Merge branch 'SiB64-strict-parameter-declaration'

Pulled from https://codeberg.org/SiB64/iverilog strict-parameter-declaration
with further enhancements.

Documentation/usage/command_line_flags.rst

@@ -131,6 +131,18 @@ These flags affect the general behavior of the compiler.
     containing an unsized constant number, and unsized constant numbers are
     not truncated to integer width.
 
+  * strict-declaration/no-strict-declaration
+
+  * strict-net-var-declaration/no-strict-net-var-declaration
+
+  * strict-parameter-declaration/no-strict-parameter-declaration
+
+    The standards require that nets, variables, and parameters must be
+    declared lexically before they are used.  Using -gno-strict-declaration
+    will allow using a data object before declaration, with a warning. The
+    warning can be suppressed with -Wno-declaration-after-use.  The option
+    can be applied for nets and variables and for parameters separately.
+
   * shared-loop-index/no-shared-loop-index
 
     Enable or disable the exclusion of for-loop control variables from
@@ -260,6 +272,7 @@ These flags affect the general behavior of the compiler.
       -Wanachronisms
       -Wimplicit
       -Wimplicit-dimensions
+      -Wdeclaration-after-use
       -Wmacro-replacement
       -Wportbind
       -Wselect-range
@@ -288,6 +301,15 @@ These flags affect the general behavior of the compiler.
     This flag is supported in release 10.1 or master branch snapshots after
     2016-02-06.
 
+  * declaration-after-use
+
+    This enables warnings for declarations after use, when those are not
+    flagged as errors (enabled by default). Use no-declaration-after-use
+    to disable this.
+
+    This flag was added in version 14.0 or later (and is in the master branch
+    as of 2026-03-21).
+
   * macro-redefinition
 
     This enables warnings when a macro is redefined, even if the macro text

compiler.h

@@ -1,7 +1,7 @@
 #ifndef IVL_compiler_H
 #define IVL_compiler_H
 /*
- * Copyright (c) 1999-2021 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 1999-2026 Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -104,6 +104,9 @@ extern bool warn_sens_entire_arr;
 /* Warn about level-appropriate anachronisms. */
 extern bool warn_anachronisms;
 
+/* Warn about declaration after use (unless flaged as errors). */
+extern bool warn_decl_after_use;
+
 /* Warn about nets that are references but not driven. */
 extern bool warn_floating_nets;
 
@@ -210,6 +213,20 @@ extern bool gn_strict_expr_width_flag;
    loop. */
 extern bool gn_shared_loop_index_flag;
 
+/* If this flag is true (default), then parameters must be declared before
+   use. `-gno-strict[-parameter]-declaration` allows to use parameters before
+   declaration, as prior to version 13.
+   A warning is emited with -Wdeclaration-after-use (default).
+ */
+extern bool gn_strict_parameter_declaration;
+
+/* If this flag is true (default), then nets and variablesmust be declared
+   before use. `-gno-strict[-net-var]-declaration` allows to use nets and
+   variables before declaration, as prior to version 13.
+   A warning is emited with -Wdeclaration-after-use (default).
+ */
+extern bool gn_strict_net_var_declaration;
+
 static inline bool gn_system_verilog(void)
 {
       if (generation_flag >= GN_VER2005_SV)

