From 5f3316d3dc68099adf1c512ae0658f99699cbab9 Mon Sep 17 00:00:00 2001
From: Wilson Snyder <wsnyder@wsnyder.org>
Date: Sat, 9 Jul 2022 08:30:57 -0400
Subject: [PATCH] * Fix empty string arguments to display (#3484).

---
 Changes                            |  1 +
 src/V3LinkResolve.cpp              | 58 +++++++++++++++---------------
 test_regress/t/t_display_merge.out |  2 ++
 test_regress/t/t_display_merge.pl  |  2 +-
 test_regress/t/t_display_merge.v   |  4 +++
 5 files changed, 38 insertions(+), 29 deletions(-)

diff --git a/Changes b/Changes
index 5f68d4a40..910eceb2f 100644
--- a/Changes
+++ b/Changes
@@ -14,6 +14,7 @@ Verilator 4.225 devel
 **Minor:**
 
 * Fix incorrect bit op tree optimization (#3470). [algrobman]
+* Fix empty string arguments to display (#3484). [Grulfen]
 * Fix table misoptimizing away display (#3488). [Stefan Post]
 
 
diff --git a/src/V3LinkResolve.cpp b/src/V3LinkResolve.cpp
index a0d198bc7..45ce55922 100644
--- a/src/V3LinkResolve.cpp
+++ b/src/V3LinkResolve.cpp
@@ -352,43 +352,45 @@ private:
             while (argp) {
                 if (skipCount) {
                     argp = argp->nextp();
-                    skipCount--;
+                    --skipCount;
                     continue;
                 }
                 const AstConst* const constp = VN_CAST(argp, Const);
                 const bool isFromString = (constp) ? constp->num().isFromString() : false;
                 if (isFromString) {
                     const int numchars = argp->dtypep()->width() / 8;
-                    string str(numchars, ' ');
-                    // now scan for % operators
-                    bool inpercent = false;
-                    for (int i = 0; i < numchars; i++) {
-                        const int ii = numchars - i - 1;
-                        const char c = constp->num().dataByte(ii);
-                        str[i] = c;
-                        if (!inpercent && c == '%') {
-                            inpercent = true;
-                        } else if (inpercent) {
-                            inpercent = false;
-                            switch (c) {
-                            case '0':  // FALLTHRU
-                            case '1':  // FALLTHRU
-                            case '2':  // FALLTHRU
-                            case '3':  // FALLTHRU
-                            case '4':  // FALLTHRU
-                            case '5':  // FALLTHRU
-                            case '6':  // FALLTHRU
-                            case '7':  // FALLTHRU
-                            case '8':  // FALLTHRU
-                            case '9':  // FALLTHRU
-                            case '.': inpercent = true; break;
-                            case '%': break;
-                            default:
-                                if (V3Number::displayedFmtLegal(c, isScan)) ++skipCount;
+                    if (!constp->num().toString().empty()) {
+                        string str(numchars, ' ');
+                        // now scan for % operators
+                        bool inpercent = false;
+                        for (int i = 0; i < numchars; i++) {
+                            const int ii = numchars - i - 1;
+                            const char c = constp->num().dataByte(ii);
+                            str[i] = c;
+                            if (!inpercent && c == '%') {
+                                inpercent = true;
+                            } else if (inpercent) {
+                                inpercent = false;
+                                switch (c) {
+                                case '0':  // FALLTHRU
+                                case '1':  // FALLTHRU
+                                case '2':  // FALLTHRU
+                                case '3':  // FALLTHRU
+                                case '4':  // FALLTHRU
+                                case '5':  // FALLTHRU
+                                case '6':  // FALLTHRU
+                                case '7':  // FALLTHRU
+                                case '8':  // FALLTHRU
+                                case '9':  // FALLTHRU
+                                case '.': inpercent = true; break;
+                                case '%': break;
+                                default:
+                                    if (V3Number::displayedFmtLegal(c, isScan)) ++skipCount;
+                                }
                             }
                         }
+                        newFormat.append(str);
                     }
-                    newFormat.append(str);
                     AstNode* const nextp = argp->nextp();
                     argp->unlinkFrBack();
                     VL_DO_DANGLING(pushDeletep(argp), argp);
diff --git a/test_regress/t/t_display_merge.out b/test_regress/t/t_display_merge.out
index 358455d76..0dcb8b10e 100644
--- a/test_regress/t/t_display_merge.out
+++ b/test_regress/t/t_display_merge.out
@@ -1,5 +1,7 @@
 Merge:
 This should merge
+Merge:
+This should also merge
 f
  1=1 a=top.t 1=1 1=1 b=top.t 1=1
  pre
diff --git a/test_regress/t/t_display_merge.pl b/test_regress/t/t_display_merge.pl
index 75570aba2..27cc0ef25 100755
--- a/test_regress/t/t_display_merge.pl
+++ b/test_regress/t/t_display_merge.pl
@@ -20,7 +20,7 @@ execute(
     );
 
 file_grep("$Self->{obj_dir}/$Self->{VM_PREFIX}__stats.txt",
-          qr/Node count, DISPLAY \s+ 41 \s+ 27 \s+ 27 \s+ 6/);
+          qr/Node count, DISPLAY \s+ 44 \s+ 27 \s+ 27 \s+ 6/);
 
 ok(1);
 1;
diff --git a/test_regress/t/t_display_merge.v b/test_regress/t/t_display_merge.v
index 0704e7728..ede4c15eb 100644
--- a/test_regress/t/t_display_merge.v
+++ b/test_regress/t/t_display_merge.v
@@ -19,6 +19,10 @@ module t (/*AUTOARG*/);
       $write("should ");
       $display("merge");
 
+      $display("Merge:");
+      $write("This ", "", "should ", "", "also ");
+      $display("merge");
+
       $display("f");
       $write(" 1=%0d a=%m 1=%0d", one, one);
       $display(" 1=%0d b=%m 1=%0d", one, one);