cg: allow input to translator to be NULL

Some translators support NULL as input pointer value.  The code generator
was performing a NULL-check on a the LHS of a PTR or DOT node before
considering the possibility that the node is subject to translator
handling.  The check should happen after translator handling.

With this patch, tst.ProcModelTrans.d works but only for the case of
NULL input.  The test is changed to actually use a real task_struct as
input.  New test tst.NullInput.d exercises the case this patch fixes.

Signed-off-by: Kris Van Hees <kris.van.hees@oracle.com>
Reviewed-by: Eugene Loh <eugene.loh@oracle.com>

libdtrace/dt_cg.c

@@ -6305,8 +6305,6 @@ dt_cg_node(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
 		assert(dnp->dn_right->dn_kind == DT_NODE_IDENT);
 		dt_cg_node(dnp->dn_left, dlp, drp);
 
-		dt_cg_check_notnull(dlp, drp, dnp->dn_left->dn_reg);
-
 		/*
 		 * If the left-hand side of PTR or DOT is a dynamic variable,
 		 * we expect it to be the output of a D translator.   In this
@@ -6340,6 +6338,8 @@ dt_cg_node(dt_node_t *dnp, dt_irlist_t *dlp, dt_regset_t *drp)
 			break;
 		}
 
+		dt_cg_check_notnull(dlp, drp, dnp->dn_left->dn_reg);
+
 		ctfp = dnp->dn_left->dn_ctfp;
 		type = ctf_type_resolve(ctfp, dnp->dn_left->dn_type);
 

test/unittest/translators/tst.NullInput.d

@@ -0,0 +1,31 @@
+/*
+ * Oracle Linux DTrace.
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * Licensed under the Universal Permissive License v 1.0 as shown at
+ * http://oss.oracle.com/licenses/upl.
+ */
+
+/*
+ * ASSERTION: Translators can receive NULL as input.
+ *
+ * SECTION: Translators/Translator Declarations
+ * SECTION: Translators/Translate Operator
+ *
+ */
+
+#pragma D option quiet
+
+struct task_struct *T;
+
+BEGIN
+{
+	T = 0;
+	mypr_addr = xlate < psinfo_t > (T).pr_addr;
+	printf("pr_addr: %p", mypr_addr);
+	exit(0);
+}
+
+ERROR
+{
+	exit(1);
+}

test/unittest/translators/tst.ProcModelTrans.d

@@ -1,29 +1,25 @@
 /*
  * Oracle Linux DTrace.
- * Copyright (c) 2006, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2006, 2023, Oracle and/or its affiliates. All rights reserved.
  * Licensed under the Universal Permissive License v 1.0 as shown at
  * http://oss.oracle.com/licenses/upl.
  */
-/* @@xfail: dtv2 */
 
 /*
- * ASSERTION:
- * Use the translators in /usr/lib/dtrace/procfs.d
+ * ASSERTION: Basic test for translators in /usr/lib/dtrace/procfs.d
  *
- * SECTION: Translators/ Translator Declarations
- * SECTION: Translators/ Translate Operator
+ * SECTION: Translators/Translator Declarations
+ * SECTION: Translators/Translate Operator
  * SECTION: Translators/Process Model Translators
  *
  */
 
 #pragma D option quiet
 
-struct task_struct *T;
-
 BEGIN
 {
-	mypr_addr = xlate < psinfo_t > (T).pr_addr;
-	printf("pr_addr: %d", mypr_addr);
+	mypr_addr = xlate < psinfo_t > (curthread).pr_addr;
+	printf("pr_addr: %p", mypr_addr);
 	exit(0);
 }