Optimize to return memory when using -build (#6192) (#6226).

Changes

@@ -24,6 +24,7 @@ Verilator 5.039 devel
 * Support multiple variables on RHS of a `force` assignment (#6163). [Artur Bieniek, Antmicro Ltd.]]
 * Support covergroup extends, etc., as unsupported (#6160). [Artur Bieniek, Antmicro Ltd.]
 * Change control file `public_flat_*` and other signal attributes to support __ in names (#6140).
+* Optimize to return memory when using -build (#6192) (#6226). [Michael B. Taylor]
 * Fix constructor parameters in inheritance hierarchies (#6036) (#6070). [Petr Nohavica]
 * Fix replicate of negative giving 'REPLICATE has no expected width' internal error (#6048).
 * Fix cmake `-Wno` compiler flag testing (#6145). [Martin Stadler]
@@ -39,7 +40,6 @@ Verilator 5.039 devel
 * Fix VPI signal range order (#6189) (#6200). [Ibrahim Burak Yorulmaz]
 * Fix structure select causing 'Wide Op' error (#6191). [Danny Oler]
 
-
 Verilator 5.038 2025-07-08
 ==========================
 

configure.ac

@@ -68,6 +68,7 @@ AC_ARG_ENABLE([tcmalloc],
                 *)   AC_MSG_ERROR([bad value '${enableval}' for --enable-tcmalloc]) ;;
                esac],
               [CFG_WITH_TCMALLOC=check;])
+AC_SUBST(CFG_WITH_TCMALLOC)
 AC_MSG_RESULT($CFG_WITH_TCMALLOC)
 
 # Flag to enable coverage build
@@ -546,10 +547,12 @@ _MY_LDLIBS_CHECK_IFELSE(
     _MY_CXX_CHECK_OPT(CFG_CXXFLAGS_SRC,-fno-builtin-calloc)
     _MY_CXX_CHECK_OPT(CFG_CXXFLAGS_SRC,-fno-builtin-realloc)
     _MY_CXX_CHECK_OPT(CFG_CXXFLAGS_SRC,-fno-builtin-free)
+    AC_DEFINE([HAVE_TCMALLOC],[1],[Defined if have tcmalloc])
    fi],
   [if test "$CFG_WITH_TCMALLOC" = "yes"; then
     AC_MSG_ERROR([--enable-tcmalloc was given but test for ${LTCMALLOC} failed])
    fi])
+AC_SUBST(HAVE_TCMALLOC)
 AC_SUBST(CFG_LIBS)
 
 # Need C++14 at least

src/V3AstNodeOther.h

@@ -1406,6 +1406,7 @@ class AstNetlist final : public AstNode {
 public:
     AstNetlist();
     ASTGEN_MEMBERS_AstNetlist;
+    void deleteContents();
     void cloneRelink() override { V3ERROR_NA; }
     string name() const override VL_MT_STABLE { return "$root"; }
     void dump(std::ostream& str) const override;

src/V3AstNodes.cpp

@@ -2296,6 +2296,25 @@ void AstNetlist::dumpJson(std::ostream& str) const {
     dumpJsonStr(str, "timeprecision", timeprecision().ascii());
     dumpJsonGen(str);
 }
+void AstNetlist::deleteContents() {
+    // Delete all netlist memory.  Only for use by Verilator.cpp
+    m_typeTablep = nullptr;
+    m_constPoolp = nullptr;
+    m_dollarUnitPkgp = nullptr;
+    m_stdPackagep = nullptr;
+    m_evalp = nullptr;
+    m_evalNbap = nullptr;
+    m_dpiExportTriggerp = nullptr;
+    m_delaySchedulerp = nullptr;
+    m_nbaEventp = nullptr;
+    m_nbaEventTriggerp = nullptr;
+    m_topScopep = nullptr;
+    if (op1p()) op1p()->unlinkFrBackWithNext()->deleteTree();
+    if (op2p()) op2p()->unlinkFrBackWithNext()->deleteTree();
+    if (op3p()) op3p()->unlinkFrBackWithNext()->deleteTree();
+    if (op4p()) op4p()->unlinkFrBackWithNext()->deleteTree();
+#undef VN_DELETE_ONE
+}
 AstPackage* AstNetlist::dollarUnitPkgAddp() {
     if (!m_dollarUnitPkgp) {
         m_dollarUnitPkgp = new AstPackage{fileline(), AstPackage::dollarUnitName(), "work"};

src/V3Os.cpp

@@ -54,6 +54,10 @@ VL_DEFINE_DEBUG_FUNCTIONS;
 #include <sys/stat.h>
 #include <sys/types.h>
 
+#ifdef HAVE_TCMALLOC
+#include <gperftools/malloc_extension.h>
+#endif
+
 // clang-format off
 #if defined(_WIN32) || defined(__MINGW32__)
 # include <windows.h>   // LONG for bcrypt.h on MINGW
@@ -402,6 +406,15 @@ void V3Os::unlinkRegexp(const string& dir, const string& regexp) {
 #endif
 }
 
+//######################################################################
+// METHODS (memory)
+
+void V3Os::releaseMemory() {
+#ifdef HAVE_TCMALLOC
+    MallocExtension::instance()->ReleaseFreeMemory();
+#endif
+}
+
 //######################################################################
 // METHODS (random)
 

src/V3Os.h

@@ -71,6 +71,9 @@ public:
     static void filesystemFlushBuildDir(const string& dirname);
     static void unlinkRegexp(const string& dir, const string& regexp);
 
+    // METHODS (memory)
+    static void releaseMemory();
+
     // METHODS (random)
     static uint64_t rand64(std::array<uint64_t, 2>& stater);
     static string trueRandom(size_t size) VL_MT_SAFE;

src/Verilator.cpp

@@ -773,6 +773,12 @@ static void verilate(const string& argString) {
 
     // Final writing shouldn't throw warnings, but...
     V3Error::abortIfWarnings();
+
+    // Free memory so compiler has more for --build
+    UINFO(1, "Releasing netlist memory");
+    v3Global.rootp()->deleteContents();
+    V3Os::releaseMemory();
+    if (v3Global.opt.stats()) V3Stats::statsStage("released");
 }
 
 static string buildMakeCmd(const string& makefile, const string& target) {

src/config_package.h.in

@@ -41,6 +41,9 @@ PACKAGE_VERSION_STRING_CHAR
 // Define if coroutines are supported on this platform
 #undef HAVE_COROUTINES
 
+// Define if compiled with tcmalloc
+#undef HAVE_TCMALLOC
+
 //**********************************************************************
 //**** This file sometimes gets truncated, so check in consumers
 #define HAVE_CONFIG_PACKAGE