Fix conditionals on obsolete --threads 0

Since we removed --threads 0 support, the 'threads()' option always
returns a value >= 1. Remove corresponding dead code.

Some of the coverage counters appear to use atomics even if the model is
single threaded. I'm under the impression this was a bug originally so
those ones I changed to use threads() > 1 instead.

src/V3EmitCFunc.h

@@ -603,7 +603,7 @@ public:
         puts(");\n");
     }
     void visit(AstCoverInc* nodep) override {
-        if (v3Global.opt.threads()) {
+        if (v3Global.opt.threads() > 1) {
             puts("vlSymsp->__Vcoverage[");
             puts(cvtToStr(nodep->declp()->dataDeclThisp()->binNum()));
             puts("].fetch_add(1, std::memory_order_relaxed);\n");

src/V3EmitCHeaders.cpp

@@ -170,7 +170,7 @@ class EmitCHeader final : public EmitCConstInit {
         if (v3Global.opt.coverage() && !VN_IS(modp, Class)) {
             decorateFirst(first, section);
             puts("void __vlCoverInsert(");
-            puts(v3Global.opt.threads() ? "std::atomic<uint32_t>" : "uint32_t");
+            puts(v3Global.opt.threads() > 1 ? "std::atomic<uint32_t>" : "uint32_t");
             puts("* countp, bool enable, const char* filenamep, int lineno, int column,\n");
             puts("const char* hierp, const char* pagep, const char* commentp, const char* "
                  "linescovp);\n");

src/V3EmitCImp.cpp

@@ -307,12 +307,12 @@ class EmitCImp final : EmitCFunc {
             // function. This gets around gcc slowness constructing all of the template
             // arguments.
             puts("void " + prefixNameProtect(m_modp) + "::__vlCoverInsert(");
-            puts(v3Global.opt.threads() ? "std::atomic<uint32_t>" : "uint32_t");
+            puts(v3Global.opt.threads() > 1 ? "std::atomic<uint32_t>" : "uint32_t");
             puts("* countp, bool enable, const char* filenamep, int lineno, int column,\n");
             puts("const char* hierp, const char* pagep, const char* commentp, const char* "
                  "linescovp) "
                  "{\n");
-            if (v3Global.opt.threads()) {
+            if (v3Global.opt.threads() > 1) {
                 puts("assert(sizeof(uint32_t) == sizeof(std::atomic<uint32_t>));\n");
                 puts("uint32_t* count32p = reinterpret_cast<uint32_t*>(countp);\n");
             } else {

src/V3EmitCMake.cpp

@@ -160,9 +160,7 @@ class CMakeEmitter final {
         if (v3Global.usesTiming()) {
             global.emplace_back("${VERILATOR_ROOT}/include/verilated_timing.cpp");
         }
-        if (v3Global.opt.threads()) {
+        global.emplace_back("${VERILATOR_ROOT}/include/verilated_threads.cpp");
-            global.emplace_back("${VERILATOR_ROOT}/include/verilated_threads.cpp");
-        }
         if (v3Global.opt.usesProfiler()) {
             global.emplace_back("${VERILATOR_ROOT}/include/verilated_profiler.cpp");
         }

src/V3EmitCModel.cpp

@@ -420,7 +420,7 @@ class EmitCModel final : public EmitCFunc {
         if (v3Global.opt.threads() == 1) {
             puts("Verilated::endOfThreadMTask(vlSymsp->__Vm_evalMsgQp);\n");
         }
-        if (v3Global.opt.threads()) puts("Verilated::endOfEval(vlSymsp->__Vm_evalMsgQp);\n");
+        puts("Verilated::endOfEval(vlSymsp->__Vm_evalMsgQp);\n");
 
         if (v3Global.opt.profExec()) puts("VL_EXEC_TRACE_ADD_RECORD(vlSymsp).evalEnd();\n");
         puts("}\n");
@@ -482,7 +482,7 @@ class EmitCModel final : public EmitCFunc {
         puts("const char* " + topClassName() + "::modelName() const { return \"" + topClassName()
              + "\"; }\n");
         puts("unsigned " + topClassName() + "::threads() const { return "
-             + cvtToStr(std::max(1, v3Global.opt.threads())) + "; }\n");
+             + cvtToStr(v3Global.opt.threads()) + "; }\n");
         puts("void " + topClassName()
              + "::prepareClone() const { contextp()->prepareClone(); }\n");
         puts("void " + topClassName() + "::atClone() const {\n");

