verilog: significant block scoping improvements

This change set contains a number of bug fixes and improvements related to
scoping and resolution in generate and procedural blocks. While many of the
frontend changes are interdependent, it may be possible bring the techmap
changes in under a separate PR.

Declarations within unnamed generate blocks previously encountered issues
because the data declarations were left un-prefixed, breaking proper scoping.
The LRM outlines behavior for generating names for unnamed generate blocks. The
original goal was to add this implicit labelling, but doing so exposed a number
of issues downstream. Additional testing highlighted other closely related scope
resolution issues, which have been fixed. This change also adds support for
block item declarations within unnamed blocks in SystemVerilog mode.

1. Unlabled generate blocks are now implicitly named according to the LRM in
   `label_genblks`, which is invoked at the beginning of module elaboration
2. The Verilog parser no longer wraps explicitly named generate blocks in a
   synthetic unnamed generate block to avoid creating extra hierarchy levels
   where they should not exist
3. The techmap phase now allows special control identifiers to be used outside
   of the topmost scope, which is necessary because such wires and cells often
   appear in unlabeled generate blocks, which now prefix the declarations within
4. Some techlibs required modifications because they relied on the previous
   invalid scope resolution behavior
5. `expand_genblock` has been simplified, now only expanding the outermost
   scope, completely deferring the inspection and elaboration of nested scopes;
   names are now resolved by looking in the innermost scope and stepping outward
6. Loop variables now always become localparams during unrolling, allowing them
   to be resolved and shadowed like any other identifier
7. Identifiers in synthetic function call scopes are now prefixed and resolved
   in largely the same manner as other blocks
     before: `$func$\func_01$tests/simple/scopes.blk.v:60$5$\blk\x`
      after: `\func_01$func$tests/simple/scopes.v:60$5.blk.x`
8. Support identifiers referencing a local generate scope nested more
   than 1 level deep, i.e. `B.C.x` while within generate scope `A`, or using a
   prefix of a current or parent scope, i.e. `B.C.D.x` while in `A.B`, `A.B.C`,
   or `A.B.C.D`
9. Variables can now be declared within unnamed blocks in SystemVerilog mode

