Fix #4857 consider NOT when checking EQ/NEQ under AND/OR tree (#4863)

src/V3Const.cpp

@@ -594,7 +594,7 @@ class ConstBitOpTreeVisitor final : public VNVisitorConst {
             const V3Number& compNum = constp->num();
 
             auto setPolarities = [this, &compNum](const LeafInfo& ref, const V3Number* maskp) {
-                const bool maskFlip = isOrTree();
+                const bool maskFlip = isAndTree() ^ ref.polarity();
                 int constantWidth = compNum.width();
                 if (maskp) constantWidth = std::max(constantWidth, maskp->width());
                 const int maxBitIdx = std::max(ref.lsb() + constantWidth, ref.msb() + 1);

test_regress/t/t_const_opt.pl

@@ -20,7 +20,7 @@ execute(
     );
 
 if ($Self->{vlt}) {
-    file_grep($Self->{stats}, qr/Optimizations, Const bit op reduction\s+(\d+)/i, 37);
+    file_grep($Self->{stats}, qr/Optimizations, Const bit op reduction\s+(\d+)/i, 39);
 }
 ok(1);
 1;

test_regress/t/t_const_opt.v

@@ -62,7 +62,7 @@ module t(/*AUTOARG*/
          $write("[%0t] cyc==%0d crc=%x sum=%x\n", $time, cyc, crc, sum);
          if (crc !== 64'hc77bb9b3784ea091) $stop;
          // What checksum will we end up with (above print should match)
-`define EXPECTED_SUM 64'hd1610f7181cbc1b4
+`define EXPECTED_SUM 64'h5a76f060ff8aba3e
 
          if (sum !== `EXPECTED_SUM) $stop;
          $write("*-* All Finished *-*\n");
@@ -95,10 +95,11 @@ module Test(/*AUTOARG*/
    logic bug4059_out;
    logic bug4832_out;
    logic bug4837_out;
+   logic bug4857_out;
 
    output logic o;
 
-   logic [16:0] tmp;
+   logic [17:0] tmp;
    assign o = ^tmp;
 
    always_ff @(posedge clk) begin
@@ -131,6 +132,7 @@ module Test(/*AUTOARG*/
       tmp[14]<= bug4059_out;
       tmp[15]<= bug4832_out;
       tmp[16]<= bug4837_out;
+      tmp[17]<= bug4857_out;
    end
 
    bug3182 i_bug3182(.in(d[4:0]), .out(bug3182_out));
@@ -144,6 +146,7 @@ module Test(/*AUTOARG*/
    bug4059 i_bug4059(.clk(clk), .in(d), .out(bug4059_out));
    bug4832 i_bug4832(.clk(clk), .in(d), .out(bug4832_out));
    bug4837 i_bug4837(.clk(clk), .in(d), .out(bug4837_out));
+   bug4857 i_bug4857(.clk(clk), .in(d), .out(bug4857_out));
 
 endmodule
 
@@ -450,3 +453,39 @@ module bug4837(input wire clk, input wire [31:0] in, output out);
 
    assign out = out_data[33] ^ out_data[32] ^ out_data[0];
 endmodule
+
+// See issue #4857
+// (1'b0 != (!a)) | b was wrongly optimized to
+// (a | b) & 1'b1
+// polarity was not considered when traversing NEQ under AND/OR tree
+module bug4857(input wire clk, input wire [31:0] in, output out);
+   logic [95:0] d;
+   always_ff @(posedge clk)
+      d <= {d[63:0], in};
+
+   wire celloutsig_12z;
+   wire celloutsig_15z;
+   wire celloutsig_17z;
+   wire celloutsig_4z;
+   wire celloutsig_67z;
+   wire celloutsig_9z;
+   logic [95:0] in_data;
+   logic result;
+
+   // verilator lint_off UNDRIVEN
+   wire [95:0] out_data;
+   // verilator lint_on UNDRIVEN
+
+   assign celloutsig_4z = ~(in_data[72] & in_data[43]);  // 1
+   assign celloutsig_67z = | { in_data[64], celloutsig_12z }; // 0
+   assign celloutsig_15z = in_data[43] & ~(celloutsig_4z); // 0
+   assign celloutsig_9z = celloutsig_17z & ~(in_data[43]); // 00000000
+   assign celloutsig_17z = celloutsig_15z & ~(in_data[43]);// 0
+   assign celloutsig_12z = celloutsig_4z != celloutsig_9z; // 1
+   assign out_data[32] = celloutsig_67z; // 1
+
+   assign in_data = d;
+   always_ff @ (posedge clk)
+      result <= out_data[32];
+   assign out = result;
+endmodule

test_regress/t/t_const_opt_dfg.pl

@@ -0,0 +1,27 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(simulator => 1);
+top_filename("t/t_const_opt.v");
+
+compile(
+    verilator_flags2 => ["-Wno-UNOPTTHREADS",
+                         "--stats", "$Self->{t_dir}/t_const_opt.cpp"],
+    );
+
+execute(
+    check_finished => 1,
+    );
+
+if ($Self->{vlt}) {
+    file_grep($Self->{stats}, qr/Optimizations, Const bit op reduction\s+(\d+)/i, 34);
+}
+ok(1);
+1;