opt_lut: add -limit option, for debugging misoptimizations.

diff --git a/passes/opt/opt_lut.cc b/passes/opt/opt_lut.cc
index befe346a389308f29f485aac045018f11402900e..ee3943f9c9f60b9344e91208384c15af27c30bd6 100644 (file)
--- a/passes/opt/opt_lut.cc
+++ b/passes/opt/opt_lut.cc
@@ -93,7 +93,7 @@ struct OptLutWorker
                }
        }
 
-       OptLutWorker(dict<IdString, dict<int, IdString>> &dlogic, RTLIL::Module *module) :
+       OptLutWorker(dict<IdString, dict<int, IdString>> &dlogic, RTLIL::Module *module, int limit) :
                dlogic(dlogic), module(module), index(module), sigmap(module)
        {
                log("Discovering LUTs.\n");
@@ -192,6 +192,12 @@ struct OptLutWorker
                pool<RTLIL::Cell*> worklist = luts;
                while (worklist.size())
                {
+                       if (limit == 0)
+                       {
+                               log("Limit reached.\n");
+                               break;
+                       }
+
                        auto lutA = worklist.pop();
                        SigSpec lutA_input = sigmap(lutA->getPort("\\A"));
                        SigSpec lutA_output = sigmap(lutA->getPort("\\Y")[0]);
@@ -398,6 +404,8 @@ struct OptLutWorker
                                        worklist.erase(lutR);
 
                                        combined_count++;
+                                       if (limit > 0)
+                                               limit--;
                                }
                        }
                }
@@ -431,17 +439,22 @@ struct OptLutPass : public Pass {
                log("        the case where both LUT and dedicated logic input are connected to\n");
                log("        the same constant.\n");
                log("\n");
+               log("    -limit N\n");
+               log("        only perform the first N combines, then stop. useful for debugging.\n");
+               log("\n");
        }
        void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
        {
                log_header(design, "Executing OPT_LUT pass (optimize LUTs).\n");
 
                dict<IdString, dict<int, IdString>> dlogic;
+               int limit = -1;
 
                size_t argidx;
                for (argidx = 1; argidx < args.size(); argidx++)
                {
-                       if (args[argidx] == "-dlogic" && argidx+1 < args.size()) {
+                       if (args[argidx] == "-dlogic" && argidx+1 < args.size())
+                       {
                                std::vector<std::string> tokens;
                                split(tokens, args[++argidx], ':');
                                if (tokens.size() < 2)
@@ -458,6 +471,11 @@ struct OptLutPass : public Pass {
                                }
                                continue;
                        }
+                       if (args[argidx] == "-limit" && argidx + 1 < args.size())
+                       {
+                               limit = atoi(args[++argidx].c_str());
+                               continue;
+                       }
                        break;
                }
                extra_args(args, argidx, design);
@@ -465,7 +483,7 @@ struct OptLutPass : public Pass {
                int total_count = 0;
                for (auto module : design->selected_modules())
                {
-                       OptLutWorker worker(dlogic, module);
+                       OptLutWorker worker(dlogic, module, limit - total_count);
                        total_count += worker.combined_count;
                }
                if (total_count)