Fix part select issues in LATCH warning. (verilator#2948) (verilator#…

…2938)

src/V3Active.cpp

@@ -309,16 +309,16 @@ class ActiveLatchCheckVisitor final : public ActiveBaseVisitor {
         }
     }
     virtual void visit(AstNodeIf* nodep) {
-        LatchDetectGraphVertex* parentp = m_graph.currentp();
-        LatchDetectGraphVertex* branchp = m_graph.addPathVertex(parentp, "BRANCH", true);
-        m_graph.addPathVertex(branchp, "IF");
-        iterateAndNextNull(nodep->ifsp());
-        m_graph.addPathVertex(branchp, "ELSE");
-        iterateAndNextNull(nodep->elsesp());
-        m_graph.currentp(parentp);
-    }
-    // Empty visitors, speed things up
-    virtual void visit(AstNodeMath* nodep) {}
+        if (!nodep->isBoundsCheck()) {
+            LatchDetectGraphVertex* parentp = m_graph.currentp();
+            LatchDetectGraphVertex* branchp = m_graph.addPathVertex(parentp, "BRANCH", true);
+            m_graph.addPathVertex(branchp, "IF");
+            iterateAndNextNull(nodep->ifsp());
+            m_graph.addPathVertex(branchp, "ELSE");
+            iterateAndNextNull(nodep->elsesp());
+            m_graph.currentp(parentp);
+        }
+    }
     //--------------------
     virtual void visit(AstNode* nodep) { iterateChildren(nodep); }
 

src/V3Ast.h

@@ -2216,12 +2216,14 @@ class AstNodeFor VL_NOT_FINAL : public AstNodeStmt {
 class AstNodeIf VL_NOT_FINAL : public AstNodeStmt {
 private:
     VBranchPred m_branchPred;  // Branch prediction as taken/untaken?
+    bool m_isBoundsCheck;  // True if this if node was inserted for array bounds checking
 protected:
     AstNodeIf(AstType t, FileLine* fl, AstNode* condp, AstNode* ifsp, AstNode* elsesp)
         : AstNodeStmt{t, fl} {
         setOp1p(condp);
         addNOp2p(ifsp);
         addNOp3p(elsesp);
+        isBoundsCheck(false);
     }
 
 public:
@@ -2238,6 +2240,8 @@ class AstNodeIf VL_NOT_FINAL : public AstNodeStmt {
     virtual bool same(const AstNode* samep) const override { return true; }
     void branchPred(VBranchPred flag) { m_branchPred = flag; }
     VBranchPred branchPred() const { return m_branchPred; }
+    void isBoundsCheck(bool flag) { m_isBoundsCheck = flag; }
+    bool isBoundsCheck() const { return m_isBoundsCheck; }
 };
 
 class AstNodeCase VL_NOT_FINAL : public AstNodeStmt {

src/V3Unknown.cpp

@@ -127,6 +127,7 @@ class UnknownVisitor final : public AstNVisitor {
                              new AstAssign(fl, prep, new AstVarRef(fl, varp, VAccess::READ)))),
                 nullptr);
             newp->branchPred(VBranchPred::BP_LIKELY);
+            newp->isBoundsCheck(true);
             if (debug() >= 9) newp->dumpTree(cout, "     _new: ");
             abovep->addNextStmt(newp, abovep);
             prep->user2p(newp);  // Save so we may LogAnd it next time

test_regress/t/t_lint_latch_4.pl

@@ -0,0 +1,17 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003-2009 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
+
+scenarios(vlt => 1);
+
+lint(
+    );
+
+ok(1);
+1;

test_regress/t/t_lint_latch_4.v

@@ -0,0 +1,27 @@
+// DESCRIPTION: Verilator: Verilog Test module for Issue#2938
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2021 by Julien Margetts (Originally provided by YanJiun)
+
+module test (
+  input      [2:0] a,
+  input      [3:0] c,
+
+  output reg [7:0] b
+);
+
+  integer i;
+
+  always @ (*)
+  begin
+    case(a)
+      {3'b000}: b = 8'd1;
+      {3'b001}:
+        for(i=0;i<4;i=i+1) b[i*2+:2] = 2'(c[i]);
+      {3'b010}: b = 8'd3;
+      {3'b011}: b = 8'd4;
+      default : b = 0;
+    endcase
+  end
+
+endmodule