driver/iverilog.man.in

@@ -124,7 +124,7 @@ to disable extended types if compiling code that clashes with the few
 new keywords used to implement the type system.
 .TP 8
 .B -gio-range-error\fI|\fP-gno-io-range-error
-The standards requires that a vectored port have matching ranges for its
+The standards require that a vectored port have matching ranges for its
 port declaration as well as any net/register declaration. It was common
 practice in the past to only specify the range for the net/register
 declaration and some tools still allow this. By default any mismatch is
@@ -150,6 +150,17 @@ parameter assignment is evaluated as a lossless expression, as is any
 expression containing an unsized constant number, and unsized constant
 numbers are not truncated to integer width.
 .TP 8
+.B -gstrict-declaration\fI|\fP-gno-strict-declaration
+.TP 8
+.B -gstrict-net-var-declaration\fI|\fP-gno-strict-net-var-declaration
+.TP 8
+.B -gstrict-parameter-declaration\fI|\fP-gno-strict-parameter-declaration
+The standards require that nets, variables, and parameters are declared
+lexically before they are used.  Using \fB\-gno\-strict\-declaration\fP
+will allow using a data object before declaration, with a warning. The
+warning can be suppressed with -Wno-declaration-after-use. The option
+can be applied for nets and variables and for parameters separately.
+.TP 8
 .B -gshared-loop-index\fI|\fP-gno-shared-loop-index
 Enable (default) or disable the exclusion of for-loop control variables
 from implicit event_expression lists. When enabled, if a for-loop control
@@ -367,6 +378,11 @@ This enables warnings for creation of implicit declarations. For
 example, if a scalar wire X is used but not declared in the Verilog
 source, this will print a warning at its first use.
 
+.TP 8
+.B declaration-after-use
+This enables warnings for declarations after use, when
+those are not flagged as errors (default).
+
 .TP 8
 .B macro-redefinition\fI | \fPmacro-replacement
 This enables preprocessor warnings when a macro is being redefined.

driver/main.c

@@ -134,6 +134,8 @@ const char*gen_strict_ca_eval = "no-strict-ca-eval";
 const char*gen_strict_expr_width = "no-strict-expr-width";
 const char*gen_shared_loop_index = "shared-loop-index";
 const char*gen_verilog_ams = "no-verilog-ams";
+const char*gen_strict_net_var_declaration = "strict-net-var-declaration";
+const char*gen_strict_parameter_declaration = "strict-parameter-declaration";
 
 /* Boolean: true means use a default include dir, false means don't */
 int gen_std_include = 1;
@@ -142,7 +144,7 @@ int gen_std_include = 1;
    of the include list. */
 int gen_relative_include = 0;
 
-char warning_flags[17] = "n";
+char warning_flags[18] = "nu";
 
 int separate_compilation_flag = 0;
 
@@ -527,6 +529,7 @@ static void process_warning_switch(const char*name)
 {
       if (strcmp(name,"all") == 0) {
 	    process_warning_switch("anachronisms");
+	    process_warning_switch("declaration-after-use");
 	    process_warning_switch("implicit");
 	    process_warning_switch("implicit-dimensions");
 	    process_warning_switch("macro-replacement");
@@ -537,6 +540,9 @@ static void process_warning_switch(const char*name)
       } else if (strcmp(name,"anachronisms") == 0) {
 	    if (! strchr(warning_flags, 'n'))
 		  strcat(warning_flags, "n");
+      } else if (strcmp(name,"declaration-after-use") == 0) {
+	    if (! strchr(warning_flags, 'u'))
+		  strcat(warning_flags, "u");
       } else if (strcmp(name,"floating-nets") == 0) {
 	    if (! strchr(warning_flags, 'f'))
 		  strcat(warning_flags, "f");
@@ -578,6 +584,12 @@ static void process_warning_switch(const char*name)
 		  cp[0] = cp[1];
 		  cp += 1;
 	    }
+      } else if (strcmp(name,"no-declaration-after-use") == 0) {
+	    char*cp = strchr(warning_flags, 'u');
+	    if (cp) while (*cp) {
+		  cp[0] = cp[1];
+		  cp += 1;
+	    }
       } else if (strcmp(name,"no-floating-nets") == 0) {
 	    char*cp = strchr(warning_flags, 'f');
 	    if (cp) while (*cp) {
@@ -815,6 +827,26 @@ static int process_generation(const char*name)
       else if (strcmp(name,"no-verilog-ams") == 0)
 	    gen_verilog_ams = "no-verilog-ams";
 
