Optimize labels as final `if` block statements (#5744).

Changes

@@ -25,6 +25,7 @@ Verilator 5.033 devel
 * Improve hierarchical DPI wrapper scheduling performance (#2583) (#5734). [Bartłomiej Chmiel, Antmicro Ltd.]
 * Improve VPI write errors (#5712). [Andrew Nolte]
 * Improve `resetall support (#5728) (#5730). [Ethan Sifferman]
+* Optimize labels as final `if` block statements (#5744).
 * Fix error message when call task as a function (#3089). [Matthew Ballance]
 * Fix VPI iteration over hierarchy (#5314) (#5731). [Natan Kreimer]
 * Fix constrained random for > 64-bit associative arrays (#5670) (#5682). [Yilou Wang]

src/V3Const.cpp

@@ -2266,6 +2266,19 @@ class ConstVisitor final : public VNVisitor {
         }
         return false;
     }
+    bool replaceJumpGoNext(AstJumpGo* nodep, AstNode* abovep) {
+        // If JumpGo has an upper JumpBlock that is to same label, then
+        // code will by normal sequential operation do the JUMPGO and it
+        // can be removed.
+        if (nodep->nextp()) return false;  // Label jumps other statements
+        AstJumpBlock* const aboveBlockp = VN_CAST(abovep, JumpBlock);
+        if (!aboveBlockp) return false;
+        if (aboveBlockp != nodep->labelp()->blockp()) return false;
+        if (aboveBlockp->endStmtsp() != nodep->labelp()) return false;
+        UINFO(4, "JUMPGO => last remove " << nodep << endl);
+        VL_DO_DANGLING(pushDeletep(nodep->unlinkFrBack()), nodep);
+        return true;
+    }
 
     // Boolean replacements
     bool operandBoolShift(const AstNode* nodep) {
@@ -3158,8 +3171,9 @@ class ConstVisitor final : public VNVisitor {
                 nodep->condp(new AstLogAnd{lowerIfp->fileline(), condp, lowerCondp});
                 lowerIfp->replaceWith(lowerThensp);
                 VL_DO_DANGLING(pushDeletep(lowerIfp), lowerIfp);
-            } else if (operandBoolShift(nodep->condp())) {
-                replaceBoolShift(nodep->condp());
+            } else {
+                // Optimizations that don't reform the IF itself
+                if (operandBoolShift(nodep->condp())) replaceBoolShift(nodep->condp());
             }
         }
     }
@@ -3390,14 +3404,14 @@ class ConstVisitor final : public VNVisitor {
             }
             // If last statement in a jump label we have JumpLabel(...., JumpGo)
             // Often caused by "return" in a Verilog function.  The Go is pointless, remove.
+            if (replaceJumpGoNext(nodep, nodep->abovep())) return;
+            // Also optimize If with a then or else's final statement being this JumpGo
+            // We only do single ifs... Ideally we'd look at control flow and delete any
+            // Jumps where any following control flow point is the label
             if (!nodep->nextp()) {
-                if (AstJumpBlock* const aboveBlockp = VN_CAST(nodep->abovep(), JumpBlock)) {
-                    if (aboveBlockp == nodep->labelp()->blockp()) {
-                        if (aboveBlockp->endStmtsp() == nodep->labelp()) {
-                            UINFO(4, "JUMPGO => last remove " << nodep << endl);
-                            VL_DO_DANGLING(pushDeletep(nodep->unlinkFrBack()), nodep);
-                            return;
-                        }
+                if (AstNodeIf* const aboveIfp = VN_CAST(nodep->abovep(), NodeIf)) {
+                    if (!aboveIfp->nextp()) {
+                        if (replaceJumpGoNext(nodep, aboveIfp->abovep())) return;
                     }
                 }
             }

test_regress/t/t_opt_ifjumpgo.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2025 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile(verilator_flags2=['--stats'])
+
+test.file_grep(test.stats, r'Node count, JUMPGO + 3 *$')
+
+test.execute()
+
+test.passes()

test_regress/t/t_opt_ifjumpgo.v

@@ -0,0 +1,67 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain, for
+// any use, without warranty, 2025 by Wilson Snyder.
+// SPDX-License-Identifier: CC0-1.0
+
+class uvm_object;
+endclass
+
+class uvm_callback;
+endclass
+
+class uvm_callbacks #(type T=uvm_object, type CB=uvm_callback);
+   bit m_registered = 1;
+   virtual function bit m_is_registered(uvm_object obj, uvm_callback cb);
+      if (m_is_for_me(cb) && m_am_i_a(obj)) begin
+         return m_registered;
+      end
+   endfunction
+
+   virtual function bit m_is_for_me(uvm_callback cb);
+      CB this_cb;
+      // verilator lint_off WIDTHTRUNC
+      return ($cast(this_cb, cb));
+      // verilator lint_on WIDTHTRUNC
+   endfunction
+
+   virtual function bit m_am_i_a(uvm_object obj);
+      T this_t;
+      // verilator lint_off WIDTHTRUNC
+      return ($cast(this_t, obj));
+      // verilator lint_on WIDTHTRUNC
+   endfunction
+endclass
+
+class my_object extends uvm_object;
+endclass
+
+class my_callback extends uvm_callback;
+endclass
+
+class other_object extends uvm_object;
+endclass
+
+module t;
+
+   initial begin
+      my_object obj;
+      other_object oobj;
+      my_callback cb;
+      uvm_callbacks#(my_object, my_callback) ucs;
+      bit i;
+
+      obj = new;
+      oobj = new;
+      cb = new;
+      ucs = new;
+
+      i = ucs.m_is_registered(obj, cb);
+      if (i !== 1) $stop;
+      i = ucs.m_is_registered(oobj, cb);
+      if (i !== 0) $stop;
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+
+endmodule