cxxrtl: add a "bare minimum" debug information level.

Useful to reduce overhead when no debug capabilities are necessary
except for access to design state.

diff --git a/backends/cxxrtl/cxxrtl_backend.cc b/backends/cxxrtl/cxxrtl_backend.cc
index 5e2f4f31a5cc2c1e7a2b153b27b7d74090630cfb..588cca12e0ea486772fbef528c3cffaf61ed66ac 100644 (file)
--- a/backends/cxxrtl/cxxrtl_backend.cc
+++ b/backends/cxxrtl/cxxrtl_backend.cc
@@ -539,6 +539,7 @@ struct CxxrtlWorker {
        bool inline_public = false;
 
        bool debug_info = false;
+       bool debug_alias = false;
        bool debug_eval = false;
 
        std::ostringstream f;
@@ -2425,7 +2426,7 @@ struct CxxrtlWorker {
                        for (auto item : flow.bit_has_state)
                                bit_has_state.insert(item);
 
-                       if (debug_info) {
+                       if (debug_info && debug_alias) {
                                // Find wires that alias other wires or are tied to a constant; debug information can be enriched with these
                                // at essentially zero additional cost.
                                //
@@ -2575,7 +2576,7 @@ struct CxxrtlWorker {
 
 struct CxxrtlBackend : public Backend {
        static const int DEFAULT_OPT_LEVEL = 6;
-       static const int DEFAULT_DEBUG_LEVEL = 2;
+       static const int DEFAULT_DEBUG_LEVEL = 3;
 
        CxxrtlBackend() : Backend("cxxrtl", "convert design to C++ RTL simulation") { }
        void help() override
@@ -2793,14 +2794,18 @@ struct CxxrtlBackend : public Backend {
                log("        more visibility and generate more code, but do not pessimize evaluation.\n");
                log("\n");
                log("    -g0\n");
-               log("        no debug information.\n");
+               log("        no debug information. the C API is unavailable.\n");
                log("\n");
                log("    -g1\n");
-               log("        debug information for non-optimized public wires. this also makes it\n");
-               log("        possible to use the C API.\n");
+               log("        debug information for member public wires only. this is the bare minimum\n");
+               log("        necessary to access all design state. enables the C API.\n");
                log("\n");
                log("    -g2\n");
-               log("        like -g1, and compute debug information on demand for all public wires\n");
+               log("        like -g1, and include debug information for public wires that are tied\n");
+               log("        to a constant or another public wire.\n");
+               log("\n");
+               log("    -g3\n");
+               log("        like -g2, and compute debug information on demand for all public wires\n");
                log("        that were optimized out.\n");
                log("\n");
        }
@@ -2832,13 +2837,13 @@ struct CxxrtlBackend : public Backend {
                                continue;
                        }
                        if (args[argidx] == "-Og") {
-                               log_warning("The `-Og` option has been removed. Use `-g2` instead for complete "
+                               log_warning("The `-Og` option has been removed. Use `-g3` instead for complete "
                                            "design coverage regardless of optimization level.\n");
                                continue;
                        }
                        if (args[argidx] == "-O" && argidx+1 < args.size() && args[argidx+1] == "g") {
                                argidx++;
-                               log_warning("The `-Og` option has been removed. Use `-g2` instead for complete "
+                               log_warning("The `-Og` option has been removed. Use `-g3` instead for complete "
                                            "design coverage regardless of optimization level.\n");
                                continue;
                        }
@@ -2900,9 +2905,12 @@ struct CxxrtlBackend : public Backend {
                }
                switch (debug_level) {
                        // the highest level here must match DEFAULT_DEBUG_LEVEL
-                       case 2:
+                       case 3:
                                worker.debug_eval = true;
                                YS_FALLTHROUGH
+                       case 2:
+                               worker.debug_alias = true;
+                               YS_FALLTHROUGH
                        case 1:
                                worker.debug_info = true;
                                YS_FALLTHROUGH