+      else if (strcmp(name,"strict-declaration") == 0) {
+	    gen_strict_net_var_declaration = "strict-net-var-declaration";
+	    gen_strict_parameter_declaration = "strict-parameter-declaration";
+      }
+      else if (strcmp(name,"no-strict-declaration") == 0) {
+	    gen_strict_net_var_declaration = "no-strict-net-var-declaration";
+	    gen_strict_parameter_declaration = "no-strict-parameter-declaration";
+      }
+      else if (strcmp(name,"strict-net-var-declaration") == 0)
+	    gen_strict_net_var_declaration = "strict-net-var-declaration";
+
+      else if (strcmp(name,"no-strict-net-var-declaration") == 0)
+	    gen_strict_net_var_declaration = "no-strict-net-var-declaration";
+
+      else if (strcmp(name,"strict-parameter-declaration") == 0)
+	    gen_strict_parameter_declaration = "strict-parameter-declaration";
+
+      else if (strcmp(name,"no-strict-parameter-declaration") == 0)
+	    gen_strict_parameter_declaration = "no-strict-parameter-declaration";
+
       else {
 	    fprintf(stderr, "Unknown/Unsupported Language generation "
 		    "%s\n\n", name);
@@ -837,7 +869,9 @@ static int process_generation(const char*name)
 		            "    io-range-error | no-io-range-error\n"
 		            "    strict-ca-eval | no-strict-ca-eval\n"
 		            "    strict-expr-width | no-strict-expr-width\n"
-		            "    shared-loop-index | no-shared-loop-index\n");
+		            "    shared-loop-index | no-shared-loop-index\n"
+		            "    strict-declaration | no-strict-declaration\n"
+		            "    [no-]strict-[net-var|parameter]-declaration\n");
 
 	    return 1;
       }
@@ -1385,6 +1419,8 @@ int main(int argc, char **argv)
       fprintf(iconfig_file, "generation:%s\n", gen_strict_expr_width);
       fprintf(iconfig_file, "generation:%s\n", gen_shared_loop_index);
       fprintf(iconfig_file, "generation:%s\n", gen_verilog_ams);
+      fprintf(iconfig_file, "generation:%s\n", gen_strict_net_var_declaration);
+      fprintf(iconfig_file, "generation:%s\n", gen_strict_parameter_declaration);
       fprintf(iconfig_file, "generation:%s\n", gen_icarus);
       fprintf(iconfig_file, "warnings:%s\n", warning_flags);
       fprintf(iconfig_file, "ignore_missing_modules:%s\n", ignore_missing_modules ? "true" : "false");

ivtest/gold/decl_before_use1_warn-iverilog-stderr.gold

@@ -0,0 +1,2 @@
+ivltests/decl_before_use1.v:4: warning: net/variable `v` used before declaration.
+ivltests/decl_before_use1.v:9:        : the net/variable is declared here.

ivtest/gold/decl_before_use1_warn-vvp-stdout.gold

@@ -0,0 +1,2 @@
+1
+used before declaration

ivtest/gold/decl_before_use2_warn-iverilog-stderr.gold

@@ -0,0 +1,2 @@
+ivltests/decl_before_use2.v:3: warning: net/variable `w` used before declaration.
+ivltests/decl_before_use2.v:10:        : the net/variable is declared here.

ivtest/gold/decl_before_use2_warn-vvp-stdout.gold

@@ -0,0 +1,2 @@
+00000001
+used before declaration

ivtest/gold/decl_before_use3_warn-iverilog-stderr.gold

@@ -0,0 +1,2 @@
+ivltests/decl_before_use3.v:4: warning: event `e` used before declaration.
+ivltests/decl_before_use3.v:8:        : the event is declared here.

ivtest/gold/decl_before_use3_warn-vvp-stdout.gold

@@ -0,0 +1 @@
+used before declaration

ivtest/gold/decl_before_use4_warn-vvp-stdout.gold

@@ -0,0 +1 @@
+used before declaration

ivtest/gold/decl_before_use5_warn-iverilog-stderr.gold

@@ -0,0 +1,2 @@
+ivltests/decl_before_use5.v:4: warning: parameter `w` used before declaration.
+ivltests/decl_before_use5.v:8:        : the parameter is declared here.

