Only emit VM_PARALLEL_BUILDS=1 iff --output-split caused a split.

Previously we set VM_PARALLEL_BUILDS=1 if the --output-split option was
provided. Now we only do it iff it actually causes a split.

src/V3EmitC.cpp

@@ -3234,6 +3234,8 @@ void EmitCImp::emitImp(AstNodeModule* modp) {
 
 void EmitCImp::maybeSplit(AstNodeModule* fileModp) {
     if (splitNeeded()) {
+        // Splitting file, so using parallel build.
+        v3Global.useParallelBuild(true);
         // Close old file
         VL_DO_CLEAR(delete m_ofp, m_ofp = NULL);
         // Open a new file
@@ -3652,6 +3654,8 @@ class EmitCTrace : EmitCStmts {
             m_funcp = nodep;
 
             if (splitNeeded()) {
+                // Splitting file, so using parallel build.
+                v3Global.useParallelBuild(true);
                 // Close old file
                 VL_DO_CLEAR(delete m_ofp, m_ofp = NULL);
                 // Open a new file

src/V3EmitCSyms.cpp

@@ -521,6 +521,9 @@ void EmitCSyms::checkSplit(bool usesVfinal) {
         return;
     }
 
+    // Splitting file, so using parallel build.
+    v3Global.useParallelBuild(true);
+
     m_numStmts = 0;
     string filename
         = v3Global.opt.makeDir() + "/" + symClassName() + "__" + cvtToStr(++m_funcNum) + ".cpp";

src/V3EmitMk.cpp

@@ -57,7 +57,7 @@ public:
         of.puts("\n");
         of.puts("# Parallel builds?  0/1 (from --output-split)\n");
         of.puts("VM_PARALLEL_BUILDS = ");
-        of.puts(v3Global.opt.outputSplit() ? "1" : "0");
+        of.puts(v3Global.useParallelBuild() ? "1" : "0");
         of.puts("\n");
         of.puts("# Threaded output mode?  0/1/N threads (from --threads)\n");
         of.puts("VM_THREADS = ");

src/V3Global.h

@@ -77,6 +77,7 @@ class V3Global {
     bool m_needHeavy;  // Need verilated_heavy.h include
     bool m_needTraceDumper;  // Need __Vm_dumperp in symbols
     bool m_dpi;  // Need __Dpi include files
+    bool m_useParallelBuild;  // Use parallel build for model
 
 public:
     // Options
@@ -93,7 +94,8 @@ public:
         , m_needC11(false)
         , m_needHeavy(false)
         , m_needTraceDumper(false)
-        , m_dpi(false) {}
+        , m_dpi(false)
+        , m_useParallelBuild(false) {}
     AstNetlist* makeNetlist();
     void boot() {
         UASSERT(!m_rootp, "call once");
@@ -129,6 +131,8 @@ public:
     void needTraceDumper(bool flag) { m_needTraceDumper = flag; }
     bool dpi() const { return m_dpi; }
     void dpi(bool flag) { m_dpi = flag; }
+    void useParallelBuild(bool flag) { m_useParallelBuild = flag; }
+    bool useParallelBuild() const { return m_useParallelBuild; }
 };
 
 extern V3Global v3Global;

test_regress/driver.pl

@@ -1416,6 +1416,15 @@ sub have_sc {
     return 0;
 }
 
+sub make_version {
+    my $ver = `make --version`;
+    if ($ver =~ /make ([0-9]+\.[0-9]+)/i) {
+        return $1;
+    } else {
+        return -1;
+    }
+}
+
 sub have_cmake {
     return cmake_version() >= version->declare("3.8");
 }

test_regress/t/t_flag_csplit.pl

@@ -32,7 +32,6 @@ while (1) {
               "-C ".$Self->{obj_dir},
               "-f $Self->{VM_PREFIX}.mk",
               "-j 4",
-              #"VM_PARALLEL_BUILDS=1",  # Check is set by makefile
               "VM_PREFIX=$Self->{VM_PREFIX}",
               "TEST_OBJ_DIR=$Self->{obj_dir}",
               "CPPFLAGS_DRIVER=-D".uc($Self->{name}),
@@ -46,7 +45,10 @@ while (1) {
         check_finished => 1,
         );
 
