vlog95: block generating a concat-Z LPM device in the compiler.

Since the vlog95 code generator needs the strength information we do
not want to hide it behind a concat-Z optimization. For now we abort
the optimization, but in the future we could add parts of this back
in (e.g. all the drivers have matching strength then replace with a
normal concat and a buf-Z if the strength are not both strong. The
original buf-Z should be removed to reduce the number of LPM devices).

compiler.h

@@ -1,7 +1,7 @@
 #ifndef __compiler_H
 #define __compiler_H
 /*
- * Copyright (c) 1999-2011 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 1999-2013 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
@@ -107,6 +107,10 @@ extern bool debug_optimizer;
 /* Possibly temporary flag to control virtualization of pin arrays */
 extern bool disable_virtual_pins;
 
+/* The vlog95 code generator does not want the compiler to generate concat-Z
+ * LPM objects so this flag is used to block them from being generated. */
+extern bool disable_concatz_generation;
+
 /* Limit to size of devirtualized arrays */
 extern unsigned long array_size_limit;
 

main.cc

@@ -1,5 +1,5 @@
 const char COPYRIGHT[] =
-          "Copyright (c) 1998-2012 Stephen Williams (steve@icarus.com)";
+          "Copyright (c) 1998-2013 Stephen Williams (steve@icarus.com)";
 
 /*
  *    This source code is free software; you can redistribute it
@@ -175,6 +175,7 @@ bool debug_optimizer = false;
 bool disable_virtual_pins = false;
 unsigned long array_size_limit = 16777216;  // Minimum required by IEEE-1364?
 unsigned recursive_mod_limit = 10;
+bool disable_concatz_generation = false;
 
 /*
  * Verbose messages enabled.
@@ -967,6 +968,9 @@ int main(int argc, char*argv[])
       flag_tmp = flags["RECURSIVE_MOD_LIMIT"];
       if (flag_tmp) recursive_mod_limit = strtoul(flag_tmp,NULL,0);
 
+      flag_tmp = flags["DISABLE_CONCATZ_GENERATION"];
+      if (flag_tmp) disable_concatz_generation = strcmp(flag_tmp,"true")==0;
+
 	/* Parse the input. Make the pform. */
       pform_set_timescale(def_ts_units, def_ts_prec, 0, 0);
       int rc = pform_parse(argv[optind]);

netmisc.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001-2012 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 2001-2013 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
@@ -1127,6 +1127,17 @@ void collapse_partselect_pv_to_concat(Design*des, NetNet*sig)
 
       ivl_assert(*sig, idx == ps_map.size());
 
+	/* The vlog95 and possibly other code generators do not want
+	 * to have a group of part selects turned into a transparent
+	 * concatenation. */
+      if (disable_concatz_generation) {
+// HERE: If the part selects have matching strengths then we can use
+//       a normal concat with a buf-Z after if the strengths are not
+//       both strong. We would ideally delete any buf-Z driving the
+//       concat, but that is not required for the vlog95 generator.
+	    return;
+      }
+
 	// Ah HAH! The NetPartSelect::PV objects exactly cover the
 	// target signal. We can replace all of them with a single
 	// concatenation.

tgt-vlog95/logic_lpm.c

@@ -888,8 +888,14 @@ static void emit_lpm_as_ca(ivl_scope_t scope, ivl_lpm_t lpm)
 	    emit_nexus_as_ca(scope, ivl_lpm_data(lpm, 1), 0);
 	    fprintf(vlog_out, ")");
 	    break;
-	case IVL_LPM_CONCAT:
+	  /* A concat-Z should never be generated, but report it as an
+	   * error if one is generated. */
 	case IVL_LPM_CONCATZ:
+	    fprintf(stderr, "%s:%u: vlog95 error: Transparent concatenations "
+	                    "should not be generated.\n",
+	                    ivl_lpm_file(lpm), ivl_lpm_lineno(lpm));
+	    vlog_errors += 1;
+	case IVL_LPM_CONCAT:
 	    emit_lpm_concat(scope, lpm);
 	    break;
 	case IVL_LPM_DIVIDE:

tgt-vlog95/vlog95-s.conf

@@ -2,3 +2,4 @@ functor:synth2
 functor:synth
 functor:syn-rules
 flag:DLL=vlog95.tgt
+flag:DISABLE_CONCATZ_GENERATION=true

tgt-vlog95/vlog95.conf

@@ -1 +1,2 @@
 flag:DLL=vlog95.tgt
+flag:DISABLE_CONCATZ_GENERATION=true