ivtest/gold/decl_before_use5_warn-vvp-stdout.gold

@@ -0,0 +1,2 @@
+10101010
+used before declaration

ivtest/gold/decl_before_use6_warn-vvp-stdout.gold

@@ -0,0 +1,2 @@
+10
+FAILED

ivtest/gold/pr1909940.gold

@@ -0,0 +1,3 @@
+./ivltests/pr1909940.v:4: warning: net/variable `in` used before declaration.
+./ivltests/pr1909940.v:5:        : the net/variable is declared here.
+PASSED

ivtest/gold/pr1909940b.gold

@@ -0,0 +1,3 @@
+./ivltests/pr1909940b.v:4: warning: net/variable `in` used before declaration.
+./ivltests/pr1909940b.v:5:        : the net/variable is declared here.
+PASSED

ivtest/ivltests/decl_before_use1.v

@@ -3,7 +3,7 @@ module test();
 initial begin
   v = 1;
   $display("%b", v);
-  $display("FAILED");
+  $display("used before declaration");
 end
 
 reg v;

ivtest/ivltests/decl_before_use2.v

@@ -4,7 +4,7 @@ assign w = 1;
 
 initial begin
   $display("%b", w);
-  $display("FAILED");
+  $display("used before declaration");
 end
 
 wire [7:0] w;

ivtest/ivltests/decl_before_use3.v

@@ -2,7 +2,7 @@ module test();
 
 initial begin
   ->e;
-  $display("FAILED");
+  $display("used before declaration");
 end
 
 event e;

ivtest/ivltests/decl_before_use4.v

@@ -2,7 +2,7 @@ module test();
 
 initial begin
   @(e);
-  $display("FAILED");
+  $display("used before declaration");
 end
 
 event e;

ivtest/ivltests/decl_before_use5.v

@@ -2,7 +2,7 @@ module test();
 
 initial begin
   $display("%b", w);
-  $display("FAILED");
+  $display("used before declaration");
 end
 
 localparam w = 8'hAA;

ivtest/regress-vlg.list

@@ -1126,8 +1126,8 @@ pr1903324		normal			ivltests
 pr1903343		normal			ivltests gold=pr1903343.gold
 pr1903520		normal			ivltests
 pr1907192		normal			ivltests
-pr1909940		CE			ivltests
-pr1909940b		CE			ivltests
+pr1909940		normal,-gno-strict-declaration	ivltests gold=pr1909940.gold
+pr1909940b		normal,-gno-strict-declaration	ivltests gold=pr1909940b.gold
 pr1912843		normal			ivltests
 pr1913918a		normal			ivltests
 pr1913918b		normal			ivltests

ivtest/regress-vvp.list

@@ -97,6 +97,12 @@ decl_before_use3		vvp_tests/decl_before_use3.json
 decl_before_use4		vvp_tests/decl_before_use4.json
 decl_before_use5		vvp_tests/decl_before_use5.json
 decl_before_use6		vvp_tests/decl_before_use6.json
+decl_before_use1_warn		vvp_tests/decl_before_use1_warn.json
+decl_before_use2_warn		vvp_tests/decl_before_use2_warn.json
+decl_before_use3_warn		vvp_tests/decl_before_use3_warn.json
+decl_before_use4_warn		vvp_tests/decl_before_use4_warn.json
+decl_before_use5_warn		vvp_tests/decl_before_use5_warn.json
+decl_before_use6_warn		vvp_tests/decl_before_use6_warn.json
 delayed_sfunc			vvp_tests/delayed_sfunc.json
 dffsynth			vvp_tests/dffsynth.json
 dffsynth-S			vvp_tests/dffsynth-S.json

ivtest/vvp_tests/decl_before_use1_warn.json

@@ -0,0 +1,7 @@
+
+{
+    "type" : "normal",
+    "source" : "decl_before_use1.v",
+    "iverilog-args" : [ "-gno-strict-net-var-declaration" ],
+    "gold" : "decl_before_use1_warn"
+}

ivtest/vvp_tests/decl_before_use2_warn.json

@@ -0,0 +1,7 @@
+
+{
+    "type" : "normal",
+    "source" : "decl_before_use2.v",
+    "iverilog-args" : [ "-gno-strict-declaration" ],
+    "gold" : "decl_before_use2_warn"
+}

