Fix 3786 (Internal error in bit op tree optimization) (#3793)

* Tests: Add a test to reproduce 3786

* Fix #3786 (Internal error in bit op tree optimization).

src/V3Const.cpp

@@ -122,6 +122,10 @@ class ConstBitOpTreeVisitor final : public VNVisitor {
         const AstConst* constp() const { return m_constp; }
         int wordIdx() const { return m_wordIdx; }
         bool polarity() const { return m_polarity; }
+        bool missingWordSel() const {
+            // When V3Expand is skipped, WordSel is not inserted.
+            return m_refp->isWide() && m_wordIdx == -1;
+        }
         int lsb() const { return m_lsb; }
 
         int msb() const { return std::min(m_msb, varWidth() - 1); }
@@ -132,6 +136,7 @@ class ConstBitOpTreeVisitor final : public VNVisitor {
                 UASSERT_OBJ(m_wordIdx == -1, m_refp, "Bad word index into non-wide");
                 return width;
             } else {
+                if (missingWordSel()) return width;
                 UASSERT_OBJ(m_wordIdx >= 0, m_refp, "Bad word index into wide");
                 const int bitsInMSW = VL_BITBIT_E(width) ? VL_BITBIT_E(width) : VL_EDATASIZE;
                 return m_wordIdx == m_refp->widthWords() - 1 ? bitsInMSW : VL_EDATASIZE;
@@ -393,6 +398,11 @@ class ConstBitOpTreeVisitor final : public VNVisitor {
         if (!varInfop) {
             varInfop = new VarInfo{this, ref.refp(), ref.varWidth()};
             m_varInfos[idx].reset(varInfop);
+            if (ref.missingWordSel()) {
+                // ConstBitOpTreeVisitor makes some constants for masks and its type is uint64_t.
+                // That's why V3Expand, that inserts WordSel, is needed.
+                CONST_BITOP_SET_FAILED("V3Expand is skipped", ref.refp());
+            }
         } else {
             if (!varInfop->sameVarAs(ref.refp()))
                 CONST_BITOP_SET_FAILED("different var (scope?)", ref.refp());

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'h9366e49d91bfe942
+`define EXPECTED_SUM 64'h94c0495e8e279723
 
          if (sum !== `EXPECTED_SUM) $stop;
          $write("*-* All Finished *-*\n");
@@ -90,10 +90,11 @@ module Test(/*AUTOARG*/
    logic bug3509_out;
    wire  bug3399_out0;
    wire  bug3399_out1;
+   logic bug3786_out;
 
    output logic o;
 
-   logic [11:0] tmp;
+   logic [12:0] tmp;
    assign o = ^tmp;
 
    always_ff @(posedge clk) begin
@@ -121,6 +122,7 @@ module Test(/*AUTOARG*/
       tmp[9] <= bug3509_out;
       tmp[10]<= bug3399_out0;
       tmp[11]<= bug3399_out1;
+      tmp[12]<= bug3786_out;
    end
 
    bug3182 i_bug3182(.in(d[4:0]), .out(bug3182_out));
@@ -129,6 +131,7 @@ module Test(/*AUTOARG*/
    bug3470 i_bug3470(.clk(clk), .in(d), .out(bug3470_out));
    bug3509 i_bug3509(.clk(clk), .in(d), .out(bug3509_out));
    bug3399 i_bug3399(.clk(clk), .in(d), .out0(bug3399_out0), .out1(bug3399_out1));
+   bug3786 i_bug3786(.clk(clk), .in(d), .out(bug3786_out));
 
 endmodule
 
@@ -315,3 +318,16 @@ module bug3399(input wire clk, input wire [31:0] in, inout wire out0, inout wire
    assign out0 = driver[0] ? d[0] : 1'bz;
    assign out1 = driver[1] ? d[1] : 1'bz;
 endmodule
+
+// Bug3786
+// When V3Expand is skipped, wide number is not split by WORDSEL.
+// Bit op tree opt. expects that bit width is 64 bit at most.
+module bug3786(input wire clk, input wire [31:0] in, inout wire out);
+   logic [127:0] d0, d1;
+   always_ff @(posedge clk) begin
+      d0 <= {d0[127:32], in};
+      d1 <= d1;
+   end
+
+   assign out = ^{d1, d0};
+endmodule

test_regress/t/t_const_opt_no_expand.pl

@@ -0,0 +1,27 @@
+#!/usr/bin/env perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+scenarios(simulator => 1);
+top_filename("t/t_const_opt.v");
+
+compile(
+    verilator_flags2 => ["-Wno-UNOPTTHREADS", "-fno-dfg", "-fno-expand",
+                         "--stats", "$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, 2);
+}
+ok(1);
+1;