Add --localize-max-size option and optimization (#5072).

Changes

@@ -15,9 +15,10 @@ Verilator 5.025 devel
 
 * Support __en/__out signals on top level inout ports (#4812) (#4856). [Paul Wright]
 * Support empty queue as dynarray default value (#5055). [Arkadiusz Kozdra, Antmicro Ltd.]
+* Add error on zero width select (#5028).
 * Add CITATION.cff (#5057) (#5058). [Gijs Burghoorn]
 * Add VPI eval needed tracking (#5065). [Todd Strader]
-* Add error on zero width select (#5028).
+* Add `--localize-max-size` option and optimization (#5072).
 * Fix missing flex include path variable (#4970) (#4971). [Christopher Taylor]
 * Fix missing parameters with comma to be errors (#4979) (#5012). [Paul Swirhun]
 * Fix bound queue printing (#5032). [Aleksander Kiryk, Antmicro Ltd.]

bin/verilator

@@ -387,6 +387,7 @@ detailed descriptions of these arguments.
     --lib-create <name>         Create a DPI library
      +libext+<ext>+[ext]...     Extensions for finding modules
     --lint-only                 Lint, but do not make output
+    --localize-max-size <value>  Tune localize optimization variable size
     --make <build-tool>         Generate scripts for specified build tool
      -MAKEFLAGS <flags>         Arguments to pass to make during --build
     --main                      Generate C++ main() file

docs/guide/exe_verilator.rst

@@ -817,6 +817,11 @@ Summary:
    If the design is not to be completely Verilated, see also the
    :vlopt:`--bbox-sys` and :vlopt:`--bbox-unsup` options.
 
+.. option:: --localize-max-size <value>
+
+   Rarely needed.  Set the maximum variable size in bytes for it to be
+   subject to localizing-to-stack optimization.  Defaults to 1024.
+
 .. option:: --make <build-tool>
 
    Generates a script for the specified build tool.

src/V3Localize.cpp

@@ -63,9 +63,12 @@ class LocalizeVisitor final : public VNVisitor {
 
     // METHODS
     bool isOptimizable(AstVarScope* nodep) {
-        return !nodep->user1() ||  // Not marked as not optimizable, or ...
+        return ((!nodep->user1()  // Not marked as not optimizable, or ...
-               (nodep->varp()->varType() == VVarType::BLOCKTEMP
+                                  // .. a block temp used in a single CFunc
-                && m_accessors(nodep).size() == 1);  // .. a block temp used in a single CFunc
+                 || (nodep->varp()->varType() == VVarType::BLOCKTEMP
+                     && m_accessors(nodep).size() == 1))
+                // and under size limit
+                && nodep->varp()->dtypep()->widthTotalBytes() <= v3Global.opt.localizeMaxSize());
     }
 
     static bool existsNonLeaf(const std::unordered_set<AstCFunc*>& funcps) {

src/V3Options.cpp

@@ -1307,6 +1307,9 @@ void V3Options::parseOptsList(FileLine* fl, const string& optdir, int argc,
     });
 
     DECL_OPTION("-LDFLAGS", CbVal, callStrSetter(&V3Options::addLdLibs));
+    DECL_OPTION("-l2-name", Set, &m_l2Name);
+    DECL_OPTION("-no-l2name", CbCall, [this]() { m_l2Name = ""; }).undocumented();  // Historical
+    DECL_OPTION("-l2name", CbCall, [this]() { m_l2Name = "v"; }).undocumented();  // Historical
     const auto setLang = [this, fl](const char* valp) {
         const V3LangCode optval{valp};
         if (optval.legal()) {
@@ -1323,9 +1326,7 @@ void V3Options::parseOptsList(FileLine* fl, const string& optdir, int argc,
     DECL_OPTION("-language", CbVal, setLang);
     DECL_OPTION("-lib-create", Set, &m_libCreate);
     DECL_OPTION("-lint-only", OnOff, &m_lintOnly);
-    DECL_OPTION("-l2-name", Set, &m_l2Name);
+    DECL_OPTION("-localize-max-size", Set, &m_localizeMaxSize);
-    DECL_OPTION("-no-l2name", CbCall, [this]() { m_l2Name = ""; }).undocumented();  // Historical
-    DECL_OPTION("-l2name", CbCall, [this]() { m_l2Name = "v"; }).undocumented();  // Historical
     DECL_OPTION("-main-top-name", Set, &m_mainTopName);
 
     DECL_OPTION("-MAKEFLAGS", CbVal, callStrSetter(&V3Options::addMakeFlags));

src/V3Options.h

@@ -309,6 +309,7 @@ private:
     int         m_instrCountDpi = 200;   // main switch: --instr-count-dpi
     bool        m_jsonEditNums = true; // main switch: --no-json-edit-nums
     bool        m_jsonIds = true; // main switch: --no-json-ids
+    int         m_localizeMaxSize = 1024;  // main switch: --localize-max-size
     VOptionBool m_makeDepend;  // main switch: -MMD
     int         m_maxNumWidth = 65536;  // main switch: --max-num-width
     int         m_moduleRecursion = 100;  // main switch: --module-recursion-depth
@@ -546,6 +547,7 @@ public:
     int ifDepth() const { return m_ifDepth; }
     int inlineMult() const { return m_inlineMult; }
     int instrCountDpi() const { return m_instrCountDpi; }
+    int localizeMaxSize() const { return m_localizeMaxSize; }
     bool jsonEditNums() const { return m_jsonEditNums; }
     bool jsonIds() const { return m_jsonIds; }
     VOptionBool makeDepend() const { return m_makeDepend; }

test_regress/t/t_opt_localize_max_size.pl

@@ -0,0 +1,25 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(vlt => 1);
+
+compile(
+    verilator_flags2 => ["--stats"],
+    );
+
+execute(
+    check_finished => 1,
+    );
+
+# Value must differ from that in t_opt_localize_max_size.pl
+file_grep($Self->{stats}, qr/Optimizations, Vars localized\s+(\d+)/i, 5);
+
+ok(1);
+1;

test_regress/t/t_opt_localize_max_size.v

@@ -0,0 +1,12 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2016 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+module t;
+   initial begin
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+endmodule

test_regress/t/t_opt_localize_max_size_1.pl

@@ -0,0 +1,27 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(vlt => 1);
+
+top_filename("t/t_opt_localize_max_size.v");
+
+compile(
+    verilator_flags2 => ["--stats --localize-max-size 1"],
+    );
+
+execute(
+    check_finished => 1,
+    );
+
+# Value must differ from that in t_opt_localize_max_size.pl
+file_grep($Self->{stats}, qr/Optimizations, Vars localized\s+(\d+)/i, 4);
+
+ok(1);
+1;