Added "read_verilog -nomeminit" and "nomeminit" attribute

README

@@ -257,6 +257,11 @@ Verilog Attributes and non-standard features
 - The "mem2reg" attribute on modules or arrays forces the early
   conversion of arrays to separate registers.
 
+- The "nomeminit" attribute on modules or arrays prohibits the
+  creation of initialized memories. This effectively puts "mem2reg"
+  on all memories that are written to in an "initial" block and
+  are not ROMs.
+
 - The "nolatches" attribute on modules or always-blocks
   prohibits the generation of logic-loops for latches. Instead
   all not explicitly assigned values default to x-bits. This does

frontends/ast/ast.cc

@@ -53,7 +53,7 @@ namespace AST {
 
 // instanciate global variables (private API)
 namespace AST_INTERNAL {
-	bool flag_dump_ast1, flag_dump_ast2, flag_dump_vlog, flag_nolatches, flag_nomem2reg, flag_mem2reg, flag_lib, flag_noopt, flag_icells, flag_autowire;
+	bool flag_dump_ast1, flag_dump_ast2, flag_dump_vlog, flag_nolatches, flag_nomeminit, flag_nomem2reg, flag_mem2reg, flag_lib, flag_noopt, flag_icells, flag_autowire;
 	AstNode *current_ast, *current_ast_mod;
 	std::map<std::string, AstNode*> current_scope;
 	const dict<RTLIL::SigBit, RTLIL::SigBit> *genRTLIL_subst_ptr = NULL;
@@ -958,6 +958,7 @@ static AstModule* process_module(AstNode *ast, bool defer)
 
 	current_module->ast = ast_before_simplify;
 	current_module->nolatches = flag_nolatches;
+	current_module->nomeminit = flag_nomeminit;
 	current_module->nomem2reg = flag_nomem2reg;
 	current_module->mem2reg = flag_mem2reg;
 	current_module->lib = flag_lib;
@@ -969,13 +970,14 @@ static AstModule* process_module(AstNode *ast, bool defer)
 }
 
 // create AstModule instances for all modules in the AST tree and add them to 'design'
-void AST::process(RTLIL::Design *design, AstNode *ast, bool dump_ast1, bool dump_ast2, bool dump_vlog, bool nolatches, bool nomem2reg, bool mem2reg, bool lib, bool noopt, bool icells, bool ignore_redef, bool defer, bool autowire)
+void AST::process(RTLIL::Design *design, AstNode *ast, bool dump_ast1, bool dump_ast2, bool dump_vlog, bool nolatches, bool nomeminit, bool nomem2reg, bool mem2reg, bool lib, bool noopt, bool icells, bool ignore_redef, bool defer, bool autowire)
 {
 	current_ast = ast;
 	flag_dump_ast1 = dump_ast1;
 	flag_dump_ast2 = dump_ast2;
 	flag_dump_vlog = dump_vlog;
 	flag_nolatches = nolatches;
+	flag_nomeminit = nomeminit;
 	flag_nomem2reg = nomem2reg;
 	flag_mem2reg = mem2reg;
 	flag_lib = lib;
@@ -1037,6 +1039,7 @@ RTLIL::IdString AstModule::derive(RTLIL::Design *design, dict<RTLIL::IdString, R
 	flag_dump_ast2 = false;
 	flag_dump_vlog = false;
 	flag_nolatches = nolatches;
+	flag_nomeminit = nomeminit;
 	flag_nomem2reg = nomem2reg;
 	flag_mem2reg = mem2reg;
 	flag_lib = lib;
@@ -1103,6 +1106,7 @@ RTLIL::Module *AstModule::clone() const
 
 	new_mod->ast = ast->clone();
 	new_mod->nolatches = nolatches;
+	new_mod->nomeminit = nomeminit;
 	new_mod->nomem2reg = nomem2reg;
 	new_mod->mem2reg = mem2reg;
 	new_mod->lib = lib;

frontends/ast/ast.h

@@ -265,13 +265,13 @@ namespace AST
 	};
 
 	// process an AST tree (ast must point to an AST_DESIGN node) and generate RTLIL code
-	void process(RTLIL::Design *design, AstNode *ast, bool dump_ast1, bool dump_ast2, bool dump_vlog, bool nolatches, bool nomem2reg, bool mem2reg, bool lib, bool noopt, bool icells, bool ignore_redef, bool defer, bool autowire);
+	void process(RTLIL::Design *design, AstNode *ast, bool dump_ast1, bool dump_ast2, bool dump_vlog, bool nolatches, bool nomeminit, bool nomem2reg, bool mem2reg, bool lib, bool noopt, bool icells, bool ignore_redef, bool defer, bool autowire);
 
