Tests: Check dist bucket draw is per-element in foreach (#8023)

test_regress/t/t_constraint_dist_foreach_if.v

@@ -6,10 +6,19 @@
 
 // Test that dist constraints nested inside if / -> inside foreach produce
 // values only within the declared distribution and cover all buckets.
+//
+// The bucket draw must also be made PER ELEMENT, not once per solve and then
+// shared by every element. Counting buckets across all solves cannot tell those
+// apart: a single hoisted draw still hits both buckets over 100 solves, it just
+// never mixes them inside one solve. So each block also counts solves in which
+// at least one element landed in each bucket. With dist {0 := 3, [1:4] := 1}
+// over 4 elements a per-element draw mixes in about 86 of 100 solves, whereas a
+// hoisted draw can never mix and gives exactly 0.
 
 // verilog_format: off
 `define stop $stop
 `define checkd(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got=%0d exp=%0d\n", `__FILE__,`__LINE__, (gotv), (expv)); `stop; end while(0);
+`define check_mixed(what,gotv) do if ((gotv) == 0) begin $write("%%Error: %s:%0d: dist inside foreach+%s: bucket draw is not per-element, no solve mixed buckets\n", `__FILE__,`__LINE__, what); `stop; end while(0);
 // verilog_format: on
 
 // foreach (a[i]) if (gate) a[i] dist {...}
@@ -64,10 +73,14 @@ module t;
     begin
       static ClsIf obj = new();
       int seen_zero, seen_nonzero;
+      int this_zero, this_nonzero, mixed;
       obj.gate = 1'b1;
       seen_zero = 0;
       seen_nonzero = 0;
+      mixed = 0;
       repeat (100) begin
+        this_zero = 0;
+        this_nonzero = 0;
         `checkd(obj.randomize(), 1)
         foreach (obj.a[i]) begin
           if (obj.a[i] > 4) begin
@@ -75,9 +88,16 @@ module t;
                    obj.a[i]);
             $stop;
           end
-          if (obj.a[i] == 0) seen_zero++;
-          else seen_nonzero++;
+          if (obj.a[i] == 0) begin
+            seen_zero++;
+            this_zero++;
+          end
+          else begin
+            seen_nonzero++;
+            this_nonzero++;
+          end
         end
+        if (this_zero > 0 && this_nonzero > 0) mixed++;
       end
       if (seen_zero == 0 || seen_nonzero == 0) begin
         $write(
@@ -85,16 +105,21 @@ module t;
             `__FILE__, `__LINE__, seen_zero, seen_nonzero);
         $stop;
       end
+      `check_mixed("if", mixed)
     end
 
     // Test -> (implication) form
     begin
       static ClsImpl obj = new();
       int seen_zero, seen_nonzero;
+      int this_zero, this_nonzero, mixed;
       obj.gate = 1'b1;
       seen_zero = 0;
       seen_nonzero = 0;
+      mixed = 0;
       repeat (100) begin
+        this_zero = 0;
+        this_nonzero = 0;
         `checkd(obj.randomize(), 1)
         foreach (obj.a[i]) begin
           if (obj.a[i] > 4) begin
@@ -102,9 +127,16 @@ module t;
                    obj.a[i]);
             $stop;
           end
-          if (obj.a[i] == 0) seen_zero++;
-          else seen_nonzero++;
+          if (obj.a[i] == 0) begin
+            seen_zero++;
+            this_zero++;
+          end
+          else begin
+            seen_nonzero++;
+            this_nonzero++;
+          end
         end
+        if (this_zero > 0 && this_nonzero > 0) mixed++;
       end
       if (seen_zero == 0 || seen_nonzero == 0) begin
         $write(
@@ -112,17 +144,22 @@ module t;
             `__FILE__, `__LINE__, seen_zero, seen_nonzero);
         $stop;
       end
+      `check_mixed("->", mixed)
     end
 
     // Test doubly-nested -> (chained implication) form
     begin
       static ClsImplChained obj = new();
       int seen_zero, seen_nonzero;
+      int this_zero, this_nonzero, mixed;
       obj.gateA = 1'b1;
       obj.gateB = 1'b1;
       seen_zero = 0;
       seen_nonzero = 0;
+      mixed = 0;
       repeat (100) begin
+        this_zero = 0;
+        this_nonzero = 0;
         `checkd(obj.randomize(), 1)
         foreach (obj.a[i]) begin
           if (obj.a[i] > 4) begin
@@ -130,9 +167,16 @@ module t;
                    obj.a[i]);
             $stop;
           end
-          if (obj.a[i] == 0) seen_zero++;
-          else seen_nonzero++;
+          if (obj.a[i] == 0) begin
+            seen_zero++;
+            this_zero++;
+          end
+          else begin
+            seen_nonzero++;
+            this_nonzero++;
+          end
         end
+        if (this_zero > 0 && this_nonzero > 0) mixed++;
       end
       if (seen_zero == 0 || seen_nonzero == 0) begin
         $write(
@@ -140,6 +184,7 @@ module t;
             `__FILE__, `__LINE__, seen_zero, seen_nonzero);
         $stop;
       end
+      `check_mixed("->->", mixed)
     end
 
     $write("*-* All Finished *-*\n");