+    # Splitting should set VM_PARALLEL_BUILDS to 1 by default
+    file_grep("$Self->{obj_dir}/$Self->{VM_PREFIX}_classes.mk", qr/VM_PARALLEL_BUILDS\s*=\s*1/);
     check_splits();
+    check_no_all_file();
     check_gcc_flags("$Self->{obj_dir}/vlt_gcc.log");
 
     ok(1);
@@ -54,15 +56,6 @@ while (1) {
 }
 1;
 
-sub make_version {
-    my $ver = `make --version`;
-    if ($ver =~ /make ([0-9]+\.[0-9]+)/i) {
-        return $1;
-    } else {
-        return -1;
-    }
-}
-
 sub check_splits {
     my $got1;
     my $gotSyms1;
@@ -78,6 +71,14 @@ sub check_splits {
     $gotSyms1 or error("No Syms__1 split file found");
 }
 
+sub check_no_all_file {
+    foreach my $file (glob("$Self->{obj_dir}/*.cpp")) {
+        if ($file =~ qr/__ALL.cpp/) {
+            error("__ALL.cpp file found: $file");
+        }
+    }
+}
+
 sub check_cpp {
     my $filename = shift;
     my $size = -s $filename;

test_regress/t/t_flag_csplit_off.pl

@@ -0,0 +1,88 @@
+#!/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_all => 1);
+
+top_filename("t/t_flag_csplit.v");
+
+while (1) {
+    # Thi rule requires GNU make > 4.1 (or so, known broken in 3.81)
+    #%__Slow.o: %__Slow.cpp
+    #        $(OBJCACHE) $(CXX) $(CXXFLAGS) $(CPPFLAGS) $(OPT_SLOW) -c -o $@ $<
+    if (make_version() < 4.1) {
+        skip("Test requires GNU Make version >= 4.1");
+        last;
+    }
+
+    compile(
+        v_flags2 => ["--trace --output-split 0 --exe ../$Self->{main_filename}"],
+        verilator_make_gmake => 0,
+        );
+
+    # We don't use the standard test_regress rules, as want to test the rules
+    # properly build
+    run(logfile => "$Self->{obj_dir}/vlt_gcc.log",
+        tee => $self->{verbose},
+        cmd=>["make",
+              "-C ".$Self->{obj_dir},
+              "-f $Self->{VM_PREFIX}.mk",
+              "-j 4",
+              "VM_PREFIX=$Self->{VM_PREFIX}",
+              "TEST_OBJ_DIR=$Self->{obj_dir}",
+              "CPPFLAGS_DRIVER=-D".uc($Self->{name}),
+              ($opt_verbose ? "CPPFLAGS_DRIVER2=-DTEST_VERBOSE=1":""),
+              "OPT_FAST=-O2",
+              "OPT_SLOW=-O0",
+              ($param{make_flags}||""),
+        ]);
+
+    execute(
+        check_finished => 1,
+        );
+
+    # Never spliting, so should set VM_PARALLEL_BUILDS to 0 by default
+    file_grep("$Self->{obj_dir}/$Self->{VM_PREFIX}_classes.mk", qr/VM_PARALLEL_BUILDS\s*=\s*0/);
+    check_no_splits();
+    check_all_file();
+    check_gcc_flags("$Self->{obj_dir}/vlt_gcc.log");
+
+    ok(1);
+    last;
+}
+1;
+
+sub check_no_splits {
+    foreach my $file (glob("$Self->{obj_dir}/*.cpp")) {
+        if ($file =~ qr/__\d/) {
+            error("Split file found: $file");
+        }
+    }
+}
+
+sub check_all_file {
+    foreach my $file (glob("$Self->{obj_dir}/*.cpp")) {
+        if ($file =~ qr/__ALL.cpp/) {
+            return;
+        }
+    }
+    error("__ALL.cpp file not found");
+}
+
+sub check_gcc_flags {
+    my $filename = shift;
+    my $fh = IO::File->new("<$filename") or error("$! $filenme");
+    while (defined (my $line = $fh->getline)) {
+        chomp $line;
+        print ":log: $line\n" if $Self->{verbose};
+        if ($line =~ /\.cpp/ && $line =~ qr/-O0/) {
+            error("File built as slow (should be in __ALL.cpp) : $line");
+        }
+    }
+}