Addresses the following issues: 656, 2423, 2493

9 files changed, 173 insertions, 0 deletions

diff --git a/tests/verilog/bug2493.ys b/tests/verilog/bug2493.ys
new file mode 100644
index 000000000..380d2a823
--- /dev/null
+++ b/tests/verilog/bug2493.ys
@@ -0,0 +1,12 @@
+logger -expect error "Failed to detect width for identifier \\genblk1\.y!" 1
+read_verilog <<EOT
+module top1;
+    wire x;
+    generate
+        if (1) begin
+            mod y();
+            assign x = y;
+        end
+    endgenerate
+endmodule
+EOT
diff --git a/tests/verilog/bug656.v b/tests/verilog/bug656.v
new file mode 100644
index 000000000..068d045fd
--- /dev/null
+++ b/tests/verilog/bug656.v
@@ -0,0 +1,21 @@
+module top #(
+	parameter WIDTH = 6
+) (
+	input [WIDTH-1:0] a_i,
+	input [WIDTH-1:0] b_i,
+	output [WIDTH-1:0] z_o
+);
+	genvar g;
+	generate
+		for (g = 0; g < WIDTH; g = g + 1) begin
+			if (g > 2) begin
+				wire tmp;
+				assign tmp = a_i[g] || b_i[g];
+				assign z_o[g] = tmp;
+			end
+			else begin
+				assign z_o[g] = a_i[g] && b_i[g];
+			end
+		end
+	endgenerate
+endmodule
diff --git a/tests/verilog/bug656.ys b/tests/verilog/bug656.ys
new file mode 100644
index 000000000..7f367341a
--- /dev/null
+++ b/tests/verilog/bug656.ys
@@ -0,0 +1,13 @@
+read_verilog bug656.v
+
+select -assert-count 1 top/a_i
+select -assert-count 1 top/b_i
+select -assert-count 1 top/z_o
+
+select -assert-none top/genblk1[0].genblk1.tmp
+select -assert-none top/genblk1[1].genblk1.tmp
+select -assert-none top/genblk1[2].genblk1.tmp
+
+select -assert-count 1 top/genblk1[3].genblk1.tmp
+select -assert-count 1 top/genblk1[4].genblk1.tmp
+select -assert-count 1 top/genblk1[5].genblk1.tmp
diff --git a/tests/verilog/genblk_case.v b/tests/verilog/genblk_case.v
new file mode 100644
index 000000000..081fb09d3
--- /dev/null
+++ b/tests/verilog/genblk_case.v
@@ -0,0 +1,26 @@
+module top;
+	parameter YES = 1;
+	generate
+		if (YES) wire y;
+		else wire n;
+
+		if (!YES) wire n;
+		else wire y;
+
+		case (YES)
+			1: wire y;
+			0: wire n;
+		endcase
+
+		case (!YES)
+			0: wire y;
+			1: wire n;
+		endcase
+
+		if (YES) wire y;
+		else wire n;
+
+		if (!YES) wire n;
+		else wire y;
+	endgenerate
+endmodule
diff --git a/tests/verilog/genblk_case.ys b/tests/verilog/genblk_case.ys
new file mode 100644
index 000000000..3c1bb51f9
--- /dev/null
+++ b/tests/verilog/genblk_case.ys
@@ -0,0 +1,15 @@
+read_verilog genblk_case.v
+
+select -assert-count 0 top/genblk1.n
+select -assert-count 0 top/genblk2.n
+select -assert-count 0 top/genblk3.n
+select -assert-count 0 top/genblk4.n
+select -assert-count 0 top/genblk5.n
+select -assert-count 0 top/genblk6.n
+
+select -assert-count 1 top/genblk1.y
+select -assert-count 1 top/genblk2.y
+select -assert-count 1 top/genblk3.y
+select -assert-count 1 top/genblk4.y
+select -assert-count 1 top/genblk5.y
+select -assert-count 1 top/genblk6.y
diff --git a/tests/verilog/hidden_decl.ys b/tests/verilog/hidden_decl.ys
new file mode 100644
index 000000000..aed7847dc
--- /dev/null
+++ b/tests/verilog/hidden_decl.ys
@@ -0,0 +1,11 @@
+logger -expect error "Identifier `\\y' is implicitly declared and `default_nettype is set to none" 1
+read_verilog <<EOT
+`default_nettype none
+module top1;
+    wire x;
+    generate
+        if (1) wire y;
+    endgenerate
+    assign x = y;
+endmodule
+EOT
diff --git a/tests/verilog/unnamed_block.ys b/tests/verilog/unnamed_block.ys
new file mode 100644
index 000000000..0f209a089
--- /dev/null
+++ b/tests/verilog/unnamed_block.ys
@@ -0,0 +1,28 @@
+read_verilog <<EOT
+module top;
+    initial begin : blk
+        integer x;
+    end
+endmodule
+EOT
+
+delete
+
+read_verilog -sv <<EOT
+module top;
+    initial begin
+        integer x;
+    end
+endmodule
+EOT
+
+delete
+
+logger -expect error "Local declaration in unnamed block is only supported in SystemVerilog mode!" 1
+read_verilog <<EOT
+module top;
+    initial begin
+        integer x;
+    end
+endmodule
+EOT
diff --git a/tests/verilog/unnamed_genblk.sv b/tests/verilog/unnamed_genblk.sv
new file mode 100644
index 000000000..41828b1b0
--- /dev/null
+++ b/tests/verilog/unnamed_genblk.sv
@@ -0,0 +1,39 @@
+// This test is taken directly from Section 27.6 of IEEE 1800-2017
+
+module top;
+	parameter genblk2 = 0;
+	genvar i;
+
+	// The following generate block is implicitly named genblk1
+
+	if (genblk2) logic a; // top.genblk1.a
+	else logic b; // top.genblk1.b
+
+	// The following generate block is implicitly named genblk02
+	// as genblk2 is already a declared identifier
+
+	if (genblk2) logic a; // top.genblk02.a
+	else logic b; // top.genblk02.b
+
+	// The following generate block would have been named genblk3
+	// but is explicitly named g1
+
+	for (i = 0; i < 1; i = i + 1) begin : g1 // block name
+		// The following generate block is implicitly named genblk1
+		// as the first nested scope inside g1
+		if (1) logic a; // top.g1[0].genblk1.a
+	end
+
+	// The following generate block is implicitly named genblk4 since
+	// it belongs to the fourth generate construct in scope "top".
+	// The previous generate block would have been
+	// named genblk3 if it had not been explicitly named g1
+
+	for (i = 0; i < 1; i = i + 1)
+		// The following generate block is implicitly named genblk1
+		// as the first nested generate block in genblk4
+		if (1) logic a; // top.genblk4[0].genblk1.a
+
+	// The following generate block is implicitly named genblk5
+	if (1) logic a; // top.genblk5.a
+endmodule
diff --git a/tests/verilog/unnamed_genblk.ys b/tests/verilog/unnamed_genblk.ys
new file mode 100644
index 000000000..2b9aa9d69
--- /dev/null
+++ b/tests/verilog/unnamed_genblk.ys
@@ -0,0 +1,8 @@
+read_verilog -sv unnamed_genblk.sv
+select -assert-count 0 top/genblk1.a
+select -assert-count 1 top/genblk02.b
+select -assert-count 0 top/genblk1.a
+select -assert-count 1 top/genblk02.b
+select -assert-count 1 top/g1[0].genblk1.a
+select -assert-count 1 top/genblk4[0].genblk1.a
+select -assert-count 1 top/genblk5.a