 	// parametric modules are supported directly by the AST library
 	// therfore we need our own derivate of RTLIL::Module with overloaded virtual functions
 	struct AstModule : RTLIL::Module {
 		AstNode *ast;
-		bool nolatches, nomem2reg, mem2reg, lib, noopt, icells, autowire;
+		bool nolatches, nomeminit, nomem2reg, mem2reg, lib, noopt, icells, autowire;
 		virtual ~AstModule();
 		virtual RTLIL::IdString derive(RTLIL::Design *design, dict<RTLIL::IdString, RTLIL::Const> parameters);
 		virtual RTLIL::Module *clone() const;
@@ -295,7 +295,7 @@ namespace AST
 namespace AST_INTERNAL
 {
 	// internal state variables
-	extern bool flag_dump_ast1, flag_dump_ast2, flag_nolatches, flag_nomem2reg, flag_mem2reg, flag_lib, flag_noopt, flag_icells, flag_autowire;
+	extern bool flag_dump_ast1, flag_dump_ast2, flag_nolatches, flag_nomeminit, flag_nomem2reg, flag_mem2reg, flag_lib, flag_noopt, flag_icells, flag_autowire;
 	extern AST::AstNode *current_ast, *current_ast_mod;
 	extern std::map<std::string, AST::AstNode*> current_scope;
 	extern const dict<RTLIL::SigBit, RTLIL::SigBit> *genRTLIL_subst_ptr;

frontends/ast/simplify.cc

@@ -83,11 +83,15 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 			{
 				AstNode *mem = it.first;
 				uint32_t memflags = it.second;
+				bool this_nomeminit = flag_nomeminit;
 				log_assert((memflags & ~0x00ffff00) == 0);
 
 				if (mem->get_bool_attribute("\\nomem2reg"))
 					continue;
 
+				if (mem->get_bool_attribute("\\nomeminit") || get_bool_attribute("\\nomeminit"))
+					this_nomeminit = true;
+
 				if (memflags & AstNode::MEM2REG_FL_FORCED)
 					goto silent_activate;
 
@@ -97,7 +101,7 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 				if (memflags & AstNode::MEM2REG_FL_SET_ASYNC)
 					goto verbose_activate;
 
-				if ((memflags & AstNode::MEM2REG_FL_SET_INIT) && (memflags & AstNode::MEM2REG_FL_SET_ELSE))
+				if ((memflags & AstNode::MEM2REG_FL_SET_INIT) && (memflags & AstNode::MEM2REG_FL_SET_ELSE) && this_nomeminit)
 					goto verbose_activate;
 
 				if (memflags & AstNode::MEM2REG_FL_CMPLX_LHS)

frontends/verilog/verilog_frontend.cc

@@ -83,11 +83,20 @@ struct VerilogFrontend : public Frontend {
 		log("        this can also be achieved by setting the 'nomem2reg'\n");
 		log("        attribute on the respective module or register.\n");
 		log("\n");
+		log("        This is potentially dangerous. Usually the front-end has good\n");
+		log("        reasons for converting an array to a list of registers.\n");
+		log("        Prohibiting this step will likely result in incorrect synthesis\n");
+		log("        results.\n");
+		log("\n");
 		log("    -mem2reg\n");
 		log("        always convert memories to registers. this can also be\n");
 		log("        achieved by setting the 'mem2reg' attribute on the respective\n");
 		log("        module or register.\n");
 		log("\n");
+		log("    -nomeminit\n");
+		log("        do not infer $meminit cells and instead convert initialized\n");
+		log("        memories to registers directly in the front-end.\n");
+		log("\n");
 		log("    -ppdump\n");
 		log("        dump verilog code after pre-processor\n");
 		log("\n");
@@ -139,6 +148,7 @@ struct VerilogFrontend : public Frontend {
 		bool flag_dump_ast2 = false;
 		bool flag_dump_vlog = false;
 		bool flag_nolatches = false;
+		bool flag_nomeminit = false;
 		bool flag_nomem2reg = false;
 		bool flag_mem2reg = false;
 		bool flag_ppdump = false;
@@ -186,6 +196,10 @@ struct VerilogFrontend : public Frontend {
 				flag_nolatches = true;
 				continue;
 			}
+			if (arg == "-nomeminit") {
+				flag_nomeminit = true;
+				continue;
+			}
 			if (arg == "-nomem2reg") {
 				flag_nomem2reg = true;
 				continue;
@@ -288,7 +302,7 @@ struct VerilogFrontend : public Frontend {
 						child->attributes[attr] = AST::AstNode::mkconst_int(1, false);
 		}
 
-		AST::process(design, current_ast, flag_dump_ast1, flag_dump_ast2, flag_dump_vlog, flag_nolatches, flag_nomem2reg, flag_mem2reg, flag_lib, flag_noopt, flag_icells, flag_ignore_redef, flag_defer, default_nettype_wire);
+		AST::process(design, current_ast, flag_dump_ast1, flag_dump_ast2, flag_dump_vlog, flag_nolatches, flag_nomeminit, flag_nomem2reg, flag_mem2reg, flag_lib, flag_noopt, flag_icells, flag_ignore_redef, flag_defer, default_nettype_wire);
 
 		if (!flag_nopp)
 			delete lexin;