ivtest/vvp_tests/decl_before_use3_warn.json

@@ -0,0 +1,7 @@
+
+{
+    "type" : "normal",
+    "source" : "decl_before_use3.v",
+    "iverilog-args" : [ "-gno-strict-net-var-declaration" ],
+    "gold" : "decl_before_use3_warn"
+}

ivtest/vvp_tests/decl_before_use4_warn.json

@@ -0,0 +1,7 @@
+
+{
+    "type" : "normal",
+    "source" : "decl_before_use4.v",
+    "iverilog-args" : [ "-gno-strict-declaration", "-Wno-declaration-after-use" ],
+    "gold" : "decl_before_use4_warn"
+}

ivtest/vvp_tests/decl_before_use5_warn.json

@@ -0,0 +1,7 @@
+
+{
+    "type" : "normal",
+    "source" : "decl_before_use5.v",
+    "iverilog-args" : [ "-gno-strict-parameter-declaration" ],
+    "gold" : "decl_before_use5_warn"
+}

ivtest/vvp_tests/decl_before_use6_warn.json

@@ -0,0 +1,7 @@
+
+{
+    "type" : "normal",
+    "source" : "decl_before_use6.v",
+    "iverilog-args" : [ "-gno-strict-declaration", "-Wno-declaration-after-use" ],
+    "gold" : "decl_before_use6_warn"
+}

main.cc

@@ -117,6 +117,8 @@ bool gn_strict_ca_eval_flag = false;
 bool gn_strict_expr_width_flag = false;
 bool gn_shared_loop_index_flag = true;
 bool gn_verilog_ams_flag = false;
+bool gn_strict_parameter_declaration = true;
+bool gn_strict_net_var_declaration = true;
 
 /*
  * For some generations we allow a system function to be called
@@ -172,6 +174,7 @@ bool warn_ob_select = false;
 bool warn_sens_entire_vec = false;
 bool warn_sens_entire_arr = false;
 bool warn_anachronisms = false;
+bool warn_decl_after_use = false;
 bool warn_floating_nets = false;
 
 /*
@@ -386,6 +389,18 @@ static void process_generation_flag(const char*gen)
       } else if (strcmp(gen,"no-shared-loop-index") == 0) {
 	    gn_shared_loop_index_flag = false;
 
+      } else if (strcmp(gen,"strict-parameter-declaration") == 0) {
+	    gn_strict_parameter_declaration = true;
+
+      } else if (strcmp(gen,"no-strict-parameter-declaration") == 0) {
+	    gn_strict_parameter_declaration = false;
+
+      } else if (strcmp(gen,"strict-net-var-declaration") == 0) {
+	    gn_strict_net_var_declaration = true;
+
+      } else if (strcmp(gen,"no-strict-net-var-declaration") == 0) {
+	    gn_strict_net_var_declaration = false;
+
 	  } else {
       }
 }
@@ -760,6 +775,9 @@ static void read_iconfig_file(const char*ipath)
 		      case 'n':
 			warn_anachronisms = true;
 			break;
+		      case 'u':
+			warn_decl_after_use = true;
+			break;
 		      default:
 			break;
 		  }

net_scope.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000-2025 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 2000-2026 Stephen Williams (steve@icarus.com)
  * Copyright (c) 2016 CERN Michele Castellana (michele.castellana@cern.ch)
  *
  *    This source code is free software; you can redistribute it
@@ -462,6 +462,14 @@ unsigned NetScope::get_parameter_lexical_pos(perm_string key) const
       return 0;
 }
 
+void NetScope::set_parameter_lexical_pos(perm_string key, unsigned lexical_pos)
+{
+      map<perm_string,param_expr_t>::iterator idx;
+
+      idx = parameters.find(key);
+      if (idx != parameters.end()) idx->second.lexical_pos = lexical_pos;
+}
+
 void NetScope::print_type(ostream&stream) const
 {
       switch (type_) {

netlist.h

@@ -1274,6 +1274,7 @@ class NetScope : public Definitions, public Attrib {
       LineInfo get_parameter_line_info(perm_string name) const;
 
       unsigned get_parameter_lexical_pos(perm_string name) const;
+      void set_parameter_lexical_pos(perm_string name, unsigned lexical_pos);
 
