Support assert under assert (#6146).

Changes

@@ -142,6 +142,7 @@ Verilator 5.042 2025-11-02
 * Support modports referencing clocking blocks (#4555) (#6436). [Ryszard Rozak, Antmicro Ltd.]
 * Support class package reference on pattern keys (#5653). [Todd Strader]
 * Support digits in `$sscanf` field width formats (#6083). [Iztok Jeras]
+* Support assert under assert (#6146). [Alex Solomatnikov]
 * Support pure functions in sensitivity lists (#6393). [Krzysztof Bieganski, Antmicro Ltd.]
 * Support simple alias statements (#6339) (#6501). [Ryszard Rozak, Antmicro Ltd.]
 * Support simple cycle delay sequence expressions inside properties (#6508). [Bartłomiej Chmiel, Antmicro Ltd.]

src/V3AssertPre.cpp

@@ -80,10 +80,6 @@ private:
         }
         return newp;
     }
-    void clearAssertInfo() {
-        m_senip = nullptr;
-        m_disablep = nullptr;
-    }
     AstPropSpec* getPropertyExprp(const AstProperty* const propp) {
         // The only statements possible in AstProperty are AstPropSpec (body)
         // and AstVar (arguments).
@@ -476,12 +472,14 @@ private:
     void visit(AstNodeCoverOrAssert* nodep) override {
         if (nodep->sentreep()) return;  // Already processed
 
-        clearAssertInfo();
+        VL_RESTORER(m_senip);
+        VL_RESTORER(m_disablep);
+        m_senip = nullptr;
+        m_disablep = nullptr;
 
         // Find Clocking's buried under nodep->exprsp
         iterateChildren(nodep);
         if (!nodep->immediate()) nodep->sentreep(newSenTree(nodep));
-        clearAssertInfo();
     }
     void visit(AstFalling* nodep) override {
         if (nodep->user1SetOnce()) return;
@@ -684,7 +682,6 @@ public:
     // CONSTRUCTORS
     explicit AssertPreVisitor(AstNetlist* nodep)
         : m_netlistp{nodep} {
-        clearAssertInfo();
         // Process
         iterate(nodep);
         // Fix up varref names

src/V3LinkResolve.cpp

@@ -50,7 +50,6 @@ class LinkResolveVisitor final : public VNVisitor {
     string m_randcIllegalWhy;  // Why randc illegal
     AstNode* m_randcIllegalp = nullptr;  // Node causing randc illegal
     AstNodeFTask* m_ftaskp = nullptr;  // Function or task we're inside
-    AstNodeCoverOrAssert* m_assertp = nullptr;  // Current assertion
     int m_senitemCvtNum = 0;  // Temporary signal counter
     std::deque<AstGenFor*> m_underGenFors;  // Stack of GenFor underneath
     bool m_underGenerate = false;  // Under GenFor/GenIf
@@ -119,14 +118,6 @@ class LinkResolveVisitor final : public VNVisitor {
             VL_DO_DANGLING(pushDeletep(nodep), nodep);
         }
     }
-    void visit(AstNodeCoverOrAssert* nodep) override {
-        if (m_assertp) {
-            nodep->v3warn(E_UNSUPPORTED, "Unsupported: Assert not allowed under another assert");
-        }
-        VL_RESTORER(m_assertp);
-        m_assertp = nodep;
-        iterateChildren(nodep);
-    }
     void visit(AstVar* nodep) override {
         iterateChildren(nodep);
         if (m_classp && !nodep->isParam()) nodep->varType(VVarType::MEMBER);

test_regress/t/t_assert_assert.py

@@ -0,0 +1,18 @@
+#!/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()
+
+test.execute()
+
+test.passes()

test_regress/t/t_assert_assert.v

@@ -0,0 +1,58 @@
+// 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
+
+// verilog_format: off
+`define stop $stop
+`define checkd(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got=%0d exp=%0d (%s !== %s)\n", `__FILE__,`__LINE__, (gotv), (expv), `"gotv`", `"expv`"); `stop; end while(0);
+// verilog_format: on
+
+module t (
+    input clk
+);
+
+  int cyc;
+
+  reg [2:0] value;
+
+  int cnt_tt;
+  int cnt_tf;
+  int cnt_ft;
+  int cnt_ff;
+
+  assert property (@(negedge clk) disable iff (value[1]) value[2]) begin
+    assert (value[0]) ++cnt_tt;
+    else ++cnt_tf;
+  end
+  else begin
+    assert (value[0]) ++cnt_ft;
+    else ++cnt_ff;
+  end
+
+  // Test loop
+  always @(posedge clk) begin
+    cyc <= cyc + 1;
+    if (cyc == 10) begin
+      assert(cyc == 10);  // For debug to compare with other asserts
+      value <= 0;
+      cnt_tt = 0;
+      cnt_tf = 0;
+      cnt_ft = 0;
+      cnt_ff = 0;
+    end
+    else if (cyc > 10 && cyc < 90) begin
+      value <= cyc[2:0];
+    end
+    else if (cyc == 99) begin
+      `checkd(cnt_tt, 10);
+      `checkd(cnt_tf, 10);
+      `checkd(cnt_ft, 19);
+      `checkd(cnt_ff, 11);
+      $write("*-* All Finished *-*\n");
+      $finish;
+    end
+  end
+
+endmodule

test_regress/t/t_cover_assert.out

@@ -1,5 +1,17 @@
-%Error-UNSUPPORTED: t/t_cover_assert.v:42:16: Unsupported: Assert not allowed under another assert
-   42 |            A2: assert (b);
-      |                ^~~~~~
+%Warning-PROCASSINIT: t/t_cover_assert.v:13:18: Procedural assignment to declaration with initial value: 'cyc'
+                                              : ... note: In instance 't'
+                                              : ... Location of variable initialization
+   13 |    integer cyc = 0;
+      |                  ^
+                      t/t_cover_assert.v:19:7: ... Location of variable process write
+                                             : ... Perhaps should initialize instead using a reset in this process
+   19 |       cyc <= cyc + 1;
+      |       ^~~
+                      ... For warning description see https://verilator.org/warn/PROCASSINIT?v=latest
+                      ... Use "/* verilator lint_off PROCASSINIT */" and lint_on around source to disable this message.
+%Error-UNSUPPORTED: t/t_cover_assert.v:39:11: Unsupported: Procedural concurrent assertion with clocking event inside always (IEEE 1800-2023 16.14.6)
+                                            : ... note: In instance 't'
+   39 |       C1: cover property(a)
+      |           ^~~~~
                     ... For error description see https://verilator.org/warn/UNSUPPORTED?v=latest
 %Error: Exiting due to