verilog: fix size and signedness of array querying functions

genrtlil.cc and simplify.cc had inconsistent and slightly broken
handling of signedness for array querying functions. These functions are
defined to return a signed result. Simplify always produced an unsigned
and genrtlil always a signed 32-bit result ignoring the context.

Includes tests for the the relvant edge cases for context dependent
conversions.

CHANGELOG

@@ -12,6 +12,8 @@ Yosys 0.17 .. Yosys 0.17-dev
     - Fixed an issue where simplifying case statements by removing unreachable
       cases could result in the wrong signedness being used for comparison with
       the remaining cases
+    - Fixed size and signedness computation for expressions containing array
+      querying functions
 
 Yosys 0.16 .. Yosys 0.17
 --------------------------

frontends/ast/genrtlil.cc

@@ -1089,8 +1089,7 @@ void AstNode::detectSignWidthWorker(int &width_hint, bool &sign_hint, bool *foun
 			break;
 		}
 		if (str == "\\$size" || str == "\\$bits" || str == "\\$high" || str == "\\$low" || str == "\\$left" || str == "\\$right") {
-			width_hint = 32;
-			sign_hint = true;
+			width_hint = max(width_hint, 32);
 			break;
 		}
 		if (current_scope.count(str))

frontends/ast/simplify.cc

@@ -3450,7 +3450,7 @@ skip_dynamic_range_lvalue_expansion:;
 				else {
 					result = width * mem_depth;
 				}
-				newNode = mkconst_int(result, false);
+				newNode = mkconst_int(result, true);
 				goto apply_newNode;
 			}
 

tests/verilog/sign_array_query.ys

@@ -0,0 +1,52 @@
+logger -expect-no-warnings
+
+read_verilog -formal <<EOT
+module top(input clk);
+    reg [-1:-1] x;
+    reg good = 0;
+    reg signed [31:0] zero = 0;
+
+    always @(posedge clk) begin
+        case ($left(x) + zero) 36'shfffffffff: good = 1; endcase
+        assert (good);
+    end
+endmodule
+EOT
+
+prep -top top
+sim -n 3 -clock clk
+
+design -reset
+
+read_verilog -formal <<EOT
+module top(input clk);
+    reg [-1:-1] x;
+    reg good = 0;
+
+    always @(posedge clk) begin
+        case ($left(x)) 36'sh0ffffffff: good = 1; (32'h0 + $left(good)): ; endcase
+        assert (good);
+    end
+
+endmodule
+EOT
+
+prep -top top
+sim -n 3 -clock clk
+
+design -reset
+
+read_verilog -formal <<EOT
+module top(input clk);
+    reg [-1:-1] x;
+    reg good = 1;
+
+    always @(posedge clk) begin
+        case (36'sh100000000 + $left(x)) -1: good = 0; endcase
+        assert (good);
+    end
+endmodule
+EOT
+
+prep -top top
+sim -n 3 -clock clk