opt_expr: improve simplification of comparisons with large constants.

The idea behind this simplification is that a N-bit signal X being
compared with an M-bit constant where M>N and the constant has Nth
or higher bit set, it either always succeeds or always fails.

However, the existing implementation only worked with one-hot signals
for some reason. It also printed incorrect messages.

This commit adjusts the simplification to have as much power as
possible, and fixes other bugs.

1 files changed, 18 insertions, 0 deletions

diff --git a/tests/opt/opt_expr_cmp.v b/tests/opt/opt_expr_cmp.v
index 500b15f1b..5aff4b80f 100644
--- a/tests/opt/opt_expr_cmp.v
+++ b/tests/opt/opt_expr_cmp.v
@@ -19,4 +19,22 @@ module top(...);
   output o3_2 = 4'b0100 <= a;
   output o3_3 = a <  4'b0100;
   output o3_4 = a >= 4'b0100;
+
+  output o4_1 = 5'b10000 >  a;
+  output o4_2 = 5'b10000 >= a;
+  output o4_3 = 5'b10000 <  a;
+  output o4_4 = 5'b10000 <= a;
+  output o4_5 = a <  5'b10000;
+  output o4_6 = a <= 5'b10000;
+  output o4_7 = a >  5'b10000;
+  output o4_8 = a >= 5'b10000;
+
+  output o5_1 = 5'b10100 >  a;
+  output o5_2 = 5'b10100 >= a;
+  output o5_3 = 5'b10100 <  a;
+  output o5_4 = 5'b10100 <= a;
+  output o5_5 = a <  5'b10100;
+  output o5_6 = a <= 5'b10100;
+  output o5_7 = a >  5'b10100;
+  output o5_8 = a >= 5'b10100;
 endmodule