(const string& filename) {
-    string::size_type pos;
-    if ((pos = filename.rfind('/')) != string::npos) {
-        return filename.substr(0, pos);
-    } else {
+string V3Os::filenameDir(const string& filename) VL_PURE {
+    // std::filesystem::path::parent_path
+    auto it = filename.rbegin();
+    for (; it != filename.rend(); ++it) {
+        if (isSlash(*it)) break;
+    }
+    if (it.base() == filename.begin()) {
         return ".";
+    } else {
+        return {filename.begin(), (++it).base()};
     }
 }
 
 string V3Os::filenameNonDir(const string& filename) VL_PURE {
-    string::size_type pos;
-    if ((pos = filename.rfind('/')) != string::npos) {
-        return filename.substr(pos + 1);
-    } else {
-        return filename;
+    // std::filesystem::path::filename
+    auto it = filename.rbegin();
+    for (; it != filename.rend(); ++it) {
+        if (isSlash(*it)) break;
     }
+    return string{it.base(), filename.end()};
 }
 
 string V3Os::filenameNonExt(const string& filename) VL_PURE {
@@ -202,7 +208,7 @@ string V3Os::filenameSubstitute(const string& filename) {
     return result;
 }
 
-string V3Os::filenameRealPath(const string& filename) {
+string V3Os::filenameRealPath(const string& filename) VL_PURE {
     // Get rid of all the ../ behavior in the middle of the paths.
     // If there is a ../ that goes down from the 'root' of this path it is preserved.
     char retpath[PATH_MAX];
@@ -219,8 +225,12 @@ string V3Os::filenameRealPath(const string& filename) {
     }
 }
 
-bool V3Os::filenameIsRel(const string& filename) {
+bool V3Os::filenameIsRel(const string& filename) VL_PURE {
+#if defined(_MSC_VER)
+    return std::filesystem::path(filename).is_relative();
+#else
     return (filename.length() > 0 && filename[0] != '/');
+#endif
 }
 
 //######################################################################
@@ -251,12 +261,14 @@ void V3Os::createDir(const string& dirname) {
 
 void V3Os::unlinkRegexp(const string& dir, const string& regexp) {
 #ifdef _MSC_VER
-    for (const auto& dirEntry : std::filesystem::directory_iterator(dir.c_str())) {
-        if (VString::wildmatch(dirEntry.path().filename().string(), regexp.c_str())) {
-            const string fullname = dir + "/" + dirEntry.path().filename().string();
-            _unlink(fullname.c_str());
+    try {
+        for (const auto& dirEntry : std::filesystem::directory_iterator(dir.c_str())) {
+            if (VString::wildmatch(dirEntry.path().filename().string(), regexp.c_str())) {
+                const string fullname = dir + "/" + dirEntry.path().filename().string();
+                _unlink(fullname.c_str());
+            }
         }
-    }
+    } catch (std::filesystem::filesystem_error const& ex) {}
 #else
     if (DIR* const dirp = opendir(dir.c_str())) {
         while (struct dirent* const direntp = readdir(dirp)) {
diff --git a/src/V3Os.h b/src/V3Os.h
index 4f4d44bb9..da1bcb1d0 100644
--- a/src/V3Os.h
+++ b/src/V3Os.h
@@ -35,20 +35,22 @@ public:
     static void setenvStr(const string& envvar, const string& value, const string& why);
 
     // METHODS (generic filename utilities)
-    static string filenameFromDirBase(const string& dir, const string& basename);
-    /// Return non-directory part of filename
+    static string filenameFromDirBase(const string& dir, const string& basename) VL_PURE;
+    ///< Return non-directory part of filename
     static string filenameNonDir(const string& filename) VL_PURE;
-    /// Return non-extensioned (no .) part of filename
+    ///< Return non-extensioned (no .) part of filename
     static string filenameNonExt(const string& filename) VL_PURE;
     ///< Return basename of filename
     static string filenameNonDirExt(const string& filename) VL_PURE {
         return filenameNonExt(filenameNonDir(filename));
     }
-    static string filenameDir(const string& filename);  ///< Return directory part of filename
+    ///< Return directory part of filename
+    static string filenameDir(const string& filename) VL_PURE;
     /// Return filename with env vars removed
     static string filenameSubstitute(const string& filename);
-    static string filenameRealPath(const string& filename);  ///< Return realpath of filename
-    static bool filenameIsRel(const string& filename);  ///< True if relative
+    ///< Return realpath of filename
+    static string filenameRealPath(const string& filename) VL_PURE;
+    static bool filenameIsRel(const string& filename) VL_PURE;  ///< True if relative
 
     // METHODS (file utilities)
     static string getline(std::istream& is, char delim = '\n');
diff --git a/src/V3Table.cpp b/src/V3Table.cpp
index 26f37f970..6e1c4d6db 100644
--- a/src/V3Table.cpp
+++ b/src/V3Table.cpp
@@ -181,7 +181,7 @@ public:
             // We'll make the table with a separate natural alignment for each output var, so
             // always have 8, 16 or 32 bit widths, so use widthTotalBytes
             m_outWidthBytes += nodep->varp()->dtypeSkipRefp()->widthTotalBytes();
-            m_outVarps.emplace_back(vscp, m_outVarps.size());
+            m_outVarps.emplace_back(vscp, static_cast<unsigned>(m_outVarps.size()));
         }
         if (nodep->access().isReadOrRW()) {
             m_inWidthBits += nodep->varp()->width();