src/V3EmitCSyms.cpp

@@ -489,7 +489,7 @@ void EmitCSyms::emitSymHdr() {
 
     if (m_coverBins) {
         puts("\n// COVERAGE\n");
-        puts(v3Global.opt.threads() ? "std::atomic<uint32_t>" : "uint32_t");
+        puts(v3Global.opt.threads() > 1 ? "std::atomic<uint32_t>" : "uint32_t");
         puts(" __Vcoverage[");
         puts(cvtToStr(m_coverBins));
         puts("];\n");

src/V3EmitMk.cpp

@@ -106,7 +106,7 @@ public:
                     }
                     if (v3Global.usesProbDist()) putMakeClassEntry(of, "verilated_probdist.cpp");
                     if (v3Global.usesTiming()) putMakeClassEntry(of, "verilated_timing.cpp");
-                    if (v3Global.opt.threads()) putMakeClassEntry(of, "verilated_threads.cpp");
+                    putMakeClassEntry(of, "verilated_threads.cpp");
                     if (v3Global.opt.usesProfiler()) {
                         putMakeClassEntry(of, "verilated_profiler.cpp");
                     }

src/V3HierBlock.cpp

@@ -159,7 +159,7 @@ V3StringList V3HierBlock::commandArgs(bool forCMake) const {
     opts.push_back(" --lib-create " + modp()->name());  // possibly mangled name
     if (v3Global.opt.protectKeyProvided())
         opts.push_back(" --protect-key " + v3Global.opt.protectKeyDefaulted());
-    opts.push_back(" --hierarchical-child " + cvtToStr(std::max(1, v3Global.opt.threads())));
+    opts.push_back(" --hierarchical-child " + cvtToStr(v3Global.opt.threads()));
 
     const StrGParams gparamsStr = stringifyParams(gparams(), true);
     for (StrGParams::const_iterator paramIt = gparamsStr.begin(); paramIt != gparamsStr.end();
@@ -227,9 +227,6 @@ void V3HierBlock::writeCommandArgsFile(bool forCMake) const {
     for (const string& opt : commandOpts) *of << opt << "\n";
     *of << hierBlockArgs().front() << "\n";
     for (const auto& hierblockp : m_children) *of << hierblockp->hierBlockArgs().front() << "\n";
-    // Hierarchical blocks should not use multi-threading,
-    // but needs to be thread safe when top is multi-threaded.
-    if (v3Global.opt.threads() > 0) *of << "--threads 1\n";
     *of << v3Global.opt.allArgsStringForHierBlock(false) << "\n";
 }
 
@@ -425,9 +422,7 @@ void V3HierBlockPlan::writeCommandArgsFiles(bool forCMake) const {
     if (v3Global.opt.protectKeyProvided()) {
         *of << "--protect-key " << v3Global.opt.protectKeyDefaulted() << "\n";
     }
-    if (v3Global.opt.threads() > 0) {
+    *of << "--threads " << cvtToStr(v3Global.opt.threads()) << "\n";
-        *of << "--threads " << cvtToStr(v3Global.opt.threads()) << "\n";
-    }
     *of << (v3Global.opt.systemC() ? "--sc" : "--cc") << "\n";
     *of << v3Global.opt.allArgsStringForHierBlock(true) << "\n";
 }

src/V3Options.cpp

@@ -875,11 +875,8 @@ void V3Options::notify() VL_MT_DISABLED {
     }
 
     if (trace()) {
-        // With --trace-fst, --trace-threads implies --threads 1 unless explicitly specified
-        if (traceFormat().fst() && traceThreads() && !threads()) m_threads = 1;
-
         // With --trace, --trace-threads is ignored
-        if (traceFormat().vcd()) m_traceThreads = threads() ? 1 : 0;
+        if (traceFormat().vcd()) m_traceThreads = 1;
     }
 
     UASSERT(!(useTraceParallel() && useTraceOffload()),
@@ -906,6 +903,9 @@ void V3Options::notify() VL_MT_DISABLED {
         m_dumpLevel["tree"] = m_dumpLevel["tree-dot"];
     }
 
+    // Sanity check of expected configuration
+    UASSERT(threads() >= 1, "'threads()' must return a value >= 1");
+
     // Preprocessor defines based on options used
     if (timing().isSetTrue()) V3PreShell::defineCmdLine("VERILATOR_TIMING", "1");
 }

src/V3Options.h

@@ -549,7 +549,7 @@ public:
     int traceThreads() const { return m_traceThreads; }
     bool useTraceOffload() const { return trace() && traceFormat().fst() && traceThreads() > 1; }
     bool useTraceParallel() const {
-        return trace() && traceFormat().vcd() && threads() && (threads() > 1 || hierChild() > 1);
+        return trace() && traceFormat().vcd() && (threads() > 1 || hierChild() > 1);
     }
     bool useFstWriterThread() const { return traceThreads() && traceFormat().fst(); }
     unsigned vmTraceThreads() const {