 	/* Module instance arrays are collected here for access during
 	   the multiple elaboration passes. */

symbol_search.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003-2024 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 2003-2026 Stephen Williams (steve@icarus.com)
  * Copyright CERN 2012 / Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
@@ -164,12 +164,22 @@ bool symbol_search(const LineInfo*li, Design*des, NetScope*scope,
 		  }
 
 		  if (NetNet*net = scope->find_signal(path_tail.name)) {
-			if (prefix_scope || (net->lexical_pos() <= lexical_pos)) {
+			bool decl_after_use = !prefix_scope && !(net->lexical_pos() <= lexical_pos);
+			if (!gn_strict_net_var_declaration || !decl_after_use) {
 			      path.push_back(path_tail);
 			      res->scope = scope;
 			      res->net = net;
 			      res->type = net->net_type();
 			      res->path_head = path;
+			      if (warn_decl_after_use && decl_after_use) {
+				    cerr << li->get_fileline()
+					 << ": warning: net/variable `" << path_tail.name
+					 << "` used before declaration." << endl;
+				    cerr << net->get_fileline()
+					 << ":        : the net/variable is declared here." << endl;
+				    // suppress further warnings for this net
+				    net->lexical_pos(lexical_pos);
+			      }
 			      return true;
 			} else if (!res->decl_after_use) {
 			      res->decl_after_use = net;
@@ -177,11 +187,21 @@ bool symbol_search(const LineInfo*li, Design*des, NetScope*scope,
 		  }
 
 		  if (NetEvent*eve = scope->find_event(path_tail.name)) {
-			if (prefix_scope || (eve->lexical_pos() <= lexical_pos)) {
+			bool decl_after_use = !prefix_scope && !(eve->lexical_pos() <= lexical_pos);
+			if (!gn_strict_net_var_declaration || !decl_after_use) {
 			      path.push_back(path_tail);
 			      res->scope = scope;
 			      res->eve = eve;
 			      res->path_head = path;
+			      if (warn_decl_after_use && decl_after_use) {
+				    cerr << li->get_fileline()
+					 << ": warning: event `" << path_tail.name
+					 << "` used before declaration." << endl;
+				    cerr << eve->get_fileline()
+					 << ":        : the event is declared here." << endl;
+				    // suppress further warnings for this event
+				    eve->lexical_pos(lexical_pos);
+			      }
 			      return true;
 			} else if (!res->decl_after_use) {
 			      res->decl_after_use = eve;
@@ -189,11 +209,22 @@ bool symbol_search(const LineInfo*li, Design*des, NetScope*scope,
 		  }
 
 		  if (const NetExpr*par = scope->get_parameter(des, path_tail.name, res->type)) {
-			if (prefix_scope || (scope->get_parameter_lexical_pos(path_tail.name) <= lexical_pos)) {
+			bool decl_after_use = !prefix_scope
+			      && !(scope->get_parameter_lexical_pos(path_tail.name) <= lexical_pos);
+			if (!gn_strict_parameter_declaration || !decl_after_use) {
 			      path.push_back(path_tail);
 			      res->scope = scope;
 			      res->par_val = par;
 			      res->path_head = path;
+			      if (warn_decl_after_use && decl_after_use) {
+				    cerr << li->get_fileline()
+					 << ": warning: parameter `" << path_tail.name
+					 << "` used before declaration." << endl;
+				    cerr << par->get_fileline()
+					 << ":        : the parameter is declared here." << endl;
+				    // suppress further warnings for this parameter
+				    scope->set_parameter_lexical_pos(path_tail.name, lexical_pos);
+			      }
 			      return true;
 			} else if (!res->decl_after_use) {
 			      res->decl_after_use = par;