[mono][interp] Make bblock reordering more conservative

If we are unlikely to gain anything from propagating the condition (if we don't have information about any of the condition operand vars), simply avoid the optimization.

src/mono/mono/mini/interp/transform.c

@@ -8257,6 +8257,20 @@ interp_mark_reachable_bblocks (TransformData *td)
 	}
 }
 
+static gboolean
+interp_prev_ins_defines_var (InterpInst *ins, int var1, int var2)
+{
+	// Check max of 5 instructions
+	for (int i = 0; i < 5; i++) {
+		ins = interp_prev_ins (ins);
+		if (!ins)
+			return FALSE;
+		if (mono_interp_op_dregs [ins->opcode] && (ins->dreg == var1 || ins->dreg == var2))
+			return TRUE;
+	}
+	return FALSE;
+}
+
 static void
 interp_reorder_bblocks (TransformData *td)
 {
@@ -8267,10 +8281,11 @@ interp_reorder_bblocks (TransformData *td)
 		if (first && MINT_IS_CONDITIONAL_BRANCH (first->opcode)) {
 			// This means this bblock has a single instruction, the conditional branch
 			int i = 0;
+			int lookup_var2 = (mono_interp_op_dregs [first->opcode] > 1) ? first->sregs [1] : -1;
 			while (i < bb->in_count) {
 				InterpBasicBlock *in_bb = bb->in_bb [i];
 				InterpInst *last_ins = interp_last_ins (in_bb);
-				if (last_ins && last_ins->opcode == MINT_BR) {
+				if (last_ins && last_ins->opcode == MINT_BR && interp_prev_ins_defines_var (last_ins, first->sregs [0], lookup_var2)) {
 					// This bblock is reached unconditionally from one of its parents
 					// Move the conditional branch inside the parent to facilitate propagation
 					// of condition value.